FDA Briefing Document

for the

Anti-Infective Drug Products Advisory Committee

Artesunate Rectal Capsules

World Health Organization

NDA 21-242

![](media/image1.png)July 10, 2002

Food and Drug Administration

Center for Drug Evaluation and Research

Division of Special Pathogen and Immunologic Drug Products

**Table of Contents**

Background [1](#background)

Efficacy [1](#efficacy)

Safety [2](#safety)

Alternative treatments [2](#alternative-treatments)

Issues related to the study of rectal Artesunate in patients with acute
malaria
[3](#issues-related-to-the-study-of-rectal-artesunate-in-patients-with-acute-malaria)

Pharmacotoxicology [6](#pharmacotoxicology)

Microbiology [9](#microbiology)

Clinical Issues [16](#clinical-issues)

Efficacy [16](#efficacy-1)

Pivotal studies [16](#pivotal-studies)

Additional supportive studies [23](#additional-supportive-studies)

Safety [23](#safety-1)

Summary of data presented to the Chinese regulatory authorities
[23](#summary-of-data-presented-to-the-chinese-regulatory-authorities)

Summary of a systemic review of published and unpublished data
[23](#summary-of-a-systemic-review-of-published-and-unpublished-data)

Summary of WHO-specific studies in the NDA submission
[23](#summary-of-who-specific-studies-in-the-nda-submission)

Special populations [23](#special-populations)

Neurotoxocity [23](#neurotoxocity)

# Background

> *(The reader is referred to the briefing package provided by WHO. This
> document provides a detailed perspective on the problem of malaria in
> endemic regions of the world and the potential role of rectal
> artesunate in malaria control).*

**Rationale for developing rectal artesunate:**

In malaria endemic regions of the world, *Plasmodium falciparum* is
responsible for hundreds of thousands of deaths, especially among
children. One of the most important reasons for the very high malaria
mortality is the delay in receiving effective medication. Unfortunately,
many patients with acute malaria are unable to tolerate oral therapy.
Consequently, parenteral treatment is usually necessary, and this may
only be available at clinics or hospitals. These facilities are often
difficult to reach because of long distances and poor infrastructure in
terms of roads and transport.

The aim of the applicant was to develop a product that could be
administered on an emergency basis to patients too ill to take anything
orally.

The goal was to reduce mortality by early intervention in the field,
providing some cover over the first 24 hours to allow patients to reach
definitive treatment.

An artemisinin derivative for rectal administration was selected as a
suitable candidate.

## Efficacy

Artemisinin derivatives have been used for many years as antimalarial
agents in Asia. Published literature indicates that artemisinins given
orally or parenterally are effective in causing rapid decreases in the
parasite count in smears of peripheral blood. They are used extensively
in areas of the world where *P. falciparum* shows resistance to quinine,
and they are reportedly effective in quinine-resistant infections.

Artesunate is rapidly biotransformed to the principle metabolite:
dihydroartemisinin (DHA). Both the parent drug and metabolite are active
against the malaria parasite. The plasma half-life of these products
(both parent-drug and metabolite) is relatively short compared with
other antimalarial agents and frequent dosing has been used. Following a
single rectal dose, artesunate (AS) and dihydroartemisinin (DHA) are
detectable in plasma beginning about 30 minutes after dosing in most
adult and pediatric patients. Concentrations of artesunate and DHA
become undetectable in plasma after about 5 hours and 12 hours,
respectively.

Despite their efficacy in reducing parasite counts, these products have
been associated with high rates of recrudescence. To address this, they
are often used in combination with other antimalarial agents, and are
given repeatedly over several days.

## Safety

Literature reports indicate that certain artemisinins have been
associated with neuropathological changes in a variety of animal species
(mice, rats, dogs, and rhesus monkeys). These changes include
chromatolysis and gliosis in the brainstem nuclei associated with
auditory, vestibular and muscle-control functions. They have been most
strongly associated with the oil-based artemisinin derivatives,
artemether and arteether.

Neurological abnormalities have not been reported in human subjects.
However, the assessment of neurological changes in patients who present
with acute malaria is difficult, since the disease itself may result in
baseline neurological abnormalities and rarely in neurological sequelae.
Further, the assessment of neurological symptoms in children may be
difficult.

## Alternative treatments 

Drugs approved by the US Food and Drug Administration (FDA) for the
treatment of malaria cause by *P. falciparum* include chloroquine (oral,
IV or IM), fansidar (oral), mefloquine (oral), quinidine (IV or oral),
quinine (IV IM or oral), malarone (oral) and halofantrine (oral). Since
all these alternatives require oral or parenteral administration, none
is suitable for patients in the bush who are unable to take orally, and
who have no immediate access to trained medical personnel.

***Proposed indication*:**

> *"Artesunate Rectal Capsules is indicated for the initial management
> of acute malaria in patients who cannot take medication by mouth and
> for whom parenteral treatment is not available.*
>
> *Warning: Artesunate rectal capsules are not intended for the initial
> treatment of malaria if it is possible to provide immedidate treatment
> of the patient with orally or parenterally (intravenous or
> intramuscular) administered antimalarials.*
>
> *Precautions: Artesunate rectal capsules have not been evaluated as
> sole therapy for malaria; consequently all patient who are initially
> treated with artesunate rectal capsules should be promptly referred
> and evaluated at the nearest health care facility able to provide a
> full curative course of treatment for malaria.*
>
> *General: Artesunate rectal capsules are indicated only for use in
> initial management of acute non per-os [P. falciparum]{.underline}
> malaria and MUST be supplemented and/or followed by effective oral or
> parenteral drug therapy for malaria as soon as possible."*

# Issues related to the study of rectal Artesunate in patients with acute malaria

**Challenge to develop appropriate studies:**

Since rectal artesunate is to be used as emergency treatment for malaria
when no alternatives are available, the practical question is whether
the emergency use of a single dose of rectal artesunate is more
effective than no treatment in reducing malaria morbidity and mortality.

Given the high mortality from untreated malaria and the dangers of
delaying effective therapy, treatment cannot be ethically withheld for
the first 24 hours. For these reasons, the product has been studied in
trials employing active comparators. In these studies, provisions are
made for the "rescue" of patients showing an unsatisfactory clinical or
parasitological response. While these studies do not directly address
the advantages of rectal artesunate over no treatment, they give a
relative idea of efficacy versus the "standard of care".

**Approach**:

Three pivotal studies used a single dose of rectal artesunate alone for
the first 24 hours and compared this with standard therapy for 24 hours.
This was followed by a definitive or "consolidation" regimen in both
treatment arms.

**Shortcomings in reflecting projected use:**

-   The diagnosis of malaria was confirmed in study participants. This
    would not be the case in the bush where malaria might be confused
    with meningitis, typhoid and a host of other febrile illnesses.

-   The studies provided ancillary treatment: fluid, transfusions,
    antipyretics, and anticonvulsants. These would not be available in
    the bush.

-   Drug administration was well supervised. In the bush, supervision
    would depend upon family members.

-   Patients in the field might get a false sense of security after
    rectal treatment and fail to present for definitive therapy.

    **Design problems**:

Study populations were drawn from communities where malaria was
prevalent and were likely to show various degrees of malarial immunity.

Difficulties were apparent in attempts to standardize the severity of
disease.

-   In some studies the inability to take orally was taken as a sign of
    severity.

-   In others impairment of consciousness was taken as a sign of
    severity.

-   Baseline parasitemia varied from study to study.

-   Where malaria was more prevalent, subjects were likely to have some
    immunity and to tolerate higher parasitemias with milder clinical
    manifestations.

Mindful of the serious consequences if treatment failed, the applicant
allowed subjects in the rectal artesunate arm of the studies to be
rescued with standard therapy if the parasite count failed to reach 60%
of baseline by 12 hours. (Rescue of subjects in the comparator arm was
permitted in 2 of the 3 pivotal studies.)

Since the efficacy of AS is being tested for 24 hours, the evaluation of
patients rescued before this time is difficult.

\- Evaluating them as successes effectively ignores the contribution of
the rescue therapy.

> \- Evaluating them as failures discounts the possibility that in some
> patients, the parasitological response may be a little slower
>
> \- Excluding them from the analysis relegates the efficacy analysis to
> "successes amongst the successes"

**The problem of endpoints:**

*Is parasitemia an appropriate surrogate for clinical response?*

Responses in peripheral parasitemia are an useful indication of the
activity of antimalarial drugs for several reasons:

-   Since untreated patients generally demonstrate rising levels of
    parasitemia with time, decreases in parasitemia are a persuasive
    reflection of drug activity.

-   Parasite counts provide a quantifiable measurement of drug activity
    allowing a measurable comparison of different treatment regimens.

-   The parasite count is a simple and robust test that is easy to
    perform and easy to interpret.

However, responses in peripheral parasitemia may not always reflect the
clinical outcome and the following pitfalls should be borne in mind:

-   Sequestration of parasites in the spleen and other organs has been
    described and may account for the morbidity and mortality in some
    patients with low peripheral parasite counts. Thus resolution of
    peripheral parasitemia may not always reflect the clinical outcome.

-   Potentially fatal complications of malaria, such as renal failure or
    pulmonary edema, may supervene even when the peripheral parasite
    count is very low.

-   The degree of parasitemia correlates to some extent with severity of
    disease. In non-immune patients, parasitemias affecting more than 5%
    of peripheral erythrocytes are taken to indicate severe malaria
    according to WHO (Trans Roy Soc Trop Med Hyg 1990, 84 Supple 2
    1-65). However the parasite count may not always reflect malaria
    severity, as semi-immune patients may tolerate this degree of
    parasitemia with minimal symptoms.

    *Issues in selecting appropriate endpoints to reflect drug efficacy*

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```
-   The rate of parasite clearance indicates one aspect of drug
    performance that may correlate with efficacy. However, to date, no
    clinical advantage (in terms of morbidity or mortality) has been
    identified using artemisinins (which clear parasites very rapidly)
    compared to quinine (which clears parasites more slowly).

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```
-   The median rate of parasite clearance in a group of patients may
    also fail to reflect the percentage of outlying individuals who
    respond poorly.

-   Clinical failures may occur despite disappearance of parasites from
    peripheral blood.

-   An evaluation several weeks after presentation generally should
    reflect the initial outcome of treatment but is complicated by
    losses to follow up, new infections and recrudescent infection. In
    the clinical trials reflected in this NDA, the long-term outcome
    depends substantially on the efficacy of the drugs used following
    the initial dose of rectal artesunate.

-   The relative morbidity and mortality of initial attacks of malaria
    versus recrudescent attacks after therapy in patients without access
    to medical care is not clear.

Ultimately, the evaluation of efficacy depends on the aggregate of
clinical and parasitological responses evaluated over several weeks.

**Safety:**

Safety may be difficult to assess in sick patients with malaria.
Neurological symptoms are difficult to determine in young children.
Malaria itself may produce neurological symptoms. Occasionally these may
be severe and long lasting.

# Pharmacotoxicology

Based on the known toxicity profile of the artemisinin compounds, the
applicant agreed to conduct a nonclinical study to determine the
neurotoxic potential of artesunate. The study was to determine the dose,
duration of dosing, and possibly the total systemic exposure to
artesunate needed to produce unacceptable neurotoxicity in an
appropriate animal model. A subacute repeat-dose oral and intravenous
toxicity study in rats was conducted to address these issues. In the
original study design, rat dosing groups (16 rats/group) received oral
doses of 33, 75, or 150 mg/kg/day or intravenous doses of 10 mg/kg (3
times daily), or 30 mg/kg (3 times daily), for seven days followed by
either necropsy (8 rats/group) or a 14-day recovery (8 rats/group).
During the study, mortality, weight loss, hypoactivity, decreased food
consumption and perianal/urogenital staining were observed in the 75 and
150 mg/kg/day oral dose groups and 90 mg/kg/day intravenous group as
early as Day 3.

Of particular concern was the failure to conduct either behavioral
assessments or specific neuropathologic examinations needed to determine
the parameters of interest (dose and duration of dosing needed to
produce neurotoxicity). Especially troubling was the fact that rats died
on study (1/16 and 2/16 receiving 75 and 150 mg/kg, respectively, after
as little as three days of dosing), or were sacrificed early (90
mg/kg/day intravenous group, day 3) because of poor health. The cause of
death was not determined, leaving open the possibility that the animals
died due to neurotoxic effects (or possibly other toxicities). To
further compound the problem, treatment was discontinued in the
surviving rats in these dose groups, limiting actual exposure to
artesunate. Necropsy results on these animals cannot be taken to
indicate lack of neurotoxicity since these animals received much less
drug than originally planned and were sacrificed as long as 10 days
after the final oral doses. (In fact, in rats surviving until scheduled
sacrifice, hepatic toxicity was noted in all treatment groups,
consisting of centrilobular hepatocyte hypertrophy, sinusoidal
inflammation cells, single cell necrosis, diffuse hepatocyte vacuolation
and periportal vacuolation. Hepatic effects were not observed in
recovery group animals.)

Histopathologic sectioning of CNS tissues obtained from animals
sacrificed at the end of the study was of uncertain precision. The study
report does not specify that brain loci known to be targets of
artemisinin-induced neuronal damage were examined; it is thus possible
that lesions were present but not observed. Studies have been published
in which the neurotoxicity of artemisinins, including artesunate, was
assessed in rodents using appropriate methods (neurohistology and
functional assays); these published reports could have been used by the
applicant to design an appropriate study to address the issues of
concern (Kamchonwongpaisan et al, 1996; Genovese et al, 1998). These
studies, as well as other published papers, can be taken to indicate
that artesunate is *less* neurotoxic than other artemisinin derivatives
(using both neuropathology as well as functional assays such as drug
effect on balance and gait). However, in one published study
(Nontprasert et al, 2000), artesunate was given to mice by daily oral
gavage for 28 consecutive days followed by a 120-day recovery period;
neurotoxic effects were observed at exposures similar to clinical doses

A further problem in assessing the findings in the subacute oral
toxicity study in rats is that an inappropriate method of comparing
rodent to human doses was used. Dose comparisons should be made based on
relative body surface areas, not body weights. Using comparative body
surface areas for calculations of dose equivalents, the safety margin
between the proposed human dose and doses that produced adverse effects
in rats (poor condition and death) is not of the same magnitude as
reported by the applicant (see the table below). Based on this method,
the following human equivalent doses were used in the subacute oral
toxicity study in rats:

**Table 1**: Dose comparison based on body surface area differences

+-----------------+---------------+------------+------------+--------+
| Rat dose        | Human         | Multiple   | Toxicity   | Mor    |
| (mg/kg),        | equivalent    | of human   |            | tality |
|                 | dose          | dose       |            |        |
| 7-day study,    |               |            |            |        |
| oral dose       | (mg/kg)       |            |            |        |
+-----------------+---------------+------------+------------+--------+
| 33              | 5.5           | 0.55       | Liver (?)  |        |
+-----------------+---------------+------------+------------+--------+
| 75              | 12.5          | 1.25       | Liver (?)  | 1/16   |
+-----------------+---------------+------------+------------+--------+
| 150             | 25            | 2.5        | Liver (?)  | 2/16   |
+-----------------+---------------+------------+------------+--------+

Determination of systemic drug exposures (C~max~, AUC) at which
toxicities were observed in animals is the most useful method for
establishing safe doses in humans. However, the ability to compare
systemic artesunate exposure in nonclinical studies conducted by the
applicant is limited by the quality of the available data. In a single
dose toxicity study in rats, C~max~ of 442.3 ng/ml at 150 mg/kg , p.o.,
were calculated with AUC of 520 ng•hr/ml. If linear pharmacokinetics are
assumed an extrapolation for the 75 mg/kg p.o. dose in rats provides a
C~max~ of about 220 ng/ml and AUC of 250 ng•hr/ml. These exposures, at
which deaths occurred, compare to clinical exposures following a rectal
dose of 10 mg/kg producing a C~max~ of about 1100 ng/ml and AUC of 4300
ng•hr/ml. Unfortunately, pharmacokinetic data supplied by the applicant
are not reliable based on careful review. The limited cumulative dose
exposure from the 7-day rat study in which the dosing duration was
shortened does not permit a valid toxicity comparison relevant to human
exposure. Therefore, safe doses can only be determined by calculation
using relative body surface areas.

Additional non-GLP studies performed in the People's Republic of China
during the 1980's were included in support of the application. The
studies are of uncertain value since these could not be audited and the
translations from Chinese are of poor quality. However, adverse effects,
such as hepatotoxicity and hematotoxicity, were reported in dogs and
rats given both acute and repeated oral and intravenous doses of
artesunate.

In summary, the apparent major safety concern for artesunate,
neurotoxicity, remains inadequately characterized. The nonclinical study
designed to assess neurotoxic potential was not performed in a way that
provides useful data. Published studies provide some relevant
information for determining safety. While artesunate appears to have
less neurotoxic potential compared to other artemisinins, mice exhibited
neurotoxicity after prolonged exposure. The issue of an unacceptably
toxic dose has not been addressed and neurotoxicity must be considered a
risk following multiple-dose exposure in humans. The possibility that
artesunate also produces hepatotoxicity has not been adequately
addressed (this was an unanticipated finding.)

# Microbiology

**Biology of the parasite:**

Over 100 species of *Plasmodium* have been shown to cause malaria in a
wide variety of vertebrate hosts. The four species known to infect man
are *P. falciparum*, *P. vivax*, *P. malaria*, and *P. ovale*. The life
cycle of the malaria parasite (*Plasmodium*) is divided between 2 hosts:
mosquitoes (as a vector) and vertebrates (Figure 1). Infection in humans
is initiated by the bite of infected mosquitoes and sporozoites are
inoculated into the blood stream. Within 2 hours, the sporozoites
migrate to the liver and penetrate the hepatocytes. After 1 to 2 weeks,
the sporozoites undergo nuclear division to produce thousands of
merozoites that are released by the rupture of the host cell. This phase
of the life cycle of *Plasmodium* is called **exoerythrocytic** or
**liver schizogonic phase**. The merozoites invade the erythrocytes and
progress through a series of developmental forms into mature
erythrocytic schizonts. Each merozoite matures into a schizont,
undergoes asexual multiplication, and forms 24 merozoites. The red blood
cells rupture and the merozoites invade other erythrocytes. This part of
the life cycle is called the **erythrocytic phase** and takes about 24
to 72 hours. Fever is associated with the rupture of infected red blood
cells. Severe or fatal complications can occur at any time and are
related to blockage of blood vessels in the internal organs such as
brain, spleen, bone marrow, etc. Some merozoites mature into male and
female gametocytes within the erythrocytes. The maturation of these
gametes occurs once the infected blood is ingested by the mosquitoes.
The gametes undergo fertilization within the vector and form a zygote.
This is followed by the elongation of a zygote to form an ookinete in
about 12 to 48 hours. The ookinetes invade the stomach of the mosquito
and develop into oocysts. The oocyst enlarges forming over 10,000
sporozoites (in about a week after the formation of the oocyst). The
sporozoites released by the rupture of the oocyst migrate to the
salivary glands of the mosquitoes and are inoculated into humans the
next time the mosquito feeds (i.e., during a blood meal).

![](media/image2.png){width="4.882638888888889in"
height="3.252083333333333in"}

## 

In patients with *P. falciparum* infection, recurrence is generally
thought to be due to **recrudescence,** which is caused by residual
erythrocytic forms; whereas in *P. vivax* and *P. ovale* **relapse** of
an infection is considered to be due to dormant parasites
(**hypnozoites**) in the liver which undergo development and release
merozoites into circulation.

**Mechanism of action:**

Artesunate is a water soluble derivative of artemisinin, an antimalarial
compound isolated from the Chinese herb Qinghao (*Artemisia annua*).
Artesunate is rapidly metabolized to dihydroartemisinin (DHA) in the
body. Chemically, artesunate, and its active metabolite, DHA, are
sesquiterpene lactones with a trioxane ring containing a peroxide
bridge. The peroxide bridge appears to be essential for the antimalarial
activity of artesunate. Structure-activity relationship studies show
that the deoxy derivative of DHA (that lack the peroxide bridge) was
277-fold less active than DHA. The activity of deoxyartesunate was not
measured. Deoxy derivatives of other artemisinin analogs were 10- to
1000-fold less active compared to the parent compounds. Artesunate
increases superoxide anion production and lipid peroxidation in
falciparum-infected erythrocytes *in vitro*. However, artesunate does
not suppress the activity of antioxidant enzymes (superoxide dismutase,
catalase, glutathione reductase, and glutathione peroxidase) in infected
or uninfected erythrocytes.

Erythrocytes infected with the ring or trophozoite forms *in vitro*
accumulate 100- and 180- fold higher concentrations of DHA (12 nM i.e.,
3.40 ng/ml), respectively, compared to uninfected erythrocytes. These
experiments were performed in a medium containing 10% human serum. The
relevance of these findings to the uptake *in vivo* is unclear. The
precise mechanism by which artesunate exhibits antiplasmodial activity
is not understood.

**Activity *in vitro*:**

Artesunate and DHA exhibit activity against the erythrocytic stages of
*P. falciparum*, which includes laboratory strains and several clinical
isolates from different geographical areas. The antiparasitic activity
was measured by incorporation of ^3^H-hypoxanthine or by microscopic
observations. A majority of these studies were done by incubating the
asynchronous parasites with the drug for 24 to 48 hours. The results
expressed as 50% inhibitory concentration (IC~50~) show the artesunate
and DHA IC~50~ values against the laboratory strains or clinical
isolates to be \< 7 and \< 24 ng/ml, respectively (Tables 2 and 3).

**Table 2**: *In vitro* activity against the laboratory strains of *P.
falciparum*.

+---------------+-------------------+-----------------+---------------+
| **Strain**    | **Resistance**    | **Artesunate**  | **DHA**       |
|               |                   |                 |               |
|               |                   | **IC~50~        | **IC~50~      |
|               |                   | (ng/ml)**       | (ng/ml)**     |
+---------------+-------------------+-----------------+---------------+
| FCC-1/HN      | Chloroquine       | 1.04            | ND            |
|               | sensitive         |                 |               |
+---------------+-------------------+-----------------+---------------+
| D10           | Chlo              | 2.14 (0.12 -    | (0.28 -       |
|               | roquine-sensitive | 2.46)\*         | 1.15)\*       |
+---------------+-------------------+-----------------+---------------+
| 3D7           | Chlo              | (0.12 - 0.20)\* | (0.28 -       |
|               | roquine-sensitive |                 | 1.15)\*       |
+---------------+-------------------+-----------------+---------------+
| RSA11         | Chlo              | 1.32 (1.01 -    | ND            |
|               | roquine-resistant | 1.63)\*         |               |
+---------------+-------------------+-----------------+---------------+
| FCD-3         | Chlo              | ND              | 2.70          |
|               | roquine-resistant |                 |               |
+---------------+-------------------+-----------------+---------------+
| K1            | Chlo              | 5.60 (4.70 -    | 3.60 (2.30 -  |
|               | roquine-resistant | 6.90)\*         | 3.80)\*       |
|               |                   |                 |               |
|               |                   | 4.60 (4.00 -    | 3.10 (2.90 -  |
|               |                   | 5.50)\*         | 3.60)\*       |
+---------------+-------------------+-----------------+---------------+
| W2/ Indochina | Chlo              | 0.64            | 0.68          |
|               | roquine-resistant |                 |               |
|               | and               |                 |               |
|               |                   |                 |               |
|               | Mef               |                 |               |
|               | loquine-sensitive |                 |               |
+---------------+-------------------+-----------------+---------------+
| D6/Sierra     | Chlo              | 0.84            | 0.70          |
| Leone         | roquine-sensitive |                 |               |
|               | and               |                 |               |
|               |                   |                 |               |
|               | Mef               |                 |               |
|               | loquine-resistant |                 |               |
+---------------+-------------------+-----------------+---------------+

> \*Represents the results of multiple testing. ND = not done.

**Table 3**: *In vitro* activity against *P. falciparum* isolates from
different geographical regions.

+-----------+----+----------------+-----------+----------+------------+
| *         | *  | **Resistance** | **Art     | **DHA**  | **R        |
| *Region** | *N |                | esunate** |          | eference** |
|           | ** |                |           | **Mean   |            |
|           |    |                | **Mean    | (range)  |            |
|           |    |                | (range)   | IC~50~   |            |
|           |    |                | IC~50~**  | ng/ml**  |            |
|           |    |                |           |          |            |
|           |    |                | **ng/ml** |          |            |
+-----------+----+----------------+-----------+----------+------------+
| Ph        | 24 | Chloroquine    | 0.35      | ND       | Bustos *et |
| ilippines |    | and            | (0.12 -   |          | al.,* 1994 |
|           |    | amodiaquine    | 3.15)     |          |            |
+-----------+----+----------------+-----------+----------+------------+
| Vietnam   | 10 | Chloroquine,   | 1.24      | 0.92     | Wongsr     |
|           |    | amodiaquine,   | (1.13 -   | (0.84 -  | ichanalani |
|           |    | mefloquine,    | 1.36)     | 1.01)    | *et al.,*  |
|           |    | and            |           |          | 1997       |
|           |    | sulfadoxine    |           |          |            |
|           |    | /pyrimethamine |           |          |            |
+-----------+----+----------------+-----------+----------+------------+
| Vietnam   | 4  | Chloroquine    | NA        | NA       | Skinner    |
| and China |    |                | (0.08 -   | (0.23 -  | *et al.,*  |
|           |    |                | 0.24)     | 0.85)    | 1997       |
+-----------+----+----------------+-----------+----------+------------+
| Chin      | 51 | Chloroquine    | 2.30 (NA) | 3.70 -   | Yang *et   |
| a-Mynamar |    |                |           | 3.98     | al.,* 1997 |
|           |    |                |           | (NA)^a^  |            |
+-----------+----+----------------+-----------+----------+------------+
| Chi       | 42 | Chloroquine    | 1.92 -    | 1.14 -   | Yang *et   |
| na-LaoPDR |    |                | 2.69 (NA) | 1.42     | al.,* 1997 |
|           |    |                |           | (NA)     |            |
+-----------+----+----------------+-----------+----------+------------+
| Thailand  | 86 | Chloroquine    | NA        | NA       | Wongsr     |
|           |    | and mefloquine | (0.36 -   | (0.34 -  | ichanalani |
|           |    |                | 1.65)     | 0.98)^b^ | *et al.,*  |
|           |    |                |           |          | 1999       |
+-----------+----+----------------+-----------+----------+------------+
| Africa    | 79 | Chloroquine    | ND        | NA       | Le Bras    |
|           |    |                |           | (0.25 -  | *et al.,*  |
|           |    |                |           | 0.43)    | 1998       |
+-----------+----+----------------+-----------+----------+------------+
| Tha       | 1  | Chloroquine,   | 1.62      | 1.22 (   | Brockman   |
| i-Burmese | 78 | amodiaquine,   | (0.19 -   | 0.15 -   | *et al.,*  |
| Border    |    | sulfadoxine    | 13        | 6.       |            |
|           | 72 | -pyrimethamine | .30)^c,e^ | 60)^c,f^ | 2000       |
|           |    |                |           |          |            |
|           |    | and mefloquine | 2.35      | 1.43     |            |
|           |    |                | (0.34 -   | (0.24 -  |            |
|           |    |                | 23        | 8.       |            |
|           |    |                | .40)^d,g^ | 10)^d,h^ |            |
+-----------+----+----------------+-----------+----------+------------+
| **IC~50~  |    |                |           |          |            |
| Range**   |    |                |           |          |            |
| 0.08 -    |    |                |           |          |            |
| 23.4      |    |                |           |          |            |
| 0.15 -    |    |                |           |          |            |
| 8.10      |    |                |           |          |            |
|           |    |                |           |          |            |
| **        |    |                |           |          |            |
| (ng/ml)** |    |                |           |          |            |
| (n = 467) |    |                |           |          |            |
| (n = 322) |    |                |           |          |            |
+-----------+----+----------------+-----------+----------+------------+

> NA = Not available;
>
> ND = not done;
>
> ^a^14 isolates were tested;
>
> ^b^ 45 isolates were tested;
>
> ^c^ primary infection isolates
>
> ^d^ recrudescent isolates \[after treatment with mefloquine (25
> mg/kg) + artesunate (12 mg/kg x 3 days)\]
>
> ^e^ 95% CI (1.4 - 1.8 ng/ml)
>
> ^f^ 84 isolates, 95% CI (1.9 - 2.9 ng/ml)
>
> ^g^ 95% CI (1.0 - 1.5 ng/ml)
>
> ^h^ 44 isolates, 95% CI (1.1 - 1.8 ng/ml)

Studies using synchronous culture show a rapid inhibition of the ring,
trophozoites, and schizont forms of *P. falciparum* within 2 hours of
exposure to DHA at a concentration equivalent to the IC~90~ value
(Figure 2).

![](media/image3.png){width="3.9881944444444444in"
height="4.029861111111111in"}

> Figure 2: Stage-specific activities of quinine, artemisinin,
> artemether, and DHA on culture-adapted parasites of *Plasmodium
> falciparum*. Synchronized cultures of rings (0 h; •), trophozoites
> (20-24 h; ) and schizonts (36 h; ) were exposed to the IC~90~
> concentration (not specified) of each drug up to 10 hours. The data
> are presented as percentage growth inhibition ± S.D. with time of drug
> exposure for the 3 asexual stages compared with untreated controls.
> The IC~50~ values were as shown below:
>
> Drug IC~50~ values (M)
>
> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
>
> DHA 0.8 - 3.0 x 10^-9^
>
> (0.28 - 0.85 ng/ml)
>
> Artemisinin 2.0 - 30.0 x 10^-9^
>
> Artemether 7.0 - 30.0 x 10^-12^
>
> Quinine 3.0 - 10.0 x 10^-8^
>
> (Skinner *et al.,* 1996)

Studies using predominantly gametocytes in culture showed that the DHA
IC~50~ value to be 6.6 ng/ml. Time to gametocyte kill was not measured.

The activity of artesunate may vary with the source of erythrocytes. For
example, artesunate was 3- to 10-fold less active against the K1 strain
of *P. falciparum* using genetically variant erythrocytes from patients
with α-thalassemia (hemoglobin Hb\[H\] and Constant spring, HbCS) than
normal RBCs. The activity of chloroquine was similarly altered whereas
that of pyrimethamine was not altered by the source of the erythrocytes.

No studies were done to demonstrate the *in vitro* activity of
artesunate or DHA against the hepatic stage of the *Plasmodium* species.

**Activity *in vivo*:**

The activity of artesunate and DHA was measured against the erythrocytic
forms of *P. falciparum, P. berghei, P. knowlesi*, and *P. coatneyi* in
mice or monkeys. In a preliminary study conducted in immunocompromised
mice infected with the T24 strain (chloroquine and quinine resistant) of
*P. falciparum*, a complete clearance of parasite from the blood was
observed on Day 2 of treatment with DHA (50 mg/kg for 2 days) by the
oral route. Microscopic observations at 24 hours showed predominantly
pycnotic forms (76%), some altered trophozoites (10%), few trophozoites
(1%), and schizonts (3%). At 48 hours, only pycnotic forms were
observed. Chloroquine and quinine were not effective in clearing the
parasitemia in mice infected with the T24 strain. Treatment with
chloroquine induced minimal alterations in morphology (11 - 16% pycnotic
forms). However, against a chloroquine sensitive strain (NF54)
morphological changes after treatment with chloroquine were similar to
that of DHA against the chloroquine-resistant strain. The activity of
artesunate was not measured.

In mice infected with *P. berghei (*173N strain) and treated with
intravenous artesunate or chloroquine*,* a 50% and 90% reduction in
parasitemia was observed by 18 to 24 hours, and 24 to 30 hours,
respectively. Recrudescence was observed on Day 28 in mice treated with
artesunate (110 mg/kg) for 5 days by the intravenous route. However,
chloroquine (14.9 mg/kg for 5 days) completely cured the mice on Day 28.
In another study, mice infected with another strain of *P. berghei*
(ANKA strain) showed complete cure on Day 60 after intramuscular
treatment with ≥ 56 mg/kg artesunate. Complete clearance of the
parasitemia was observed within 2 days of treatment. Similar
observations were made with DHA. The variation in the activity of
artesunate in the different studies may be due to the different strains
of *P. berghei* used for infection, the route of drug administration or
severity of infection.

In monkeys infected with *P. knowlesi*, the intravenous administration
of artesunate (10 mg/kg for 7 days) reduced the parasitemia by 90% at 13
hours. The parasite clearance time (PCT) was 42 hours and all 3 monkeys
remained negative for 28 days of observation. However, at the lower dose
(3.16 mg/kg), although the PCT was 40 hours, 1/3 monkeys showed
recrudescence on Day 15. At a higher dose (31.6 mg/kg), the mean
parasite clearance time was 56 hours and no recrudescence was observed.
Quinine at 10 mg/kg dose was effective in reducing the parasitemia by
50% in 3.3 hours, however, a 90% reduction of parasitemia was not
attained. At a higher dose (31.6 mg/kg), the mean time to parasite
clearance was 104 hours and recrudescence was observed 2 to 10 days
after parasite clearance.

In another study, normal and splenectomized monkeys infected with *P.
coatneyi* were treated with artesunate. The clearance of parasitemia was
slower in splenectomized animals compared to normal controls. The
reduction in parasitemia at 24 hours in the splenectomized and
non-splenectomized animals was 86% and 99%, respectively. Infected
erythrocytes showed ultrastructural changes such as enlargement of food
vacuoles and ribosomal clumping 4 hours after administration of
artesunate.

The activity of artesunate against hepatic stages of the *Plasmodium*
species was not examined.

**Resistance:**

A potential for resistance development by *Plasmodium* species to
artesunate was examined *in vitro* and *in vivo*. In a preliminary
study, the erythrocytic forms of the FCR3 strain of *P. falciparum* were
passaged by exposure to increasing concentrations of artesunate
(starting with 4 ng/ml) for 48 hours each, followed by growth in
drug-free medium for 18 days (equivalent to 9 life cycles). The
artesunate IC~50~ value increased by 3-fold after 6 to 7 passages over a
period of 130 days. Such an effect was reversible when the parasites
were grown in drug free medium for 5 weeks.

Studies *in vivo* show that serial passage of the N strain of *P.
berghei* in mice treated with escalating doses of artesunate for 4 days
each, increased the 90% effective dose (ED~90~) by about 29-fold after
21 passages (85 days). The effect was reversible after discontinuation
of therapy. However, the clinical significance of these observations is
unknown.

In patients with severe or moderate malaria, treatment with a single
dose of rectal artesunate decreased the parasite count by \> 90% in 24
hours. In patients treated with multiple doses of artesunate (oral,
rectal or IV) the parasite clearance time was 16 to 56 hours. However,
recrudescence was reported on Days 10 to 28 after discontinuation of
therapy. In the absence of genotyping and phenotyping it is unclear
whether the recrudescence is due to resistance. Also, the presence of
dormant parasites cannot be ruled out.

**Cross-resistance:**

*P. falciparum* strains with chloroquine resistance (IC~50~ \> 100 nM)
and mefloquine resistance (\> 20 nM) were susceptible to artesunate *in
vitro*. However, a positive correlation was observed between the *in
vitro* activity of artesunate and those of halofantrine, mefloquine,
quinine, or atovaquone, suggesting cross-resistance. The clinical
significance of the *in vitro* observations is unclear.

Although no correlation was observed between the *in vitro* activity of
artesunate and chloroquine against *P. falciparum*, a 16 - 17 fold
higher concentration of artesunate was required to suppress 90% of
asexual forms of *P. berghei* chloroquine-resistant RC strain than the
chloroquine-sensitive N strain in mice, suggesting likelihood of
cross-resistance. However, in another study DHA was effective in
clearing parasitemia in mice infected with a chloroquine-resistant T24
strain of *P. falciparum.*

In clinical studies, artesunate was effective in the treatment of *P.
falciparum* infections from regions known to be resistant to
chloroquine.

**Drug combination:**

The *in vitro* activity of artesunate in combination with other drugs
against *P. falciparum* was measured. A combination of artesunate with
mefloquine or quinine was synergistic against *P. falciparum*. However,
a combination of artesunate with pyrimethamine was antagonistic. The
combination of artesunate with chloroquine varied from additive to
anatgonistic against the different *P. falciparum* strains tested. The
oxidant drugs (miconazole and doxorubicin) also show a synergistic
effect in combination with artesunate. The *in vivo* activity of
artesunate in combination with other antimalarials was not examined.

The activity of artemisinin in combination with other antimalarial drugs
against *P. falciparum* was measured *in vitro* and against *P. berghei*
*in vivo*. A combination of artemisinin with mefloquine was synergistic
whereas that with pyrimethamine was antagonistic *in vitro* and *in
vivo*. A combination of artemisinin with other antimalarials
(sulfadiazine, sulfadoxine, sulfadoxine-pyrimethamine, cycloguanil, and
dapsone) was also shown to be antagonistic *in vivo*.

# Clinical Issues

## Efficacy

An overview of the studies supporting clinical efficacy is provided
below.

**Table 4**: Synopsis of data supporting the efficacy of rectal
artesunate in NDA 21-242

  -------------- -------------- -------------- -------------- --------------
  **Study        **Clinical     **\# Allocated **\# Allocated **Type of
  number**       Site           to Rectal      to             Patient**
                 Location**     Artesunate**   Comparator**   

  003            Thailand       24             24             Adults

  004            Ghana          24             12             Children

  005            Thailand       46             17             Children

  006            Malawi         87             22             Children

  007            South Africa   27             8              Adults

  014            Thailand       69             0              Adults

  009            (literature)                                 

  010            (literature)                                 

  011            (literature)                                 
  -------------- -------------- -------------- -------------- --------------

**Studies in patients with clinical malaria**

Six studies were performed on patients with clinical malaria.

Three comparative studies (005, 006, and 007) employed the projected
dose of rectal artesunate given alone for the first 24 hours of therapy
in the experimental arm. These were regarded as pivotal studies.

A bioequivalence study (Thailand 014) comparing 3 formulations of rectal
artesunate in the projected dosing regimen provided further
non-comparative data on the safety and efficacy of rectal artesunate,
when used as proposed.

Two further studies (Thailand 003, Ghana 004) employed regimens for
rectal artesunate that differed either in dosage or duration from the
projected use and provided supportive information.

Data from three older published studies (009, 010, and 011) were
reanalyzed by the applicant and presented as supportive data. The dose
of rectal artesunate in each of these studies was twice the proposed
clinical dose. As such, these studies did not support the efficacy of
the proposed dose, although the information provided some evidence of
safety.

### Pivotal studies

FDA considered three studies, performed in Thailand, Malawi and South
Africa, as pivotal in supporting this indication. In each of these
studies the experimental arm involved treatment with rectal artesunate
10mg/kg as a single dose for the first 24 hours, followed by one of
several follow-up or "consolidation" antimalarial regimens. All three
studies were randomized, comparative and unblinded.

The studies differed in several ways from the envisaged use of the
product. In all three studies, patients were admitted to hospital. The
diagnosis of malaria was confirmed on smear, and the progress of
parasitemia was monitored. Permitted ancillary treatment including
transfusions, parenteral fluids, anticonvulsants, antipyretics, and
glucose given at the clinicians' discretion.

The study designs are compared below

**Table 5**: Drug regimens used in pivotal studies

+------------+-------------------+------------------+------------------+
|            | **Location (Study |                  |                  |
|            | No)**             |                  |                  |
+------------+-------------------+------------------+------------------+
|            | **Thailand        | **Malawi (006)** | **South Africa   |
|            | (005)**           |                  | (007)**          |
+------------+-------------------+------------------+------------------+
| Ex         | Rectal AS         | Rectal AS        | Rectal AS        |
| perimental | (10mg/kg) single  | (10mg/kg) single | (10mg/kg) single |
| arm        | dose              | dose             | dose             |
+------------+-------------------+------------------+------------------+
| Comparator | [Oral             | [Quin            | [Quin            |
|            | AS]{.underline}   | ine]{.underline} | ine]{.underline} |
|            | (4 mg/kg) single  | 10mg/kg IM or IV | 10mg/kg IM or IV |
|            | dose              | at 0, 4 hrs then | at 0, 4 and      |
|            |                   | 12 hourly till   | 12hrs            |
|            |                   | oral treatment   |                  |
|            |                   | tolerated        |                  |
+------------+-------------------+------------------+------------------+
| Con        | **24 hrs**:       | **24 hrs**:      | **24 hrs**:      |
| solidation |                   |                  |                  |
| regimen    | [Oral             | [Oral            | [Oral            |
|            | AS]{.underline}   | S                | SP]{.underline}  |
|            | (2mg/kg)          | P\*]{.underline} | (3 tablets)      |
|            |                   | (25mg/kg SDX)    | single dose      |
|            | **48 hrs**:       |                  |                  |
|            |                   | (or "standard    | (or IM quinine   |
|            | [Oral             | dose" parenteral | 10mg/kg if       |
|            | AS]{.underline}   | quinine if       | unable to take   |
|            | (2mg/kg)          | unable to take   | orally)          |
|            |                   | orally)          |                  |
|            | \+                |                  |                  |
|            | [MQ]{.underline}  | SP given at 24   |                  |
|            | (15mg/kg)         | hours in         |                  |
|            |                   | experimental arm |                  |
|            | **72 hrs**:       |                  |                  |
|            |                   | SP given after a |                  |
|            | [Oral             | minimum of 2     |                  |
|            | AS]{.underline}   | doses of quinine |                  |
|            | (1mg/kg)          | in comparator    |                  |
|            |                   | arm              |                  |
|            | \+                |                  |                  |
|            | [MQ]{.underline}  |                  |                  |
|            | (10mg/kg)         |                  |                  |
|            |                   |                  |                  |
|            | **Daily for 6     |                  |                  |
|            | more days**:      |                  |                  |
|            |                   |                  |                  |
|            | [Oral             |                  |                  |
|            | AS]{.underline}   |                  |                  |
|            | (1mg/kg)          |                  |                  |
+------------+-------------------+------------------+------------------+

\*SP - sulfadoxine-pyrimethamine

> \[The raw pharmacokinetic data from Study 07 have not been submitted
> and therefore a detailed review has not been performed to verify the
> pharmacokinetic parameters obtained in this study.\]

**Comment on treatment regimens:**

The final treatment outcome, several weeks after completing therapy, is
a reflection of the efficacy of the total treatment regimen. Recurrences
of parasitemia shortly after finishing treatment may reflect a treatment
regimen that is inadequate in terms of dose or duration, or infection
with a parasite that has some degree of resistance to the drug.

SP is a long-acting agent and the recommended regimen for the treatment
of acute malaria in adults is a single dose of 3 tablets. (In children,
an appropriate single dose is calculated on a mg/kg basis.) Malaria that
is resistant to SP is common, and may vary by geographic region. Thus,
studies performed in different locations may show different long-term
outcomes when SP is used. In parts of Africa, resistance to SP may be
present in up to 60% of cases.

Mefloquine is a long-acting agent and the recommended regimen for the
treatment of acute malaria in adults is a single dose of 1250mg.
Mefloquine resistance appears less prevalent than SP resistance.
Mefloquine has been used in combinations with artemisinin derivatives
for the clinical management of malaria in parts of Thailand where
multidrug resistant *P falciparum* is prevalent.

Quinine sulphate is used to treat malaria in adults at a dose of 600 mg
tid for 7 days, often in combination with doxycycline. Shorter courses
are prone to result in recrudescences.

The entry criteria aimed to capture "moderately severe" malaria.

**Table 6**: Inclusion and exclusion criteria for pivotal studies

+------------+------------------+------------------+------------------+
|            | **Location       |                  |                  |
|            | (Study No.)**    |                  |                  |
+------------+------------------+------------------+------------------+
|            | **Thailand       | **Malawi (006)** | **South Africa   |
|            | (005)**          |                  | (007)**          |
+------------+------------------+------------------+------------------+
| Age        | 6 months-15      | 1 -- 10 years    | 16 years -- 65   |
|            | years            |                  | years            |
+------------+------------------+------------------+------------------+
| Eligible   | \>4%             | \>0.4%           | \-               |
| p          | (200,000/l)     | (\<20,000/l)    |                  |
| arasitemia |                  |                  |                  |
+------------+------------------+------------------+------------------+
| Clinical   | \-               | Unable to eat or | Unable to eat or |
| e          |                  | drink            | drink            |
| ligibility |                  | [or]{.underline} |                  |
|            |                  |                  |                  |
|            |                  | Impaired         |                  |
|            |                  | consciousness    |                  |
+------------+------------------+------------------+------------------+
| Exclusion  | Diarrhea         | Diarrhea         | Diarrhea         |
+------------+------------------+------------------+------------------+
|            | Unable to eat or | \-               | \-               |
|            | drink            |                  |                  |
+------------+------------------+------------------+------------------+
|            | Previous         | Previous         | Previous         |
|            | antimalarial in  | antimalarial in  | antimalarial in  |
|            | past 24 hrs      | past 24 hours    | past 24 hours    |
+------------+------------------+------------------+------------------+
|            | Severe malaria:  | Severe malaria:  | Severe           |
|            |                  |                  | malaria\*:       |
|            | -   Acidotic     | -   Deep         |                  |
|            |                  |     breathing    | -   Respiratory  |
|            | -   Hct \< 15%   |                  |     distress     |
|            |                  | -   Hct \< 18%   |                  |
|            | -   Jaundice     |                  | -   Jaundice     |
|            |                  | -   Jaundice     |                  |
|            | -   Bleeding     |                  | -   Bleeding     |
|            |                  | -   Bleeding     |                  |
|            | -   Shock        |                  | -   Shock        |
|            |                  | -   Shock        |                  |
|            | -   Decreased    |                  | -   Coma         |
|            |                  | -   Stupor or    |                  |
|            |    consciousness |     coma         | -   \>1          |
|            |                  |                  |     Convulsion   |
|            |                  | -   Convulsions  |                  |
|            |                  |                  | -   Renal        |
|            |                  |                  |     failure      |
|            |                  |                  |                  |
|            |                  |                  | ```{=html}       |
|            |                  |                  | <!-- -->         |
|            |                  |                  | ```              |
|            |                  |                  | -   Hypoglycemia |
|            |                  |                  |                  |
|            |                  |                  | -   Lactate \< 5 |
|            |                  |                  |     mmol/l       |
+------------+------------------+------------------+------------------+
|            | Parasitemia      | Parasitemia      | Parasitemia      |
|            | \>20%            | \>10%            | \>10%            |
+------------+------------------+------------------+------------------+

\* Two additional arms were originally included in this study to
incorporate patients with the features of [severe malaria]{.underline}.
Since the treatment in [all]{.underline} these patients was to be
quinine with or without artesunate, the results in these arms were not
considered pivotal to this application. During the study, it was
determined that facilities were inadequate for such sick patients and
these arms were discontinued after recruiting a total of 11 patients.
Among the 11 patients there were 3 deaths. Ultimately all 3 deaths were
attributed to the complications of severe malaria.

**Results**

Characteristics of the study populations are described below:

(In each row of the table, results are listed for the rectal
artesunate-arm above and the comparator-arm below)

**Table 7**: Baseline characteristics of patients in pivotal studies

+-----------------+-----------------+-----------------+-----------------+
|                 | **Location      |                 |                 |
|                 | (Study No.)**   |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
|                 | **Thailand      | **Malawi        | **South Africa  |
|                 | (005)**         | (006)**         | (007)**         |
+-----------------+-----------------+-----------------+-----------------+
| Number of       | 46              | 87              | 27              |
| patients        |                 |                 |                 |
|                 | 17              | 22              | 8               |
| Artesunate      |                 |                 |                 |
|                 |                 |                 |                 |
| Comparator      |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| Mean Age        | 7 years         | 4 ½ years       | 29 yrs          |
|                 |                 |                 |                 |
| Artesunate      | 7 years         | 4 years         | 25 yrs          |
|                 |                 |                 |                 |
| Comparator      |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| \% Males        | 63.5%           | 61.5%           | 51%             |
+-----------------+-----------------+-----------------+-----------------+
| Entry           | Geom mean       | Geom mean       | Median          |
| parasitemia     | 260,600         | 180,000         |                 |
|                 |                 |                 | 55,000          |
| Artesunate      | 409,900         | 217,000         |                 |
|                 |                 |                 | 101,000         |
| Comparator      |                 |                 |                 |
+-----------------+-----------------+-----------------+-----------------+
| Platelet count  | Median          | Geom mean       | Mean            |
|                 |                 |                 |                 |
| Artesunate      | 85,000          | 74,500          | 75,000          |
|                 |                 |                 |                 |
| Comparator      | 129,000         | 67,000          | 72,500          |
+-----------------+-----------------+-----------------+-----------------+

In all three studies, the patient demographics, the severity of disease,
and clinical laboratory results at baseline were balanced between the
treatment arms.

Protocol defined criteria for "rescue" with other antimalarial agents
included:

-   A parasite density 60% of the admission parasite density after 12
    hours.

-   Clinical deterioration with the development of features of severe
    malaria, repeated convulsions or coma.

In each study, "rescue" was permitted as shown:

**Table 8**: Provisions for rescue therapy in pivotal studies

  ----------------------- ----------------------- -----------------------
  **Thailand (005)**      **Malawi (006)**        **South Africa (007)**

  Rescue in both arms     Rescue                  Rescue in both arms
                          [only]{.underline} in   
                          rectal artesunate arm   
  ----------------------- ----------------------- -----------------------

Once a patient was rescued with a non-study drug, any clinical or
parasitological finding subsequent to rescue could not be clearly
attributed to the study drug. The FDA regarded rescued patients as
clinical failures.

It is recognized that this approach erred on the side of stringency
since many patients treated for malaria do not reach a parasite density
\<60% of baseline at 12 hours, despite which they proceed to recover
clinically.

The applicant used the fractional reduction in parasite counts at 12 and
24 hours as the primary basis for the determination of comparative drug
efficacy. In this analysis, clinical and parasitological failures who
received non study-therapy were treated as "withdrawals". Clinical
failures and those patients receiving rescue therapy were separately
presented.

The FDA defined the following clinical and parasitological endpoints to
incorporate data from all patients randomized to treatment, including
those who were rescued because of clinical or parasitological
deterioration.

**Table 9**: FDA defined endpoints

+----------------------+-----------------------------------------------+
| **24-hour clinical   | All treated patients:                         |
| success**            |                                               |
|                      | -   who were evaluated after 24 hours on      |
|                      |     study drug                                |
|                      |                                               |
|                      | ```{=html}                                    |
|                      | <!-- -->                                      |
|                      | ```                                           |
|                      | -   who had not received rescue therapy or    |
|                      |     alternative antimalarial therapy          |
|                      |                                               |
|                      | ```{=html}                                    |
|                      | <!-- -->                                      |
|                      | ```                                           |
|                      | -   who neither died nor deteriorated         |
|                      |     clinically since the baseline evaluation  |
+----------------------+-----------------------------------------------+
| **24-hour            | All 24-hour clinical successes whose 24 hour  |
| parasitological**    | parasite count was 10% of the baseline       |
| **success**          | count\*                                       |
+----------------------+-----------------------------------------------+
| **28-day             | Any patient who received study drug and was   |
| recrudescence/**     | found to have a recurrence of parasitemia     |
|                      | between the time that therapy was stopped and |
| **re-infection**     | day 28.                                       |
+----------------------+-----------------------------------------------+

> \* This composite endpoint was created since it represented the
> outcome just before administration of the follow-up regimen and was
> considered to reflect the activity of rectal artesunate when used as
> proposed while taking into account prior rescue therapy. Since
> parasite clearance \>90% of baseline was a parameter that the
> applicant determined in all studies, and was a clear indicator of a
> favorable treatment response, it provided a suitable representation of
> the parasitological component in the 24-hour efficacy assessment.

Study-related events with an impact on the clinical results are
described in the table below.

**Table 10**: Study related events with an impact on clinical results
for pivotal studies

(In each row of the table, results are listed for the rectal
artesunate-arm above and the comparator-arm below)

+---------------------+-------------+-------------------+-------------+
|                     | **Location  |                   |             |
|                     | (Study      |                   |             |
|                     | No.)**      |                   |             |
+---------------------+-------------+-------------------+-------------+
|                     | **Thailand  | **Malawi (006)**  | **South     |
|                     | (005)**     |                   | Africa      |
|                     |             |                   | (007)**     |
+---------------------+-------------+-------------------+-------------+
| Number of patients  | 46          | 87                | 27          |
|                     |             |                   |             |
| > Artesunate        | 17          | 22                | 8           |
| >                   |             |                   |             |
| > Comparator        |             |                   |             |
+---------------------+-------------+-------------------+-------------+
| Exclusions          | 5           | 3                 | 1           |
|                     |             |                   |             |
| > Artesunate        | 3           | 0                 | 1           |
| >                   |             |                   |             |
| > Comparator        |             |                   |             |
+---------------------+-------------+-------------------+-------------+
| Rescued for 12 hour | 7           | 3                 | 1           |
| parasitemia 60% of |             |                   |             |
| baseline            | 4           | 0 ( no provision  | 2           |
|                     |             | for rescue)       |             |
| > Artesunate        |             |                   |             |
| >                   |             |                   |             |
| > Comparator        |             |                   |             |
+---------------------+-------------+-------------------+-------------+
| Clinical            | 1           | 4                 | 0           |
| deterioration       |             |                   |             |
|                     | 0           | 0                 | 0           |
| > Artesunate        |             |                   |             |
| >                   |             |                   |             |
| > Comparator        |             |                   |             |
+---------------------+-------------+-------------------+-------------+
| Death               | 1           | 0                 | 0           |
|                     |             |                   |             |
| > Artesunate        | 0           | 0                 | 0           |
| >                   |             |                   |             |
| > Comparator        |             |                   |             |
+---------------------+-------------+-------------------+-------------+
| Other failures      | 1 (expelled | 1                 | 0           |
|                     | supps)      |                   |             |
| > Artesunate        |             | N/A               | 0           |
| >                   | N/A         |                   |             |
| > Comparator        |             |                   |             |
+---------------------+-------------+-------------------+-------------+

As detailed above, there was one death in a patient in study 005. The
description of this case is provided below.

**Case report of death on study**

> This 3-year-old boy was admitted following a 24-hour history of fever.
> He was able to sit, stand, drink and eat unaided. Admission parasite
> count was 40/1000 RBC (4%) HCT was 34% WBC 15.3, and platelet count
> 211K. Glucose was 3.3mmol/L. The child was given 3 x 50mg rectal
> capsules.
>
> As the child was not drinking and IV infusion was started at 20 drops
> per minute. It was later noted that 650cc were accidentally infused
> over 77 minutes. Despite this, the child seemed well and was eating
> cake. Two and a half hours after starting therapy the child vomited
> and died suddenly. A parasite count shortly before death was 65/500
> WBC. (Since the RBC was not given, only an approximate comparison of
> this count and the admission count was possible. The follow up count
> (\~0.01%) was substantially lower than the admission count. It was
> found that sodium levels had fallen from 139 to 117, potassium levels
> from 3.5 to 2.5 and albumin from 3.8 to 3.2 over 2 hours. The
> consensus of the investigators and expert consultants was that the
> cause of death was water intoxication, and not malaria. Plasma levels
> of dihydroartemisinin were noted to be high in this patient although
> this was not thought to have accounted for his death. (This is further
> addressed in the section on safety.)

The final clinical outcome at 24 hours, according to the FDA-defined
endpoints is summarized in the table below.

**Table 11**: Clinical and parasitological outcomes at 24 hours,
according to FDA defined

endpoints

+----------------------+-------------+----------------+----------------+
|                      | **Location  |                |                |
|                      | (Study      |                |                |
|                      | No.)**      |                |                |
+----------------------+-------------+----------------+----------------+
|                      | **Thailand  | **Malawi       | **South Africa |
|                      | (005)\***   | (006)\*\***    | (007)\***      |
+----------------------+-------------+----------------+----------------+
| Randomized           | 46          | 87             | 27             |
|                      |             |                |                |
| > Artesunate         | 17          | 22             | 9              |
| >                    |             |                |                |
| > Comparator         |             |                |                |
+----------------------+-------------+----------------+----------------+
| Excluded             | 5           | 3              | 1              |
|                      |             |                |                |
| > Artesunate         | 3           | 0              | 1              |
| >                    |             |                |                |
| > Comparator         |             |                |                |
+----------------------+-------------+----------------+----------------+
| Clinical Failures    | 11          | 8              | 1              |
|                      |             |                |                |
| > Artesunate         | 4           | 0              | 2              |
| >                    |             |                |                |
| > Comparator         |             |                |                |
+----------------------+-------------+----------------+----------------+
| 24-hr clinical       | 30/41 (73%) | 76/84 (90.5%)  | 25/26 (96%)    |
| success rate         |             |                |                |
|                      | 10/14       | 22/22 (100%)   | 6/8 (75%)      |
| > Artesunate         | (71.4%)     |                |                |
| >                    |             | (-38.6, 14.3)  | (-16.5, 95.9)  |
| > Comparator         | (-26.9,     |                |                |
|                      | 36.9)       | 0.2006         | 0.1310         |
| *95% CI Artesunate   |             |                |                |
| -- Comp.*            | 1.0000      |                |                |
|                      |             |                |                |
| *P --value\*\*\**    |             |                |                |
+----------------------+-------------+----------------+----------------+
| 24-hr                | 30/41 (73%) | 74/84 (88%)    | 22/26 (84.6%)  |
| parasitological      |             |                |                |
| success rate         | 10/14       | 3/22 (13.6%)   | 2/8 (25%)      |
|                      | (71.4%)     |                |                |
| > Artesunate         |             | (42.1, 80.2)   | (15.3, 87.9)   |
| >                    | (-26.9,     |                |                |
| > Comparator         | 36.9)       | \<0.0001       | 0.0034         |
|                      |             |                |                |
| *95% CI Artesunate   | 1.0000      |                |                |
| -- Comp*             |             |                |                |
|                      |             |                |                |
| *P --value\*\*\**    |             |                |                |
+----------------------+-------------+----------------+----------------+

\* Rescue was permitted in both arms in these studies

\*\* Rescue was only permitted in the AS arm in this study.

\*\*\* Exact confidence interval and Fishers Exact Test

Following completion of treatment, patients were to be followed for 28
days from the time of study entry. During this time, weekly visits were
scheduled and in addition, patients with a recurrence of clinical
symptoms were seen at the time when they presented to study centers. The
attendance at these follow-up visits was poor. For example, in Study
006, 55% of the patients in the artesunate arm and 73% of patients in
the control arm did not attend the 28-day follow-up visit. For Studies
005 and 007 the number of patients lost to follow-up by Day 28 was not
available.

Since the study centers also served as the local clinical treatment
centers, we assumed that in general, subjects who did not report to the
clinic between the day that therapy was completed and Day 28 were
clinically well. However, we can not exclude the possibility that
several of the patients lost to follow-up may have developed malaria.

The 28-day recrudescence/new infection rate was calculated based on the
number of patients initially enrolled, and the number of patients with a
laboratory confirmed recurrence of parasitemia.

**Table 12**:

28-day recrudescence/reinfection rates per number of patients enrolled
in the study:

+----------------+----------------+----------------+-----------------+
|                | **Location     |                |                 |
|                | (Study No.)**  |                |                 |
+----------------+----------------+----------------+-----------------+
|                | **Thailand     | **Malawi       | **South Africa  |
|                | (005)\***      | (006)\***      | (007)\***       |
+----------------+----------------+----------------+-----------------+
| 28-day         | 0/41 (0%)      | 39/86 (45.3%)  | 2/26 (8%)\*\*   |
| recrudescence/ |                |                |                 |
|                | 0/14 (0%)      | 5/22 (22.7%)   | 2/8 (25%)\*\*   |
| reinfection    |                |                |                 |
| rate           |                |                |                 |
|                |                |                |                 |
| > Artesunate   |                |                |                 |
| >              |                |                |                 |
| > Comparator   |                |                |                 |
+----------------+----------------+----------------+-----------------+

\* Number of patients lost to follow-up is not available, thus the
denominator represents the number of patients randomized. Patients with
missing data are assumed not to have developed recrudescent malaria for
the purpose of this analysis.

\*\* Recrudescence diagnosed by PCR only, smears negative

These rates are presumed to reflect the combined efficacy of rectal
artesunate or the comparator drug plus the efficacy of the follow up
regimen. This is turn is related to the prevalent drug sensitivity of
*P. falciparum* in the region where the study was conducted. In general,
resistance to Fansidar is more common than resistance to mefloquine.
This may account in part for the low recrudescence rates in study 005
compared to studies 006 and 007.

**Parasitological clearance**

The figures below show individual subject-level parasite counts over
time for each of the pivotal studies. Results for the experimental arm
and the control arm are show separately.

![](media/image4.wmf){width="3.87992125984252in"
height="2.1834645669291337in"}![](media/image5.wmf){width="3.9200787401574804in"
height="2.206299212598425in"}

![](media/image6.wmf){width="3.856299212598425in"
height="2.6708661417322834in"}![](media/image7.wmf){width="3.89251968503937in"
height="2.7043307086614172in"}

![](media/image8.wmf){width="4.060236220472441in"
height="2.840944881889764in"}![](media/image9.wmf){width="4.02007874015748in"
height="2.810236220472441in"}While these results demonstrate the rapid
parasite clearance in most subjects treated with artesunate, a small
number of patients, described previously, who failed to reach 60% of
baseline parasitemia at 12 hours were given rescue therapy. In study 005
there were 7 (17%) and 4 (29%) rescued subjects in the Artesunate and
Quinine groups, respectively. Study 006 had 3 (4%) Artesuante subjects
rescued and no provisions for rescue in the Quinine group. Finally,
Study 007 had 1 (4%) and 2 (25%) rescued subjects in the Artesunate and
Quinine groups, respectively. Parasite counts obtained in these subjects
after rescue are included in the figures above. Although this analysis
represents an unfairly favorable parasitological response to therapy for
the rescued subjects, the fact that rescue was performed in both the
arms of studies 005 and 007 permits some comparison between the arms.

### Additional supportive studies

**Study 14**

Study 14 was a bioequivalence study to demonstrate the parasitological
efficacy of three different formulations of rectal artesunate and did
not provide comparative data with other antimalarial agents.

This three-arm study compared the formulation used in phase I and II
studies, the formulation used in phase III studies, and the formulation
proposed for marketing.

> (A prior bioequivalence study in healthy male volunteers \[Study 009\]
> comparing these formulations failed to show equivalence for both AS
> and DHA. The intrasubject variability in C~max~ and AUC for both AS
> and DHA was relatively high and ranged from 60 to 70%. The lack of
> adequate sensitivity of the assay resulted in a large number of
> non-measurable samples and lost data points, limiting the power for
> the analysis. Other potential reasons for variability in the study
> include: inconsistencies in rectal absorption, variability in the
> amount of drug substance absorption in the dosage form, variability in
> drug product quality, dissolution rate limitations from the
> formulation, and individual variability in drug metabolism. Study 14
> was designed to address these difficulties.)

**Table 13**: Initial treatment in Study 14:

+---------------------+----------------+------------------------------+
| Moderately severe   | Group A        | Rectal AS                    |
| malaria             |                |                              |
|                     |                | 2 x 200mg suppositories      |
+---------------------+----------------+------------------------------+
|                     | Group B        | 4 x 100mg suppositories      |
+---------------------+----------------+------------------------------+
|                     | Group C        | 1 x 400mg suppository        |
+---------------------+----------------+------------------------------+

**Table 14**: Consolidation regimens in Study 14

+-----------------------------------------------------------------------+
| **All groups (if able to take orally)**                               |
|                                                                       |
| 24 hours after entry, oral artesunate (4 x 50mg tablets) for 3 days   |
|                                                                       |
| 24 hours after last dose of oral AS, 3 x 250mg tablets of mefloquine  |
|                                                                       |
| 48 hours after last dose of oral AS, 2 x 250mg tablets of mefloquine  |
+-----------------------------------------------------------------------+
| **All groups (if unable to take orally)**                             |
|                                                                       |
| 24 hours after entry, IV artesunate (120mg)                           |
|                                                                       |
| then IV artesunate 60mg 12 hourly till able to tolerate oral          |
| medications and complete a total dose of 480-600mg artesunate         |
|                                                                       |
| 24 hours after last dose of oral AS, 3 x 250mg tablets of mefloquine  |
|                                                                       |
| 48 hours after last dose of oral AS, 2 x 250mg tablets of mefloquine  |
+-----------------------------------------------------------------------+

The study was performed on 69 hospitalized adult patients (23 per arm)
with moderately severe malaria.

Inclusion criteria required a baseline parasitemia 100,000/l and/or
non-per os status. Exclusion criteria resembled those for studies 005,
006, and 007 where patients with complicated malaria or decreased level
of consciousness were not enrolled.

All 69 patients completed the study successfully without the need for
rescue therapy.

Parasitemia was rapidly cleared as shown below:

**Table 15**: Median parasite counts /l at 0, 12, 24 and 48 hours

  -------------- -------------- -------------- -------------- --------------
                 **Baseline**   **12 hours**   **24 hours**   **48 hours**

  Group A        46,720         3,890          30             1

  Group B        30,960         9,980          86             0

  Group C        40,680         13,080         62             0
  -------------- -------------- -------------- -------------- --------------

The [mean fractional reduction in parasitemia]{.underline} at 24 hours
for the 3 groups ranged from 83.1% to 97.3% and by 48 hours, all
patients had effectively cleared parasites.

[Fever clearance time]{.underline} was similar for all three groups with
a mean of 21.6 hours in Group A, 21.9 hours in Group B and 24.8 hours in
group C.

Data beyond 7 days were not described and recrudescence/new infection
rates for this population are not known.

**Studies 003 and 004**

These were two randomized, open-label, crossover studies between IV and
rectal artesunate performed on hospitalized patients with "moderately
severe" malaria. These studies were designed to provide both clinical
and pharmacokinetic data. The WHO conducted population pharmacokinetic
analyses using pharmacokinetic data from both of these studies. The
review of these analyses is currently ongoing; therefore, the WHO\'s
conclusions cannot be verified at this time.

The clinical data from these studies are summarized in the following
pages.

The treatment arms involved crossover between rectal and intravenous
artesunate at 2 dosing strengths as shown in the table.

**Table 16**: Treatment arms in Studies 003 and 004

+-------------------------+---------------------+---------------------+
|                         | **Location (Study   |                     |
|                         | No.)**              |                     |
+-------------------------+---------------------+---------------------+
|                         | **Thailand (003)**  | **Ghana (004)**     |
+-------------------------+---------------------+---------------------+
| IV AS 2.4mg/kg          | 12 patients (Group  | 0 patients          |
|                         | 1)                  |                     |
| After 12 hrs, Rectal AS |                     |                     |
| 10mg/kg                 |                     |                     |
+-------------------------+---------------------+---------------------+
| Rectal AS 10mg/kg       | 12 patients (Group  | 12 patients (Group  |
|                         | 2)                  | 1)                  |
| After 12 hours IV AS    |                     |                     |
| 2.4mg/kg                |                     |                     |
+-------------------------+---------------------+---------------------+
| IV AS 2.4mg/kg          | 12 patients (Group  | 12 patients (Group  |
|                         | 3)                  | 3)                  |
| After 12 hrs, Rectal AS |                     |                     |
| 20mg/kg                 |                     |                     |
+-------------------------+---------------------+---------------------+
| Rectal AS 20mg/kg       | 12 patients (Group  | 12 patients (Group  |
|                         | 4)                  | 2)                  |
| After 12 hours IV AS    |                     |                     |
| 2.4mg/kg                |                     |                     |
+-------------------------+---------------------+---------------------+

Notably none of these arms included initial rectal artesunate according
to the proposed regimen (Rectal artesunate, 10mg/kg alone during the
first 24 hours of therapy).

**Table 17**: Consolidation regimen for studies 003 and 004

+----------------+--------------------------+--------------------------+
|                | Location (Study No.)     |                          |
+----------------+--------------------------+--------------------------+
|                | Thailand (003)           | Ghana (004)              |
+----------------+--------------------------+--------------------------+
| "consolidation | Mefloquine at 36 and 48  | Chloroquine over 3 days  |
| therapy"       | hours                    |                          |
|                |                          | (s                       |
|                |                          | ulfadoxine-pyrimethamine |
|                |                          | if intolerant of         |
|                |                          | chloroquine)             |
+----------------+--------------------------+--------------------------+

**Table 18**: Inclusion and exclusion criteria for studies 003 and 004

  ------------------------------------- ---------------------------------
  **Thailand (003)**                    **Ghana (004)**

  *Inclusion criteria*                  

  Adults 16-50 years                    Children 18 months to 7 years

  Entry parasite count ≥ 100,000 /l    Entry parasite count ≥ 10,000 /l

  Non per-os patient                    Non per-os patient

  No vital organ dysfunction            

  *Exclusion criteria*                  

  Cerebral malaria or complicated       Cerebral malaria (coma ≤ 2 on
  malaria (e.g. pulmonary edema, renal  Blantyre scale) hypoglycemia,
  failure, shock)                       blood lactate ≥ 5 mmol/l or Hct
                                        \< 15%

  Rectal abnormalities/acute diarrhea   Rectal abnormalities/acute
                                        diarrhea

                                        Previous antimalarial treatment
  ------------------------------------- ---------------------------------

[Short term (24-hour) clinical outcome]{.underline}:

Patients given the same initial treatment regimens were
[pooled]{.underline} and the clinical outcome at 24 hours was determined
as successful if the patient completed treatment and did not require
"rescue" therapy with additional antimalarial drugs.

**Table 19**: 24-hour clinical success rates

  ------------------------------- ---------------------------------------
  **Regimen**                     **Short term clinical success**

  IV AS 2.4 mg/kg, Rectal AS 10   12/12
  mg/kg                           

  Rectal AS 10 mg/kg, IV AS 2.4   23/24
  mg/kg                           

  IV AS 2.4 mg/kg, Rectal AS 20   22/23
  mg/kg                           

  Rectal AS 20 mg/kg, IV AS 2.4   22/24 \*
  mg/kg                           
  ------------------------------- ---------------------------------------

\*In this treatment group, 2 patients progressed clinically to severe
malaria

[Short term (24 hour) parasitological outcome]{.underline}

**Table 20**: Pooled parasitological results showing the numbers of
patients with ≥90% reduction of baseline parasitemia at 12 and 24 hours:

+-----------------------+-----------------------+---------------------+
| **Regimen**           | **12 hours**          | **24 hours**        |
+-----------------------+-----------------------+---------------------+
| IV AS 2.4 mg/kg,      | 1/12                  | 8/12                |
|                       |                       |                     |
| Rectal AS 10 mg/kg    |                       |                     |
+-----------------------+-----------------------+---------------------+
| Rectal AS 10 mg/kg,   | 5/23                  | 21/23               |
|                       |                       |                     |
| IV AS 2.4 mg/kg       |                       |                     |
+-----------------------+-----------------------+---------------------+
| IV AS 2.4 mg/kg       | 5/23                  | 20/22               |
|                       |                       |                     |
| Rectal AS 20 mg/kg    |                       |                     |
+-----------------------+-----------------------+---------------------+
| Rectal AS 20 mg/kg    | 3/24                  | 21/23 \*            |
|                       |                       |                     |
| IV AS 2.4 mg/kg       |                       |                     |
+-----------------------+-----------------------+---------------------+

\*In this treatment group, 2 patients progressed clinically to severe
malaria

[Recrudescences or new infections]{.underline}

**Table 21**:Recurrent parasitemia during the first 2 to 3 weeks after
completion of therapy

  ----------------------------- -----------------------------------------
                                **Recrudescence rate among patients
                                allocated to treatment**

  Mefloquine                    7/48 15%

  Chloroquine                   7/23 30%

  Sulfadoxine-pyrimethamine     2/9 22%
  ----------------------------- -----------------------------------------

*Discussion of efficacy results*

In the studies described above, rectal artesunate results in a rapid
clearance of parasites in most patients. The clearance of parasites is
notably slower when quinine is used for treatment.

At 24 hours, the clinical outcome in the pivotal studies is similar for
rectal artesunate and for comparator regimens.

It is unclear what the clinical outcome would have been without
additional therapy in the small number of patients rescued for
unsatisfactory parasitologic responses in the first 12 hours.

While these studies characterize the benefits of emergency rectal
artesunate compared to standard therapy in the hospital setting, the
benefits of emergency rectal artesunate compared to no treatment in the
bush, without ancillary supportive therapy, are not directly determined.
Such an evaluation should take into account the mortality of untreated,
moderately severe malaria, which is estimated to be high.

By Day 28, high rates of recrudescence occur in some studies. This
presumably depends in part on the follow-up regimen used and the
prevalent patterns of drug resistance. However recrudescence rates
appear higher for artesunate-treated patients than for comparator
treated patients, even when both are given the same follow-up regimen.
In evaluating the benefit of early treatment versus the risk of a higher
recrudescence rate with rectal artesunate, the anticipated mortality
from initial malaria versus recrudescent malaria should be considered.
This may depend on several factors including access to medical attention
and patients' understanding of the disease.

## Safety

> *(The reader is referred to WHO's Briefing Document pages 30-39
> regarding safety and the corresponding references. Direct statements
> from the WHO's application and safety briefing will be presented as
> [Arial font]{.underline} in quotes.)*

The applicant proposes to use artesunate rectally at the dose of 10
mg/kg x 1 in the initial treatment of malaria when the patient cannot
tolerate oral route medications and parenteral administration is not
available. In support of safety, three sets of data have been submitted
as part of NDA 21-242, and a recent safety update, which contains data
from an on-going field trial (Study 13, which is not part of this NDA
review).

### Summary of data presented to the Chinese regulatory authorities 

For the registration of artesunate as injection in 1989, there was one
Phase 1 study with 26 healthy subjects, two phase 2 studies with 70
patients in total which also contained a control arm (Quinine IV) with
12 subjects, and 3 clinical studies with patients having varying degrees
of falciparum malaria totaling 236 subjects. All of these studies were
open-labeled and only one phase 2 study seems to have had a control arm.
It appears that there were children included in the clinical studies but
to what extent is unclear. There was one single-dose study, four
multi-dose studies (4 dose over 3 days), and one 7-day study. The
highest total dose (these are all intravenous doses) was in the 7-day
study of 9.6 mg/kg. The clinical studies in ill patients all gave a
total dose ranging from 4.8 to 6 mg/kg over a 3-day period. Adverse
events described included bitter taste, mild pain at the injection site,
bradycardia, paroxysmal ventricular premature beat, incomplete right
bundle branch block, first-degree atrio-ventricular block, and
urticaria. No major setbacks were due to safety issues with artesunate.
The IV quinine group experienced tinnitus, deafness, nausea, dizziness,
headache, and ECG abnormalities including bradycardia and incomplete
right bundle branch block. Laboratory abnormalities described included
decreased reticulocyte count on the 3^rd^ day returning to baseline by
the 7^th^ day (in normal volunteers), increased SGOT, SGPT, and BUN,
proteinuria, haematuria, and pyuria.

These documents with the corresponding commentaries are supportive only.
There were no datasets submitted. Neither inspection nor audits are
possible at this time (over a decade later). Given these faacts, the
applicant's interpretation was that the data collected by the Chinese
investigators provided "... a favorable tolerability profile of
artesunate. The drug was given through the intravenous route on a
variety of doses and up to a maximum of 7 days with no major safety
setbacks. Although not all of these trials were controlled and none was
blinded, they provide supportive data in support of the use of
artesunate for a limited indication."

### Summary of a systemic review of published and unpublished data 

A systemic review of all available safety information from published
(n=151) and unpublished (n=18) studies was the second set of supportive
evidence submitted for review. The applicant's summary included a total
of 15,567 patients from 169 studies exposed to artemisinin derivatives,
with safety information on 13,639 patients from 130 studies across a
spectrum of disease. In the artesunate safety database, there was a
total of 6258 patients with the majority coming from studies in
uncomplicated malaria (n=5485). There were 417 patients in studies for
severe malaria, 10 in moderate malaria, and 1346 in "other". The
Systemic Review does not cover the dosage used in these studies.
However, from the available literature, the highest total dose used for
rectal artesunate was 45.71mg/kg given over 4 days divided in 8 doses in
adult patients and 57 mg/kg total dose given over 3 days in 3 divided
doses in children. The number of patients exposed to these doses was
small, both sets of patients being \< 30. Adverse events described
include few cases of bitter taste, pain at the injection site, fever and
slight burning sensation as adverse events seen in studies on healthy
normal volunteers. For comparative studies, the review describes the
most commonly reported adverse events (in the order of \<1%) to be mild
gastrointestinal (nausea, vomiting, diarrhea, abdominal pain) events. In
severe malaria, artemisinin derivatives had fewer incidences of
hypoglycemia, skin reactions (pruritis, urticaria, rash), tinnitus, and
dizziness than quinine. In uncomplicated malaria, pruritis was more
common with chloroquine, nausea, dizziness, and tinnitus more common
with quinine, and vomiting more common with mefloquine than artemisinin
derivatives. Laboratory abnormalities described include neutropenia,
reticulocytopenia, eosinophilia, anemia, transaminitis, culture-negative
pyuria, hemoglobinuria, ECG abnormal-bradycardia, and prolongation of QT
interval in the order of 1% of the tests done. There were a few cases of
elevated bilirubin, atrial extra-systoles and T-wave abnormalities. The
vast majority of the studies included in the Systemic Review did not
have neurological assessments done. However of the available
information, dizziness was the most common neurological adverse event.
Thus far, there is a lack of evidence to suggest an association between
artemisinin derivatives and increased neurological deficits/sequelae.

There are obvious methodological deficiencies of compiling published and
unpublished data (with no available raw data) from various studies over
a span of time. Some of those deficiencies which make the synthesis of
the data problematic may include variation in study design and quality,
inadequate data collection, subjects representing different disease
severity (especially since many of the side effects of the drug may be
similar to the actual disease manifestations of malaria) and the
uncertainty of pooling adverse events from individual studies to come up
with an overall incidence. Given that, this systemic review is "the most
comprehensive attempt to identify all the available information on the
safety of artemisinin-type compounds". There were few side effects
reported with these compounds overall in the available literature and
these side effects were mainly mild and transient.

### Summary of WHO-specific studies in the NDA submission 

This safety dataset consisted of 14 study protocols and 13 study reports
of which 2 were bioavailibility studies, 2 were bioequivalency studies,
3 were pediatric "pivotal" studies, 3 adult "pivotal" studies, and 3
supportive (re-analyzed raw data from published literature) studies. The
total safety database for subjects exposed to rectal artesunate was 501
subjects (all hospitalized patients mainly in Southeast Asia and Africa)
which included 135 healthy volunteers, 275 patients with moderately
severe disease and 91 patients with severe malaria. One hundred
sixty-six of these patients were children and all of them had the
diagnosis of moderately severe malaria. All pharmacokinetic and
"pivotal" studies were one rectal dose studies with a majority receiving
10 mg/kg x 1 dose with a range of 6.8 to 22.2 mg/kg. Repeated dosing
with rectal artesunate was given in the supportive studies (Studies 10,
11, and 12) over 3 to 4 days with mean total doses between 25- and 32
mg/kg dose with a range of 11.3 to 45.7 mg/kg. If all formulations of
artesunate administered in these studies are viewed collectively, the
maximum dose exposure for adults was 45.7 mg/kg total dose given over 4
days in 8 divided doses. For children, the maximum dose exposure was
21.4 mg/kg and the longest duration of exposure was 7 days (rectal dose
x 1 followed by oral dosing). In the literature, the highest total
rectal artesunate dosage used was 57 mg/kg given over 3 days in daily
divided doses.

The integrated adverse event count from one-dose rectal studies (this
excludes multiple dose supportive Studies 10-12) yielded 63 adverse
events in 219 adults receiving single dose rectal artesunate verses 34
adverse events from 14 comparator regimens (all IV quinine in Study 7:
patients with severe malaria). Adverse event incidence comparison is not
possible for the adult patients due to the extremely small number and
type (severe disease patients only) of comparator cases. The numbers and
type of adverse evnets (all children had diagnosis of moderately severe
malaria) for comparison are better for the pediatric population where 33
adverse events were reported in 166 children (19.9%) receiving rectal
artesunate as compared to 10 adverse events in 39 (25.6%)
comparator-group children (17 with PO artesunate and 22 with IV
quinine). The leading adverse events reported were gastrointestinal in
all groups (mostly vomiting, and abdominal pain). Collectively, central
nervous system/neurologic adverse events were 10/166 (6%) in the rectal
artesunate dosed pediatric patients vs. 2/39 (5%) in the comparator
group. Of the three remaining supportive studies, only one study
reported adverse events. Of the 9 adverse events reported, 8 were
gastrointestinal in nature and 1 case of dizziness. In all, very few
events led to treatment discontinuation and were classified as treatment
emergent or serious in nature.

There were 7 deaths (1.4%) out of the 501 patients in the total safety
database or 1/275 (0.36%) in patients with moderately severe malaria and
6/91 (6.6%) in patients with severe malaria. These are within rates for
patients treated in a hospitalized setting. Overall, the reported
mortality rates in the literature range from 0.1% in the uncomplicated
malaria diagnosis to up to 40% for severe disease with cerebral malaria
in areas with poor access to care. The single pediatric death occurred
in a 3-year old boy in Study 5 who received rectal artesunate (11.5
mg/kg). The probable cause of death was determined by the study
investigators and the WHO reviewers to be due to "water intoxication".
The narrative and the chemistry laboratory values (i.e., his serum
sodium decreased from 139 to 117 over 2 hours) corroborate this as
likely. Although the applicant surmised that the PK analyses "indicated
that rectal AS administration was felt not to be likely related to the
death of the patient", his dihydroartemisin (DHA) level at both 2 hours
and 4 hours post dose was over 2 to 3 times the mean dose of children
from Ghana (subject SA09: 2002 ng/ml at 2 hrs and 977 at 4 hrs compared
to Ghana children 652 ± 353.2 ng/ml at 2 hrs and 396.8 ± 545.2 at 4 hrs)
Since the metabolite DHA is considered to be the most neurotoxic of all
the artemisinin derivatives and in light of the our lack of knowledge
regarding the PK/PD of this drug in humans, the high levels of DHA seen
in this child at the time of death is concerning. Nevertheless, the
investigator's alternate explanation of death was satisfactory. Three
other deaths occurred in another pivotal trial (Study 7) and all three
patients were in the group of patients diagnosed with severe malaria.
One death was in the rectal artesunate arm and two deaths were in the IV
quinine arm. The investigator's explanation for these three deaths was
underlying malarial disease with inadequate supportive care in all three
cases. The narratives are consistent with the investigator's
assessments. The last three death reports come from Study 10 (a
supportive study), which also had patients with severe malaria. Here
however, the investigators were unable to offer a clear explanation of
the deaths since in all three cases, the patients had cleared their
parasitemia at the time of death.

Laboratory monitoring was limited. Only Study 3 recorded had
comprehensive CBC, Chemistry and LFTs. Overall, there was a transient
decrease in hematocrit at 12-24 hours with return to baseline levels by
day 7 and reaching normal values by Day 28. Previous healthy human
studies had shown mild reticulocytopenia in patients receiving
artesunate however, reticulocyte levels were not measured in these
studies. The transient decrease in hematocrit was not attributable to
any treatment categories. Post-treatment, platelet counts, bilirubin
levels, glucose and lactate levels gradually normalized. There were
three patients with normal baseline levels whose SGOT and SGPT rose over
3 times above the upper limits of normal (not clinically symptomatic),
peaked at Day 7-14, and started to come back down on day 21. Increased
transaminases have been reported in the literature with many studies
confounded by mefloquine co-administration. A preclinical toxicology
study submitted with this application (Study No. BDC/002) did show liver
toxicity (centrilobar hepatocyte hypertrophy, sinusoidal inflammatory
cells, single cell necrosis and diffuse hepatocyte vacuolation) and it
is known that artesunate's major metabolite DHA is mainly cleared via
glucuronidation. Thus, increased liver enzymes may be a related event
with artesunate. However, this event has not translated thus far to
symptomatic liver toxicity in known clinical experience. Only in Study 3
was ECG monitored. No significant abnormalities were noted.

#### Special populations

With regards to pediatric patients, there were too few patients \< 2
years old in these studies (8 out of 166 pediatric subjects) and the
applicant is limiting the indication of this drug to patients older than
2 years of age at this time. Also, the applicant has not shown any data
for the geriatric patient population (6 out of 335 adult subjects were
above the age of 50). Specific studies in patients with hepatic and
renal impairments were not performed. Pregnant patients were not
included in any of the WHO-specific studies. Consistent findings of
impaired fetal survival (but no evidence of teratogenicity) following
first trimester exposure to artemisinins in animal studies are of
concern. However, the applicant states:

> "carefully conducted human studies have not confirmed a level of
> toxicity or risk of teratogenicity attributable to the artemisinins,
> and neither has evidence been demonstrated of other fetal injury or
> impairment of maternal health over and above the effects on
> reproductive health of malaria itself".

#### Neurotoxocity

Since neurotoxicity is considered a serious class effect for artemisinin
derivatives (dose-related unique pattern of neuropathology showing
necrosis of some neurons in vestibular, cochlear, olivary, red and other
nuclei in the brainstem of animals), the applicant has attempted to
address this issue by providing:

1)  Non-clinical summary data from the Chinese studies,

2)  Non-clinical WHO-commissioned toxicology studies performed by Quest
    of United Kingdom,

3)  A 1998 WHO-sponsored expert review of all available pathological
    material as well as published and unpublished information,

4)  Neurological assessments in clinical Studies 5, 6 and 7, and

5)  Literature sources citing human clinical experience regarding
    neurological adverse events/sequelae.

The Chinese data (as per the FDA Toxicology Review) was mainly not
interpretable and could not be validated. The WHO-commissioned
toxicology data submission was disappointing (FDA had asked for a
specific neurotoxicity study; however the submitted study was a 7-day
rat toxicology study without specific neurotoxicology assays, staining,
or behavioral assessments) and concerning (the high-dose arms were
prematurely discontinued due to unexplained deaths; 1 /16 rat died on
day 4 of 75 mg/kg dosing and 2/16 rats died on day 3 of 150 mg/kg
dosing). The 1998 WHO sponsored expert review discussed neurotoxic
effects of artemisinin derivatives in 3 animal species. The NOAEL for
arteether and artemether in rats was thought to be at 45 -- 75 mg/kg IM
x 1 or over 7 days; in dogs at 3 -- 6.25 mg/kg/day IM x 7 days; and in
monkeys 100 mg/kg IM x 1 or over 7 days. The limited information for
Artesunate did not show neuronal necrosis at 420 mg/kg x 1 IM or 200
mg/kg/day PO x 5-7 days.

The WHO briefing document states:

> "The conclusion is that the administration of artesunate by the oral
> or intravenous route to the study animals at dose levels and duration
> that gave a total dose of 210-300 mg/kg (21-30 fold greater than the
> total proposed human dose) did not result in clinical or
> neuropathological findings, nor indicate any neurotoxic action".

This direct dose comparison between animal and clinical doses relating
to safety margin (not accounting for body surface area) is
inappropriate. The body surface area conversion of the rat dosages of
210-300 mg/kg provides equivalent human doses of approximately 35-50
mg/kg, which is only 3 to 5 times the proposed 10 mg/kg x 1 proposed
human dose, not "21-30 fold greater" as claimed by the applicant. Body
surface area conversion of the rat dosages at which deaths occurred in
the WHO-commissioned studies (75 and 150 mg/kg PO) provides equivalent
human doses of approximately 12 and 25 mg/kg, respectively, which
considerably narrows the margin of safety.

Neurological assessments in WHO-specific clinical studies were performed
for Studies 5, 6, and 7 only. This should provide data on approximately
164 rectal artesunate recipients tested (neurological assessments
consisting of cranial nerves, nystagmus, hearing, tandem walking, the
Romberg test, line drawing, picking tablets, rapid alternating
movements, and finger tapping) out of the 501 total patients. However,
missing data was extremely common and, according to the applicant, many
of the young patients did not cooperate with the assessments.
Nevertheless, no pattern of neurological abnormalities was concerning.
The WHO's main argument for the safety of artesunate and the lack of
human neurotoxicity draws upon the large body of literature and the
actual usage experience. The applicant states:

> "careful neurological examinations have also been made in 1303
> patients treated with the artemisinins, 806 in patients treated with
> artesunate....The analysis of a large body of clinical data by Price
> et al to assess patients treated with artemisinins, including dosing
> by the oral, intravenous, and rectal routes, did not identify any
> neurotoxic effects".

Unfortunately, a closer look at the reference that the applicant is
citing in the Briefing Document (Reference 14; Price et al 1999),
identifies that it discusses patients with acute uncomplicated malaria,
which is not the population that the applicant proposes to treat.
Furthermore, the authors of the article write that "neurologic
examinations could be performed reliably only in patients \>5 years
old". It is very young children who are not able to take PO that the
proposed indication will most likely include.

This leads us to a brief look at the **120-day Safety Update** which
contained data from Study 13 (a field study that is on-going in
Bangladesh, Ghana, and Tanzania) where the proposed indication is being
studied in placebo-controlled fashion and with patients as young as 6
months of age. This study remains blinded at this time. The update
highlights the fundamental differences in the populations between the
WHO-specific studies submitted to the NDA (e.g., all hospitalized
patients, all with proven malaria disease, mainly moderately-severe
malaria disease, only 8 patients \< 2 years of age) versus the on-going
field study (patients at remote sites, 74% of available malaria smears
positive, 12% of patients unconscious at baseline, 23% with repeated
convulsions, and 1093/1947 (56%) of patients enrolled in Ghana and
Tanzania aged \<2 years). Moreover, of the 16 patients thus far being
followed for neurological sequelae, only 50% had a positive malaria
smear at baseline and 25% had confirmed bacterial meningitis by
cerebrospinal fluid analysis (although not all had a lumbar puncture).
The low incidence of neurological sequelae thus far (0.47%) is
reassuring. However, this safety update calls attention to the
likelihood that the population that the proposed indication will
actually serve will be very young children with severe malaria disease
and/or other severe disease such as bacterial meningitis. This is a
population in whom little information is available (even in the large
body of clinical experience, and certainly none in the actual
WHO-specific studies of this NDA) to draw upon for an adequate safety
evaluation of artesunate.

Although we are in agreement with the applicant's overall summary which
stated:

> "it is apparent that artesunate, whether given as a rectal dose of 10
> mg/kg, 20 mg/kg (pivotal studies) or in a total rectal dose of 1200 mg
> or 1600 mg over 3 days followed by mefloquine (non pivotal studies) or
> in different formulations (oral or intravenous), has a highly
> favorable safety profile. The number of adverse events is small and,
> even if they were drug-related in such a severely ill group of
> patients, the incidence is very low. No consistent pattern of toxicity
> has been identified",

we are mindful of the many uncertain safety issues including the
as-of-yet undetermined safety margin for neurotoxicity in particular,
and the as-of-yet undetermined safety parameters for the population that
will be treated with the proposed indication in general. Nevertheless,
as we consider the risk/benefit ratio, the cost of the *disease* malaria
(especially with rising multi-drug resistant malaria) to individual
human suffering and global public health becomes the paramount challenge
to overcome. In this light, the use of artesunate at the dose and
formulation proposed (10 mg/kg x 1) is within the safety limits of the
collective currently available knowledge. However, the uncertainties and
our concerns regarding safety would drastically expand if repeated
dosing with rectal artesunate becomes an issue.