######## Guidance for Industry

Clozapine Tablets: In Vivo Bioequivalence and In Vitro

####### Dissolution Testing

**U.S. Department of Health and Human Services**

**Food and Drug Administration**

**Center for Drug Evaluation and Research (CDER)**

##### 

##### 

##### June 2005

**BP**

**Revision I**

######## Guidance for Industry

Clozapine Tablets: In Vivo Bioequivalence and In Vitro

#### Dissolution Testing

*Additional copies are available from:*

*Office of Training and Communication*

*Division of Drug Information, HFD-240*

*Center for Drug Evaluation and Research*

*Food and Drug Administration*

*5600 Fishers Lane*

*Rockville, MD 20857*

*(Tel) 301-827-4573*

[*http://www.fda.gov/cder/guidance/index.htm*](http://www.fda.gov/cder/guidance/index.htm)

**U.S. Department of Health and Human Services**

**Food and Drug Administration**

**Center for Drug Evaluation and Research (CDER)**

##### 

##### 

##### June 2005

**BP**

**Revision 1**

**TABLE OF CONTENTS**

I. INTRODUCTION [1](#introduction)

II\. BACKGROUND [1](#background)

III\. IN VIVO STUDIES [2](#in-vivo-studies)

**A. Product Information** [2](#product-information)

B. Steady-State Bioequivalence Study
[3](#steady-state-bioequivalence-study)

C. Other Recommendations [6](#__RefHeading___Toc102467288)

IV\. IN VITRO TESTING CRITERIA [7](#in-vitro-testing-criteria)

A. Dissolution Testing [7](#dissolution-testing-2)

B. Content Uniformity Test [7](#content-uniformity-test)

V. WAIVER REQUIREMENTS [7](#waiver-requirements)

###### Guidance for Industry[^1]

###### Clozapine Tablets: In Vivo Bioequivalence and In Vitro Dissolution Testing

This guidance represents the Food and Drug Administration\'s (FDA\'s)
current thinking on this topic. It does not create or confer any rights
for or on any person and does not operate to bind FDA or the public. You
can use an alternative approach if it satisfies the requirements of the
applicable statutes and regulations. If you want to discuss an
alternative approach, contact the FDA staff responsible for implementing
this guidance. If you cannot identify the appropriate FDA staff, call
the appropriate number listed on the title page of this guidance.

# INTRODUCTION

This guidance provides recommendations for sponsors of abbreviated new
drug applications (ANDAs) designing bioequivalence studies for generic
clozapine products. This document revises the recommendations provided
in a guidance on the same topic issued in November 1996. In the 1996
guidance, the Agency recommended that doses of clozapine tablets be
administered to healthy subjects as well as to the appropriate patient
population in bioequivalence studies for generic clozapine products.
Because a high number of healthy subjects experienced serious adverse
effects such as hypotension, bradycardia, syncope, and asystole during
clozapine bioequivalence studies, FDA is recommending that studies not
be conducted using healthy subjects. In addition, a single-dose study
using a 12.5 mg dose is no longer recommended. Instead, this guidance
recommends a multiple-dose bioequivalence study conducted in patients
using the highest dosage strengths (e.g., 100 mg tablets).

The protocols described in this guidance are designed to reduce the
likelihood of adverse events or, if adverse events should occur, to
ensure that adequate treatment is available.

FDA\'s guidance documents, including this guidance, do not establish
legally enforceable responsibilities. Instead, guidances describe the
Agency\'s current thinking on a topic and should be viewed only as
recommendations, unless specific regulatory or statutory requirements
are cited. The use of the word *should* in Agency guidances means that
something is suggested or recommended, but not required.

# BACKGROUND

Clozapine, a dibenzodiazepine derivative with potent antipsychotic
properties, is indicated for the management of patients with severe
schizophrenia who fail to respond adequately to standard antipsychotic
drug treatment. A significant risk of agranulocytosis and seizures
associated with its use is a major factor restricting wide use of
clozapine in psychiatric practice.

The FDA recommends that treatment with clozapine begin with one-half of
a 25 milligram (mg) tablet (12.5 mg) once or twice daily and that
treatment be continued with daily dosage increments of 25-50 mg per day,
if well tolerated, to achieve a target dose of 300 to 400 mg per day by
the end of 2 weeks. While many patients respond adequately at doses
between 300 and 600 mg per day, it may be necessary to raise the daily
dose to between 600 and 900 mg to obtain an acceptable response. Dosing
should not exceed 900 mg per day.

In humans, clozapine from 25 mg and 100 mg tablets is equally
bioavailable relative to a clozapine solution. Following a dosage of 100
mg twice a day, the average steady-state peak plasma concentration
occurs at an average of 2.5 hours (range 1-6 hours) after dosing. Food
does not appear to affect clozapine systemic bioavailability. The mean
elimination half-life of clozapine after a single 75 mg dose is 8 hours
(range 4-12 hours), compared to a mean steady-state half-life of 12
hours (range 4-66 hours) following 100 mg twice a day dosing. The
elimination half-life increases significantly upon multiple dosing
relative to single-dose administration, raising the possibility of
concentration dependent pharmacokinetics. However, at steady-state,
linearly dose-proportional changes have been observed in AUC, peak, and
minimum clozapine plasma concentrations after administration of 37.5 mg,
75 mg, and 150 mg (twice daily).

Orthostatic hypotension with or without syncope can occur with clozapine
treatment. Orthostatic hypotension is more likely to occur during
initial titration in association with rapid dose escalation and may even
occur with the first dose. Due to the hypotensive effects associated
with administration of clozapine to healthy subjects, the original
recommendations in a guidance on clozapine tablets published in November
1996 are being changed. This document revises and supersedes the
previous version of the guidance. The Agency currently recommends that
steady-state studies to evaluate the bioequivalence of clozapine
products be performed only on patients who are already receiving an
established maintenance dose of an approved clozapine product and have
failed to respond adequately to standard antipsychotic drug treatment.
The Agency believes that the previously recommended study design using
half tablets in healthy subjects was adequate to establish
bioequivalence of generic clozapine products; however, the safety
concerns associated with the use of clozapine in healthy subjects are
significant, and it is recommended that this practice not be continued.

# IN VIVO STUDIES

## Product Information

### FDA Designated Reference Product

> Applicants may consult FDA's *Approved Drug Products with Therapeutic
> Equivalence Evaluations (Orange Book)* for the appropriate reference
> product.

### Batch size

> The test batch or lot should be manufactured under production
> conditions and should be at least 10% of the size of the largest lot
> planned for full production, or a minimum of 100,000 units,
> **whichever is larger**.

### Potency

> The assayed potency of the reference product should not differ from
> that of the test product by more than 5%.

## Steady-State Bioequivalence Study

The objective of this steady-state bioequivalence study is to compare
the rate and extent of absorption of a generic formulation with a
reference formulation when administered at equal doses, as labeled.

> Potential sponsors should consider the following study design. This
> study is appropriate for institutionalized or noninstitutionalized
> patients. Procedures should be in place to ensure medication
> compliance in either setting.

###  Steady-State Study in Patients Receiving a Stable Dose of Clozapine

> The study would be conducted in patients who are receiving a stable
> daily dose of clozapine administered in equally divided doses at
> 12-hour intervals. Patients who are receiving multiples of 100 mg
> every 12 hours would be eligible to participate in the study of the
> 100 mg strength by continuing their established maintenance dose.
> According to the randomization schedule, an equal number of patients
> would receive either the generic formulation (Treatment A) or the
> reference formulation (Treatment B) in the same dose as administered
> prior to the study every 12 hours for 10 days.
>
> Patients would then be switched to the other product for a second
> period of 10 days. No washout period is necessary between the two
> treatment periods. After the study is completed, patients could be
> continued on their current dose of clozapine using an approved
> clozapine product as prescribed by their clinicians.

###  Procedures for the Study

> Before the study begins, the proposed protocol must be approved by an
> institutional review board (IRB).[^2]
>
> The FDA recommends that applicants enroll a sufficient number of
> patients to ensure adequate statistical power.
>
> Patients should receive study treatment A or B with 240 milliliters
> (ml) of water at fixed 12-hour intervals for 10 days, using multiples
> of the 100 mg strength.
>
> Blood samples should be collected over a dosing interval on day 10,
> following preliminary sampling on days 7, 8, and 9 to confirm
> steady-state conditions. The last dose of clozapine to be taken before
> blood sampling for each period should be administered at the clinical
> site to assure exact timing of sampling.

###  Patient Entry Criteria and Facilities

> To enter into this study, patients should be appropriate candidates
> for clozapine therapy (as stated in product labeling) and have been
> taking a stable dose of clozapine for at least three months. Patients
> should be otherwise healthy as determined by physical examination,
> medical history, and routine hematologic and biochemical tests.
>
> Outpatients should be hospitalized for at least 2 days during the
> collection of each set of pharmacokinetic samples. The clinical and
> analytical laboratories used for the study should be identified in the
> study report, along with the names, titles, and curriculum vitae of
> the medical and scientific/analytical directors.

###  Safety Monitoring

> White blood cell (WBC) counts should be monitored and clozapine
> treatment modified, if necessary, in accordance with the
> agranulocytosis warning in the labeling of the reference listed drug
> product. Patients requiring modification of clozapine treatment should
> be dropped from the study and provided with prompt medical care. Blood
> pressure, heart rate, and body temperature should be monitored during
> the study and immediate medical care provided for any significant
> abnormalities.

###  Restrictions

Patients should fast for at least 8 hours prior to and 4 hours after the
administration of the morning dose of the test or reference treatment on
day 10 of each period (i.e., the days on which blood samples are to be
collected to assess the concentration-time curve). All meals on day 10
should be standardized during the study.

Water may be allowed, except for 1 hour before and 1 hour after drug
administration, when no liquid should be permitted other than that
needed for drug dosing.

Patients with any of the following should be excluded from the study:

-   A history of allergic reactions to clozapine or other chemically
    related psychotropic drugs

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-   Concurrent primary psychiatric or neurological diagnosis, including
    organic mental disorder, severe tardive dyskinesia, or idiopathic
    Parkinson's disease

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-   A total white blood cell count below 4000/ml, or an absolute
    neutrophil count below 2000/ml

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-   A history of granulocytopenia or myeloproliferative disorders
    (drug-induced or idiopathic)

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-   Significant orthostatic hypotension (i.e., a drop in systolic blood
    pressure of 30 mm Hg or more and/or a drop in diastolic blood
    pressure of 20 mm Hg or more on standing)

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-   Concurrent use of antihypertensive medication or any medication that
    might pre-dispose to orthostatic hypotension

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-   A medical or surgical condition that might interfere with the
    absorption, metabolism, or excretion of clozapine

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-   A history of epilepsy or risk for seizures

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-   Concurrent use of other drugs known to suppress bone marrow function

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-   Expected changes in concomitant medications during the period of
    study

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-   Positive tests for drug or alcohol abuse at screening or baseline

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-   A history of alcohol or drug dependence by *Diagnostic and
    Statistical Manual of Mental Disorders IV (DSM-IV)* criteria during
    the 6-month period immediately prior to study entry

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-   Compliance with outpatient medication schedule not expected

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-   History of multiple syncopal episodes

###  Blood Sampling 

Venous blood samples should be collected after the day 10 morning dose
to assess the concentration-time curve at predose (0 hours) and at 0.25,
0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 5.0, 6.0, 8.0, 10.0, 12.0 hours.
The predose blood sampling should include at least three successive
trough level samples (C~min~). These samples should be collected on the
last 3 days of dosing in each period to ensure that steady-state blood
plasma/serum levels are achieved in each study period.

[]{#__RefHeading___Toc102467288 .anchor}

## Other Recommendations

### Precautions and Safety Issues

-   Patients should be confined for at least 12 hours after the first
    dose of the test and reference products.

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-   Patients should remain in the supine position for the first 6 hours
    after the first dose, even if they were previously on a stable dose
    of clozapine.

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-   Patients should be adequately hydrated. This may be achieved by
    administering 240 ml of water before the overnight fast, 240 ml of
    water one hour before dosing, 240 ml of water with the study dose,
    and 240 ml of water every 2 hours for 6 hours post-dosing.

-   Patients must be adequately informed of possible cardiovascular
    adverse effects in the consent form.[^3]

### Statistical Analysis of Pharmacokinetic Data (Blood Plasma/Serum)

The following pharmacokinetic data should be used for the evaluation of
bioequivalence of the multiple dose study:

-   Individual and mean blood drug concentration levels

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-   Individual and mean trough levels (C~min~ ss)

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-   Individual and mean peak levels (C~max~ ss)

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-   Calculation of individual and mean steady-state AUC~interdose~
    (AUC~interdose~ is AUC during a dosing interval at steady-state)

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-   Individual and mean percent fluctuation \[ =100 \* (C~max~ ss --
    C~min~ ss)/C~average~ ss\]

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-   Individual and mean time to peak concentration

> The log-transformed AUC and C~max~ data should be analyzed
> statistically using analysis of variance. The 90% confidence interval
> for the ratio of the geometric means of the pharmacokinetic parameters
> (AUC and Cmax) should be within 80-125%. Fluctuation for the test
> product should be evaluated for comparability with the fluctuation of
> the reference product. The trough concentration data should also be
> analyzed statistically to verify that steady-state was achieved prior
> to Period 1 and Period 2 pharmacokinetic sampling.

### Clinical Report and Adverse Reactions

> Patient medical histories, physical examination and laboratory
> reports, and all incidents of possible adverse reactions should be
> reported.

# IN VITRO TESTING CRITERIA 

## Dissolution Testing

Dissolution testing on 12 dosage units of the test product versus 12
units of the reference product should be conducted for all strengths.
The lot used in the biostudy should be used for dissolution testing as
well. The United States Pharmacopeia (USP) method is recommended for
this product. Sampling times of 15, 30, 45 and 60 minutes are
recommended.

> The percent of label claim dissolved at each specified testing
> interval should be reported for each individual dosage unit. The mean
> percent dissolved, the range (highest, lowest) of dissolution, the
> coefficient of variation (relative standard deviation), and similarity
> comparisons of dissolution profiles (f2 calculations) should be
> reported.

## Content Uniformity Test

> Content uniformity testing on the test product lots should be
> performed as described in the latest edition of the USP.

# WAIVER REQUIREMENTS

Waiver of in vivo bioequivalence study requirements for the lower
strengths of a generic product can be granted if the following
conditions are met:[^4]

1.  The in vivo study on the 100 mg tablet is acceptable.

2.  The strengths are proportionally similar in active and inactive
    ingredients to the strength tested in vivo.

3.  All strengths meet an appropriate in vitro dissolution test.

[^1]: This guidance has been prepared by the Office of Generic Drugs
    (OGD) in the Office of Pharmaceutical Science, Center for Drug
    Evaluation and Research, Food and Drug Administration.

[^2]: See 21 CFR 314.94(a)(7)(iii).

[^3]: See 21 CFR 50.25.

[^4]: See 21 CFR 320.22(d)(2)