**Synergisms Among Pharmaceuticals with Different Modes of Action that
Affect the Same Physiological Functions:**

**Anti-Hypertensive Drugs**

**WateReuse Foundation 06-004**

**Background**

Anti-hypertensive drugs fall into several pharmacological classes. The
pharmacologic classes include the angiotensin-converting enzyme
inhibitors (ACE inhibitors), angiotensin II receptor blockers,
calcium-channel blockers, α-adrenergic receptor blockers and
α2-adrenergic agonists. Six of the ACE inhibitors are among the 200 most
prescribed drugs (Lacy et al., 2007), with Lisinopril being the most
popular as the 4^th^ most frequently prescribed. There are four members
of the angiotensin II receptor blockers that are among the most
frequently prescribed drugs, with Valsartan being number 58. This
pharmacologic group is frequently prescribed in combined dosage form
with potent diuretics such as hydrochlorothiazide and furosemide that
also are considered risks to the fetus (Lacy et al. 2007). For example,
four products containing irbesartan are among the top 200 drugs
prescribed. There are 6 drugs in the calcium-channel blocker group,
including 4 that are in the top 200 prescribed drugs (amlodipine, at 54
and 114; diltiazem at 138 and 183; nifedipine at 192 and verapamil at
84). Two α-blockers are among the top 200 most prescribed drugs
(doxazosin at 133^rd^ and terazosin at 172). One α2-adrenergic agent,
clonidine, is 77^th^ on the most prescribed drug list. Furosemide is the
7^th^ most prescribed drug and hydrochlorothiazide is a component of the
5, 28, 73, 148, 170, and 176^th^ most frequently prescribed drugs. These
drugs are almost exclusively used in adult populations and explicit
warnings against use in pregnancy for many of the therapeutic classes
except in cases of life-threatening circumstances (Lacy et al. 2007;
Facts & Comparisons, 2008). It is important to recognize that some drugs
within these pharmacologic classes have other therapeutic uses that have
not been considered for the sake of simplicity.

The diversity of the mechanisms that are represented among drugs that
are used to control blood pressure raises questions of potential
synergy. By definition, synergy can arise when multiple mechanisms
affect the same physiological processes.

The lowest effective therapeutic doses among these classes vary widely.
ACE inhibitor doses are in the 0.7 to 10 mg/day range, while angiotensin
II receptor blockers are given at doses of 25 to 80 mg/day.
α2-adrenergic agonists are most potent with doses beginning at 0.05
mg/day (clonidine). The lowest therapeutic dose for the two α-blockers
is 1 mg/day. The potency of calcium-channel blockers vary the most, with
lowest therapeutic doses of ranging from 2.5 mg/day (amlodipine and
felodipine) to as high as 120 mg/day (diltiazem). Consequently, the
pharmacologic potency of some of these drugs is quite high.

Drugs within these classes carry a pregnancy classification of C
(studies in animals have indicated adverse effects during pregnancy --
generally teratogenic or embryotoxic effects) or D (there are positive
indications of human fetal risk -- but the drugs may be used in
life-threatening circumstances) (Lacy et al., 2007). At least some of
these effects have been attributed to low blood flow to the placenta. In
the case of the ACE-inhibitors effects are thought to arise from direct
pharmacologic effects on the fetus. Thus, risks to the fetus from this
group of drugs appear to arise from the activity for which they are
marketed and used in the adult population.

The major health effects concern with drugs used in the treatment of
hypertension is whether or not the simultaneous occurrence of multiple
compounds acting by at least 5 distinct mechanisms of action represents
a potential for synergy in producing adverse effects on the fetus.

**Specific Concern for Residual Contaminants in Indirect (direct)
Potable Reuse of Wastewater**

a.  Occurrence in municipal wastewaters

There are limited occurrence data on drugs within the antihypertensive
therapeutic group. Vanderford and Snyder (2006) reported enalapril at
less than 1 ng/L in wastewater effluent, but no other anti-hypertensives
appear to have been included among the target compounds. Castiglioni et
al. (2005) surveyed eight STP effluents in Italy and did not detect
enalapril. Lisinopril was targeted as an analyte by Levine et al. (2006)
but was not detected at a detection limit of 5 ng/L. Diltiazem was
detected in a denitrified effluent at a detection limit of 12 ng/L by
the same group. On the other hand, Kolpin et al. (2002) reported
diltiazem at a maximum of 49 ng/L and a median concentration of 21 ng/L
in 13.1% of the samples analyzed in a national survey of U.S. streams.
These authors reported a single detection of enalaprilat at 46 ng/L in
the same survey.

Bueno et al. (2007) reported mean concentrations of furosemide and
hydrochlorothiazide at 1 and 5 µg/L in waste water influents,
respectively. The corresponding maximum concentrations were 3 and 15
µg/L. There appear to be no other data on the occurrence of these widely
used diuretics.

Atenolol, a β-blocker, has been reported in WWTP influents at mean
concentrations of 1.6 and maximum of 4.9 µg/L in Spain (Bueno et al.,
2007; Radjenovic et al. 2007). Vanderford and Snyder (2006) reported
atenolol at 3 µg/L in WWTP influent and 0.9 µg/L in WWTP effluent.
Corresponding mean values for WWTP effluent were reported by Huggett et
al. 2003) for metaprolol, nadalol, and propanolol were 0.04, 0.052, and
0.117 µg/L, respectively. The maximum levels observed by Huggett et al.
(2003) were 1.2, 0.36 and 1.9 µg/L. A presentation available on line
indicates that atenolol was reduced to about 20 ng/L after reverse
osmosis (Snyder,
http://www.clw.csiro.au/video_html/2007/ShaneSnyder/SnyderPresentation.pdf).
We were unable locate further information on whether to whether
β-blockers are removed effectively by other treatments of wastewater to
be used as a source of potable drinking water.

The only calcium channel blocker that appears to have been measured in
wastewater is diltiazem where concentrations in WWTP influents and
effluents were found to be 57 [+]{.underline} 13 and 53 [+]{.underline}
25 ng/L (Benotti and Brownawall, 2007). These same authors indicated
that they did not detect nifedipine in wastewater. Nifedipine is less
widely used than diltiazem.

Other drugs used in treatment of hypertension do not seem to have been
targets of surveys. This is of most concern for those drugs that have
very low therapeutic doses (e.g. clonidine). Within the broad class of
antihypertensives, Lienert et al. (2007) finds that an average of 50% is
eliminated in the urine. This suggests that some members of these
classes should occur in wastewater.

b.  Adequacy of current health effects data

Most pharmaceuticals have substantial health effects databases. Among
the antihypertensives, some drugs are used that are quite old and may
have limited data. However, ACE-inhibitors and angiotensin II receptor
antagonists are modern drugs and detailed data will have been required.
This literature will have to be pursued further after the workshop
looking at the FDA data summaries (Leadscope, 2008).

It is surmised that the developmental toxicology data base for this
class of pharmaceuticals may be adequate for individual drugs. However,
it is anticipated that there are no data available that addresses
interactions of the variety of drugs that are in this therapeutic class.
Therefore, the question of whether components act synergistically in
producing reproductive/developmental toxicities is probably necessary.
This issue will have to be pursued with FDA to determine whether studies
that address this issue have been conducted in anticipation of the
co-occurrence of these chemicals in wastewater that might serve as a
source for potable water.

c.  Increased Treatment Requirements

The occurrence data on antihypertensive drugs is limited to a few
therapeutic groups. The data that are available indicate that some of
these drugs do occur at measurable concentrations in wastewater. In most
cases it is anticipated that reverse osmosis may remove these agents.
However, it is not clear how effective other treatment processes might
be for removing these agents (e.g. GAC or soil aquifer treatment).

# Regulatory Concerns

a\. Probable occurrence in wastewater, if not documented

There are few data that address the occurrence of these potent
pharmaceuticals in waste water. Sedlak et al. (2005) projected possible
concentrations of these compounds based upon their usage rates in 1998.
Furosemide was predicted by Sedlak et al. (2005) to occur in wastewater
at 450-1900 ng/L in the U.S. and concentrations of 25-2000 ng/L were
found in STP effluents in Italy (Castiglioni et al. 2005). The
prediction for hydrochlorothiazide was a range of 1,400 to 2,600 ng/L
but with metabolism was expected to be in the 830-1,600 ng/L range
(Sedlak et al. 2005). Castiglioni et al. (2005) found concentrations
ranging from 60-1250 ng/L. Atenolol was predicted to occur at a
concentration of 520-4100 ng/L (Sedlak et al., 2005) and was measured at
3050 ng/L by Vanderford and Snyder, 2006) in WWTP effluent and 899 ng/L
in WWTP effluents. The measured concentrations are remarkably close to
predicted levels.

The limited measurements that have been made of the ACE inhibitors
(enalapril and lisinopril); suggest that these drugs occur at
concentrations significantly below those projected (Sedlak et al. 2005).

The concentrations of these compounds that will be in wastewater treated
by various means to be used as a potable water source are not clear. The
available data would suggest that reverse osmosis will substantially
decrease the concentrations of most of these drugs.

b\. Screening values (e.g. TTC or specific chemical "risk analyses")

The ACE inhibitors form the group with the lowest margin of exposure
(MOE) between the therapeutic dose and predicted concentrations (e.g.
590 for lisinopril). The estimated MOE between the lowest therapeutic
dose and predicted concentrations for hydrochlorothiazide and furosemide
are both approximately 5,000. The MOE for the individual calcium channel
blockers ranged from 1,000,000 to 20,000,000 while the MOE for the
remaining antihypertensives ranged from 15,000 to 90,000. This analysis
suggests that there is little concern over the individual occurrence of
these compounds. However, because of their diverse mechanisms of action
affecting the same modification of blood pressure and that the
therapeutic doses utilized do not consider effects on the fetus, they
will remain of concern.

# Ongoing Research Activities

There is a considerable volume of toxicological data that is developed
in support of new drug applications and systematic postmarket follow-up
in the [treated]{.underline} populations. Much of this data is
unavailable because it is confidential business information. As these
drugs are generally contraindicated in pregnant individuals, it is
unlikely there has been follow-up with respect to reproductive and
developmental toxicities. If we are directed to give this project a high
priority at the workshop, we will conference with FDA officials to
insure that appropriate information has not been developed.

**Recommended Research**

a.  Gaps in general toxicological characterization

The antihypertensives are generally viewed as not appropriate for use
during pregnancy. There are animal data and some human data to suggest
that these drugs pose some hazard to the fetus. It appears that these
risks arise directly from the pharmacological properties of the
compounds. As the antihypertensive therapeutic group includes chemicals
with a diverse set of mechanisms, interactions among these compounds is
likely to be synergistic. Therefore, experiments should be conducted to
determine whether the selected chemicals from these classes act
synergistically in producing harm to the fetus.

b.  Need for refined information for risk assessment

Most of these drugs have a long history in human uses. Adequate data
appear to be available to characterize risks to adults that are
utilizing these medications. However, their use is counterindicated in
pregnancy. Data addressing the potential synergies in producing harm to
the fetus would provide a basis for assessing their combined risk.

c.  Needs of the water industry that maybe overlooked

These drugs have all been developed for chronic use in adults. Most
classes are contraindicated during pregnancy because of observed adverse
effects on the developing fetus in animal studies or in postmarket
follow-up studies in humans. These effects are not of concern in the
patient populations treated with these chemicals.

# Agencies to be approached

The key agency is the FDA because they are the repository of the
toxicological data and postmarket human data that bear on this issue. On
the other hand, the issue is an environmental one in that it was not the
intent of the FDA regulations to assess. The USEPA has an active program
in assessing the toxicology of mixtures. This would be a good and
relevant project for testing for the occurrence of non-additive
interactions between environmental contaminants.

# Criticality of the issue

a.  Will the lack of adequate health effects information create doubts
    about safety of reused water? Should it? How can the doubts be
    accommodated without a continuous search for additional
    toxicological data?

It is unlikely that the interactions among the mechanisms that are
involved in the therapeutic effects of the drugs in this group on fetal
development have been considered. Nevertheless, the CDER program at the
FDA would be consulted on this question before a formal nomination is
made.

b.  Is it likely that a better fix on potential health effects avoid
    unnecessary treatment?

Some of the drugs in this therapeutic group have been shown to occur in
wastewater. It is probable that most would be removed by reverse osmosis
based on their molecular weights. Some occur in wastewater at predicted
concentrations while others appear to appear much below theoretical,
suggesting that wastewater treatment is effective in some cases.
Quantification of the dose-response of interactions among these
chemicals could show that reverse osmosis is not required to address
members of this therapeutic group.

c.  Can better source control programs mitigate concerns altogether?

While drug recovery programs that avoid dumping drugs in this class into
the sewer system, the major input relates to their routine use and
elimination in urine and feces.

**Key References**

Benotti, MJ. and B.J. Brownawell. 2007. Distributions of pharmaceuticals
in an urban estuary during both dry- and wet-weather conditions.
Environ. Sci. Technol. 41:5795-5802.

Bueno, M.J.M., A. Agüera, M.J. Gómez, M.D. Hernando, J.F. Garcia-Reyes,
and A.R. Fernández-Alba. 2007. Application of liquid
chromatography/quadrupole-linear ion trap mass spectrometry and
time-of-flight mass spectrometry to the determination of pharmaceuticals
and related contaminants in wastewater. Anal. Chem. 79:9372-9384.

Castiglioni, S., R. Bagnati, D. Calamari, R. Fanelli, and E. Zuccato.
2005. A multiresidue analytical method using solid-phase extraction and
high-pressure liquid chromatography tandem mass spectrometry to measure
pharmaceuticals of different therapeutic classes in urban wastewaters.
J. Chromatograph. 1092:206-215.

Facts & Comparisons. 2008. Facts and Comparisons^®^ Version 4.0. Wolters
Kluwer, St. Louis, MO 63146.

Huggett, D.G., I.A. Khan, C.M. Foran, and D. Schlenk. 2003.
Determination of beta-adrenergic receptor blocking pharmaceuticals in
United States wastewater effluent. Environ. Pollut. 121:199-205.

Kolpin, D.W., E.T. Furlong, M.T. Meyer, E.M. Thurman, S.D. Zaugg, L.B.
Barber, and H.T. Buxton. 2002. Pharmaceuticals, hormones, and other
organic wastewater contaminants in U.S. streams, 1999-2000: A national
reconnaissance. Environ. Sci. Technol. 36:1202-1211.

Lacy, C.F., L.L. Armstrong, M.P. Goldman, and L.L. Lance. 2007. Drug
Information Handbook. 15^th^ Ed.

Leadscope 2008. FDA Toxicity Database. www.leadscope.com

Radjenovic, J., M. Petrovic, D. Barceló. 2007. Analysis of
pharmaceuticals in wastewater and removal using a membrane bioreactor.
Anal. Bioanal. Chem. 387:1365-1377.

Levine, A.D., M.T. Meyer, and G. Kish. 2006. Evaluation of the
persistence of micropollutants through pure-oxygen activated sludge and
denitrification. Water Environ. Res. 78:2276-2285.

Vanderford, B.I. and S. A. Snyder. 2006. Analysis of pharmaceuticals in
water by isotope dilution liquid chromatography/tandem mass
spectrometry. Environ. Sci. Technol. 40:7312-7320.