One area of opportunity is improvement in the designs of pre-marketing reproductive toxicity studies.
CHALLENGES FOR THE FUTURE
Existing
methods of pharmacovigilance for medication-induced birth defects, taken
individually or as a whole, are limited in capacity to recognize a potential
teratogenic effect with a new pharmaceutical agent or, conversely, to provide
reassurance that a new drug does not pose a substantial risk. These limitations
are amplified if the drug is infrequently used by women of reproductive age, if
the relative risk for congenital anomalies is not high or if the associated
birth defect(s) pattern is not unique, is difficult to diagnose or is not
likely to be recognized at birth. Existing methods also suffer from the need
for large enough sample sizes and the costs associated with supporting studies
that are adequately powered.
One
area of opportunity is improvement in the designs of pre-marketing reproductive
toxicity studies. If the cross-species predictive value of these experiments
can be increased, then it may be possi-ble in the pre-clinical setting to
accurately identify and avoid human pregnancy exposure to those agents that
will be new teratogens (Moore et al.,
1995; Lau et al., 2000; Selevan,
Kimmel and Mendola, 2000). Another
possibility for the future is to take advan-tage of the efficiency and
cost-effectiveness of large existing databases to ‘screen’ for possible signals
of major teratogenic effects of new and older medica-tions. When strong signals
are identified, other meth-ods, such as case–control surveillance studies or
small follow-up studies, might be appropriate for confirma-tion or refutation.
However,
it is important to recognize that no single study design or methodology is
sufficient to assure that new teratogens will be identified in a timely
fash-ion or that medications that can be used relatively safely in pregnancy
are also identified as quickly as possible. Therefore, a coordinated and
systematic approach to evaluating new medications, both on a national and on an
international basis, could contribute to more effective pharmacovigilance for
birth defects and provide information that is critically and urgently needed by
clinicians and pregnant women (Olsen et
al., 2002; Mitchell, 2003). The coordinated and integrated use of existing ongoing resources includ-ing adverse
event reporting, large databases, popu-lation cohort studies and case–control
surveillance along with the additional complementary information provided by
pregnancy registries and small cohort studies would require substantial efforts
toward the harmonization of purposes and methods. However, a comprehensive
systematic surveillance system offers far more promise for effective
pharmacovigilance than the fragmented and often sporadic methods that are
currently in place to evaluate drug safety for preg-nant women and their
infants. With the large number of prescription and over-the-counter medications
used by pregnant women, a teratogen surveillance system that can adequately
address these safety issues could substantially reduce the uncertainty around
the safety of medications used during pregnancy.
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