The Potential for Pregnancy While on a Trial Drug

What is the risk of pregnancy occurring in a study participant while a new drug is being developed? The author is not aware of any published figures, but from the author's experience in industry and from questions to colleagues, pregnancy does occur during drug development, even in those patients apparently taking adequate contraceptive precautions. A typical NDA database for most drugs will involve between 2000-4000 patients, of which perhaps one-third are female and exposed to study medication. It is not surprising, therefore, that given an average failure rate of the contraceptive pill of 2%, or even with the most stringent compliance, a failure fate of 0.5/100 women years will result in occasional pregnancy (Trussell et al, 1990). Other methods, such as the diaphragm, condoms and IUDs, can carry even higher failure rates, depending on whether 'usual' or 'perfect compliance' calculation of 18-6%, 12-2% and 30.5%, respectively, are used (Trussell et al, 1990). If we assume an average NDA database of 4000 patients, one-third or more female, it is likely that half of these will be females of child-bearing potential (the other half being post-menopausal or elderly). Thus, approximately 660 females of child-bearing potential may be exposed to the drug, the comparator, or a placebo. In the best circumstances of perfect contraceptive compliance, in a 1-year exposure and at a 0.5% failure fate, 3.3 fetuses are likely to be exposed. With a 'typical compliance' of the contraceptive pill, a 3% failure rate would leave about 19 fetuses exposed to experimental entities, one-third of which would be lost due to spontaneous miscarriage.

Few patients would be exposed for a full year, but more typically probably only to between 2 weeks to 3 months of study medication. Given all the above assumptions, between 0.8 and 5 early embryos will be exposed in a full drug development program. From the author's personal experience of over 27 years in industry, an average of two children are born exposed to a new chemical entity. This is most likely to occur in Phase 3 studies, which have many more patients and are often of longer duration. Currently, pharmaceutical firms, with the agreement of the FDA, follow up all possible exposures until any resultant child is 12-14

years of age, and a full medical examination (including a full neurological work-up) is done at yearly intervals.

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