Dose-Dependent Teratology in Humans: Clinical Implications for Prevention

Since the inception of clinical teratology, the vast majority of scientific work has focused on identification of drugs and environmental agents causing malformations in humans as a dichotomous variable (i.e. yes or no), as well as the relative and absolute risks of such occurrences. Generally, the dose dependency of such events has not been investigated. With the establishment of large pregnancy databases, dose-dependence relationships are being uncovered for increasing numbers of medications, including valproic acid, carbamazepine, phenobarbital, lamotrigine, topiramate, and lithium. In this review we discuss newly recognized dose-dependent human teratogens and the implications to counseling and clinical management of pregnant women. The option of limiting the dose below a teratogenic threshold for women who may need these drugs may be important in managing such pregnancies. Similarly, in women that were exposed before they realized they had conceived, this new knowledge may lead to significant improvement in risk assessment. A common denominator of all studies calculating dose-dependent teratogenicity in humans is their use of total daily drug dose. None of these studies have standardized their calculations for women's body weight. It is quite possible that the teratogenic dose threshold may be below the clinically effective dose levels for specific women, and hence such information needs to be considered and applied individually. With large administrative databases now reporting on drug safety in pregnancy, more accurate data will likely emerge on dose dependency of human teratogens, and these will likely increase the accuracy of risk assessment.