Applicability of the principles of developmental pharmacology to the study of environmental toxicants.

Although nontherapeutic xenobiotics represent the vast majority of environmental exposures during childhood, study of these compounds in children has lagged behind drug studies. Some useful extrapolation can be made from the latter, however. An increased impetus for pediatric pharmacology studies resulted from evidence of shortcomings in algorithmic approaches to dosing and the recognition of differing efficacy and toxicity in children compared with adults. With some drugs, developmental differences resulted in increased toxicity or failed efficacy; however, in others, decreased toxicity has been demonstrated. Thus, pediatric patients may not be classified arbitrarily as a susceptible population but certainly a different one compared with adults. Better designed pediatric pharmacology studies use well-documented, nonlinear changes in body composition across childhood, as well as knowledge about the impact of physical growth, mediated by complex hormonal changes. Developmental differences in all components of drug disposition, including absorption, distribution, metabolism, and excretion, have been characterized. Of these, the ontogeny of metabolism, particularly tissue-specific metabolism, is the most complex. Many knowledge gaps persist within developmental pharmacology; however, recent Food and Drug Administration regulatory action likely will ensure continued accumulation of pediatric therapeutic data. Although these data can provide important a priori information for improved environmental study design, evaluation-specific toxicant disposition by pediatric patients is clearly needed.