Regulatory review of acetaminophen clinical pharmacology in young pediatric patients.

The acetaminophen dosage schedule in pediatric patients below 12 years of age for the over-the-counter (OTC) monograph is one of the many issues being evaluated and discussed in the development of the Proposed Rule for Internal Analgesic, Antipyretic, and Anti-rheumatic drug products. The dosage regimen based on age and weight, with instructions that weight-based dosage should be used if a child's weight is known, is currently being assessed by the agency. This review summarizes the available pharmacokinetic and pharmacodynamic (fever reduction) data of oral acetaminophen in pediatric patients of 6 months to 12 years of age. Acetaminophen is metabolized in the liver mainly through glucuronidation, sulfation, and to a lesser extent oxidation. Because of the difference in the ontogeny of various metabolizing pathways, the relative contribution of each pathway to the overall acetaminophen metabolism in children changes with age. The sulfation pathway plays a more important role in metabolizing acetaminophen than the glucuronidation pathway in younger children as compared with older children and adults. The pharmacokinetic exposure of acetaminophen in pediatric patients of 6 months to 12 years of age given oral administration of 10-15 mg/kg is within the adult exposure range given the OTC monograph dose. The antipyretic effect of acetaminophen is dose dependent and appears to be better than placebo at the dose range of 10-15 mg/kg in pediatric patients of 6 months to 12 years of age.