J Clin Pharmacol 58 (5): 650 - 661, 2018. doi: 10.1002 / jcph.1054 Metabolism and elimination Drug metabolism and elimination vary with age and depend on the substrate or drug, but most drugs, and most notably phenytoin, barbiturates, analgesics, and cardiac glycosides, have plasma half-lives 2 to 3 times longer in neonates than in adults.