title: Phenytoin elimination in newborns.
abstract: We measured the apparent half-life (t50%) of phenytoin (PHT) 30 times in 16 infants (aged 2 to 36 days) who had seizures. During the first week of life, the t50%s ranged from 6 to 140 hours. After the first week, the concentration dependence of PHT elimination was demonstrated; the t50% was related to the initial concentration (Ci). The t50% also decreased with postnatal age. Controlling for a Ci of 18 mg per liter, the average t50% decreased threefold between the first (57.3 +/- 48.2 hours) and fourth weeks (19.7 +/- 1.31). In newborns, both age-related changes and the concentration dependence of PHT elimination can cause PHT levels to decrease when constant doses are given.
mesh_terms: D000367:Age Factors; D006207:Half-Life; D006801:Humans; D007231:Infant, Newborn; D007232:Infant, Newborn, Diseases / Q000097:blood / Q000378:metabolism*; D007700:Kinetics; D010672:Phenytoin / Q000097:blood / Q000378:metabolism*; D012640:Seizures / Q000097:blood / Q000188:drug therapy / Q000378:metabolism*
chemical_list: D010672:Phenytoin