BACKGROUND There is little published, objective information about pseudoephedrine and phenylpropanolamine in the treatment of children. Our goal was to determine the pharmacokinetics of these medications in young subjects. METHODS In two sequential double-blind, parallel-group, single-dose studies, 21 children received either pseudoephedrine, 30 or 60 mg, or placebo, and 20 children received either phenylpropanolamine, 20 or 37.5 mg, or placebo. Before dosing and at intervals up to 7 hours after dosing, serum pseudoephedrine or phenylpropanolamine concentrations were measured, and pulse and blood pressure were recorded. In two children receiving each drug, these tests were also performed at 12 and 24 hours, and urine was collected from 0 to 12 and from 12 to 24 hours. RESULTS In children, the mean (+/-SEM) terminal elimination half-life values for pseudoephedrine, 3.1 +/- 0.5 hours, and for phenylpropanolamine, 2.6 +/- 0.6 hours, were significantly shorter than those found by other investigators in adults. Pharmacokinetics were not dose dependent in the dose ranges studied. CONCLUSIONS Further studies of pseudoephedrine and phenylpropanolamine should be performed in children with the use of objective measurements. The widespread use of these medications in young subjects should be reevaluated.