Pharmacokinetics of trimethoprim-sulfamethoxazole in children.

The present report extends experience with the use of trimethoprim-sulfamethoxazole (TMP-SMX) in children aged 3 months to 10 years. The regimen was TMP (200 mg)--SMX (1000 mg)/m-2d given in two equal doses. The drug was easily administered, well tolerated and efficacious in the treatment of a variety of infections in 12 children. A steady state had been achieved by the third dose of medication and accumulation of either component during days 1 through 4 did not occur. Serum concentrations of TMP were slightly lower in children aged less than 3 years compared with those aged 3 to 6 years but the differences were small and these results are preliminary. Peak mean serum TMP concentration was highest at day 3 when it reached 1.63 mug/ml. It is concluded that this regimen may be suboptimal for some major parenchymal infections even though the therapeutic result was excellent in most children.