Difference in trimethoprim pharmacokinetics between children and adults.

We used a new micromethod, an application of a previously published high-performance liquid chromatography assay, to investigate trimethoprim (TMP) pharmacokinetics in children. The subjects were 5 girls who were treated for urinary tract infection with a TMP suspension, 6 mg/kg/day, twice daily for 10 days. Elimination studies were done after the last dose. The girls were 1.08-9.71 years old. 3 healthy adult males, aged 26.35-37.31 served as controls. The half-life (t 1/2) of TMP in the children was 3.0-5.5 versus 9.3-13.6 h in the adults. The volume of distribution (Vd) was 0.7-1.1 1/kg in the children and 0.5-0.9 1/kg in the adults. Plasma clearance (Clp) was 2.1-2.8 ml/min/kg for the children. The adults had a smaller Clp of 0.4-1.2 ml/min/kg. From this and previous studies we conclude that the t 1/2 of TMP is much shorter in children than in adults.