Determination of trimethoprim in pediatric samples by high-performance liquid chromatography

We describe and evaluate modifications to a known high-performance liquid chromatography assay of trimethoprim. The sensitivity, specificity and wide range of linearity (0.11-690 mumol/l) of this method make it suitable for analysing samples with large variations in volume and concentration. We have used it to study the pharmacokinetics of trimethoprim in children, including newborns. Automated injection is a useful option if the sample volume is not limited. The recovery (at 3.44 mumol/l) of the method was 99.8% with a coefficient of variation of 6.8% for manually injected samples. The corresponding results for automated injection were 97.9% and 12.8%.