HPLC serum assay methods for trimethoprim and sulpha-methoxazole are described. Octadecylsilane coated silica is used as the stationary phase in both analyses. The determination of trimethoprim involves extraction and chromatography employing reversed phase ion-pair HPLC with u.v. detection at 229nm. Using lml of serum, trimethoprim at levels of 10ng/ml can be measured. Sample preparation of sulphamethoxazole consists of protein precipitation only. Chromatography is by ion-supression and monitoring at 254nm. The sulphamethoxazole can be detected in serum at concentrations in the region of 0.1#x3BC;g/ml. Results are presented to show the variation of trimethoprim and sulphamethoxazole in serum of eight healthy subjects over a 72 hour period following ingestion of 20ml co-trimoxazole suspensions from two manufacturers.
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