Assay of tolfenamic acid and its metabolites by liquid chromatography on dynamically modified silica: application in pharmacokinetics.

An LC method able to separate all known metabolites of tolfenamic acid was developed. It was applied to characterize the metabolic profiles after single and multiple peroral doses of tolfenamic acid to volunteers. Up to 80% of the dose, mostly conjugated metabolites, could be recovered in the urine by this method. Two of the metabolites showed plasma half-lives of several days and peculiar conjugation properties.