Metronidazole bioassay.

Urine from patients receiving metronidazole [1-(2-hydroxyethyl)-2-methyl-5-nitromidazole] orally or per vagina were subjected to paper chromatographic fractionation and examined for anticlostridial activity. Unmodified metronidazole and several metabolites were detected. These findings indicate that the clostridial bioassay may be limited in its applicability to the study of the pharmacodynamics of metronidazole as it does not differentiate between the parent substance and some of its metabolites. Moreover, some of the latter, although they possess antibacterial activity, may not have antiprotozoan activity.