Biologic activity of metronidazole in plasma and urine of volunteers with normal or impaired renal function.

In this study, we have compared a bioassay procedure with high-pressure liquid chromatography (HPLC) for the determination of metronidazole levels in serum and urine. Plasma and urine of volunteers with normal or impaired renal function were obtained at various intervals after a single intravenous dose of 500 mg metronidazole. In plasma of normal volunteers 30 hours after dosing, the bioassay gave results comparable to the total values of the parent compound plus metabolites. In patients with renal failure, the course of the plasma regression curve of metronidazole as measured by the bioassay procedure was intermediate between the values of metronidazole alone and the total values of parent compound plus metabolites. Recovery of metronidazole activity in urine, as determined by this bioassay method, was somewhat less than one half (in normal volunteers) to one quarter (in patients with renal failure) of metronidazole plus metabolites as measured by HPLC. These discrepancies might be explained by the lower antibacterial activity of the hydroxy (congruent to 40%) and acetic acid (congruent to 2%) metabolites as compared with that of the parent compound in the test system used.