The pharmacokinetics of one single preoperative dose of metronidazole or tinidazole

Eight patients who were subjected to colorectal surgery received 1500 mg metronidazole and another 8 patients 1600 mg tinidazole. The two groups of patients were comparable in respect to age, body size, diagnoses, types of operations, premedication, and anaesthesia. Concentrations of the parent compounds and hydroxy-metronidazole were determined by high pressure liquid chromatography in serum and tissues (subcutaneous fat, rectus abdominal muscle, peritoneum, greater omentum, distal ileum, colon, appendix). The serum and tissue concentrations of metronidazole and tinidazole were within overlapping ranges. Hydroxy-metronidazole but not hydroxy-tinidazole was detected. The total area under the serum curves was 505 (SD: +/- 181) mg . h/l for metronidazole, 137 (+/- 38) mg . h/l for hydroxy-metronidazole, and 810 (+/- 286) mg . h/l for tinidazole. The serum half-life values in the same order were 8.5, 11.2, and 14.2 hours. The distribution volume (Vd,area) were 30.1 liter for metronidazole and 38.8 liter for tinidazole. The range of tissue concentrations were completely overlapping. The two regimens can, consequently, be assessed as pharmacokinetically similar.