High-dose metronidazole: pharmacokinetics and bioavailability using an iv preparation and application of its use as a radiosensitizer.

As an extension of studies on the clinical use of nitroimidazoles as radiosensitizers, single-dose pharmacokinetic studies of iv metronidazole (500 mg/100-ml vials) were performed in eight consenting patients. Single doses of 0.5, 1.0, 1.5, and 2.0 g (0.29-1.21 g/m2) were administered iv by a zero-order infusion pump. Serial timed blood and urine samples were assayed for metronidazole and its two metabolites (acetic acid and ethoxy compounds) using a high-pressure liquid chromatographic assay. Open two-compartment kinetic characteristics of metronidazole were computed from simultaneous plasma infusion and urine excretion-rate equations using a nonlinear least-squares regression analysis program (NONLIN). Means of the four kinetic parameters were (h-1): k12, 1.18; k21, 0.86; k10, 0.22; and k'e, 0.46 x 10(-4). Means of the apparent volumes of distribution were (liters/kg): Vc, 0.41; VB, 1.02; and Vss, 0.75. The mean (+/- SD) for alpha-half-life was 1.2 +/- 1.3 hours, and that for beta-half-life was 9.8 +/- 5.9 hours. Seven of the eight patients received a second identical dose orally 1 week later, and the absolute bioavailability was estimated to approximate 100%. Unless the oral route is not feasible and if immediate high peak blood levels are not necessary, oral metronidazole is the preferred route of administration of metronidazole for its radiosensitizing effects.