Metronidazole metabolism following oral benzoylmetronidazole suspension in children with giardiasis

A suspension of benzoylmetronidazole (6.4% w/v) was given orally at a dose of 15-25 ml, equivalent to 0.6-1 g metronidazole, once a day for three days to 11 children with giardiasis. Blood samples were collected after the first and third doses for analysis of plasma metronidazole and its main oxidative metabolite by high performance liquid chromatography. Peak metronidazole concentrations were 22.60±8.52 mg/l (mean±S.D.) after the first dose, and 30.22±10.06 mg/1 after the third dose, occurring at 3.6±1.4 and 4.4±2.9 hours post-dose, respectively. Peak concentrations of the metabolite were 4.26±1.94 mg/l after the first dose and 7.96±3.63 mg/1 after the third dose, occurring 7.2±1.6 and 9.1±3.3 h post-dose, respectively. Calculation of plasma metronidazole half-life and clearance values was not possible.This study shows that oral administration of metronidazole as its benzoyl ester slows the rate of metronidazole absorption, followed by sustained plasma concentrations and a prolonged elimination phase. Giardiasis does not appear to prevent metronidazole absorption. Concurrent giardiasis is unlikely to influence metronidazole therapy for systemic anaerobic infections. © 1986, by The British Society for Antimicrobial Chemotherapy.