Department of Comparative Medicine, College of Veterinary Medicine, The University of Tennessee, Knoxville, TN, USA
Anaerobic bacterial infections are a common problem in reptiles, and although they are frequently treated with metronidazole, there are no reported pharmacokinetic studies on metronidazole in any reptile. This study examined metronidazole pharmacokinetics in wild-caught, yellow rat snakes, Elaphe obsoleta quadrivitatta. A preliminary dosage trial evaluated 20 mg/kg and 100 mg/kg PO; each dose given to two rat snakes. These snakes were bled by cardiocentesis at 0, 4, 8, 11.5, and 23 hours. Plasma metronidazole levels were analyzed by high-performance liquid chromatography and indicated that the 20 mg/kg dose produced peak metronidazole levels above reported minimum inhibitory concentrations (MIC) for most anaerobic bacterial pathogens (MIC 2–4 µg/ml). Steady-state pharmacokinetics were then evaluated in five rat snakes. The snakes were dosed with metronidazole at 20 mg/kg PO every 48 hours for six doses. Snakes were bled by cardiocentesis at 0, 4, 8, 12, 24, and 48 hours prior to and following the initial and the final treatment, and plasma metronidazole levels were obtained. Based on these data, maximum plasma metronidazole concentrations following the initial and final treatment were 14 µg/ml and 13 µg/ml, respectively. Time of maximum concentration following the initial and final treatment were 1.4 and 4.0 hours, respectively. Mean metronidazole levels remained above 4.0 µg/ml for 24 hours following initial treatment and 48 hours following the last treatment. No adverse effects were observed in any snake. These data indicate that a metronidazole dosage of 20 mg/kg PO every 48 hours should be adequate for the treatment of most anaerobic infections in yellow rat snakes.