Population pharmacokinetics of ceftazidime after a single intramuscular injection in wild turtles

Ceftazidime, a third-generation cephalosporin, is important for treating opportunistic bacterial infections in turtles. Antibacterial dosage regimens are not well established for wild turtles and are often extrapolated from other reptiles or mammals. This investigation used a population pharmacokinetic approach to study ceftazidime in wild turtles presented for rehabilitation. Ceftazidime was administered to 24 wild turtles presented to the Turtle Rescue Team at North Carolina State University. A sparse blood sampling protocol was used to collect samples from 0 to 120 hr with three samples per individual after injection. Plasma samples were analyzed by high-pressure liquid chromatography (HPLC). A nonlinear mixed-effects model (NLME) was fitted to the data to determine typical values for population parameters. We identified a long half-life (T½) of approximately 35 hr and volume of distribution (V_SS ) of 0.26 L/kg. We concluded that this long T½ will allow for a dose of 20 mg/kg injected IM to maintain concentrations above the MIC of most wild-type bacteria for 5 days. Because of long intervals between injections, stability of stored formulations was measured and showed that 90% strength was maintained for 120 hr when stored in the refrigerator and for 25 days when stored in the freezer.