Disposition of sulfadimethoxine in camels (Camelus dromedarius) following single intravenous and oral doses

Single-dose pharmacokinetics of sulfadimethoxine were determined in six adult camels (Camelus dromedarius) following administration of a mean dosage of 17.5 ± 2.7 mg/kg both i.v. and p.o. Serial blood samples were collected through an indwelling jugular catheter intermittently for 5 days for both routes. Sulfadimethoxine was assayed using high-performance liquid chromatography. Serum drug concentration versus time data for each animal was subjected to linear regression, with the best-fit model selected based on residual analysis. The data fit best into a two-compartment open model, with first-order input for oral administration. For orally administered drug, mean maximum serum concentration of 19.3 ± 1.7 μg/ml was reached at 11.41 ± 2.59 hr, with an elimination rate constant of 0.09/hr ± 0.05/hr and an elimination half-life of 11.7 ± 3 hr. Mean peak serum concentration following i.v. administration was 223 ± 48 μg/ml. Mean volume of distribution at steady state was 0.393 ± 0.049 L/kg. Elimination rate constants differed with i.v. and oral administration, suggesting a flip-flop model. Oral bioavailability was 103% ± 38%. Comparison of maximum serum concentrations to the microbial breakpoint concentration reported for sulfadimethoxine (512 μg/ml) suggests that the dose used in this study, 17.5 ± 2.7 mg/kg, is insufficient for achieving therapeutic serum levels.