Pharmacokinetics of sulfonamides and trimethoprim in the donkey (Equus asinus)

The body disposition of sulfadimidine (SDM), sulfadiazine (SDZ), suifamethoxypyridazine (SMPZ) and a trimethoprim-sulfadimethoxine combination (TMP-SDMX) was investigated in the donkey. The four sulfonamides and TMP were injected intravenously at doses of 20 mg/kg (SDM, SDZ, SMPZ), 12.5 mg/kg (SDMX) and 2.5 mg/kg (TMP). The body clearance (Cl-B) of SDZ (1.70 +/- 0.14 ml/min/kg) was significantly higher than those of SDM (1.13 +/- 0.18 ml/min/kg), SMPZ (1.10 +/- 0.09 ml/min/kg) and SDMX (0.75 +/- 0.04 ml/min/kg). In contrast, the volume of distribution at steady state (V-ss) was similar for the four sulfonamides (0.68 +/- 0.08 L/kg, 0.63 +/- 0.07 L/kg, 0.47 +/- 0.06 L/kg, and 0.46 +/- 0.05 L/kg for SDM, SDZ, SMPZ and SDMX, respectively). Both Cl-B acid V-ss were significantly higher for TMP (4.36 +/- 0.60 ml/min/kg and 2.71 +/- 0.86 L/kg) than for sulfonamides. Antipyrine Cl-B (3.49 +/- 0.35 ml/min/kg) and V-ss (0.66 +/- 0.16 L/kg), determined in order to assess hepatic oxidative function and total body water volume, respectively, were either different from (Cl-B) or similar to (V-ss), values calculated for sulfonamides. The results obtained were compared to those reported in horses.