Pharmacokinetics of sulfaphenazole in sheep

Proprietary formulations of sulfaphenazole were administered intravenously and orally to sheep. After intravenous injection the disposition of sulfaphenazole was described by an open two compartment model, and the elimination half-time was on average 5.58 h. The apparent volume of distribution was 0.273 1/kg and total body clearance 34.1 ml/kg/h. Judged from the area under the curves, the oral dose was completely absorbed, Drug plasma concentrations versus time fitted an open one compartment model, the half-time of absorption and elimination being 2.66 and 7.12 h, respectively. The binding to plasma proteins was high i.e. 93–96 % at therapeutic concentrations, and concentration dependent. The results demonstrate that the doses indicated by the manufacturer appear to be low and more appropriate for drugs with a longer elimination half-time. Consequently, considerable adjustments in the dosage regimen are recommended.