Pharmacokinetics of sulfamethoxypyridazine and its binding to plasma proteins in the camel (Camelus dromedaries)

Abstract

The pharmacokinetics of sulfamethoxypyridazine (SMPD) were investigated in the camel after intravenous and oral administration. After intravenous injection, the plasma concentration of the drug followed the kinetics of a two-compartment model. The steady-state volume of distribution (Vss) of 0.47 l/kg suggested that sulfamethoxy-pyridazine was mostly distributed within the vascular compartment and the strongly vascularized tissues. The elimination from the body was rather slow, with a biological half-life [t_1/2(ß)] and a total plasma clearance of about 9.5 h and 0.037 l/kg.h, respectively. Oral treatment showed that the maximum plasma concentration was reached 17 hours post drug administration and that the bioavailability ranged around 57 %. Study of the plasma protein binding showed that the percentage of SMPD binding to plasma proteins varied from 47 to 72 % and seemed to be concentration-dependent. The total binding capacity and the dissociation constant at equilibrium were 196 µg/ml and 335 µg/ml, respectively.