Bioavailability of sulfamethoxypyridazine following intramuscular or subcutaneous administration in goats

The pharmacokinetics of sulfamethoxypyridazine (SMP) was investigated in goats after a single intramuscular (im) or subcutaneous (sc) administration (100 mg/kg body weight). The biological half lives of SMP following im and sc administration were found to be 11.0 and 13.7 h, respectively. The systemic availabilities of the drug were calculated to be 68.6 and 58.7% following im and sc injections, respectively. The rapidity of absorption, almost similar availability, comparatively longer biological half-life and ease of administration suggest that the sc route of administration might be preferred over the im route. To achieve and maintain serum concentrations 25 micrograms/mL, a rational dosage regimen of SMP for goats would be 55 and 38 mg/kg body weight as the loading and maintenance doses, respectively, with a dosage interval of 24 h by the sc route.