Sulfamethoxypyridazine (CL 13494) is a sulfanilamide antibacterial agent.

In goats, following intramuscular (im) and subcutaneous (sc) administration, Sulfamethoxypyridazine has half-lives of 11.0 h and 13.7 h with bioavailabilities of 68.6% and 58.7%, respectively. The distribution and elimination half-lives are 0.1 h and 6.28 h, while the steady-state volume of distribution and total body clearance rates are 0.39 ml/kg/min and 0.73 ml/kg/min, respectively. Preliminary studies in rats infected with Pneumocystis carinii demonstrated that Sulfamethoxypyridazine is very effective. It was also found that treatment of Pneumocystis carinii infection in rats with Sulfamethoxypyridazine (1 mg/kg) is as effective as sulfamethazole. In a mouse model, Sulfamethoxypyridazine effectively combats Pneumocystis carinii, with ED50s based on silver stain and Giemsa stain scoring of 0.08 mg/kg/day and 0.06 mg/kg/day, respectively. Treatments of 0.1 mg/kg/day or 0.3 mg/kg/day show more pronounced effects against Pneumocystis carinii in the mouse model than the 0.47 mg/kg/day dose.