THE PHARMACOLOGY OF SULFAETHOXYPYRIDAZINE IN THE HEIFER

¹ Agricultural Division, American Cyanamid Company, Princeton, New Jersey

Heifers were treated with a single dose (25 mg/lb body weight) of sulfaethoxypyridazine by intravenous and oral routes. Concentrations of sulfonamide as total, free, and polar metabolite or "glucuronide" were measured in plasma and urine samples. Persistent plasma levels were maintained. A plasma half-life of 10 hours was calculated from the intravenous data. The parent sulfonamide was bound to plasma proteins to the extent of 96 to 90% at concentrations of 5 to 10 mg %. Cumulative urinary excretion of sulfonamide accounted for 62% of the intravenous dose and 63% of the oral dose at 72 hours. Ethyl acetate extraction, paper strip and column chromatography techniques showed that of the sulfonamide in the plasma, 10% was the N⁴ acetyl conjugate, 87% as unchanged sulfaethoxypyridazine, and 3% as possibly a glucuronide. In the urine, 84% was the N⁴ acetylated derivative, 9.5% was sulfaethoxy-pyridazine, and 6.5% was the unidentified glucuronide. Two other minor sulfonamide components, found only in the urine, appear to be formed in vitro.