Effect of spironolactone on antipyrine metabolism in calves.

Ten female calves of the Black and White breed aged seven to eight days were studied before and after seven days of treatment with spironolactone at a dose rate of 1 mg kg bodyweight-1 twice a day. The treatment was associated with a statistically significant decrease in the half-life of antipyrine in plasma and an increase in its rate of metabolic clearance. The excretion of 4-hydroxyantipyrine in urine was significantly increased after the treatment with spironolactone, but there were no changes in the rates of excretion of 3-hydroxymethylantipyrine or norantipyrine. These results indicate that spironolactone enhanced the activity of the microsomal drug-metabolising enzyme system and induced cytochrome P-450 in the calves.