Effects of oral cimetidine on plasma concentrations of phenylbutazone in horses.
Phenylbutazone was administered to six Thoroughbred horses in a cross-over study in which the horses received cimetidine pretreatment or no cimetidine pretreatment. Blood samples were collected at various times for 48 h after phenylbutazone administration and the plasma was analysed for phenylbutazone. Cimetidine pretreatment elevated phenylbutazone plasma concentrations during the first 8 h after phenylbutazone administration. The absorption rate, maximum phenylbutazone plasma concentrations and AUC were significantly greater with cimetidine pretreatment. The half-life of phenylbutazone did not change with cimetidine pretreatment; however, lower plasma concentrations of the metabolite gamma-hydroxyphenylbutazone were observed with cimetidine pretreatments. Plasma concentrations of the metabolite oxyphenbutazone were unchanged with cimetidine pretreatment compared to control values. Twenty-four-hour plasma concentrations of phenylbutazone were not different from control values with cimetidine pretreatment. This study suggests that concurrent treatment with cimetidine and phenylbutazone 24 h before race time does not result in elevations of plasma phenylbutazone concentrations above control values.
D000284:Administration, Oral; D000818:Animals; D002927:Cimetidine / Q000494:pharmacology*; D004347:Drug Interactions; D005260:Female; D006207:Half-Life; D006736:Horses / Q000097:blood*; D010653:Phenylbutazone / Q000097:blood*
D002927:Cimetidine; D010653:Phenylbutazone