Effect of probenecid on the pharmacokinetics of flunixin meglumine and phenylbutazone in healthy mares.

Pharmacokinetic values for flunixin meglumine (1 mg/kg of body weight) and phenylbutazone (4 mg/kg) dosages were determined after a single IV injection with and without concurrent intragastric administration of probenecid (50 mg/kg) in 6 healthy mares. Significant difference was not apparent in the pharmacokinetic values of flunixin meglumine with and without concurrent probenecid administration. Significant (P less than or equal to 0.05) increase was evident in the 12-hour mean concentration of phenylbutazone (11.45 +/- 1.66 micrograms/ml without probenecid; 14.56 +/- 1.20 micrograms/ml with probenecid) along with significant (P less than or equal to 0.05) reduction in its volume of distribution at steady state associated with concurrent probenecid administration (218.6 +/- 11.52 ml/kg without probenecid; 169.4 +/- 9.25 ml/kg with probenecid).