Studies of meclofenamic acid and two metabolites in horses--pharmacokinetics and effects on exercise tolerance

The pharmacokinetics and the effects on treadmill exercise of the anti-inflammatory drug meclofenamic acid were studied in seven Standardbred horses after single intravenous and/or oral doses. The decline in plasma concentration after a single intravenous dose of meclofenamic acid (2.2 mg/kg b.wt) was described by a two-compartment open model. The average elimination half-life was 1.4 h, the apparent volume of distribution 0.14 l/kg and the plasma clearance 0.12 l/h kg. Absorption was the rate-limiting step after oral administration. Non-compartmental analysis showed a mean absorption time of 4.3 h. The pharmacokinetics of two metabolites of meclofenamic acid were also studied in two of the horses. The elimination half-lives of the two metabolites were virtually the same in each horse (3.0 h and 3.4 h). The blood lactate response to exercise was significantly decreased after treatment with meclofenamic acid, indicating a lower utilization of the glycolytic ('anaerobic') energy contribution during exercise. Circulatory capacity was apparently unaffected with an unchanged heart rate response to exercise.