The pharmacokinetics of meclofenamic acid in the horse.

The research article investigates the behavior of a drug, meclofenamic acid, in Thoroughbred horses and ponies following oral, intravenous, and intramuscular administration. This was carried out in order to better understand how the drug is absorbed, distributed, and eliminated in these animals.

Study Aim and Methodology

• The research was intended to understand how meclofenamic acid behaves inside the body of Thoroughbreds and ponies. This involves understanding how quickly and efficiently the drug is absorbed into the bloodstream, how it is distributed within the body, and also how it is eliminated.
• The study was carried out by administering the drug in two forms – as meclofenamic acid and sodium meclofenamate, and through three routes – orally, intravenously, and intramuscularly. The doses were either 2 mg/kg or 4 mg/kg.

Key Findings

• The half-life for the elimination of the drug was approximately 0.9 hours after intravenous administration. The volume of distribution was 0.128 litre/kg, suggesting that the drug is rapidly distributed through the body.
• The researchers found that elimination was in accordance with a one-compartment model, suggesting that the drug does not undergo extensive distribution to other body compartments beyond the blood.
• After oral administration, the terminal half-life was significantly longer than that calculated for the elimination rate constant (Kel) from intravenous data. This discrepancy indicated the presence of the ‘flip-flop’ phenomenon, where the absorption rate constant (Ka) is higher than Kel.
• Sodium meclofenamate resulted in quicker and higher peak levels than meclofenamic acid, although the total bioavailability was similar for both. This would suggest that sodium meclofenamate may be more easily absorbed into the bloodstream compared to meclofenamic acid.
• In ponies, meclofenamic acid showed a lower absorption than that in Thoroughbreds.
• Fasting overnight prior to administering meclofenamic acid did not affect the rate or extent of absorption, indicating that the drug’s behavior is not significantly influenced by food intake.
• Following intramuscular administration of sodium meclofenamate, plasma concentrations were low and even after 25 hours, only 46% of the drug had been absorbed. This suggests that this drug may not be effectively absorbed when administered intramuscularly.