Pharmacokinetics and pharmacodynamics of three formulations of firocoxib in healthy horses.

This research compares the effectiveness and absorption rate (pharmacokinetics) and dose-response behavior (pharmacodynamics) of three different forms (intravenous, oral paste, oral tablet) of a medication called firocoxib in horses.

Research Design & Methodology

• The study was conducted on six healthy adult horses using a three-way, randomized, crossover design. This means that each horse served as its own control and received all three treatments in a randomized order with sufficient time between treatments to eliminate any residual effects.
• The treatments were a single dose of 57 mg firocoxib, delivered either intravenously, or by oral paste or tablet.
• Blood samples were taken at set times after administering the drug to measure concentrations of PGE2 and TXB2 (indicators of COX inhibition), as well as plasma drug concentrations.

Key Findings

• As seen in previous studies, firocoxib was found to have a long elimination half-life, a large volume of distribution, and a slow clearance rate, indicating that it remains in the body for a prolonged period.
• Comparing the two oral formulations, the paste achieved a higher peak concentration (Cmax), a faster time to reach peak concentration (Tmax), and a greater exposure to the drug (AUC) compared to the tablet.
• The absorption rates were 112% and 88% for the paste and tablet respectively, which means that more firocoxib was available in the body when delivered by paste.
• The study also evaluated effectiveness by how much PGE2 the firocoxib inhibited – the intravenous form had the highest inhibition rate, followed by the oral paste and then the tablet.
• The researchers observed no inhibition of TXB2 production, indicating that firocoxib specifically inhibits COX-2 without affecting COX-1.
• The study concluded that the oral tablet and paste forms of firocoxib are not bioequivalent and thus do not have the same therapeutic effects when administered as a single dose to healthy horses.

Implications

• The difference in pharmacokinetics and pharmacodynamics between the forms of firocoxib suggests that one form cannot be substituted by another without considering dosage adjustments.
• This research could guide veterinarians in choosing the most appropriate formulation of firocoxib based on the therapeutic needs of individual horses.