The pharmacology and pharmacokinetics of high-dose methocarbamol in horses.

This study explores the effects and pharmacokinetics of a muscle relaxant, methocarbamol, administered in high doses intravenously and orally to eight healthy adult horses. There were no significant changes found in several monitored physiological parameters but mild to moderate depression was noted in some cases. Pharmacokinetic analysis showed a rapid initial decline of plasma methocarbamol concentration after intravenous administration with a half-life of 59 to 90 minutes, and variable oral bioavailability.

Objective of the Study

• The research seeks to investigate the pharmacological effects and pharmacokinetics of high-dose methocarbamol in horses. The study evaluates the substance’s effects on various physiological parameters (heart rate, respiratory rate, blood pressure, etc.) and its behavior in the body after administration through two routes: intravenous and oral.

Research Methodology

• Eight healthy, adult horses were used as subjects. The two modes of methocarbamol administration studied were intravenous, at a dose of 30 mg/kg of the horse’s bodyweight, and oral, at two doses: 50 and 100 mg/kg bodyweight.
• Hemodynamic, respiratory, and behavioral effects were observed and documented. Several specific parameters, including heart rate, cardiac output, blood pressure, respiratory rate, and arterial blood gases, were evaluated.

Key Findings

• The study found that these physiological parameters remained unchanged following the administration of methocarbamol, regardless of the mode of administration and dosage.
• Mild to moderate depression was observed in five of the eight horses after intravenous injection of methocarbamol. All the horses showed similar symptoms after oral administration of the drug.
• The concentration of methocarbamol in the blood (plasma methocarbamol concentration) declined very rapidly after intravenous injection during the initial phase. The terminal elimination half-life, or the time taken for the quantity of the drug in the body to be reduced by half, varied between 59 and 90 minutes.
• In terms of oral administration, peak plasma methocarbamol concentrations were detected within 15 to 45 minutes. The study also revealed that oral bioavailability, the rate and extent to which the active drug ingredient is absorbed and becomes available in the bloodstream, varied widely from 50.7% to 124%.