Pharmacokinetics of tolfenamic acid in the horse.

This research investigated how horses absorb, distribute, metabolize and eliminate a drug called tolfenamic acid. The study found that the drug was quickly absorbed regardless of being delivered via intravenous or oral administration, but its complete elimination from the horse’s body took upwards of 48 hours.

Introduction

• The study focuses on understanding the pharmacokinetics of tolfenamic acid in ponies and horses. Pharmacokinetics is the branch of pharmacology focused on the movement of drugs within the body, which includes absorption, distribution, metabolism, and excretion.
• Tolfenamic acid is an anti-inflammatory medication commonly used in veterinary medicine for its analgesic and antipyretic properties.

Methodology

• The study was performed on five ponies intravenously administered tolfenamic acid (2 mg/kg bodyweight), and on four horses orally administered the same drug (30 mg/kg bodyweight).
• The researchers measured the plasma (the clear, non-cellular part of blood) levels of the drug using two methods: high pressure liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS).
• For the intravenously administered ponies, the researchers used a three-compartment model, a mathematical model commonly used in pharmacokinetics, to describe the drug’s concentration-time curve in the plasma.

Results

• The study found that the elimination half-life of the tolfenamic acid, which is the time it takes for the body to reduce the amount of drug in the plasma by half, averaged 6.1 hours (with a variation of 1.5 hours).
• The total body clearance, a measure of the body’s efficiency in eliminating the drug, was calculated to be 72.4 ml/kg bodyweight/hour.
• The steady-state volume of distribution, an indicator of how widely the drug is distributed throughout the body, was 0.32 liters/kg bodyweight.
• For the orally administered horses, the drug was absorbed at a slower rate, with a mean time to absorption of 32 minutes. The elapsed time from drug administration to achieving the highest concentration in the plasma was variable, ranging from 1.9 to 6.5 hours after administration.
• The terminal half-life after oral administration was similar to that of intravenous administration, averaging around 4.2 hours.
• Using the described analytical methods, tolfenamic acid could not be detected in equine plasma more than 48 hours post-administration, indicating it had been fully metabolized and eliminated from the body.

Implications

• The findings of this study provide valuable insights into the pharmacokinetics of tolfenamic acid in horses, which can guide optimal dosing strategies for veterinary use.
• The observed similarities in the half-life of the drug with both delivery methods also suggest that repeated dosing may not be necessary for maintaining effective therapeutic levels in the body.