Pharmacokinetics of lignocaine in Icelandic horses after infiltration anaesthesia.

The study examines the absorption and elimination rates of the anaesthetic drug lignocaine in Icelandic horses, which was injected into the foreleg.

Introduction and Methodology

• The research sought to understand the pharmacokinetics, which is the way the body absorbs, distributes, metabolizes, and excretes a drug, of lignocaine in Icelandic horses.
• Four Icelandic horses were used for the study and each horse was given an infiltration anaesthesia consisting of 240 mg of lignocaine.
• The drug was injected into the left foreleg of each horse, specifically over the medial and lateral branches of the palmar nerve.
• Blood samples were taken at several points in time, up to seven hours post-injection.
• The concentrations of lignocaine in the plasma of these samples were then measured using gas chromatography/mass spectrometry, a highly sensitive and selective analytical tool.

Results

• Lignocaine was found to be rapidly absorbed by the horses. The highest average concentration of the drug in the bloodstream (232 ng/ml) was observed 20 minutes after the initial injection.
• The decline of the drug in the bloodstream over time was exponential. In three out of four horses, this exponential decline could be split into two parts. In the fourth horse, the decline was purely exponential, meaning it did not have two separate phases.
• The half-life of the drug, or the time it took for the concentration of lignocaine to reduce by half, was measured in two phases: the ‘distribution phase’ (alpha) and the ‘elimination phase’ (beta).
• The average half-life during the distribution phase was 9.8 minutes, indicating a quick distribution of the drug throughout the horse’s body.
• During the elimination phase, the average half-life was longer at 48.4 minutes. This suggests it takes a longer time for the body to break down and eliminate the drug from the body.
• After six hours, the concentration of lignocaine in the blood was below the detection limit, indicating the drug had been largely eliminated from the horse’s system.
• One horse was tested for anaesthesia and the effect lasted for one hour.