Mepivacaine: its pharmacological effects and their relationship to analytical findings in the horse.

The study explores Mepivacaine, a local anesthetic used in horse medicine, its effects, and how the drug and its byproducts are detected in horse urine. The crucial takeaway is that the drug at a specific dose doesn’t produce anesthetic effects and can be detected through specific detection methods, which can affect racing regulations.

Study Objectives and Methods

• The study aimed to build a comprehensive database for Mepivacaine and its metabolites from both an analytical and pharmacological perspective. Since Mepivacaine use in professional horse racing can attract severe penalties if identified as a residue in post-race urine samples, understanding its pharmacology becomes vital.
• The team used an abaxial sesamoid local anesthetic model. They determined the highest no-effect dose (HNED), i.e., the maximum dose that does not cause an anesthetic effect, to be 2 mg.
• The research team utilized the enzyme-linked immunosorbent assay (ELISA) screening method. This test showed the peak urinary concentration at 63 ng/mL, observed 2 hours after injecting the HNED dosage of Mepivacaine.

Main Findings

• 3-hydroxymepivacaine is the primary identifiable metabolite found in equine urine after Mepivacaine administration. The research team synthesized, purified, and characterized 3-hydroxymepivacaine, and also developed a quantitative mass spectrometric method to measure this metabolite in horse urine.
• After injecting the HNED of Mepivacaine, the 3-hydroxymepivacaine concentration in horse urine peaked at around 64.6 ng/mL, four hours after administration. These results were obtained using GC/MS, which is a powerful analytical tool for testing samples.

Implications of the Study

• The study suggests that concentrations of Mepivacaine and its metabolites in equine urine from a HNED dose are detectable using mass spectral techniques.
• The results imply that the presence of less than about 65 ng/mL of 3-hydroxymepivacaine in post-race urine samples may not necessarily be due to a recent use of Mepivacaine for anesthetic effects.