Detection of levamisole and its metabolites in horses after oral levamisole administration over seven days.

This research article explores the detection rates of levamisole and its byproducts in horses after the administration of multiple oral doses over a week. The findings suggest variations in the clearance of the drug and its metabolites, emphasizing the need for clearance sample testing for treated horses.

Research Study Methodology

• The study subjects were six healthy Thoroughbred geldings that were administered levamisole, a controlled substance used to treat protozoal myelitis in horses.
• Each horse received 500mg of compounded levamisole hydrochloride paste orally every 12 hours, making a total of 13 doses over a period of one week.
• Serum and urine samples from the horses were analyzed over 28 days after the final levamisole dosage. The analyses focused on the detection of levamisole and its metabolites, including compound II, aminorex, and pemoline. Notably, aminorex and pemoline are prohibited substances under the Horseracing Integrity and Safety Authority rules.

Research Study Findings

• The half-life of levamisole in serum was inconsistent amongst the horses. Post the final dosage, it took 3 to 14 days for the serum levamisole levels of 5 out of the 6 horses to fall beneath the limit of detection (LOD).
• One horse’s serum consistently tested above the LOD for levamisole until the last testing day (day 28).
• In urine samples, it took 6 days after the final dose for levamisole to fall below LOD, and 3 days for aminorex.
• On the last sample collection day, compound II was still detectable in urine samples of 4 out of the 5 horses. This suggests a longer detection time for this particular metabolite.

Research Conclusions

• The study proved that levamisole and its metabolites could be detected in horses for variable lengths of time. In some cases, detection lasted for weeks following the administration of multiple doses.
• The insights gained from this study align with the Racing Medication and Testing Consortium Advisory’s recommendations to conduct clearance sample testing on treated horses. This will ensure the elimination of levamisole and its metabolites from the horses’ system.