Comparative plasma and milk dispositions, faecal excretion and efficacy of per os ivermectin and pour-on eprinomectin in horses.

This study compares the impact and potential side effects of two drugs, ivermectin (IVM) and eprinomectin (EPM), in horses. The results indicate that both drugs can be safely used with lactating mares whose milk is intended for human consumption, despite differences in how the drugs are metabolized and excreted by the horses.

Research Methodology

• The study involved ten mares, which were divided into two groups. One group was given ivermectin orally, while the other received a topical application of eprinomectin.
• The dosages of both drugs were administered at 0.2 and 0.5 mg per kg of body weight.
• Blood, milk, and faecal samples were taken from the horses and analyzed using high-performance liquid chromatography to identify and measure the amounts of both drugs.
• The researchers also monitored the efficacy of both drugs in reducing faecal strongyle egg counts (EPG), which is a measure of parasite infestation in horses.

Key Findings

• The concentration of ivermectin in the blood (plasma) and its persistence were significantly greater than that of eprinomectin. However, eprinomectin showed a much higher rate of transference into the milk than ivermectin did.
• Ivermectin was found to be excreted through faeces at a much higher rate but for a shorter period than eprinomectin, which was excreted less but for a longer duration.
• In terms of efficacy, ivermectin was found to be more effective than eprinomectin in reducing the EPG. Ivermectin achieved a reduction of 96-100% for up to eight weeks, while eprinomectin only achieved a reduction of 78-99%.

Conclusion and Recommendations

• The study concludes that due to their relatively low excretion in milk, both ivermectin and eprinomectin can be safely used in lactating horses whose milk is designated for human consumption.
• However, the study suggests using eprinomectin with caution. While it presents less of a presence in the horse’s bloodstream and faeces, this could lead to subtherapeutic levels of the drug, which may increase the risk of drug resistance in parasites if the drug is administered topically.