Faecal excretion profile of moxidectin and ivermectin after oral administration in horses.
Authors: Pérez R, Cabezas I, Sutra J F, Galtier P, Alvinerie M
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Faecal Excretion Profiles of Moxidectin and Ivermectin in Horses Understanding how antiparasitic drugs are eliminated is crucial for optimising treatment efficacy and managing anthelmintic resistance, particularly as these agents rely on adequate faecal concentrations to control parasites in the equine gastrointestinal tract. Pérez and colleagues administered either moxidectin (0.4 mg/kg) or ivermectin (0.2 mg/kg) orally to ten healthy adult horses and tracked faecal drug concentrations using high-performance liquid chromatography over a 75-day period. Both drugs peaked in faecal concentration at 2.5 days post-administration, but moxidectin demonstrated substantially prolonged elimination, remaining detectable for 75 days compared to 40 days for ivermectin, with ivermectin clearing 90% of its total faecal load by day four versus day eight for moxidectin. Remarkably, despite moxidectin's higher dose and superior plasma persistence, only 44.3% of administered moxidectin reached the faeces versus 74.3% of ivermectin, indicating extensive hepatic metabolism of moxidectin in equines. For practitioners, these findings suggest that moxidectin's extended faecal presence may offer prolonged parasiticide activity, though its greater metabolic biotransformation could have implications for drug interactions and individual variation in efficacy—considerations particularly relevant when designing rotation strategies or treating horses with compromised liver function.
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Practical Takeaways
- •Moxidectin's prolonged faecal excretion (75 days) provides extended environmental availability compared to ivermectin (40 days), which may affect pasture contamination and parasite control strategies
- •The higher metabolization rate of moxidectin means less drug reaches the gut lumen despite higher dosing, relevant when selecting anthelmintics for efficacy in horses with malabsorption issues
- •Both drugs show similar initial kinetics, so choice between them may depend on desired duration of action and metabolic capacity of individual horses rather than pharmacokinetic differences alone
Key Findings
- •Moxidectin remained detectable in faeces for 75 days post-administration compared to 40 days for ivermectin, despite using a 100% higher dose
- •Both drugs reached maximum faecal concentration at 2.5 days post-administration with no significant differences between treatment groups
- •Ivermectin showed 90% total faecal excretion by day 4, whereas moxidectin required 8 days to reach the same elimination level
- •Moxidectin concentration in faeces represented only 44.3% of total administered drug compared to 74.3% for ivermectin, indicating greater hepatic metabolism of moxidectin in horses