Faecal excretion profile of moxidectin and ivermectin after oral administration in horses.

This study evaluates how horses excrete two types of orally administered drugs, moxidectin and ivermectin, by comparing how long these drugs remain detectable in faeces. The findings show that even though moxidectin was administered at a higher dose and had greater plasma levels, ivermectin was represented as a larger portion of the total drug administered in faeces, which suggests moxidectin is more quickly metabolized in the horse.

Methodology

• The researchers used ten clinically healthy adult horses of weights ranging from 390-446 kg for the study. These horses were divided into two experimental groups.
• Group I was treated with an oral gel formulation of moxidectin at a dose recommended by the manufacturer, 0.4 mg/kg body weight.
• Group II was treated with an oral paste formulation of ivermectin at a dose of 0.2 mg/kg body weight.
• Faecal samples were collected at varying times between 1 and 75 days after the treatment was administered.
• Horse faecal drug extractions were performed and samples were analysed using a high-performance liquid chromatography method that uses fluorescence detection and computerized kinetic analysis.

Findings

• Both the moxidectin and ivermectin achieved their highest concentrations in faeces at 2.5 days after administration.
• The faecal concentrations of ivermectin remained above detectable levels for 40 days after treatment. Moxidectin’s faecal concentrations remained above a detectable level for 75 days.
• Ivermectin was eliminated from the system faster than moxidectin, with 90% of the total drug excreted in faeces four days after treatment. By comparison, moxidectin took eight days to reach this level.
• Both drugs showed similar patterns of drug transfer from blood plasma to the gastrointestinal tract, with no significant difference in the times and quantities that they were found in faecal matter.
• Though administered at a 100% higher dosage than ivermectin, the concentration of moxidectin in faeces only represented 44.3% of the total drug administered, compared to 74.3% for ivermectin. This indicates that moxidectin is metabolized at a higher rate in horses.

Conclusion

• This research suggests a higher metabolization rate for moxidectin in horses compared to ivermectin, despite the dose of moxidectin being twice as high.
• The findings of this study could provide valuable insight into drug metabolization in horses, which could aid in the proper administration of these drugs in clinical settings.