Plasma disposition and faecal excretion of oxfendazole, fenbendazole and albendazole following oral administration to donkeys.
Authors: Gokbulut Cengiz, Akar Ferda, McKellar Quintin A
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Anthelmintic Pharmacokinetics in Donkeys When treating donkey parasites with benzimidazole anthelmintics, practitioners should be aware that these drugs behave quite differently in donkeys compared to horses and ruminants—a distinction with potentially significant implications for efficacy. Researchers administered fenbendazole, oxfendazole and albendazole at 10 mg/kg to donkeys, then tracked plasma concentrations and faecal excretion via high-performance liquid chromatography over five days. Oxfendazole achieved the highest plasma concentrations (Cmax 0.49–0.60 μg/mL), whilst albendazole produced minimal measurable plasma levels (only 0.08 μg/mL), indicating extensive first-pass metabolism in donkeys; notably, all three drugs were predominantly eliminated via faeces rather than systemic circulation, with peak faecal concentrations occurring between 30–34 hours post-administration. The extensive hepatic metabolism and reduced bioavailability documented here suggests that donkeys may require adjusted dosing strategies or more frequent treatment intervals compared to horses for equivalent anthelmintic coverage, particularly with albendazole, and clinicians should factor in this species-specific pharmacokinetic difference when selecting parasite control protocols.
Read the full abstract on PubMed
Practical Takeaways
- •Fenbendazole bioavailability appears reduced in donkeys compared to horses due to enhanced first-pass metabolism, suggesting licensed dosing protocols for horses may not provide equivalent efficacy in donkeys
- •The substantial conversion of administered drugs to metabolites in donkeys indicates that metabolite concentrations rather than parent drug concentrations may be more relevant for assessing anthelmintic efficacy in this species
- •Consider species-specific pharmacokinetic data when treating donkeys for parasites, as equine-derived dosing recommendations may be suboptimal due to donkeys' higher metabolic capacity for benzimidazoles
Key Findings
- •Fenbendazole parent compound was not detected in plasma following oral administration to donkeys, while oxfendazole showed Cmax of 0.49 µg/mL and albendazole was completely metabolized via first-pass mechanisms
- •Oxfendazole sulphone metabolite had significantly higher AUC (10.33 µg h/mL) than parent drug (5.17 µg h/mL), indicating substantial first-pass metabolism
- •Fenbendazole demonstrated the highest faecal AUC of parent molecule compared to oxfendazole and albendazole, with peak faecal concentrations detected at 30-34 hours post-administration
- •Donkeys show higher metabolic capacity and greater first-pass effects for benzimidazoles compared to ruminants, resulting in lower bioavailability and potentially reduced efficacy despite licensed use of fenbendazole in horses