Plasma disposition, milk excretion and efficacy of mebendazole in lactating donkeys naturally infected by Cyathostominae

Therapeutics are administered to donkeys based on dosage and intervals recommended for horses because few drugs have donkey-specific indications. Although, mebendazole (MBZ) has been licensed for use in horses there are no data available regarding its pharmacokinetic disposition and effectiveness in donkeys. The plasma disposition, milk excretion and efficacy of a paste formulation of MBZ in donkeys were examined in a field trial. Two groups of six donkeys received MBZ paste at horse dosage 10 mg/kg body weight (MBZ 1) and at double horse dosage 20 mg/kg body weight (MBZ 2) in animals naturally infected by Cyathostominae. Heparinised blood and milk samples were collected at times between 1 and 120 h post treatment. The samples were analysed by high performance liquid chromatography. Individual FECs (Faecal Egg Count) were performed on each animal before the treatment (day -3) and weekly from day 7 until day 56 post treatment using a modified McMaster technique with a sensitivity of 10 EPG. The results of FECRT for both MBZ dosages were efficient (>95% efficacy) until day 28. The plasma concentrations and systemic exposure of MBZ in donkeys were relatively lower compared with the other benzimidazoles. Dose-dependent plasma dispositions were observed at the increased dose (10 vs 20 mg/kg). This study indicated that oral administration of MBZ has a minimal disposition rates into the milk (ratio of AUC milk/plasma was 0.18±0.02) and may be used safely in lactating donkeys with zero milk-withdrawal period. Therefore, horse dose of MBZ could be used for parasite control in donkeys.