Residue depletion and withdrawal time estimation of moxidectin and triclabendazole in cattle following pour-on administration

Moxidectin-triclabendazole pour-on solution is a broad-spectrum antiparasitic formulation used to control both ectoparasites and endoparasites in livestock. This study evaluated the residue depletion of moxidectin (MOX) and triclabendazole ketone (keto-TCB), the major metabolite of triclabendazole, in edible bovine tissues following pour-on administration at a dose of 0.1 mL/kg body weight. A validated LC-MS/MS method was employed for residue quantification. The method demonstrated tissue-specific limits of detection (LOD) and limits of quantification (LOQ) for MOX and keto-TCB. For MOX, LODs were 2, 10, 5, and 50 μg/kg, and LOQs were 5, 20, 10, and 100 μg/kg in muscle, liver, kidney, and fat, respectively. For keto-TCB, LODs were 10, 100, 50, and 10 μg/kg, and LOQs were 50, 200, 100, and 20 μg/kg in muscle, liver, kidney, and fat, respectively. Tissue samples from muscle, liver, kidney, and fat were collected up to 180 days after administration. MOX showed prolonged persistence in fat, which was identified as the critical tissue for withdrawal period evaluation, whereas keto-TCB depleted more rapidly overall. Based on the corresponding maximum residue limits, the withdrawal intervals were estimated to be at least 121 days for MOX and at least 53 days for keto-TCB. These findings provide residue depletion data to support withdrawal period evaluation and food safety assessment of this formulation in cattle.