Pharmacological evaluation on benzimidazole anthelmintics for eradication of the gill fluke Microcotyle sebastis infesting a black rockfish, Sebastes schlegelii

This study comprehensively evaluated the in vitro and in vivo anthelmintic efficacy and pharmacokinetics of four benzimidazole compounds: febantel (FB), fenbendazole (FBZ), albendazole (ABZ), and mebendazole (MBZ) against the gill fluke Microcotyle sebastis in cultured black rockfish (Sebastes schlegelii). In vitro tests with isolated adult parasites demonstrated that ABZ exhibited the highest efficacy, followed by FBZ, while MBZ showed minimal activity and FB remained largely inactive at lower concentrations. At the highest concentration tested (200 mg/L), FB showed only weak, nonspecific activity. In in vivo experiments, ABZ was the most effective drug when orally administered at 50 mg/kg for three consecutive days, while FB demonstrated greater efficacy than FBZ, and MBZ exhibited the lowest efficacy under the tested conditions. Pharmacokinetic analysis revealed marked variation among the drugs, with FB achieving the highest active metabolite levels at 100 mg/kg. ABZ, at 50 mg/kg, achieved comparable systemic exposure to FBZ at 100 mg/kg through its active metabolite albendazole sulfoxide (ABZSO). These findings highlight ABZ as the most efficacious compound, with FB showing promise through metabolic conversion to FBZ, and MBZ demonstrating limited efficacy due to poor absorption and rapid inactivation. Overall, this study provides an integrated evaluation of both efficacy and pharmacokinetics, indicating that ABZ and FB are effective candidates for managing M. sebastis infections in aquaculture.