Benzimidazoles Pharmacodynamics in Equine Strongyles

Our research aimed to assess the effectiveness of four benzimidazoles: albendazole, fenbendazole, mebendazole and thiabendazole against equine strongyles. The tests were performed between March 2015 and May 2016, on samples collected from 20 horses and 8 donkeys living in Harghita County. In vivo, Faecal Egg Count Reduction Test (FECRT) was used to evaluate fenbendazole pharmacodynamics. In vitro, Egg hatch assay (EHA) and Larval development assay (LDA) were used to evaluate the effectiveness of albendazole, fenbendazole, mebendazole and thiabendazole. The predominance of small strongyle species was observed, mostly Cyathostomum type A. In the horse group, before treatment, the average intensity was 1595.5 EPG, the maximum value being 4000, and extensivity 55%. Tested again at 14 days after treatment, all samples were negative. In the donkey group, before treatment, the total number was 6550 EPG, intensity of 935.7 and extensivity of 87.5%. 14 days after treatment, the average intensity was 150 and the extensivity 50%. In the horse group, EHA proved the efficacy of fenbendazole (0.0192%), albendazole (0.3740%) and thiabendazole (11.62%) and a major risk of inducing adaptive phenomena for mebendazole (Y parameter 1009.92). In the donkey group, all benzimidazoles had limited effectiveness: thiabendazole (73.93%), mebendazole (87.51%), fenbendazole (94.05%), albendazole (111.67%). All benzimidazoles inhibited larval development. For all tested benzimidazoles, the resistance induction predictive comparative risk analysis highlighted the benefit of their use, provided that the treatment protocol allows sufficient contact time.