In Vivo and In Vitro Pharmacodynamics of Anthelmintic Medication Used in Sheep

Our research aimed to evaluate the efficacy of anthelmintic treatments in sheep, as well as the resistance occurrence risk for the most commonly used substances. Anthelmintic medication efficacy was evaluated on 30 animals from a private farm, located in Sânmihaiu Almaşului, Sălaj County. In vivo studies were performed by using Fecal Egg Count Reduction Test (FECRT) and testing an albendazole-based (ABZ) product. In vitro, we used Egg Hatch Assay (EHA) and Larval Development Assay (LDA) for albendazole (ABZ), mebendazole (MBZ), fenbendazole (FBZ), thiabendazole (TBZ) and ivermectin (IVM) (only for LDA). FECRT showed that intestinal nematodes developed resistance phenomena against the ABZ-based product, with an extensivity of 80% at seven days post therapy, an egg reduction percentage of 41.89% at seven days post-therapy and 43.9% at 14 days post-therapy. The in vitro EHA highlighted a superior efficacy of TBZ (egg hatch percentage at reference concentration being 51.21) compared to ABZ (71.89%), MBZ (84.46%) and FBZ (79.22%), with a minimum risk of anthelmintic resistance. The LDA test revealed the superior efficacy of FBZ (MIC 0.59 mcg/ml) and IVM (MIC 0.078 mcg/ml), with a minimal risk of inducing parasitic resistance. All in vivo and in vitro tests revealed a limited ABZ efficacy, recommending avoiding the therapy with this substance.