ASSESSMENT OF THE RICOBENDAZOLE PLUS LEVAMISOLE NEMATODICIDAL COMBINATION IN CATTLE

CANTON, C.1; CEBALLOS, L.1; MORENO, L.1; FIEL, C.2; DOMÍNGUEZ, P.1,2; BERNAT, G. 2,3; LANUSSE, C.1; ALVAREZ, L.1

Liverpool

Congreso; Congreso Mundial de la World Association of Veterinary Parasitology; 2015

Mixtures of drugs with different mechanisms of action have been proposed as a useful tool to delay the development of resistance. In theory, this is a valid strategy if the efficacy of each of the anthelmintic molecules approaches 100%. This situation is more feasible to be applied in cattle production, where the development of anthelmintic resistance is less widespread than in sheep farms. The main goal of the current trial was to study the clinical efficacy and the potential pharmacokinetic (PK) interactions occurring after the subcutaneous (SC) administration of ricobendazole (RBZ) and levamisole (LEV) given either separately or co-administered to parasitized calves in two seasons, winter and spring, with predominance of different nematode population. Sixty (60) male calves naturally infected with gastrointestinal nematodes susceptible to both drugs were randomly allocated into four groups (n= 15): Control group: animals did not receive anthelmintic treatment; RBZ group: treated with RBZ by the SC route (3.75 mg/kg); LEV group: treated with LEV by the SC route (8 mg/kg); RBZ+LEV group: simultaneously treated by the SC route with RBZ and LEV (at the same dose rates). Eight (8) animals from each treated group were randomly selected to perform the PK study. Drug concentrations were measured by HPLC. The clinical efficacy was determined at 14 days after treatment by the Faecal Egg Count Reduction Test (FECRT). No pharmacokinetic interactions were observed after the combined treatment, with similar PK parameters (P>0.05) obtained between the single-drug and combination-based strategy. In winter time (June/July in the southern hemisphere) with only 10% of Ostertagia spp. observed in the faecal cultures (control group), the FECRT at 14 days post-treatment were 96.1% (RBZ), 99.8% (LEV) and 100% (RBZ+LEV). However, in spring (October) where Ostertagia spp. represent 28% of the total L3 composition, the FECRT were 95.1(RBZ), 93.1(LEV) and 96.1% (RBZ+LEV). The increased presence of Ostertagia spp. in spring determined a tendency to reduced clinical efficacies compared to winter time, even for the combined nematodicidal treatment. Overall, the potential therapeutic advantages of combined anthelmintic treatment should be cautiously assessed before implementing under field conditions.