The use of benzimidazole-levamisole mixtures for the control and prevention of anthelmintic resistance in sheep nematodes: an assessment of their likely effects.

Literature relevant to the use of benzimidazole-levamisole combinations for the control and prevention of anthelmintic resistance in gastrointestinal nematodes in sheep is reviewed and the likely consequences of such a strategy are considered. It is suggested that while a system of multiple attack involving the simultaneous administration of both compounds, each given at their full recommended individual dose rates, may have limited scope in combatting resistance once it has arisen, as a means of delaying or preventing its emergence in the first place it may be more appropriate. In these latter circumstances, it seems unlikely that the use of a benzimidazole-levamisole mixture would result in a faster build-up of resistance then would the sequential application of either drug on its own, and indeed may greatly delay it.