Current problems for the approval of anthelmintic selleck screening library combination products include the lack of universally accepted guidelines for their development; various regulatory agencies employ different approaches and policies for granting approval of combination anthelmintic products for use in ruminant livestock and horses. This situation may result in poor management practices caused by the present reluctance to

accept anthelmintic combinations in some jurisdictions (e.g., the European Union and the United States of America). Since the control of resistant nematodes may be similarly accomplished by separate dosing with multiple constituent actives in individual products, a practice not prevented under existing regulations, it is unlikely that a combination anthelmintic product would incentivize irresponsible use to a greater extent than what already exists with single-active products. As noted, guidelines governing the approval of combinations of anthelmintic constituent actives

in fixed-dose, single dosage form products vary among countries. The driving Stem Cell Compound Library force for approval in countries in which these products are registered has been the provision of medicines capable of controlling multiple species of drug-resistant nematodes (including populations Thiamine-diphosphate kinase resistant to one or more classes of anthelmintic),

primarily of sheep and more recently cattle, and also to retard the development and spread of AR as a longer-term goal. Control of existing populations of resistant parasites is much easier to demonstrate and serves as the basis for approval in countries in which combination products are allowed. Data are emerging to support the use of combination anthelmintic products to slow the development and spread of AR, but it would be challenging to incorporate data for this indication per se to support regulatory approval. Instead, label requirements for these products include demonstration of high efficacy (e.g., in Australia >95%, Anonymous, not dated) against a panel of resistant parasite species relevant for the country. This is feasible for sheep parasites, but may be difficult to attain for resistant parasites of cattle, which are less readily available as experimental isolates; the same situation pertains to equine parasites. This new guideline relating to combination anthelmintic products containing two or more constituent actives is developed in the context of those used by countries that already approve their use along with the W.A.A.V.P. and VICH guidelines for general efficacy of anthelmintics (Anonymous, 1999a, Anonymous, 1999b, Anonymous, 2000a, Anonymous, 2000c, Anonymous, 2001, Vercruysse et al.