The developing resistance to current chemical classes of broad-spectrum anthelmintics and insecticides presents an undeniable threat to the long-term viability of the animal health industry. Alternative treatment strategies including vaccines, biological control and breeding of parasite-resistant animals are unlikely to be widely available in the near future and even then they will be integrated with chemotherapy. The significant cost of research and development of new therapeutics for food-producing animals, together with the small market share of animal health products, particularly in Australia and New Zealand, is a positive disincentive for drug development. The chemical actives that are currently available are all that we are likely to have for the foreseeable future and they must be used more efficiently. Understanding the pharmacokinetic behaviour of antiparasitics and recognising the potential for the animal's physiological characteristics to assist drug action is crucial. Careful administration, coupled with a reduction of feed intake before oral anthelmintic treatment, maximises drug availability and therefore increases efficacy of the benzimidazole and ivermectin compounds. This is a cost-effective option that can be employed immediately, which not only increases efficacy of ''older'' compounds but will be instrumental in prolonging the useful life of the newer drugs. Taking care to apply topical insecticide formulations directly along the backline immediately after shearing will maximise even diffusion of active around the sheep flanks to contact lice inhabiting sites remote from the point of drug application. The use of ''intelligent'' formulation and delivery of existing compounds, based on knowledge of host physiological and pharmacological responses, holds the key to effective antiparasitic treatment. (C) 1997 Australian Society for Parasitology. Published by Elsevier Science Ltd.
