EFFECT OF FORMULATION ON THE PHARMACOKINETICS AND EFFICACY OF DORAMECTIN

The pharmacokinetics of doramectin, a novel avermectin, were evaluated following parenteral administration in a range of oil-based formulati ons in an attempt to optimise the formulation. Therapeutic and persist ent efficacies against Cooperia oncophora were also evaluated. This ap proach led to the identification of formulations based upon sesame oil and ethyl oleate which gave more prolonged doramectin plasma concentr ations with no loss in therapeutic efficacy and improved persistent ef ficacy following subcutaneous administration to cattle at a dosage of 200 mug kg-1. The importance of using both pharmacokinetic and efficac y end points to distinguish between formulations is discussed. All for mulations were well tolerated as evidenced by the absence of any react ion to injection either in the form of behavioural responses, injectio n site swelling or postmortem lesions. Sesame oil with ethyl oleate wa s the best parenteral vehicle tested for doramectin, allowing the expr ession of a high level of therapeutic and persistent efficacy and offe ring the benefit of excellent injection site toleration.