DORAMECTIN - A POTENT NOVEL ENDECTOCIDE

Doramectin, hexyl-5-O-demethyl-25-de(1-methylpropyl)avermectin A1a, wa s selected as the best of a series of novel avermectins prepared by mu tational biosynthesis. The primary evaluation of its in vivo antiparas itic activity was carried out using a rat Trichostrongylus colubriform is model and a rabbit Psoroptes cuniculi model. In each case the new a vermectin performed favourably relative to dihydroavermectin B1a (DHAV M), the major component of ivermectin. Doramectin was extensively eval uated in cattle using an experimental micelle formulation, proving hig hly effective in cattle infected with Ostertagia ostertagi, Cooperia o ncophora and Dictyocaulus viviparus when administered subcutaneously a t 200 mug kg-1. The plasma pharmacokinetic characteristics of doramect in in cattle following intravenous administration revealed a plasma ha lf-life of approximately 89 h. In the micelle formulation, doramectin administered subcutaneously at 400 mug kg-1 provided persistent activi ty against infection of cattle with C. oncophora and O. ostertagi for at least 8 and 12 days respectively.