Titration of subcutaneously administered eprinomectin against mature and immature nematodes in cattle.

Eprinomectin has been approved for use as a topically applied endectocide for beef and dairy cattle. To determine if eprinomectin has utility as an injectable anthelmintic, it was titrated at 0.05, 0.1, and 0.2 mg/kg s.c. against adult (Trial 1) and at 0.05, 0.1, 0.14, and 0.2 mg/kg s.c. against immature (Trial 2) stages of lung and gastrointestinal nematodes in cattle. In Trial 1, every dose of subcutaneously delivered eprinomectin showed maximal or near-maximal (> or = 99%) efficacy against Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, T colubriformis, Cooperia punctata, Nematodirus helvetianus, Oesophagostomum radiatum, and Dictyocaulus viviparus. Adult C. oncophora was the only exception. However, even against this species, the lowest dose of 0.05 mg/kg showed 93% efficacy, and the efficacious dose necessary to kill 95% (ED95) of adults was 0.056 mg/kg. In Trial 2, every dose of subcutaneously delivered eprinomectin showed maximal or near-maximal (> or = 99%) efficacy against the immature stages of all of the above species of endoparasites. As a result, ED95 values could not be calculated. Consequently, the exquisite potency against endoparasites through parenteral administration suggests that eprinomectin may also have potential utility as an injectable product for cattle.