EPRINOMECTIN - A NOVEL AVERMECTIN FOR USE AS A TOPICAL ENDECTOCIDE FOR CATTLE

Eprinomectin (MK-397 or 4''-epi-acetylamino-4''-deoxy-avermectin B-1) is a novel avermectin selected for development as a topical endectocid e for all cattle, including lactating dairy cows. Herein, we show its anthelmintic, insecticidal and miticidal activity. To determine its an thelmintic capabilities, eprinomectin was tested topically on Jersey c alves at 0.08, 0.2, or 0.5 mg kg(-1) in a probe formulation against ex perimental infections of adult Haemonchus placei, Ostertagia ostertagi , Trichostrongylus axei, T. colubriformis, Cooperia oncophora, C. punc tata, Nematodirus helvetianus, Oesophagostomum radiatum and Dictyocaul us viviparus. Eprinomectin removed greater than or equal to 99% and gr eater than or equal to 98% of the adult stage of every species at the 0.5 and 0.2 mg kg(-1) dosage levels, respectively. The lowest dosage ( 0.08 mg kg(-1)) produced maximal or near maximal efficacy against most of the adult endoparasites with the exception of T. colubriformis (87 %) and C. oncophora (88%). In a separate test, eprinomectin was evalua ted topically against the immature stages of these species at the same dosages. Results showed greater than or equal to 99% and greater than or equal to 98% of the adult stage of every species at the 0.5 and 0. 2 mg kg(-1) dosage levels, respectively. The 0.08 mg kg(-1) dosage mai ntained greater than or equal to 97% efficacy against 6 species with r educed activity against H. placei (42%) and N. helvetianus (66%). For ectoparasites, eprinomectin was tested topically at 0.16, 0.24, 0.32 o r 0.5 mg kg(-1) on mixed breed cattle naturally infested with the suck ing louse, Linognathus vituli. Complete elimination of lice at all dos ages was observed by day 14. Topical delivery of eprinomectin at 0.16, 0.24, 0.32 or 0.5 mg kg(-1) to Holstein calves experimentally challen ged with horn fly, Haematobia irritans, produced 100% efficacy to chal lenge by week 2 post-treatment in all dosage groups and 94% and 99% ef ficacy to challenge at the 0.32 and 0.5 mg kg(-1) dosage groups, respe ctively, at week 4. Topical delivery of eprinomectin at 0.16, 0.24 or 0.5 mg kg(-1) to Deutsches Fleckvieh cattle infested with mange mites, Chorioptes bovis, produced greater than or equal to 95% control at al l dosage levels by day 14 post-treatment and was maintained at or near this efficacious level for the 6-week duration of the trial. No adver se reaction was observed in any animal in any of these tests. In summa ry, these experimental data indicate that eprinomectin is an excellent broad-spectrum endectocide for cattle and is suitable far topical del ivery.