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The pharmacodynamics of ivermectin in sheep and cattle
Author(s) -
BOGAN THE LATE'J. A.,
McKELLAR Q. A.
Publication year - 1988
Publication title -
journal of veterinary pharmacology and therapeutics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.527
H-Index - 60
eISSN - 1365-2885
pISSN - 0140-7783
DOI - 10.1111/j.1365-2885.1988.tb00151.x
Subject(s) - ivermectin , pharmacodynamics , pharmacology , veterinary medicine , biology , medicine , pharmacokinetics
Bogan, J.A. (deceased) & McKellar, Q.A. The pharmacodynamics of ivermectin in sheep and cattle. J. vet. Pharmacol. Therap. 11, 260–268. The concentrations of ivermectin in the gastrointestinal tract of sheep and cattle were determined after subcutaneous administration of ivermectin. Ivermectin was not detected (limit of detection 1 ng/ml) in abomasal and ruminal fluids either after a normal therapeutic dose of 200 μg/kg or even at an increased dose of 2000 μg/kg. It was also not detected in abomasal and ruminal fluids of a sheep infected with the abomasal parasite Osterlagia circumcincta. However, ivermectin was detectable at similar concentrations in abomasal mucus and in small intestinal mucus. Excretion of ivermectin was high in bile but the concentrations in small intestinal mucus, distal and proximal to the bile duct opening, were similar. It is hypothesized that the low efficacy of ivermectin against small intestinal nematodes compared with abomasal nematodes is not due to differences in ivermectin concentrations in the predilection sites but is probably due to tachyphylaxis in the nematodes allowing the small intestinal nematodes to re‐establish before they have left their predilection site. Ivermectin was excreted in the milk of ewes at concentrations similar to those in plasma. Lambs suckling ivermectin‐treated ewes received about 4% of a normal therapeutic dose (200 μg/kg) via the milk.