Pharmacokinetics of ivermectin in sheep following intravenous, intra‐abomasal or intraruminal administration*

Abstract
The pharmacokinetics of ivermectin in plasma following i.v. intraabomasal, and intraruminal administration to sheep was determined. When given i.v. ivermectin was very slowly eliminated with a terminal half-life of 178 h and a volume of distribution at steady state of 5.3 l/kg indicating sequestration in a temporary depot. Intraabomasal administration resulted in rapid absorption, a peak plasma concentration of 60.6 ng/ml at 4.4 h, and 100% bioavailability. However, intraruminal administration produced a much lower peak concentration (17.6 ng/ml at 23.5 h) and bioavailability (25.1%). A subsequent in vitro study indicated that ivermectin may be rapidly metabolized in the rumen.

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