The pharmacokinetics of ivermectin after oral and subcutaneous administration to sheep and horses

Antti Oksanen; Endectocide treatment of the reindeer

“…Topical (500 pg kg -1 ) and oral (200 pg kg -1 ) administrations of ivermectin to milking goats were compared by Scott et al (1990), who recorded slightly higher peak plasma concentrations after the oral treatment which declined more rapidly than in the present reindeer study. The concentration in goat plasma after topical application was lower than in the present trials A and B, but much higher than in group CT. Marriner et al (1987) and reported that ivermectin had a higher bioavailability after subcutaneous administration to sheep than after oral administration, matching the present results in reindeer.…”

“…The peak plasma concentration measured in trial C after subcutaneous injection was of the same order as that measured in cattle (44 ng ml" 1 , Fink and Porras 1989) but considerably higher than that in red deer in which even a double dose (400 pg kg" 1 ) resulted in a peak concentration of 28 ng ml" 1 (Andrews et al 1993). The difference in the plasma concentrations observed between reindeer and red deer is comparable to that between sheep and goats (Marriner et al 1987, Scott et al 1990, which are phylogenetically closer species. Topical (500 pg kg -1 ) and oral (200 pg kg -1 ) administrations of ivermectin to milking goats were compared by Scott et al (1990), who recorded slightly higher peak plasma concentrations after the oral treatment which declined more rapidly than in the present reindeer study.…”

“…1203) ng*h/ml following subcutaneous injection of ivermectin at 200 pg/kg to sheep, and 2039 (231) ng*h/ml following oral administration at the same dose (Marriner et al, 1987). The difference here was 2.8-fold.…”

Use of anthelmintics in herbivores and evaluation of risks for the non target fauna of pastures

“…The faecal excretion of orally administered ivermectin by sheep is more rapid. By seven days, the faecal residues account for 69% of the dose and 61-69% of these residues are present as the parent drug [40,76]. Other studies have shown 95% recovery of the total dose in the faeces of sheep seven days after intra-ruminal administration [2], two-thirds of this being recovered during the first two days [98].…”

“…Ivermectin is not metabolised in the rumen and a significant part of the drug may pass down the gastrointestinal tract into the faeces without absorption into the systemic circulation [5]. Oral formulations (oral paste or drench formulations) of ivermectin for sheep and horses have less bioavailability and persistence than the injectable formulation for cattle [50,65,76]. Herd [50] estimated that this formulation had fewer environmental effects, although the use of an oral paste for horses still resulted in a significant delay in dung degradation rates [52].…”