Ma. Pass et Td. Mogg, PHARMACOKINETICS AND METABOLISM OF AMITRAZ IN PONIES AND SHEEP, Journal of veterinary pharmacology and therapeutics, 18(3), 1995, pp. 210-215
Amitraz and its active metabolite BTS27271 were given intravenously to
ponies and sheep at equimolar doses of I mg/kg and 0.68 mg/kg, respec
tively and the plasma concentrations of amitraz and BTS27271 estimated
at various times thereafter. Amitraz was hydrolysed to BTS27271 in bo
th species. Amitraz was undetectable in sheep plasma after approximate
ly 5 min but persisted in the plasma of ponies for at least 90 min. Th
e persistence of unmetabolized amitraz in ponies may have implications
for the toxicity of amitraz in that species. The primary and secondar
y disposition half-lives of amitraz in ponies were 2 and 39 min, respe
ctively. BTS27271 was distributed rapidly outside the plasma in both s
pecies with a primary disposition half-life of 4.4 min In sheep and 5.
9 min in ponies. The secondary disposition half-lives were 51 and 55 m
in, respectively. The secondary phase of the disposition of BTS27271 w
as similar whether BTS27271 was given directly or derived by hydrolysi
s from amitraz. However, significant differences were evident in the p
rimary phase of the disposition of BTS27271. Sheep demonstrated a larg
er apparent volume of distribution of BTS27271 than ponies and more ra
pid body clearance.