Estimation of the Safety of Ivermectin in Collies

Abstract

The effect of Ivermectin (IVM) administered at 20, μg/kg (approximately twice the recommended dosage for prevention of Dirofilaria immitis infection in dogs 6-9μg/kg) was evaluated in 2-month-old roughhaired collies. Penetration of the compound into the central nervous system tissue was also assessed.
Four rough-haired collies and 4 mongrel dogs were given IVM once orally at 20μg/kg while 4 control dogs (2 rough-haired collies and 2 mongrel dogs) were given placebo (vehicle). Animals were observed for clinical signs for 24 hours after treatment. No abnormal findings, including neurologic signs, were observed. No abnormalities associated with IVM treatment were recorded for any variables measured on electrocardiographic, hematological, blood biochemical and histpathological evaluations.
There was no significant difference in plasma IVM levels determined 6 and 24 hours after treatment between the collie group and the mongrel dog group. No apparent difference was detectable in absorption or excretion of IVM in the two groups. In 3 collies and 4 mongrel dogs, the IVM levels in the central nervous system tissue 24 hours after treatment were not detectable. For one collie, the IVM concentration in the cerebellum determined at the same time was about one-third that of the plasma level and the levels in the brain stem and spinal cord were approximately equal to that in the plasma. These results demonstrated that IVM could penetrate into the central nervous system tissues in some collies.
The results of this study indicate that the low single oral dose of 6-9 μg/kg required for prevention of D. immitis infection in dogs is not expected to cause any adverse effects in collies.