The efficacy of
selamectin against adult ascarids was evaluated in eight controlled and masked studies in dogs. Three laboratory studies evaluated
selamectin against experimentally induced
infections of Toxocara canis; three laboratory studies evaluated
selamectin against naturally acquired
infections of T. canis; one laboratory study evaluated
selamectin against naturally acquired
infections of both T. canis and Toxascaris leonina; one field study evaluated
selamectin against naturally acquired
infections of ascarids (T. canis and/or T. leonina) in dogs presented as veterinary patients.
Selamectin was administered topically to the skin of dogs in unit doses designed to deliver a minimum of 6mgkg(-1) (range, 6-12mgkg(-1)). In all studies, dogs were allocated randomly to treatment assignments (
selamectin or vehicle control in laboratory studies:
selamectin or reference product in the field study) on the basis of pretreatment fecal egg counts. For induced
infections, there were significant reductions in geometric mean numbers of adult T. canis after a single application of
selamectin (93.9-98.1%, P=0.0001), after two monthly applications (> or =88.3%, P< or =0.0001), and after three monthly applications (100%, P< or =0.0002). In the natural
infection laboratory studies, when
selamectin was administered twice at an interval of 30 days, the percentage reductions in geometric mean numbers of adult T. canis at necropsy were 84.6, 91.3, and 97.9%, and when
selamectin was administered on days 0, 14, and 30, the percentage reductions were 91.1 and 97.6%. Geometric mean fecal T. canis egg counts were reduced by > or =92.9% (P< or =0.0067) at the end of the studies. In the field study, geometric mean fecal ascarid egg counts were reduced by 89.5 and 95. 5% (P=0.0001) for 14 and 30 days, respectively, after a single treatment with
selamectin, and by 94.0% (P=0.0001) 30 days after the second treatment with
selamectin. These reductions compared favorably with the egg count reductions from dogs treated with a reference product containing
praziquantel,
pyrantel embonate, and
febantel. There were no adverse
drug experiences or treatment-related mortalities during any of the studies.
Selamectin, when administered topically in a unit dose providing a minimum dosage of 6mgkg(-1), was safe and effective against adult T. canis and T. leonina and in reducing the fecal excretion of T. canis eggs in dogs.