Efficacy of selamectin against experimentally induced and naturally acquired ascarid (Toxocara canis and Toxascaris leonina) infections in dogs

The efficacy of selamectin against adult ascarids was evaluated in eight co ntrolled and masked studies in dogs. Three laboratory studies evaluated sel amectin against experimentally induced infections of Taxacara canis; three laboratory studies evaluated selamectin against naturally acquired infectio ns of T. canis; one laboratory study evaluated selamectin against naturally acquired infections of both T: canis and Toxascaris leonina; one field stu dy evaluated selamectin against naturally acquired infections of ascarids ( T. canis and/or T. leonina) in dogs presented as veterinary patients, Selam ectin was administered topically to the skin of dogs in unit doses designed to deliver a minimum of 6 mg kg(-1) (range, 6-12 mg kg(-1)). In all studie s, dogs were allocated randomly to treatment assignments (selamectin or Veh icle control in laboratory studies: selamectin or reference product in the field study) on the basis of pretreatment fecal egg counts. For induced inf ections, there were significant reductions in geometric mean numbers of adu lt T. canis after a single application of selamectin (93.9-98.1%, P=0.0001) , after two monthly applications (greater than or equal to 88.3%, P less th an or equal to 0.0001), and after three monthly applications (100%, P less than or equal to 0.0002). In the natural infection laboratory studies, when selamectin was administered twice at an interval of 30 days, the percentag e reductions in geometric mean numbers of adult T. canis at necropsy were 8 4.6, 91.3, and 97.9%, and when selamectin was administered on days 0, 14, a nd 30, the percentage reductions were 91.1 and 97.6%. Geometric mean fecal T: canis egg counts were reduced by greater than or equal to 92.9% (P less than or equal to 0.0067) at the end of the studies. In the field study, geo metric mean fecal ascarid egg counts were reduced by 89.5 and 95.5% (P=0.00 01) for 14 and 30 days, respectively after a single treatment with selamect in, and by 94.0% (P=0.0001) 30 days after the second treatment with selamec tin. These reductions compared favorably with the egg count reductions from dogs treated with a reference product containing praziquantel, pyrantel em bonate, and febantel. There were no adverse drug experiences or treatment-r elated mortalities during any of the studies. Selamectin, when administered topically in a unit dose providing a minimum dosage of 6 mg kg(-1), was sa fe and effective against adult T. canis and T. leonina and in reducing the fecal excretion of T. canis eggs in dogs. (C) 2000 Elsevier Science B.V. Al l rights reserved.