A four-year evaluation of the chronic toxicity of megestrol acetate in dogs

Abstract

Megestrol acetate was administered orally to female beagle dogs for 4 yr at 0.01, 0.1, or 0.25 mg/kg/day. Chlormadinone acetate was given to a comparable group at 0.25 mg/kg. Decreased evidence of estrus was noted for all megestrol acetate and the chlormadinone acetate-treated dogs. Mucoid vaginal discharges were more prevalent among the middle- and high-dose megestrol acetate-and the chlormadinone acetate-treated dogs. The mean hemoglobin, packed cell volume, and total erythrocyte values were slightly decreased, and the mean total leucocyte counts and erythrocyte sedimentation rates were slightly increased for the middle- and high-dose megestrol acetate- and chlormadinone acetate-treated groups. Tests of various measures of blood clotting did not reveal any disturbances in the clotting mechanisms. At 4 yr, evidence of diabetes consisting of bilateral cataracts, elevated serum glucose concentrations, and glycosuria was noted for 2 of 16 high-dose megestrol acetate and 6 of 15 chlormadinone acetate-treated dogs. In general, the effects of megestrol acetate were similar to, but considerably less severe than those of chlormadinone acetate.