Efficacy of oral epostane administration to terminate pregnancy in mated laboratory bitches

Epostane was administered orally for 7 days at doses of 10-300 mg/dog/day, starting at early oestrus, mid-oestrus, or metoestrus in 162 mated beagle bitches. With the exception of the early oestrus group receiving 10 mg epostane dog/day x 7 days, the incidence of dogs whelping in all other treatments was statistically lower than that of the placebo-treated control group (P less than 0.01). The ED50 and ED90 values were 19.5 and 43.2 mg/dog, respectively, for administration at early oestrus, and 8.6 and 24.0 mg/dog, respectively, for administration at metoestrus. Progesterone concentrations were significantly decreased after administration at oestrus or metoestrus in all epostane-treated groups compared to those given placebo. There were no adverse reactions or clinically significant changes in laboratory parameters or health of the bitches related to the use of epostane. There were no changes in the reproductive performance of epostane-treated bitches at the next oestrus after treatment compared to placebo controls, and there were no reproductive problems noted in the progeny of epostane-treated bitches. These results suggest that the minimally effective dose of epostane for application during metoestrus is approximately 2.5 mg/kg and the effective dose range is about 2.5-5.0 mg/kg body weight. Oral epostane is potentially a novel agent for the safe interception of unwanted pregnancy in dogs.