Summary
Progesterone was administered im to 6 adult anestrous bitches at a dosage of 2 mg/kg of body weight. Serum progesterone concentrations were measured prior to progesterone administration and for 72 hours thereafter. The serum progesterone concentration time data were analyzed by use of a pharmacokinetics modeling computer program. The mean (± sd) peak serum progesterone concentration (34.3 ± 7.8 ng/ml) was reached at 1.8 ± 0.2 hours after progesterone administration. The mean serum progesterone concentration was 6.9 ± 1.4 ng/ml at 24 hours and 2.0 ± 0.4 ng/ml at 48 hours after progesterone administration. By 72 hours after administration, mean serum progesterone concentration was 0.9 ± 0.2 ng/ml, which was comparable to serum progesterone concentrations prior to injection. The mean half-life of the absorption phase was 0.5 hours (range, 0.3 to 0.7 hours). The mean half-life of elimination was 12.1 hours (range, 9.5 to 13.8 hours). By analysis of the data, it was established that a dosage of 3 mg/kg, when the hormone was given im to dogs once a day, would maintain serum progesterone concentration > 10 ng/ml.