General Biologic Activity: Prostaglandins occur in nearly all mammalian tissues. Prostaglandins, especially PGE’s and PGF’s, have been shown, in certain species, to 1) increase at time of parturition in amniotic fluid, maternal placenta, myometrium, and blood, 2) stimulate myometrial activity, and 3) to induce either abortion or parturition. Prostaglandins, especially PGF2α, have been shown to 1) increase in the uterus and blood to levels similar to levels achieved by exogenous administration which elicited luteolysis, 2) be capable of crossing from the uterine vein to the ovarian artery (sheep), 3) be related to IUD induced luteal regression (sheep), and 4) be capable of regressing the corpus luteum of most mammalian species studied to date. Prostaglandins have been reported to result in release of pituitary tropic hormones. Data suggest prostaglandins, especially PGE’s and PGF’s, may be involved in the process of ovulation and gamete transport. Also PGF2α has been reported to cause increase in blood pressure, bronchoconstriction, and smooth muscle stimulation in certain species.
Metabolism: A number of metabolism studies have been done in laboratory animals. The metabolism of tritium labeled dinoprost (3H PGF2 alpha) in the rat and in the monkey was similar. Although quantitative differences were observed, qualitatively similar metabolites were produced. A study demonstrated that equimolar doses of 3H PGF2 alpha Tham and 3H PGF2 alpha free acid administered intravenously to rats demonstrated no significant differences in blood concentration of dinoprost. An interesting observation in the above study was that the radioactive dose of 3H PGF2 alpha rapidly distributed in tissues and dissipated in tissues with almost the same curve as it did in the serum. The half-life of dinoprost in bovine blood has been reported to be on the order of minutes. A complete study on the distribution of decline of 3H PGF2 alpha Tham in the tissue of rats was well correlated with thework done in the cow. Cattle serum collected during 24 hours after doses of 0 to 250 mg dinoprost have been assayed by RIA for dinoprost and the 15-keto metabolites. These data support previous reports that dinoprost has a half-life of minutes. Dinoprost is a natural prostaglandin. All systems associated with dinoprost metabolism exist in the body; therefore, no new metabolic, transport, excretory, binding or other systems need be established by the body to metabolize injected dinoprost.
Relative Bioavailability Study: The requirement for substantial evidence of effectiveness was fulfilled by a pharmacokinetic study comparing the relative bioavailability of the subcutaneous (SC) administration of 25 mg of LUTALYSE HighCon Injection (12.5 mg dinoprost/mL) to the approved intramuscular (IM) administration of 25 mg of LUTALYSE Injection (5 mg dinoprost/mL). The effectiveness data for LUTALYSE Injection at doses of 25 and 35 mg IM were used to support an adjusted Test/Reference (T/R) ratio of 1.4 and 90% Confidence Intervals of 80 - 164% for Cmax and AUC to demonstrate therapeutic equivalence.
The pivotal relative bioavailability study was a randomized, non-replicated, three treatment, three period, six sequence crossover study in 24 cows (4 cows per sequence). Each cow received a single dose of 25 mg dinoprost administered as 5 mL of LUTALYSE Injection IM, 5 mL of LUTALYSE Injection SC, or 2 mL of LUTALYSE HighCon SC, with a washout period of 48 hours between doses. Plasma samples were collected at 60 and 10 minutes prior to dose administration, and at 5, 10, 15, 20, 30, 75 minutes, and at 2, 3, 4.5, 6, 7.5, and 12 hours after each dose. Samples were analyzed by UPLC-MS/MS for PGF2α (dinoprost) and PGFm (metabolite) concentrations. PGFm was chosen as the analyte of interest because its concentrations are reflective of exogenously administered dinoprost (after subtraction of endogenous concentrations), and it has a longer half-life and therefore less blood level fluctuations than PGF2α. The results of the relative bioavailability study are summarized in Table 1. The Cmax and AUClast of LUTALYSE HighCon were within the adjusted 90% Confidence Intervals. Therefore, the SC administration of 25 mg of LUTALYSE HighCon was equivalent to the IM administration of 25 mg LUTALYSE Injection.
Table 1: Relative Bioavailability Results for LUTALYSE HighCon Injection
Parameter | Product/ Route | LSMean | Ratio T/ R† | Lower 90% CI | Upper 90% CI |
Cmax
(ng/mL) | LUTALYSE Injection (IM)* | 41.26 | |
LUTALYSE Injection (SC)* | 50.80 | 1.23 | 110.99 | 136.60 |
LUTALYSE HighCon Injection (SC) | 55.12 | 1.34 | 120.42 | 148.20 |
AUClast) (hr*ng/mL) | LUTALYSE Injection (IM)* | 66.85 | |
LUTALYSE Injection (SC) | 67.25 | 1.00 | 96.26 | 105.12 |
LUTALYSE HighCon Injection (SC) | 65.81 | 0.98 | 94.20 | 102.87 |
Cmax - maximum plasma concentration
AUClast - the area under the plasma concentration vs. time curve from time of injection to the limit of quantification of the assay
* Reference product and route of administration
† Geometric means