Bioavailability and pharmacodynamics of two 10-mg estradiol valerate depot formulations following IM single dose administration in healthy postmenopausal volunteers.

OBJECTIVE

To establish the bioequivalence (BE) between two i.m. estradiol valerate (E2V) depot formulations, i.e., Estradiol-Depot 10 mg® (test) and Progynon Depot-10® (reference). To compare the effect of both treatments on the vaginal maturation index and on the increase of the endometrial thickness after administration of both formulations.

METHODS

A total of 24 postmenopausal females aged 54.7 ± 5.35 year (BMI 25.84 ± 1.98 kg/m2) completed this BE assessment. The investigation was planned and designed as a single center, openlabel, single dose, cross-over study including 2 periods with 2 treatments and 2 sequences. Baseline levels were obtained for all subjects. Single doses of 10-mg E2V of each product were administered and pharmacokinetics and pharmacodynamics were assessed over 2 weeks with a washout period of 4 weeks. A gas chromatographic-mass spectrometric method with negative chemical ionization and selected ion monitoring was applied, after validation, for the determination of estradiol (E2), estrone (E1) and internal standard estradiol-D4 derivatives. The cytology of the vaginal smear (parabasal, intermediate and superficial cells from lateral wall opposite tip of cervix) was assessed by investigation of ~ 200 cells. The vaginal maturation index (VMI) was calculated by the equation: VMI (%) = (superficial cells × 1) (%) + (intermediate cells × 0.5) (%). Endometrial thickness was measured by transvaginal ultrasonic scans and recorded in mm.

RESULTS

The geometric means (Gmeans) of the measured values of Cmax and AUC0-t for E2 were 543.5 pg/ ml and 84,734 pg × h/ml for test and 505.7 pg/ml and 82,660 pg × h/ml for reference, whereas those for E1 were 219.0 pg/ml and 38,950 pg × h/ml for test and 204.9 pg/ml and 37,159 pg × h/ml for reference, respectively. The point estimates (PEs) of the Test/ Reference (T/R) mean ratios of the variables Cmax and AUC0-t for E2 (measured values) were 107.3% and 102.5%, respectively. The PEs of the T/R mean ratios of the variables Cmax and AUC0-t for E1 (measured values) were 106.9% and 105.0%, respectively. Median endometrial thickness increased in Period I from baseline levels of ~ 3 mm (Day -2) to ~ 7 mm (Day 21) after administration of both products without returning completely to baseline prior to the next administration. In Period II, median values of 7 mm were also reached (Day 21) after administration of both products. Median vaginal maturation indices increased in Period I from baseline levels of ranging from 45 - 60% (Day -2) to 86 - 94.5% (Day 21). In Period II maturation indices of ≥ 90% were calculated as baselines (Day -2) and these levels remained constant until the end of the assessment (Day 21) independently from the products. After 21 days of treatment, test and reference presented practically no differences in terms of their effects on endometrial thickness and vaginal maturation index.

CONCLUSIONS

The 95% CIs for the T/R mean ratios of AUC0-t and Cmax for E2 and E1 fell within the acceptance limits of 80 - 125% and therefore bioequivalence could be demonstrated for both formulations. The changes in endometrial thickness and the vaginal maturation index indicated that the pharmacodynamic effect is pronounced already after the first administration and that the effect continued notably for longer time compared to the presence of E2 and E1 in plasma. A 4-week washout phase was insufficient to avoid residual pharmacological effects after the administration of both preparations.