Extended regimen of a levonorgestrel/ethinyl estradiol transdermal delivery system: Predicted serum hormone levels using a population pharmacokinetic model.

Objective: This study employed population pharmacokinetic (popPK) models to predict levonorgestrel (LNG) and ethinyl estradiol (EE) exposure after dosing with the transdermal contraceptive TWIRLA® (LNG/EE TDS) as a 12-week extended regimen in a healthy female population.

Methods: PopPK models were developed using data from a previously published phase 1, open-label, randomized clinical trial, ATI-CL14 (NCT01243580), in 36 healthy individuals. Models used cycle 2 data from 18 individuals who received the LNG/EE TDS, delivering LNG 120 μg/day and EE 30 μg/day, followed by a 1-week TDS-free period. Noncompartmental PK analyses were performed on simulated concentration-time profiles of 12 consecutive weeks of LNG/EE TDS use.

Results: The simulated concentration-time profiles and PK parameters for the simulated extended regimen indicated that predicted LNG and EE exposures at week 12 were similar to week 3 (predicted geometric mean EE area under the concentration-time curve from time 0 to 168 h [AUC0-168] on week 3 was 0.2% lower than week 12 and LNG AUC0-168 on week 3 was 0.9% lower than week 12), suggesting both were at steady state by week 3. Therefore, no notable accumulation beyond that at week 3 is predicted for LNG and EE following a 12-week extended regimen. The results are supported by the accumulation ratios based on maximum concentration and the area under the curve being similar at weeks 3 and 12 for LNG and EE.

Conclusion: These results indicate that a 12-week extended LNG/EE regimen would provide similar systemic hormonal exposure as that seen by week 3 in a standard 28-day regimen, without further hormonal accumulation. The data support the safe use of a non-daily, low-dose hormonal contraceptive in an extended regimen but should be confirmed in a clinical PK study.