Comparative pharmacokinetic analysis of levonorgestrel-releasing intrauterine systems and levonorgestrel-containing contraceptives with oral or subdermal administration route.

OBJECTIVE

To compare systemic exposure to levonorgestrel (LNG) released from commercially available intrauterine systems (IUSs), a subdermal implant, and oral contraceptives.

METHODS

An integrated population pharmacokinetic (popPK) analysis of data from over 3400 individuals in ten clinical studies with six different LNG-releasing contraceptives (four long-acting reversible contraceptives [LARCs: LNG-IUS 8, 12, and 20, initially releasing LNG 14, 17.5, and 20 μg/day, a subdermal implant initially releasing LNG 100 μg/day according to label]; progestin-only pill [POP: LNG 30 μg/day]; and combined oral contraceptive [COC] pill [LNG 100 μg/day and ethinylestradiol 20 μg/day]), was conducted to generate a popPK model. LNG release rates, and total and unbound serum/plasma LNG concentrations with LARCs were estimated over the indicated period of use; maximum (Cmax) and average (Cav) serum LNG concentrations were estimated at steady state for oral contraceptives. Influence of body weight on LNG PK was also investigated.

RESULTS

Serum LNG concentration with LARCs increased with increasing daily LNG release rate, being lowest with LNG-IUS 8, higher with LNG-IUS 12 and LNG-IUS 20, and highest with the subdermal implant (1.7-2.1-times that with LNG-IUS 20). Compared with early serum LNG concentrations with LNG-IUS 20, Cav and Cmax were 1.7- and 4.5-fold higher with POP, and 8.6- and 18-fold higher with COC. Total LNG bioavailability was >97% for the LNG-IUSs and 66-80% with other contraceptives. Serum/plasma LNG concentrations decreased with increasing body weight.

CONCLUSIONS

Among the contraceptives examined, COC had the highest and LNG-IUSs the lowest systemic exposure to LNG. Systemic LNG concentration was inversely correlated to body weight.