Levonorgestrel butanoate intramuscular injection does not reliably suppress ovulation for 90 days in obese and normal-BMI women: a pilot study.

Background: We performed a pilot evaluation of a new formulation of levonorgestrel butanoate (LB) designed to be a long-acting injectable (6 months) contraceptive to determine pharmacodynamic end points in normal-body mass index (BMI) and obese women.

Study Design: Obese (BMI ≥30 kg/m) and normal-BMI, otherwise healthy, women received a single intramuscular injection of LB after ovulation was confirmed in a baseline cycle. The primary outcome was return of ovulation in days.

Results: A total of 14 women enrolled and completed the study [normal BMI n=9, median BMI 22.7kg/m (range 19.4-25.8); obese n=5, median BMI 35.7kg/m (30.1-39.2)]. The first 6 subjects (normal BMI=4/9, obese BMI=2/5) received 40 mg of LB, and the remaining 8 received 20 mg. All women except one returned to ovulation prior to 6 months. Return to ovulation occurred earlier in the obese group; 3/5 obese and 0/9 normal BMI subjects returned to ovulation within 90 days (p=.03). No serious adverse events were reported during the study.

Conclusion: Return to ovulation was earlier than 6 months in both BMI groups but more so in the obese BMI group.

Implications: Since return of ovulation was earlier than expected for this LB injectable formulation, additional steps are needed to develop a preparation suitable as a longer-lasting product.