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.