Pharmacokinetic Interactions between the Hormonal Emergency Contraception, Levonorgestrel (Plan B)‎, and Efavirenz

Abstract EN

Objectives.

Compare the Plan B levonorgestrel (LNG) area under the concentration- time curve (AUC12) prior to and with efavirenz (EFV).

Design.

Prospective, open-label, single-arm, equivalence study.

Methods.

Healthy HIV-negative subjects underwent 12 hr intensive pharmacokinetic (PK) sampling following single dose LNG alone and after 14 days of EFV.

Geometric means, Geometric Mean Ratios, and 90% confidence intervals (CI) are reported for PK Parameters.

T-tests were utilized.

Clinical parameters and liver function tests (LFTs) were assessed.

Results.

24 women enrolled and 21 completed the study.

With EFV, LNG AUC12 was reduced 56% (95% CI: 49%, 62%) from 42.9 to 17.8 ng*hr/mL, and maximum concentration (Cmax) was reduced 41% (95% CI: 33%, 50%) from 8.4 to 4.6 ng/mL.

LNG was well tolerated with no grade 3 or 4 treatment-related toxicities.

Conclusions.

EFV significantly reduced LNG exposures.

Higher LNG doses may be required with EFV.

These results reinforce the importance of effective contraception in women taking EFV.