Efavirenz + Norelgestromin = Precautionary

Effect on Concentration

Efavirenz
No change
Applies within class?
No
Norelgestromin
Increase
Applies within class?
No

Pharmacologic Effects

Efavirenz
Effect
N/A
Applies within class?
No
Norelgestromin
Effect
N/A
Applies within class?
No

Interaction History

N/A

Last Updated 30-Jul-2018

Summary

Sources

Efavirenz versus Ethinyl Estradiol / Norgestimate ^

Study Design

The effect of efavirenz (600 mg once daily) on the pharmacokinetics of a tricyclic oral contraceptive containing ethinyestradiol and norgestimate was studied in 21 female HIV- subjects.

Study Results

Efavirenz had no effect on ethinylestradiol Cmax (6% increase) or AUC (10% decrease). Exposure to the active metabolites of norgestimate - norgestromin and levonorgestrel - were significantly decreased. The Cmax and AUC of norgestromin decreased by 46% and 74%, respectively, while the AUC of levonorgestrel decreased by 83% (n=6). Efavirenz pharmacokinetics were similar to historical data.

Study Conclusions

Barrier methods of contraception are recommended when efavirenz is co-administered with oral contraceptives. Although there was no significant effect on the estrogen component, the significant decrease in the progestogen component reinforces the need for additional barrier contraception when taking oral contraceptives with efavirenz

References

Sevinsky H, Eley T, Persson A, Garner D, Yones C, Nettles R, Zhang J. The effect of efavirenz on the pharmacokinetics of an oral contraceptive containing ethinyl estradiol and norgestimate in healthy hiv-negative women. Antiviral Therapy. 2011; 2: 149.