Does Emend Interact with Birth Control?
Emend (fosaprepitant/aprepitant) can reduce the effectiveness of hormonal birth control. Aprepitant, its active form, induces CYP3A4 enzymes, which metabolize progestins and estrogens in oral contraceptives, patches, rings, and implants. This lowers hormone levels, potentially leading to contraceptive failure.[1][2]
Co-administration decreases the AUC of ethinyl estradiol by 34% (fosaprepitant) and norethindrone by 8%.[3] Product labeling advises additional non-hormonal contraception (e.g., condoms) during Emend treatment and for 28 days after the last dose.[1]
How Long to Use Backup Contraception?
Use backup methods from the start of Emend through 28 days post-treatment. Emend's 3-day IV/oral regimen triggers this, as aprepitant's enzyme induction persists.[1][4]
Does This Affect Non-Hormonal Methods?
No interaction with barrier methods like condoms, diaphragms, or copper IUDs, which rely on physical blockage.[2]
Why Does Emend Cause This but Not All Antiemetics?
Aprepitant specifically induces CYP3A4 moderately over days, unlike short-acting antiemetics (e.g., ondansetron) that don't.[3][5] Netupitant (Akynzeo) has a similar warning.[4]
What About Other Hormonal Meds or Devices?
Mirena (levonorgestrel IUD) or Nexplanon (etonogestrel implant) may lose efficacy due to local hormone metabolism via CYP3A4. Backup recommended.[2][6]
Alternatives for Nausea Without This Interaction?
Ondansetron (Zofran) or dolasetron lack significant CYP3A4 induction. Promethazine or metoclopramide are options, though less effective for chemo nausea.[5]
[1]: Emend Prescribing Information (Merck)
[2]: Drugs.com - Aprepitant and Birth Control
[3]: FDA Label for Emend - Drug Interactions Section
[4]: Akynzeo Prescribing Information
[5]: UpToDate - Antiemetic Drug Interactions
[6]: Mirena HCP Info - Drug Interactions