Relugolix and Isavuconazonium: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Isavuconazonium
Relugolix
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
You've been prescribed two medicines that can interact. Isavuconazonium (Cresemba) is an antifungal, and relugolix (Orgovyx) is used to treat certain hormone-related conditions like prostate cancer.
The antifungal can slow down a 'pump' in your body that normally helps clear relugolix out. When that pump is blocked, more relugolix stays in your system. In studies with a similar pump-blocker, relugolix levels roughly tripled. Higher levels can mean more side effects, like hot flashes, fatigue, or diarrhea. The good news is your care team knows how to handle this, often by spacing out the doses or watching you more closely. Please don't change anything on your own. Just check in with your pharmacist or doctor.
Effect: Increased relugolix exposure via isavuconazole-mediated inhibition of intestinal P-glycoprotein (P-gp) efflux. Relugolix is a P-gp substrate; isavuconazonium's active moiety isavuconazole inhibits P-gp.
Magnitude: A study with erythromycin (P-gp inhibitor) raised relugolix AUC ~3.5-fold and Cmax ~2.9-fold. Direction is increased relugolix effect and adverse-reaction risk. Evidence: probable. Onset: unspecified.
Management:
- Avoid concomitant use if possible.
- If unavoidable, give relugolix first, separate by at least 6 hours, and increase monitoring for adverse reactions.
- Relugolix may be interrupted up to 2 weeks for a short antifungal course; if interrupted >7 days, restart with a 360 mg loading dose then 120 mg daily.
What happens
Increased relugolix exposure
Interaction Deep Dive
Concurrent administration of relugolix (a P-gp substrate) with a P-gp inhibitor should be avoided, since it may raise relugolix exposure and thereby heighten the risk of relugolix-related adverse reactions. When coadministration cannot be avoided, give relugolix or relugolix/estradiol/norethindrone acetate first, allow a gap of at least 6 hours between doses, and monitor for adverse reactions with greater frequency12. For a brief course involving certain P-gp inhibitors, relugolix therapy may be paused for as long as 2 weeks. Restart relugolix once the P-gp inhibitor has been stopped. Should relugolix be interrupted for more than 7 days, resume it with a 360 mg loading dose on the first day, followed by 120 mg once daily thereafter. In a drug interaction study, giving relugolix (P-gp substrate) together with erythromycin (P-gp inhibitor) raised the AUC and Cmax of relugolix by 3.5-fold and 2.9-fold, respectively1.
Why it happens (mechanism)
Inhibition of P-gp-mediated efflux transport of relugolix
How to manage this interaction
This combination is best avoided when possible, but your care team can manage it safely if both are truly needed.
- Keep taking both exactly as prescribed unless your prescriber tells you otherwise. Do not stop or change doses on your own.
- Your team may have you take relugolix first and separate the two doses by at least 6 hours.
- They may monitor you more closely for relugolix side effects such as hot flashes, tiredness, or diarrhea.
- Sometimes relugolix is paused during a short antifungal course and restarted afterward, with the dose individualized by your team.
Ask your pharmacist or doctor before starting either drug so they can plan the timing and monitoring.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In a study evaluating drug interactions, giving relugolix (a P-gp substrate) together with erythromycin (a P-gp inhibitor) raised the AUC and Cmax of relugolix by 3.5-fold and 2.9-fold, respectively 1.
Common questions
Can I take Relugolix and Isavuconazonium together?
Isavuconazonium can raise relugolix levels (possibly around 3-fold) and increase side effects; avoid combining if possible, or have your care team separate doses by at least 6 hours and monitor you more closely. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Relugolix and Isavuconazonium interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Relugolix and Isavuconazonium interaction managed?
This combination is best avoided when possible, but your care team can manage it safely if both are truly needed. Keep taking both exactly as prescribed unless your prescriber tells you otherwise. Do not stop or change doses on your own. Your team may have you take relugolix first and separate the two doses by at least 6 hours. They may monitor you more closely for relugolix side effects such as h… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Relugolix or Isavuconazonium need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (2)
- Product Information: ORGOVYX oral tablets, relugolix oral tablets. Sumitomo Pharma America, Inc (per FDA), Marlborough, MA, 2025. DailyMed
- Product Information: MYFEMBREE(R) oral tablets, relugolix, estradiol, norethindrone acetate oral tablets. Myovant Sciences Inc (per FDA), Brisbane, CA, 2021. DailyMed
Keep reading about Isavuconazonium
Keep reading about Relugolix
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