Drug interactions
Fosamprenavir + Norethisterone
Severity: Major
Fosamprenavir and Norethisterone: major interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Fosamprenavir (as amprenavir, usually boosted with ritonavir) alters hormonal contraceptive exposure in an unpredictable way. This can lead to contraceptive failure or increased progestogen adverse effects, and amprenavir levels may also change.
What this interaction means in plain words
Fosamprenavir and Norethisterone can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Amprenavir and ritonavir modulate CYP3A4 and other metabolic pathways, with mixed inhibition and induction effects on steroid hormone clearance.
What to do
Use a non-hormonal or additional barrier contraceptive method rather than relying on norethisterone alone. If hormonal therapy is needed for another indication, monitor for loss of effect or adverse effects.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Fosamprenavir and Norethisterone, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
Other interactions of Norethisterone
- Acitretin + Norethisterone Contraindicated
- Amobarbital + Norethisterone Major
- Apalutamide + Norethisterone Major
- Belzutifan + Norethisterone Major
- Bosentan + Norethisterone Major
- Brigatinib + Norethisterone Major
Frequently asked questions
Can I take Fosamprenavir with Norethisterone?
MediHelp rates the interaction as major. Fosamprenavir and Norethisterone can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Fosamprenavir (as amprenavir, usually boosted with ritonavir) alters hormonal contraceptive exposure in an unpredictable way. This can lead to contraceptive failure or increased progestogen adverse effects, and amprenavir levels may also change.
How serious is the interaction between Fosamprenavir and Norethisterone?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Use a non-hormonal or additional barrier contraceptive method rather than relying on norethisterone alone. If hormonal therapy is needed for another indication, monitor for loss of effect or adverse effects.
What other medicines interact with Norethisterone?
MediHelp also lists interactions of Norethisterone with, for example, Acitretin, Amobarbital, Apalutamide. The full list is on the Norethisterone page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
