Drug interactions
Fosamprenavir + Quinidine
Severity: Major
Fosamprenavir and Quinidine: major interaction.
Last updated Sources: US FDA label
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, through its active metabolite amprenavir, inhibits CYP3A4 and can raise quinidine concentrations. Higher quinidine levels increase the risk of QT prolongation, torsades de pointes and other toxicity. Boosting with ritonavir makes the effect larger.
What this interaction means in plain words
Fosamprenavir and Quinidine 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 inhibits CYP3A4, reducing the metabolic clearance of quinidine.
What to do
Avoid the combination where possible and choose another antiarrhythmic or antiretroviral. If it must be used, monitor ECG and quinidine concentrations and reduce the quinidine dose as needed.
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?
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References
Other interactions of Quinidine
- Adagrasib + Quinidine Contraindicated
- Arsenic trioxide + Quinidine Contraindicated
- Artemether / lumefantrine + Quinidine Contraindicated
- Chloroquine + Quinidine Contraindicated
- Dofetilide + Quinidine Contraindicated
- Dronedarone + Quinidine Contraindicated
Frequently asked questions
Can I take Fosamprenavir with Quinidine?
MediHelp rates the interaction as major. Fosamprenavir and Quinidine 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, through its active metabolite amprenavir, inhibits CYP3A4 and can raise quinidine concentrations. Higher quinidine levels increase the risk of QT prolongation, torsades de pointes and other toxicity. Boosting with ritonavir makes the effect larger.
How serious is the interaction between Fosamprenavir and Quinidine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination where possible and choose another antiarrhythmic or antiretroviral. If it must be used, monitor ECG and quinidine concentrations and reduce the quinidine dose as needed.
What other medicines interact with Quinidine?
MediHelp also lists interactions of Quinidine with, for example, Adagrasib, Arsenic trioxide, Artemether / lumefantrine. The full list is on the Quinidine page.
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