Drug interactions
Erythromycin + Nirmatrelvir / ritonavir
Severity: Major
Erythromycin and Nirmatrelvir / ritonavir: major interaction.
Last updated Sources: UK SmPC
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
Ritonavir-boosted nirmatrelvir strongly inhibits CYP3A4 and can substantially raise erythromycin levels. This increases the risk of QT prolongation, arrhythmia and gastrointestinal intolerance, and erythromycin may also modestly raise nirmatrelvir exposure.
What this interaction means in plain words
Erythromycin and Nirmatrelvir / ritonavir 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
Ritonavir potently inhibits CYP3A4 and P-glycoprotein, reducing erythromycin clearance.
What to do
Prefer a non-CYP3A4-dependent antibiotic such as azithromycin or a different class. If unavoidable, obtain an ECG and monitor electrolytes and for erythromycin toxicity.
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
- Erythromycin 250 mg Gastro-resistant Tablets - SmPC sections 4.3/4.5 (class statement: Protease inhibitors; "Protease inhibitors: in concomitant administration of erythromycin and protease inhibitors, an inhibition of the decomposition of erythromycin has been observed") — electronic medicines compendium (UK SmPC)
Other interactions of Erythromycin
- Conivaptan + Erythromycin Contraindicated
- Dihydroergotamine intranasal + Erythromycin Contraindicated
- Dihydroergotamine + Erythromycin Contraindicated
- Domperidone + Erythromycin Contraindicated
- Dronedarone + Erythromycin Contraindicated
- Droperidol + Erythromycin Contraindicated
Frequently asked questions
Can I take Erythromycin with Nirmatrelvir / ritonavir?
MediHelp rates the interaction as major. Erythromycin and Nirmatrelvir / ritonavir 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. Ritonavir-boosted nirmatrelvir strongly inhibits CYP3A4 and can substantially raise erythromycin levels. This increases the risk of QT prolongation, arrhythmia and gastrointestinal intolerance, and erythromycin may also modestly raise nirmatrelvir exposure.
How serious is the interaction between Erythromycin and Nirmatrelvir / ritonavir?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Prefer a non-CYP3A4-dependent antibiotic such as azithromycin or a different class. If unavoidable, obtain an ECG and monitor electrolytes and for erythromycin toxicity.
What other medicines interact with Erythromycin?
MediHelp also lists interactions of Erythromycin with, for example, Conivaptan, Dihydroergotamine intranasal, Dihydroergotamine. The full list is on the Erythromycin page.
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