Drug interactions
Erythromycin + Foscarnet
Severity: Major
Erythromycin and Foscarnet: 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
Foscarnet can prolong the QT interval and causes electrolyte disturbances such as low calcium, magnesium and potassium. Combined with erythromycin, which also prolongs QT, the arrhythmia risk is increased.
What this interaction means in plain words
Erythromycin and Foscarnet 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.
Erythromycin belongs to Anti Bacterial; Foscarnet belongs to Anti Virals.
Why it happens
Additive QT prolongation, aggravated by foscarnet-induced electrolyte depletion.
What to do
Avoid the combination if possible; otherwise monitor ECG and serum electrolytes and replace magnesium, potassium and calcium 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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Other interactions of Erythromycin
- Conivaptan + Erythromycin Contraindicated
- Dihydroergotamine intranasal + Erythromycin Contraindicated
- Dihydroergotamine + Erythromycin Contraindicated
- Domperidone + Erythromycin Contraindicated
- Dronedarone + Erythromycin Contraindicated
- Droperidol + Erythromycin Contraindicated
Other interactions of Foscarnet
- Cidofovir + Foscarnet Contraindicated
- Foscarnet + Pimozide Contraindicated
- Foscarnet + Thioridazine Contraindicated
- Foscarnet + Vandetanib Contraindicated
- Adagrasib + Foscarnet Major
- Adefovir + Foscarnet Major
Frequently asked questions
Can I take Erythromycin with Foscarnet?
MediHelp rates the interaction as major. Erythromycin and Foscarnet 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. Foscarnet can prolong the QT interval and causes electrolyte disturbances such as low calcium, magnesium and potassium. Combined with erythromycin, which also prolongs QT, the arrhythmia risk is increased.
How serious is the interaction between Erythromycin and Foscarnet?
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 if possible; otherwise monitor ECG and serum electrolytes and replace magnesium, potassium and calcium as needed.
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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