Drug interactions
Clarithromycin + Foscarnet
Severity: Major
Clarithromycin 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
Both drugs can prolong the QT interval, and foscarnet additionally causes hypocalcemia, hypomagnesemia and hypokalemia that heighten the risk of torsades de pointes. Combined use can therefore be arrhythmogenic.
What this interaction means in plain words
Clarithromycin 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.
Clarithromycin belongs to Anti Bacterial; Foscarnet belongs to Anti Virals.
Why it happens
Additive QT prolongation, worsened by foscarnet-induced electrolyte depletion.
What to do
Use an alternative antibiotic if possible; otherwise monitor ECG and serum calcium, magnesium and potassium, and replace deficits promptly.
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 Clarithromycin
- Astemizole + Clarithromycin Contraindicated
- Avanafil + Clarithromycin Contraindicated
- Cisapride + Clarithromycin Contraindicated
- Clarithromycin + Colchicine Contraindicated
- Clarithromycin + Conivaptan Contraindicated
- Clarithromycin + Dihydroergotamine 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 Clarithromycin with Foscarnet?
MediHelp rates the interaction as major. Clarithromycin 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. Both drugs can prolong the QT interval, and foscarnet additionally causes hypocalcemia, hypomagnesemia and hypokalemia that heighten the risk of torsades de pointes. Combined use can therefore be arrhythmogenic.
How serious is the interaction between Clarithromycin 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: Use an alternative antibiotic if possible; otherwise monitor ECG and serum calcium, magnesium and potassium, and replace deficits promptly.
What other medicines interact with Clarithromycin?
MediHelp also lists interactions of Clarithromycin with, for example, Astemizole, Avanafil, Cisapride. The full list is on the Clarithromycin page.
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