Drug interactions
Foscarnet + Trimethoprim
Severity: Moderate
Foscarnet and Trimethoprim: moderate 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 cause electrolyte changes, while trimethoprim may cause hyperkalemia and affect renal function. Together they may increase arrhythmia and renal risk.
What this interaction means in plain words
Foscarnet and Trimethoprim can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Foscarnet belongs to Anti Virals; Trimethoprim belongs to Anti Bacterial.
Why it happens
Additive QT prolongation and electrolyte or renal effects, including trimethoprim-induced hyperkalemia and creatinine rise.
What to do
Monitor potassium, magnesium, calcium and creatinine, and obtain an ECG in patients with cardiac risk factors. Adjust doses for renal function.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Foscarnet
- Cidofovir + Foscarnet Contraindicated
- Foscarnet + Pimozide Contraindicated
- Foscarnet + Thioridazine Contraindicated
- Foscarnet + Vandetanib Contraindicated
- Adagrasib + Foscarnet Major
- Adefovir + Foscarnet Major
Other interactions of Trimethoprim
Frequently asked questions
Can I take Foscarnet with Trimethoprim?
MediHelp rates the interaction as moderate. Foscarnet and Trimethoprim can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Foscarnet can prolong the QT interval and cause electrolyte changes, while trimethoprim may cause hyperkalemia and affect renal function. Together they may increase arrhythmia and renal risk.
How serious is the interaction between Foscarnet and Trimethoprim?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor potassium, magnesium, calcium and creatinine, and obtain an ECG in patients with cardiac risk factors. Adjust doses for renal function.
What other medicines interact with Foscarnet?
MediHelp also lists interactions of Foscarnet with, for example, Cidofovir, Pimozide, Thioridazine. The full list is on the Foscarnet page.
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