Drug interactions
Foscarnet + Sulfamethoxazole
Severity: Moderate
Foscarnet and Sulfamethoxazole: 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 disturb electrolytes, and sulfamethoxazole (usually with trimethoprim) has been linked to rare QT prolongation and hyperkalemia. Co-use may modestly raise arrhythmia risk and, through nephrotoxicity, may worsen renal function.
What this interaction means in plain words
Foscarnet and Sulfamethoxazole 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.
Why it happens
Additive QT prolongation and electrolyte or renal effects.
What to do
Monitor ECG in patients with cardiac risk factors and check electrolytes and renal function regularly. Adjust doses to 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
Frequently asked questions
Can I take Foscarnet with Sulfamethoxazole?
MediHelp rates the interaction as moderate. Foscarnet and Sulfamethoxazole 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 disturb electrolytes, and sulfamethoxazole (usually with trimethoprim) has been linked to rare QT prolongation and hyperkalemia. Co-use may modestly raise arrhythmia risk and, through nephrotoxicity, may worsen renal function.
How serious is the interaction between Foscarnet and Sulfamethoxazole?
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 ECG in patients with cardiac risk factors and check electrolytes and renal function regularly. Adjust doses to 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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