Drug interactions
Quinidine + Sulfamethoxazole
Severity: Moderate
Quinidine 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
Both drugs have been associated with QT prolongation, so the combination may add to arrhythmia risk. The sulfamethoxazole QT signal is weak and the risk is mainly relevant in patients with other risk factors.
What this interaction means in plain words
Quinidine 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 effects on cardiac repolarization.
What to do
Monitor the ECG and correct electrolytes, particularly in patients with other QT risk factors. Consider an alternative antibiotic if the QTc becomes prolonged.
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 Quinidine
- Adagrasib + Quinidine Contraindicated
- Arsenic trioxide + Quinidine Contraindicated
- Artemether / lumefantrine + Quinidine Contraindicated
- Chloroquine + Quinidine Contraindicated
- Dofetilide + Quinidine Contraindicated
- Dronedarone + Quinidine Contraindicated
Frequently asked questions
Can I take Quinidine with Sulfamethoxazole?
MediHelp rates the interaction as moderate. Quinidine 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. Both drugs have been associated with QT prolongation, so the combination may add to arrhythmia risk. The sulfamethoxazole QT signal is weak and the risk is mainly relevant in patients with other risk factors.
How serious is the interaction between Quinidine 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 the ECG and correct electrolytes, particularly in patients with other QT risk factors. Consider an alternative antibiotic if the QTc becomes prolonged.
What other medicines interact with Quinidine?
MediHelp also lists interactions of Quinidine with, for example, Adagrasib, Arsenic trioxide, Artemether / lumefantrine. The full list is on the Quinidine page.
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