Drug interactions
Ketoconazole + Trimethoprim
Severity: Moderate
Ketoconazole 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
Ketoconazole prolongs the QT interval, and trimethoprim, usually as sulfamethoxazole-trimethoprim, has rarely been linked to QT prolongation or arrhythmia. Combined use may add risk in patients with other risk factors, but evidence is limited.
What this interaction means in plain words
Ketoconazole 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.
Ketoconazole belongs to Anti Fungals; Trimethoprim belongs to Anti Bacterial.
Why it happens
Possible additive QT prolongation; the effect of trimethoprim is not well established.
What to do
Check baseline ECG and electrolytes in patients with additional QT risk factors. Avoid using with other QT-prolonging drugs where possible.
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 Ketoconazole
- Alfuzosin + Ketoconazole Contraindicated
- Alprazolam + Ketoconazole Contraindicated
- Avanafil + Ketoconazole Contraindicated
- Conivaptan + Ketoconazole Contraindicated
- Dihydroergotamine intranasal + Ketoconazole Contraindicated
- Dihydroergotamine + Ketoconazole Contraindicated
Other interactions of Trimethoprim
Frequently asked questions
Can I take Ketoconazole with Trimethoprim?
MediHelp rates the interaction as moderate. Ketoconazole 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. Ketoconazole prolongs the QT interval, and trimethoprim, usually as sulfamethoxazole-trimethoprim, has rarely been linked to QT prolongation or arrhythmia. Combined use may add risk in patients with other risk factors, but evidence is limited.
How serious is the interaction between Ketoconazole 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: Check baseline ECG and electrolytes in patients with additional QT risk factors. Avoid using with other QT-prolonging drugs where possible.
What other medicines interact with Ketoconazole?
MediHelp also lists interactions of Ketoconazole with, for example, Alfuzosin, Alprazolam, Avanafil. The full list is on the Ketoconazole page.
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