Drug interactions
Ketoconazole + Sulfamethoxazole
Severity: Moderate
Ketoconazole 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 agents have been associated with QT prolongation, mainly ketoconazole, with sulfamethoxazole-trimethoprim reported rarely. Combined use could add to arrhythmia risk in susceptible patients, although the clinical evidence is limited.
What this interaction means in plain words
Ketoconazole 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
Possible additive QT prolongation; ketoconazole also inhibits CYP3A4 and sulfamethoxazole is a CYP2C9 inhibitor.
What to do
Obtain a baseline ECG in patients with other QT risk factors and correct potassium and magnesium. Avoid the combination if the patient has known long QT or takes other QT-prolonging drugs.
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
Frequently asked questions
Can I take Ketoconazole with Sulfamethoxazole?
MediHelp rates the interaction as moderate. Ketoconazole 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 agents have been associated with QT prolongation, mainly ketoconazole, with sulfamethoxazole-trimethoprim reported rarely. Combined use could add to arrhythmia risk in susceptible patients, although the clinical evidence is limited.
How serious is the interaction between Ketoconazole 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: Obtain a baseline ECG in patients with other QT risk factors and correct potassium and magnesium. Avoid the combination if the patient has known long QT or takes other QT-prolonging drugs.
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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