Drug interactions
Erythromycin + Trimethoprim
Severity: Moderate
Erythromycin 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
Both drugs have been linked to QT prolongation, so combined use may increase arrhythmia risk, particularly in patients with electrolyte disturbances or heart disease. Trimethoprim can also cause hyperkalemia, which complicates rhythm assessment.
What this interaction means in plain words
Erythromycin 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.
Erythromycin belongs to Anti Bacterial; Trimethoprim belongs to Anti Bacterial.
Why it happens
Possible additive QTc prolongation; the trimethoprim effect is weak and not fully established.
What to do
Monitor ECG and serum potassium in patients with cardiac risk factors. Choose a non-QT-prolonging alternative when feasible.
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 Erythromycin
- Conivaptan + Erythromycin Contraindicated
- Dihydroergotamine intranasal + Erythromycin Contraindicated
- Dihydroergotamine + Erythromycin Contraindicated
- Domperidone + Erythromycin Contraindicated
- Dronedarone + Erythromycin Contraindicated
- Droperidol + Erythromycin Contraindicated
Other interactions of Trimethoprim
Frequently asked questions
Can I take Erythromycin with Trimethoprim?
MediHelp rates the interaction as moderate. Erythromycin 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. Both drugs have been linked to QT prolongation, so combined use may increase arrhythmia risk, particularly in patients with electrolyte disturbances or heart disease. Trimethoprim can also cause hyperkalemia, which complicates rhythm assessment.
How serious is the interaction between Erythromycin 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 ECG and serum potassium in patients with cardiac risk factors. Choose a non-QT-prolonging alternative when feasible.
What other medicines interact with Erythromycin?
MediHelp also lists interactions of Erythromycin with, for example, Conivaptan, Dihydroergotamine intranasal, Dihydroergotamine. The full list is on the Erythromycin page.
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