Drug interactions
Flecainide + Sulfamethoxazole
Severity: Moderate
Flecainide 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
Sulfamethoxazole combined with trimethoprim has been associated with QT prolongation and rare torsades, while flecainide carries its own proarrhythmic risk. Together they may increase the likelihood of ventricular arrhythmias, particularly with renal impairment or electrolyte disturbances.
What this interaction means in plain words
Flecainide 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 and conduction.
What to do
Check ECG and potassium and magnesium when co-prescribing, especially in older patients or those with heart disease. Consider a different antibiotic if QTc or QRS lengthens.
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?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Flecainide and Sulfamethoxazole, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
Other interactions of Flecainide
- Flecainide + Nirmatrelvir Contraindicated
- Flecainide + Nirmatrelvir / ritonavir Contraindicated
- Flecainide + Pimozide Contraindicated
- Flecainide + Ritonavir Contraindicated
- Flecainide + Thioridazine Contraindicated
- Flecainide + Tipranavir Contraindicated
Frequently asked questions
Can I take Flecainide with Sulfamethoxazole?
MediHelp rates the interaction as moderate. Flecainide 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. Sulfamethoxazole combined with trimethoprim has been associated with QT prolongation and rare torsades, while flecainide carries its own proarrhythmic risk. Together they may increase the likelihood of ventricular arrhythmias, particularly with renal impairment or electrolyte disturbances.
How serious is the interaction between Flecainide 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: Check ECG and potassium and magnesium when co-prescribing, especially in older patients or those with heart disease. Consider a different antibiotic if QTc or QRS lengthens.
What other medicines interact with Flecainide?
MediHelp also lists interactions of Flecainide with, for example, Nirmatrelvir, Nirmatrelvir / ritonavir, Pimozide. The full list is on the Flecainide page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
