Drug interactions
Encainide + Fluoxetine
Severity: Major
Encainide and Fluoxetine: major interaction.
Last updated Sources: US FDA label
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
Encainide is a class Ic antiarrhythmic that is activated by CYP2D6 to active metabolites. Fluoxetine inhibits CYP2D6, shifting the parent to metabolite ratio and changing the antiarrhythmic and proarrhythmic profile. Encainide carries a risk of proarrhythmia, so any change in exposure matters.
What this interaction means in plain words
Encainide and Fluoxetine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Fluoxetine inhibits CYP2D6-mediated conversion of encainide to its active metabolites, changing its pharmacokinetics.
What to do
Avoid the combination if possible; otherwise monitor ECG for QRS widening and arrhythmias and adjust the encainide dose.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Fluoxetine
- Fluoxetine + Isocarboxazid Contraindicated
- Fluoxetine + Mavacamten Contraindicated
- Fluoxetine + Methylene blue Contraindicated
- Fluoxetine + Phenelzine Contraindicated
- Fluoxetine + Pimozide Contraindicated
- Fluoxetine + Rasagiline Contraindicated
Frequently asked questions
Can I take Encainide with Fluoxetine?
MediHelp rates the interaction as major. Encainide and Fluoxetine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Encainide is a class Ic antiarrhythmic that is activated by CYP2D6 to active metabolites. Fluoxetine inhibits CYP2D6, shifting the parent to metabolite ratio and changing the antiarrhythmic and proarrhythmic profile. Encainide carries a risk of proarrhythmia, so any change in exposure matters.
How serious is the interaction between Encainide and Fluoxetine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination if possible; otherwise monitor ECG for QRS widening and arrhythmias and adjust the encainide dose.
What other medicines interact with Fluoxetine?
MediHelp also lists interactions of Fluoxetine with, for example, Isocarboxazid, Mavacamten, Methylene blue. The full list is on the Fluoxetine page.
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