Drug Interaction Report

Flecainide and Tedisamil: Interaction Details

A pharmacist-reviewed analysis of the Flecainide and Tedisamil interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Flecainide

Tambocor®
+

Tedisamil

No brand names on record
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
How we grade severity & evidence

Severity levels

  • Contraindicated: These should generally not be used together.
  • Major: Potentially serious — often needs a change or close monitoring.
  • Moderate: Can be significant — usually manageable with monitoring.
  • Minor: Usually limited clinical impact.

Evidence grades

  • Established: Well documented — supported by controlled studies or strong clinical data.
  • Probable: Good supporting evidence, though not definitively proven.
  • Suspected: Some evidence suggests this interaction, but it is not well established.
  • Possible: Limited or conflicting evidence; the interaction may occur.
  • Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.

Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.

Of 300 documented Flecainide interactions, 270 are rated major — including this one.
Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.
Onset
unspecified
Evidence
theoretical
Severity
Major

What happens

An increased risk of cardiotoxicity (QT prolongation, torsades de pointes, cardiac arrest)

Interaction Deep Dive

Coadministration of drugs that potentially prolong the QTc interval, such as Class I antiarrhythmic and Class III antiarrhythmic agents, should be approached with caution1017. Even though no formal drug interaction studies have been done, the coadministration of Class III and other drugs known to prolong the QT interval, including Class I antiarrhythmics, is not recommended 1112. It is recommended that class I antiarrhythmic agents be withheld for three half-lives before dofetilide is initiated 13.

Why it happens (mechanism)

Additive effects on QT prolongation

Literature reports

5 reports — tap to read

a) Torsade de pointes (variant of ventricular tachycardia) in a 59-year-old male following mexiletine 100 mg orally every 6 hours has been reported 2. The ventricular tachycardia did not recur upon discontinuation of the drug.

b) Flecainide slows cardiac conduction in most patients to produce dose-related increases in PR, QRS, and QT intervals 8.

c) Lorcainide has been reported to cause widening of the QRS complex and QT intervals and rarely can cause a negative inotropic effect (less than 1%). As with all antiarrhythmic agents, lorcainide can trigger rhythm disturbances 3456.

d) Aprindine-induced polymorphous ventricular tachycardia (PVT; torsades de pointes) has been reported, in both sustained and nonsustained forms, following oral and intravenous administration (125 to 600 mg/day). PVT manifested as QT prolongation and recurrent syncope. PVT occurred within 10 days after initiation of aprindine therapy and resolved within 2 to 48 hours after discontinuation of aprindine. The QT interval regressed to predrug values after discontinuation of aprindine. In some cases PVT terminated spontaneously and in other cases electrical cardioversion was necessary. In one case, hypokalemia may have contributed to the proarrhythmic effect. Patients with an antiarrhythmic drug-induced acquired QT syndrome may be predisposed to aprindine-induced PVT 7.

e) Torsades de pointes has been reported in patients taking amiodarone and mexiletine together. The QT interval was prolonged above 0.5 second in each of these patients 9.

Common questions

Can I take Flecainide and Tedisamil together?

An increased risk of cardiotoxicity (QT prolongation, torsades de pointes, cardiac arrest) Always confirm with your pharmacist or prescriber before making any change.

How serious is the Flecainide and Tedisamil interaction?

It is rated major. Potentially serious — often needs a change or close monitoring.

How quickly could this interaction happen?

The documented onset is "unspecified". The timing of this interaction is not well characterized.

How strong is the evidence for this interaction?

The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

From our Q&A

Real reader questions about these medications, each personally answered by our pharmacist:

Questions for your pharmacist

  • Does my dose of Flecainide or Tedisamil need adjusting while I take them together?
  • What symptoms should prompt me to call you or my prescriber right away?
  • Does the timing of my doses matter for this combination?
  • Is there a safer alternative to one of these medications for me?

References (13)

  1. Larochelle P, Belanger L, Lemire F, et al: Dose-response effect of propafenone in patients with ventricular arrhythmias. Curr Ther Res 1984; 36:959-969. DOI
  2. Cocco G, Strozzi C, Chu D, et al: Torsades de pointes as a manifestation of mexiletine toxicity. Am Heart J 1980; 100:878-880. PubMed
  3. Samanek M, Hrobonova V, & Bartakova H: Lorcainide treatment of Wolff-Parkinson-White syndrome in children and adolescents. Pediatr Cardiol 1987; 8:3-9. PubMed
  4. McDevitt DG: The clinical pharmacology of lidocaine congeners - Review of encainide, flecainide, lorcainide and tocainide. Eur Heart J 1984; 5(suppl B):63-66. DOI
  5. Myburgh DP, Goldman AP, & Schamroth JM: Lorcainide - an anti-arrhythmic agent for ventricular arrhythmias. S Afr Med J 1980; 57:236-239.
  6. Kasper W, Meinertz T, Kersting F, et al: Electrophysiological actions of lorcainide in patients with cardiac disease. J Cardiovasc Pharmacol 1979; 1:343-352. PubMed
  7. Scagliotti D, Strasberg B, Hai HA, et al: Aprindine-induced polymorphous ventricular tachycardia. Am J Cardiol 1982; 49:1297-1300. DOI
  8. Product Information: Tambocor(R) flecainide acetate. 3M Pharmaceuticals, Northridge, CA, 1998.
  9. Marcus FI: Drug interactions with amiodarone. Am Heart J 1983; 106:924-930. PubMed
  10. Product Information: Tambocor(R) flecainide acetate. 3M Pharmaceuticals, Northridge, CA, 1998.
  11. Product Information: Quinidex Extentabs(R), quinidine sulfate oral extended-release tablets. A.H. Robins Company, Richmond, VA, 2000. DailyMed
  12. Product Information: Tikosyn(TM), dofetilide capsules. Pfizer Labs, New York, NY, 1999. DailyMed
  13. Yamreudeewong W, DeBisschop M, Martin LG, et al: Potentially significant drug interactions of class III antiarrhythmic drugs. Drug Safety 2003; 26(6):421-438. PubMed
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Flecainide

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Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

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