Drug Interaction Report

Disopyramide and Phenobarbital: Interaction Details

A pharmacist-reviewed analysis of the Disopyramide and Phenobarbital 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

Phenobarbital

Fidoquel Sezaby
+

Disopyramide

Norpace Norpace® Norpace® CR
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 284 documented Disopyramide interactions, 247 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
delayed
Evidence
theoretical
Severity
Major

What happens

An increased risk of QT interval prolongation, reduced disopyramide exposure and reduced disopyramide efficacy

Interaction Deep Dive

In a controlled study, the concurrent use of PHENobarbital and disopyramide resulted in reduced half-life and AUC by 30 to 35% for disopyramide2. Avoid the concomitant use of PHENobarbital with other products with a known potential to prolong the QTc interval or products that may increase concentrations of PHENobarbital. PHENobarbital causes QTc interval prolongation. Concomitant use of PHENobarbital with other products that prolong the QTc interval like disopyramide may result in a greater increase in the QTc interval and adverse reactions associated with QTc interval prolongation. If concomitant use of disopyramide and PHENobarbital is unavoidable, monitor patients for increased risk of QTc interval prolongation 1.

Why it happens (mechanism)

Additive QT interval prolongation; increased hepatic clearance

Literature reports

1 report — tap to read

a) In a controlled study, the concurrent use of PHENobarbital and disopyramide resulted in reduced half-life and AUC by 30 to 35% for disopyramide 2.

Common questions

Can I take Disopyramide and Phenobarbital together?

An increased risk of QT interval prolongation, reduced disopyramide exposure and reduced disopyramide efficacy Always confirm with your pharmacist or prescriber before making any change.

How serious is the Disopyramide and Phenobarbital interaction?

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

How quickly could this interaction happen?

The documented onset is "delayed". Effects tend to build up gradually over days to weeks.

How strong is the evidence for this interaction?

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

Questions for your pharmacist

  • Does my dose of Disopyramide or Phenobarbital 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 (2)

  1. Product Information: SEZABY(TM) intravenous injection, phenobarbital sodium intravenous injection. Sun Pharmaceutical Industries Inc (per manufacturer), Cranbury, NJ, 2022. DailyMed
  2. Kapil RP, Axelson JE, Mansfield IL, et al: Disopyramide pharmacokinetics and metabolism: effect of inducers. Br J Clin Pharmacol 1987; 24:781-791. PubMed
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Phenobarbital

Keep reading about Phenobarbital

All Phenobarbital interactions (219)
Also serious with: Nifedipine Maraviroc Cabotegravir Doravirine
Disopyramide

Keep reading about Disopyramide

All Disopyramide interactions (284) Disopyramide drug information
Also serious with: Levomethadyl Mesoridazine Levoketoconazole Itraconazole
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:

Phenobarbital + 1,4-butanediol Activated Charcoal Beer Gamma-hydroxybutyrate (ghb) Henbane Kava L-tryptophan Scopolia + 166 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.