Quinidine
QUINIDEX
Pronunciation: KWIN-i-deen
“(Q)winning!”
What it isClass IA antiarrhythmic; Brugada syndrome and, with dextromethorphan, pseudobulbar affect.
Why this oneIt is one of the few agents for Brugada syndrome, and it is a potent CYP2D6 inhibitor used deliberately to block dextromethorphan metabolism.
What limits itQT prolongation and cinchonism. It raises digoxin levels; excess mortality when used for ordinary arrhythmia.
FDA-approved for
- arrhythmias (~1950)
FDA label
Read the full label on DailyMed ↗
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Conversion of symptomatic atrial fibrillation/flutter to sinus rhythm (after ventricular rate control fails) | Adults | 648 mg (2 tabs) q8h; alt: 324 mg q8h × 2 days → 648 mg q12h × 2 days → 648 mg q8h up to 4 days | If no conversion after 3–4 doses, cautiously increase; stop if not converted in reasonable time | ECG-limited: stop if QRS or QTc widens to 130% of baseline (QTc >500 ms), P waves disappear, or significant tachycardia, symptomatic bradycardia, or hypotension |
| Reduction of relapse into atrial fibrillation/flutter (high-risk, frequent symptomatic episodes) | Adults | 324 mg q8–12h | Cautiously raise if tolerated, serum level within range, and inter-episode interval not improved | ECG-limited: reduce total daily dose for QRS/QTc widening to 130% (QTc >500 ms), loss of P waves, tachy-/bradycardia, hypotension |
| Suppression of recurrent documented life-threatening ventricular arrhythmias (e.g., sustained VT) | Adults | Not adequately studied; similar to relapse-prevention regimen (324 mg q8–12h) | Guide by programmed electrical stimulation and/or Holter with exercise | Undefined |
Titration Conversion: increase only after 3–4 doses without conversion.
Renal No specific adjustment given; renal dysfunction slows elimination—reduce dose appropriately to avoid toxicity.
Hepatic No specific adjustment given; hepatic dysfunction slows elimination—reduce dose appropriately to avoid toxicity.
324 mg quinidine gluconate = 202 mg quinidine base. A single AF recurrence is not therapeutic failure; goal is longer time between episodes. CHF reduces volume of distribution—also reduce dose.
Instructions
- Tablet may be broken in half for titration; do not crush or chew (loses extended release).
- Initiate or adjust in a setting with continuous monitoring and resuscitation available, esp. with structural heart disease.
- Continue monitoring 2–3 days after starting the discharge regimen.
Available strengths
- ER tab 324 mg
- tab 200, 300 mg
Contraindications
- History of immune thrombocytopenia or thrombocytopenic purpura during prior quinidine or quinine therapy
- Rhythm dependent on junctional or idioventricular pacemaker (incl. complete AV block) without a functioning artificial pacemaker
- Patients who might be adversely affected by an anticholinergic agent (e.g., myasthenia gravis)
Cautions
- Increased mortality
- Proarrhythmia (QTc prolongation, torsades de pointes)
- Paradoxical increase in ventricular rate in atrial flutter/fibrillation
- Exacerbated bradycardia in sick sinus syndrome
- Pharmacokinetic considerations (renal/hepatic dysfunction, CHF, drug interactions)
- Vagolysis (vagal maneuvers may fail)
- Immune thrombocytopenia (do not re-expose)
Adverse reactions
- Diarrhea
- Fever
- Rash
- Arrhythmia
- Abnormal ECG
- Nausea/vomiting
- Dizziness
- Headache
- Asthenia
- Cerebral ischemia
- Cinchonism (tinnitus, hearing loss, vertigo, blurred vision)
- Hepatotoxicity (granulomatous hepatitis)
Pregnancy No animal or adequate human studies; give only if clearly needed; neonatal serum level equaled maternal in one case.
Lactation Present in milk slightly below maternal serum levels; avoid in women who continue to nurse, if possible.
Cost
| Strength | #/mo | generic $/unit | CostPlus | |
|---|---|---|---|---|
| 324 mg | ER tab | per unit | $4.92/ea | out of stock |
Available combined with: dextromethorphan / quinidine
Generic entry1982
⚠ BOXED WARNING
- Increased mortality in non-life-threatening arrhythmias
Classes and tags
Clinical profile
Legacy pregnancy categoryC
Defining liabilityQT prolongation, torsades, cinchonism and extensive CYP2D6/P-gp interactions.
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