BLACK BOX WARNING
- proarrhythmia — increased mortality in atrial fibrillation compared to no therapy in some trials
quinidine
Brand: Quinidex, Quinaglute
⚠ BBW Beers Criteria TDM Required Prototype Drug
Drug Class: antiarrhythmic (Class IA)
Drug Family: antiarrhythmic
Subclass: sodium channel blocker + potassium channel blocker
Organ Systems: cardiovascular
Mechanism of Action
Class IA antiarrhythmic that blocks both fast sodium channels (slowing phase 0 depolarization) and IKr potassium channels (prolonging repolarization and QT interval); also has anticholinergic and alpha-blocking properties.
fast sodium channels (intermediate kinetics)IKr potassium channelalpha-adrenergic receptors
Indications
- atrial fibrillation/flutter (conversion and maintenance of sinus rhythm)
- paroxysmal supraventricular tachycardia
- ventricular arrhythmias
- malaria (IV quinidine gluconate — historical)
Contraindications
- QT prolongation >500ms
- complete AV block
- myasthenia gravis
- digoxin toxicity
- quinidine hypersensitivity or prior quinidine-induced thrombocytopenia
Adverse Effects
Common
- diarrhea (up to 30-40% of patients)
- nausea/vomiting
- cinchonism (tinnitus, headache, visual disturbance — dose-related)
- QT prolongation
Serious
- torsades de pointes
- thrombocytopenia (immune-mediated)
- hypotension (via alpha-blockade)
- proarrhythmia
- hepatotoxicity (rare)
Pharmacokinetics (ADME)
| Absorption | 70-80% oral bioavailability |
| Distribution | moderate (Vd 2-3 L/kg) |
| Metabolism | hepatic CYP3A4 (major); 3-hydroxyquinidine active metabolite |
| Excretion | renal (20% unchanged), hepatic |
| Half-life | 6-8 hours |
| Onset | 1-3 hours (oral) |
| Peak | 1-2 hours (sulfate), 3-4 hours (gluconate) |
| Duration | 6-8 hours |
| Protein Binding | 80-90% |
| Vd | 2-3 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| digoxin | inhibits P-glycoprotein and renal tubular secretion of digoxin — doubles digoxin levels; reduce digoxin dose by 50% | major |
| warfarin | inhibits CYP2C9 — increases anticoagulant effect | major |
| QT-prolonging drugs | additive QT prolongation and TdP risk | major |
| cimetidine / alkalinizing agents | reduce renal clearance of quinidine — increased toxicity | moderate |
Nursing Considerations
- Obtain baseline ECG; monitor QTc — hold and notify provider if QTc >500ms or increases >25% from baseline
- GI intolerance (especially diarrhea) is the most common reason for discontinuation
- Monitor for cinchonism: tinnitus, visual changes, headache — dose-related toxicity
- Digoxin interaction: check digoxin level if given concurrently; reduce digoxin dose by 50%
- Monitor CBC for thrombocytopenia (immune-mediated, may occur even at low doses)
Clinical Pearls
- Prototype Class IA agent — historically first antiarrhythmic; largely replaced by safer agents but still used in specific arrhythmias (e.g., Brugada syndrome, short QT syndrome)
- Vagolytic (anticholinergic) effect can paradoxically accelerate ventricular rate in AF — beta-blocker or calcium channel blocker given concurrently
- Cinchonism is a classic adverse effect cluster: tinnitus, high-frequency hearing loss, visual blurring, headache
Safety Profile
Pregnancy use with caution
Lactation use with caution
Renal Adjustment Required
Hepatic Adjustment Required
TDM Required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.