QUINIDEX
Clinical safety rating
cautionComprehensive clinical and safety monograph for QUINIDEX (QUINIDEX).
Class Ia antiarrhythmic agent; blocks sodium channels (fast inward sodium current) and prolongs action potential duration; also has anticholinergic and negative inotropic effects.
| Metabolism | Primarily hepatic via CYP3A4 (major) and CYP2C9 (minor) to active metabolites (3-hydroxyquinidine, quinidine-N-oxide); also renal excretion of unchanged drug (20%). |
| Excretion | Renal excretion accounts for approximately 20% unchanged drug; hepatic metabolism (primarily CYP3A4) accounts for 80% with metabolites excreted renally and biliarily; about 5% excreted in feces. |
| Half-life | Terminal elimination half-life is 6-8 hours in adults with normal renal and hepatic function; may be prolonged to 10-12 hours in congestive heart failure or hepatic impairment. |
| Protein binding | 80-90% bound to plasma proteins: primarily albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | 2-4 L/kg; extensive tissue distribution with high affinity for myocardium (tissue-to-plasma ratio >10). |
| Bioavailability | 70-80% for immediate-release oral; 50-70% for sustained-release formulations due to first-pass metabolism; absorption reduced by food. |
| Onset of Action | Oral: 1-3 hours; delayed-release tablets: 2-4 hours. |
| Duration of Action | 6-8 hours for immediate-release; 8-12 hours for extended-release formulations; effects on QRS prolongation last up to 12 hours. |
| Molecular Weight | 324.42 |
Quinidine sulfate (QUINIDEX): 200-400 mg orally every 6 hours as arrhythmia suppression; maximum 4 g/day. Route: oral, frequency: every 6 hours.
| Dosage form | TABLET, EXTENDED RELEASE |
| Renal impairment | CrCl 30-50 mL/min: administer 75% of normal dose every 6 hours. CrCl 10-29 mL/min: administer 50% of normal dose every 8 hours. CrCl <10 mL/min: administer 50% of normal dose every 12 hours. |
| Liver impairment | Child-Pugh class A: no adjustment. Child-Pugh class B: reduce dose by 50%; monitor levels. Child-Pugh class C: contraindicated or use with extreme caution; reduce dose by 75% with therapeutic drug monitoring. |
| Pediatric use | Oral: 15-60 mg/kg/day in 4-5 divided doses; maximum single dose 600 mg. For chronic suppression: start 30 mg/kg/day in 4-5 divided doses. |
| Geriatric use | Start at lower end of dosing range (200 mg every 8 hours) due to decreased hepatic and renal function; adjust based on plasma levels and QT interval monitoring. |
| 1st trimester | Avoid. Associated with fetal harm; may cause spontaneous abortion or teratogenic effects. |
| 2nd trimester | Avoid. Potential for fetal toxicity; use only if benefit outweighs risk. |
| 3rd trimester | Avoid. Risk of neonatal thrombocytopenia, hypoglycemia, and cardiac effects. |
Clinical note
Comprehensive clinical and safety monograph for QUINIDEX (QUINIDEX).
| Placental transfer | Crosses placenta; measurable levels in fetal circulation. |
| Breastfeeding | Excreted into breast milk; avoid breastfeeding due to potential for cardiac and CNS effects in the infant. |
| Lactation Rating | L5 - Contraindicated |
| Teratogenic Risk | First trimester: Limited data, but quinidine crosses placenta. No clear increase in major malformations after first trimester exposure. Second and third trimesters: Risk of fetal QT prolongation, neonatal thrombocytopenia, and tachycardia. Fetal distress may occur. Avoid if alternative exists, but if needed, monitor fetal ECG and heart rate. |
| Fetal Monitoring | Maternal: Serum quinidine levels (target therapeutic range 2–6 mcg/mL), ECG, blood pressure, heart rate, platelets, liver function. Fetal: Heart rate monitoring, fetal ECG for QT prolongation if feasible, ultrasound for growth. |
| Fertility Effects | No specific data. Quinidine may affect uterine contractility, but no known direct adverse effects on fertility. |
■ FDA Black Box Warning
Increased mortality in treatment of non-life-threatening ventricular arrhythmias; proarrhythmic effects (torsades de pointes).
| Serious Effects |
HypersensitivityComplete AV blockDigitalis intoxication (unless related to atrial fibrillation)Myasthenia gravisHistory of quinidine-induced thrombocytopenia or torsades de pointesHepatic impairment (severe)
| Precautions | Proarrhythmia (torsades de pointes), hepatotoxicity, cinchonism, hypersensitivity reactions, worsening of heart failure, digitalis toxicity, incomplete AV block, electrolyte disturbances. |
| Food/Dietary | Grapefruit juice increases quinidine bioavailability and serum levels, raising toxicity risk. Avoid grapefruit and grapefruit juice. Alkaline foods (e.g., antacids, milk) may increase quinidine absorption. High-sodium diet may enhance potassium loss and worsen arrhythmias. Avoid excessive caffeine or stimulants. |
| Clinical Pearls | Quinidine (as Quinidex) is a class Ia antiarrhythmic; monitor QRS and QT intervals due to risk of torsades de pointes. It also has anticholinergic properties, causing diarrhea in up to 50% of patients, which can be dose-limiting. Drug interactions are critical: quinidine inhibits CYP2D6, increasing levels of digoxin, warfarin, and many beta-blockers. Consider checking serum quinidine levels (therapeutic: 2-6 mcg/mL) and ECG if initiating or adjusting dose. |
| Patient Advice | Take exactly as prescribed; do not double dose if missed. · Avoid grapefruit juice as it can increase quinidine levels and toxicity. · Report new or worsening palpitations, dizziness, syncope, or irregular heartbeat immediately. · May cause diarrhea; contact your prescriber if diarrhea becomes severe or persistent. · Quinidine can cause blurred vision, tinnitus, or headache; report these to your doctor. · Avoid over-the-counter medications without consulting your doctor (especially antacids, antihistamines, and cold remedies). |
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