QUINIDEX

Clinical safety rating: caution

Comprehensive clinical and safety monograph for QUINIDEX (QUINIDEX).

How it works

Class Ia antiarrhythmic agent; blocks sodium channels (fast inward sodium current) and prolongs action potential duration; also has anticholinergic and negative inotropic effects.

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for QUINIDEX (QUINIDEX).

Breastfeeding	Quinidine is excreted into breast milk. M/P ratio reported as 0.57–0.78. Amount is low, but monitor infant for arrhythmias, bruising, and bleeding. Generally considered compatible with breastfeeding if maternal monitoring is done.
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.

Warnings & precautions

■ FDA Black Box Warning

Increased mortality in treatment of non-life-threatening ventricular arrhythmias; proarrhythmic effects (torsades de pointes).

Side Effect Profile

Serious Effects

Absolute Contraindications

Hypersensitivity to quinidine or cinchona alkaloids, complete AV block or severe intraventricular conduction defects, myasthenia gravis, history of thrombocytopenia with quinidine, concurrent use with drugs that prolong QT interval (unless absolutely necessary).

Clinical Precautions

Precautions

Proarrhythmia (torsades de pointes), hepatotoxicity, cinchonism, hypersensitivity reactions, worsening of heart failure, digitalis toxicity, incomplete AV block, electrolyte disturbances.

Clinical Tips & Counseling

Drug interactions

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QUINIDEX

Clinical safety rating: caution

Comprehensive clinical and safety monograph for QUINIDEX (QUINIDEX).

How it works

Class Ia antiarrhythmic agent; blocks sodium channels (fast inward sodium current) and prolongs action potential duration; also has anticholinergic and negative inotropic effects.

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for QUINIDEX (QUINIDEX).

Breastfeeding	Quinidine is excreted into breast milk. M/P ratio reported as 0.57–0.78. Amount is low, but monitor infant for arrhythmias, bruising, and bleeding. Generally considered compatible with breastfeeding if maternal monitoring is done.
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.

Warnings & precautions

■ FDA Black Box Warning

Increased mortality in treatment of non-life-threatening ventricular arrhythmias; proarrhythmic effects (torsades de pointes).

Side Effect Profile

Serious Effects

Absolute Contraindications

Clinical Precautions

Precautions

Proarrhythmia (torsades de pointes), hepatotoxicity, cinchonism, hypersensitivity reactions, worsening of heart failure, digitalis toxicity, incomplete AV block, electrolyte disturbances.

Clinical Tips & Counseling

Drug interactions

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