DURAQUIN

Clinical safety rating: caution

Comprehensive clinical and safety monograph for DURAQUIN (DURAQUIN).

How it works

Quinidine is a class Ia antiarrhythmic agent that blocks sodium channels, slowing phase 0 depolarization, prolongs the action potential duration, and increases the effective refractory period. It also exhibits anticholinergic and negative inotropic effects.

What the body does with it

Metabolism	Primarily hepatic via CYP3A4, with minor contributions from CYP2C9 and CYP2E1. The major metabolite is 3-hydroxyquinidine, which is pharmacologically active.
Excretion	Primarily hepatic metabolism (90-95%) to inactive metabolites, with renal excretion of unchanged drug <5% and metabolites. Fecal elimination accounts for <5% due to biliary excretion of metabolites.
Half-life	Terminal elimination half-life is 8-12 hours in adults with normal renal and hepatic function. Clinically, dose adjustment may be needed in renal impairment (half-life prolonged to up 18 hours) or hepatic impairment.
Protein binding	70-80% bound primarily to albumin.
Volume of Distribution	0.5-1.0 L/kg. This moderate Vd indicates distribution into total body water with slight tissue binding.
Bioavailability	Oral: 70-80% (sustained release formulation has lower bioavailability due to slow release; immediate release ~80%).
Onset of Action	Oral: 1-3 hours (peak effect). Intravenous: within 15 minutes.
Duration of Action	Oral: 8-12 hours (sustained release formulation provides effect for up to 12 hours). Intravenous: 4-6 hours. Note: Lower doses may have shorter duration.

Classification & Brands

Dosing & administration

Quinidine sulfate 324 mg orally every 8-12 hours, adjusted based on serum quinidine levels.

Dosage form	TABLET, EXTENDED RELEASE
Renal impairment	For CrCl <10 mL/min: reduce dose by 25-50% and monitor ECG and serum levels. For CrCl 10-50 mL/min: reduce dose by 10-25%.
Liver impairment	Child-Pugh Class A: no adjustment. Child-Pugh Class B: reduce dose by 25%. Child-Pugh Class C: use with caution and reduce dose by 50%.
Pediatric use	Not FDA-approved for pediatric use; data limited. Off-label: 15-60 mg/kg/day orally in 4-6 divided doses, adjust based on serum levels.
Geriatric use	Initiate at lower doses (e.g., 162 mg orally every 8-12 hours) due to increased risk of QT prolongation and reduced renal clearance. Titrate slowly with monitoring.

Use during pregnancy

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

Clinical note

Comprehensive clinical and safety monograph for DURAQUIN (DURAQUIN).

Breastfeeding	Excreted into breast milk in low concentrations (M/P ratio approximately 0.1-0.2). Considered compatible with breastfeeding by the American Academy of Pediatrics, but monitor infant for signs of hemolysis (jaundice, pallor) and QT prolongation (arrhythmias).
Teratogenic Risk	FDA Pregnancy Category C. First trimester: Potential risk of hemolytic anemia, thrombocytopenia, and ototoxicity in the fetus. Second and third trimesters: Use with caution due to possible association with neonatal hemolysis and kernicterus. Avoid near term due to risk of neonatal hypoglycemia and prolonged QTc interval.

Warnings & precautions

■ FDA Black Box Warning

Quinidine can cause potentially fatal arrhythmias such as torsades de pointes, especially in patients with pre-existing QT prolongation, hypokalemia, or bradycardia. It may also cause cinchonism characterized by tinnitus, hearing loss, and blurred vision.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Hypersensitivity to quinidine or cinchona alkaloids","Complete atrioventricular block or left bundle branch block (unless paced)","History of drug-induced torsades de pointes","Myasthenia gravis","Prolonged QT interval","Concurrent use with drugs that prolong QT interval"]

Clinical Precautions

Precautions

["Risk of life-threatening arrhythmias (torsades de pointes) - monitor ECG, electrolytes","Cinchonism: tinnitus, hearing loss, visual disturbances","Hypotension and syncope due to negative inotropic effects","Hematologic effects: thrombocytopenia, agranulocytosis","Hepatotoxicity","Drug interactions with CYP3A4 inducers/inhibitors"]

Clinical Tips & Counseling

Drug interactions

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DURAQUIN

Clinical safety rating: caution

Comprehensive clinical and safety monograph for DURAQUIN (DURAQUIN).

How it works

What the body does with it

Metabolism	Primarily hepatic via CYP3A4, with minor contributions from CYP2C9 and CYP2E1. The major metabolite is 3-hydroxyquinidine, which is pharmacologically active.
Excretion	Primarily hepatic metabolism (90-95%) to inactive metabolites, with renal excretion of unchanged drug <5% and metabolites. Fecal elimination accounts for <5% due to biliary excretion of metabolites.
Half-life	Terminal elimination half-life is 8-12 hours in adults with normal renal and hepatic function. Clinically, dose adjustment may be needed in renal impairment (half-life prolonged to up 18 hours) or hepatic impairment.
Protein binding	70-80% bound primarily to albumin.
Volume of Distribution	0.5-1.0 L/kg. This moderate Vd indicates distribution into total body water with slight tissue binding.
Bioavailability	Oral: 70-80% (sustained release formulation has lower bioavailability due to slow release; immediate release ~80%).
Onset of Action	Oral: 1-3 hours (peak effect). Intravenous: within 15 minutes.
Duration of Action	Oral: 8-12 hours (sustained release formulation provides effect for up to 12 hours). Intravenous: 4-6 hours. Note: Lower doses may have shorter duration.

Classification & Brands

Dosing & administration

Quinidine sulfate 324 mg orally every 8-12 hours, adjusted based on serum quinidine levels.

Dosage form	TABLET, EXTENDED RELEASE
Renal impairment	For CrCl <10 mL/min: reduce dose by 25-50% and monitor ECG and serum levels. For CrCl 10-50 mL/min: reduce dose by 10-25%.
Liver impairment	Child-Pugh Class A: no adjustment. Child-Pugh Class B: reduce dose by 25%. Child-Pugh Class C: use with caution and reduce dose by 50%.
Pediatric use	Not FDA-approved for pediatric use; data limited. Off-label: 15-60 mg/kg/day orally in 4-6 divided doses, adjust based on serum levels.
Geriatric use	Initiate at lower doses (e.g., 162 mg orally every 8-12 hours) due to increased risk of QT prolongation and reduced renal clearance. Titrate slowly with monitoring.

Use during pregnancy

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

Clinical note

Comprehensive clinical and safety monograph for DURAQUIN (DURAQUIN).

Breastfeeding	Excreted into breast milk in low concentrations (M/P ratio approximately 0.1-0.2). Considered compatible with breastfeeding by the American Academy of Pediatrics, but monitor infant for signs of hemolysis (jaundice, pallor) and QT prolongation (arrhythmias).
Teratogenic Risk	FDA Pregnancy Category C. First trimester: Potential risk of hemolytic anemia, thrombocytopenia, and ototoxicity in the fetus. Second and third trimesters: Use with caution due to possible association with neonatal hemolysis and kernicterus. Avoid near term due to risk of neonatal hypoglycemia and prolonged QTc interval.