quinidine sulfate

Action

Slows conduction and prolongs refractory period, reducing myocardial irritability and interrupting or preventing certain arrhythmias. As an antimalarial, acts primarily as intra-erythrocytic schizonticide.

Availability

quinidine gluconate

Injection: 80 mg/ml

Tablets (extended-release): 324 mg

quinidine sulfate

Tablets: 200 mg, 300 mg

Tablets (extended-release): 300 mg

Indications and dosages

➣ Test dose

Adults: 200 mg sulfate P.O. as a single dose or 200 mg gluconate I.M. to check for idiosyncratic reaction

➣ Premature atrial and ventricular contractions

Adults: 200 to 300 mg sulfate P.O. three to four times daily, or gluconate (extended-release) given as 324 to 660 mg P.O. q 8 to 12 hours

➣ Paroxysmal supraventricular tachycardia (PSVT)

Adults: 400 to 600 mg sulfate P.O. q 2 or 3 hours until arrhythmia ends; or 324 to 660 mg (extended-release) P.O. q 8 to 12 hours. For parenteral use, 400 mg gluconate I.M., repeated q 2 hours if necessary; or 330 mg gluconate I.V. (up to 750 mg) in diluted solution, infused no faster than 1 ml/minute.

➣ To convert atrial fibrillation to sinus rhythm

Adults: 200 mg sulfate P.O. q 2 or 3 hours for five to eight doses, increased daily until sinus rhythm returns or toxic effects occur; maximum daily dosage is 4 g. Or 300 mg sulfate (extended-release) P.O. q 8 to 12 hours, increased cautiously if necessary. Or 324 to 660 mg gluconate (extended-release) P.O. q 8 to 12 hours. For parenteral use, 800 mg gluconate I.V. in diluted solution, infused no faster than 0.25 mg/kg/minute.

➣ Severe, life-threatening Plasmodium falciparum malaria

Adults: Loading dose of 10 mg/kg gluconate I.V. diluted in 5 ml/kg of normal saline solution (or 250 ml of normal saline solution in otherwise healthy, 50-kg [110-lb] patient) by continuous infusion over 1 to 2 hours, then a continuous maintenance infusion of 0.02 mg/kg/minute for 72 hours or until parasitemia drops to less than 1% or oral therapy can begin. Or alternative loading dose of 24 mg/kg gluconate I.V. diluted in 250 ml of 0.9% sodium chloride injection by intermittent infusion over 4 hours, followed by maintenance dosage of 12 mg/kg gluconate I.V. at 8-hour intervals, starting 8 hours after loading dose, infused over 4 hours for 7 days or until patient tolerates oral therapy.

Dosage adjustment

• Hepatic insufficiency

Off-label uses

• Myocardial infarction

Contraindications

• Hypersensitivity to drug or related cinchona derivatives

• Thrombocytopenia with previous quinidine therapy

• Myasthenia gravis

• Complete heart block

• Left bundle-branch block or other severe intraventricular conduction defects

• Aberrant ectopic impulses and abnormal rhythm

• History of prolonged QT interval or drug-induced torsades de pointes

• Digoxin toxicity

Precautions

Use cautiously in:

• potassium imbalance, renal or hepatic disease, heart failure, respiratory depression

• elderly patients

• pregnant or breastfeeding patients

• children.

Administration

Before first dose, assess apical pulse and blood pressure. If patient has bradycardia or tachycardia, withhold dose and contact prescriber.

• If patient has atrial fibrillation, expect to give digoxin, calcium channel blocker, beta-adrenergic blocker, and possibly an anticoagulant before administering quinidine.

• If sinus rhythm isn't restored after patient has received a total of 10 mg/kg quinidine gluconate, other means of cardioversion may be considered.

• Monitor blood pressure and ECG; titrate flow rate to correct arrhythmia.

• When giving large doses, monitor blood pressure and ECG continuously.

• Know that quinidine gluconate is the only parenteral cinchona alkaloid antimalarial commercially available in U.S. Because newer antiarrhythmics have replaced quinidine in many cardiac uses, it may not be readily available and prescribers may not be familiar with its use. For information about availability or use, contact manufacturer at 800-821-0538.

Adverse reactions

CNS: vertigo, headache, ataxia, apprehension, excitement, delirium, syncope, confusion, depression, dementia

CV: ECG changes, hypotension, vasculitis, tachycardia, premature ventricular contractions, paradoxical tachycardia, ventricular tachycardia, ventricular fibrillation, ventricular flutter, ventricular ectopy, torsades de pointes, complete atrio-ventricular (AV) block, widened QRS complex, prolonged QT interval, asystole, aggravated heart failure, arterial embolism, vascular collapse

EENT: diplopia, blurred vision, mydriasis, abnormal color perception, scotoma, photophobia, night blindness, optic neuritis, decreased hearing, tinnitus

GI: nausea, vomiting, diarrhea, abdominal pain, increased salivation, anorexia

GU: lupus nephritis

Hematologic: purpura, hemolytic anemia, hypothrombinemia, leukocytosis, shift to left in white blood cell differential, neutropenia, thrombocytopenia, thrombocytopenic purpura, agranulocytosis

Hepatic: hepatotoxicity

Respiratory: acute asthma attack, respiratory arrest

Skin: rash, pruritus, urticaria, photosensitivity, angioedema

Other: fever, cinchonism, lupuslike syndrome, hypersensitivity reaction

Interactions

Drug-drug. Amiodarone: increased quinidine blood level, causing potentially fatal arrhythmias

Antacids, cimetidine: increased quinidine blood level

Anticholinergics: additive vagolytic effect

Anticoagulants, beta-adrenergic blockers, procainamide, propafenone, tricyclic antidepressants: increased effects of these drugs

Barbiturates, hydantoins, nifedipine, rifampin, sucralfate: decreased therapeutic effect of quinidine

Cardiac glycosides: increased cardiac glycoside blood level, greater risk of toxicity

Cholinergics: decreased quinidine effect (may cause failure to terminate PSVT) Depolarizing (decamethonium, succinylcholine) and nondepolarizing (tubocurarine, pancuronium) neuromuscular blockers: potentiation of neuromuscular blockade

Diltiazem, verapamil: decreased quinidine clearance, resulting in hypotension, bradycardia, ventricular tachycardia, AV block, or pulmonary edema

Disopyramide: increased disopyramide or decreased quinidine blood level

Potassium, urinary alkalizers: increased blood level and effects of quinidine

Drug-diagnostic tests. Granulocytes, hemoglobin, platelets: decreased levels

Creatine kinase, hepatic enzymes: increased levels

Renal function tests: altered results

Drug-food. Grapefruit juice: inhibited drug metabolism

Reduced sodium intake: increased quinidine blood level

Drug-herbs. Jimsonweed: adverse cardiovascular effects

Licorice: additive effects

Patient monitoring

Monitor ECG and vital signs closely. Assess for worsening heart failure, especially with I.V. use.

• Assess CBC, kidney and liver function tests and quinidine blood level.

• Watch for signs and symptoms of blood dyscrasias.

Closely monitor respiratory status. Stay alert for asthma attacks and impending respiratory arrest.

• Monitor for adverse GI effects, which may signify drug toxicity.

Patient teaching

• Advise patient to take with food to reduce GI upset.

• Instruct patient not to crush or chew extended-release tablets.

Teach patient to recognize and immediately report signs and symptoms of toxicity, including tinnitus, nausea, headache, dizziness, and visual disturbances.

• Caution patient to avoid potassium supplements, licorice, and grapefruit juice. Tell him to maintain constant level of sodium intake.

• Advise patient to consult prescriber before taking herbs.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, foods, and herbs mentioned above.