Quinidine Sulfate

What it is and how it works

Mechanisms of action In patients with malaria, quinidine acts primarily as an intra-erythrocytic schizonticide, with little effect upon sporozites or upon pre-erythrocytic parasites. Quinidine is gametocidal to Plasmodium vivax and P. malariae , but not to P. falciparum. In cardiac muscle and in Purkinje fibers, quinidine depresses the rapid inward depolarizing sodium current, thereby slowing phase-0 depolarization and reducing the amplitude of the action potential without affecting the resting potential. In normal Purkinje fibers, it reduces the slope of phase-4 depolarization, shifting the threshold voltage upward toward zero.

Indications

INDICATIONS AND USAGE Conversion of atrial fibrillation/flutter In patients with symptomatic atrial fibrillation/flutter whose symptoms are not adequately controlled by measures that reduce the rate of ventricular response, quinidine gluconate is indicated as a means of restoring normal sinus rhythm. If this use of quinidine gluconate does not restore sinus rhythm within a reasonable time (see DOSAGE AND ADMINISTRATION ), then quinidine gluconate should be discontinued. Reduction of frequency of relapse into atrial fibrillation/flutter Chronic therapy with quinidine gluconate is indicated for some patients at high risk of symptomatic atrial fibrillation/flutter, generally patients who have had previous episodes of atrial fibrillation/flutter that were so frequent and poorly tolerated as to outweigh, in the judgment of the physician and the patient, the risks of prophylactic therapy with quinidine gluconate. The increased risk of death should specifically be considered.

Dosage and administration (summary)

DOSAGE AND ADMINISTRATION The dose of quinidine delivered by quinidine gluconate extended-release tablets may be titrated by breaking a tablet in half. If tablets are crushed or chewed, their extended-release properties will be lost. The dosage of quinidine varies considerably depending upon the general condition and the cardiovascular state of the patient.

Contraindications

CONTRAINDICATIONS Quinidine is contraindicated in patients who are known to be allergic to it, or who have a history of immune thrombocytopenia or have developed thrombocytopenic purpura during prior therapy with quinidine or quinine (see WARNINGS ). In the absence of a functioning artificial pacemaker, quinidine is also contraindicated in any patient whose cardiac rhythm is dependent upon a junctional or idioventricular pacemaker, including patients in complete atrioventricular block.

Warnings and precautions

WARNINGS Mortality: In many trials of antiarrhythmic therapy for non-life-threatening arrhythmias, active antiarrhythmic therapy has resulted in increased mortality; the risk of active therapy is probably greatest in patients with structural heart disease. In the case of quinidine used to prevent or defer recurrence of atrial flutter/fibrillation, the best available data come from a meta-analysis described under CLINICAL PHARMACOLOGY/Clinical Effects above.

Pregnancy

Pregnancy Pregnancy Category C. Animal reproductive studies have not been conducted with quinidine. There are no adequate and well-controlled studies in pregnant women. Quinidine should be given to a pregnant woman only if clearly needed.

Storage and supply

Store at 20° to 25°C (68° to 77°F). DISPENSE IN TIGHT, LIGHT-RESISTANT CONTAINER.

Source: Quinidine Gluconate (Quinidine Gluconate) — US FDA prescribing information, 2018-02-01, DailyMed. Summarised and shortened; the full label governs. Iranian registration, indications and labelling may differ.