^
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. In the patients studied in the trials there analyzed, the mortality associated with the use of quinidine was more than three times as great as the mortality associated with the use of placebo.
Another meta-analysis, also described under CLINICAL PHARMACOLOGY/Clinical Effects , showed that in patients with various non-life-threatening ventricular arrhythmias, the mortality associated with the use of quinidine was consistently greater than that associated with the use of any of a variety of alternative antiarrhythmics.
^References:
^Description
Quinidine is an antimalarial schizonticide and an antiarrhythmic agent with Class Ia activity; it is the d-isomer of quinine, and its molecular weight is 324.43. Quinidine gluconate is the gluconate salt of quinidine; its chemical name is cinchonan-9-ol, 6'-methoxy-, (9S)-, mono-D-gluconate; its structural formula is:
Its empirical formula is C 20H 24N 2O 2 • C 6H 12O 7, and its molecular weight is 520.58, of which 62.3% is quinidine base.
Each quinidine gluconate extended-release tablet contains 324 mg of quinidine gluconate (202 mg of quinidine base) in a matrix to provide extended-release; the inactive ingredients include corn starch, hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, povidone, silicon dioxide, and sodium alginate.
This product complies with USP Drug Release Test 5.
^Overdosage
Overdoses with various oral formulations of quinidine have been well described. Death has been described after a 5-gram ingestion by a toddler, while an adolescent was reported to survive after ingesting 8 grams of quinidine.
The most important ill effects of acute quinidine overdoses are ventricular arrhythmias and hypotension. Other signs and symptoms of overdose may include vomiting, diarrhea, tinnitus, high-frequency hearing loss, vertigo, blurred vision, diplopia, photophobia, headache, confusion and delirium.
^Principal Display Panel - Mg Tablet Bottle Label
Quinidine Gluconate 324mg ER Tablets 100
NDC 51407-288-01
^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.
^Information For Patients
Before prescribing quinidine gluconate as prophylaxis against recurrence of atrial fibrillation, the physician should inform the patient of the risks and benefits to be expected (see CLINICAL PHARMACOLOGY ). Discussion should include the facts:
^How Supplied
Quinidine gluconate extended-release tablets, 324 mg are white to off-white, round, unscored, debossed MP 66.
^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. The result is slowed conduction and reduced automaticity in all parts of the heart, with increase of the effective refractory period relative to the duration of the action potential in the atria, ventricles, and Purkinje tissues. Quinidine also raises the fibrillation thresholds of the atria and ventricles, and it raises the ventricular defibrillation threshold as well. Quinidine's actions fall into Class Ia in the Vaughn-Williams classification.
By slowing conduction and prolonging the effective refractory period, quinidine can interrupt or prevent reentrant arrhythmias and arrhythmias due to increased automaticity, including atrial flutter, atrial fibrillation, and paroxysmal supraventricular tachycardia.
In patients with sick sinus syndrome, quinidine can cause marked sinus node depression and bradycardia. In most patients, however, use of quinidine is associated with an increase in the sinus rate.
Like other antiarrhythmic drugs with Class Ia activity, quinidine prolongs the QT interval in a dose-related fashion. This may lead to increased ventricular automaticity and polymorphic ventricular tachycardias, including torsades de pointes (see WARNINGS ).
In addition, quinidine has anticholinergic activity, it has negative inotropic activity, and it acts peripherally as an α-adrenergic antagonist (that is, as a vasodilator).
^Adverse Reactions
Quinidine preparations have been used for many years, but there are only sparse data from which to estimate the incidence of various adverse reactions. The adverse reactions most frequently reported have consistently been gastrointestinal, including diarrhea, nausea, vomiting, and heartburn/esophagitis.
In the reported study that was closest in character to the predominant approved use of quinidine gluconate, 86 adult outpatients with atrial fibrillation were followed for six months while they received slow-release quinidine bisulfate tablets, 600 mg (approximately 400 mg of quinidine base) twice daily. The incidences of adverse experiences reported more than once were as shown in the table below. The most serious quinidine-associated adverse reactions are described above under WARNINGS .
Vomiting and diarrhea can occur as isolated reactions to therapeutic levels of quinidine, but they may also be the first signs of cinchonism, a syndrome that may also include tinnitus, reversible high-frequency hearing loss, deafness, vertigo, blurred vision, diplopia, photophobia, headache, confusion, and delirium. Cinchonism is most often a sign of chronic quinidine toxicity, but it may appear in sensitive patients after a single moderate dose.
A few cases of hepatotoxicity, including granulomatous hepatitis, have been reported in patients receiving quinidine. All of these have appeared during the first few weeks of therapy, and most (not all) have remitted once quinidine was withdrawn.
Autoimmune and inflammatory syndromes associated with quinidine therapy have included fever, urticaria, flushing, exfoliative rash, bronchospasm, psoriasiform rash, pruritus and lymphadenopathy, hemolytic anemia, vasculitis, thrombocytopenia, thrombocytopenic purpura, uveitis, angioedema, agranulocytosis, the sicca syndrome, arthralgia, myalgia, elevation in serum levels of skeletal-muscle enzymes, a disorder resembling systemic lupus erythematosus, and pneumonitis.
Convulsions, apprehension, and ataxia have been reported, but it is not clear that these were not simply the results of hypotension and consequent cerebral hypoperfusion. There are many reports of syncope. Acute psychotic reactions have been reported to follow the first dose of quinidine, but these reactions appear to be extremely rare.
Other adverse reactions occasionally reported include depression, mydriasis, disturbed color perception, night blindness, scotomata, optic neuritis, visual field loss, photosensitivity, and abnormalities of pigmentation.
^Warnings
Mortality:
^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.
Quinidine is also contraindicated in patients who, like those with myasthenia gravis, might be adversely affected by an anticholinergic agent.