DOSAGE AND ADMINISTRATION Treatment of P. Falcipum Malaria Quinidine sulfate tablets are used in one of the approved regimens for the treatment of life-threatening P. falciparum malaria. The central component of the regimen is Quinidine Gluconate Injection, and the regimen is described in the package insert of Quinidine Gluconate Injection. Conversion of Atrial Fibrillation/Flutter to Sinus Rhythm Especially in patients with known structural heart disease or other risk factors for toxicity, initiation or dose-adjustment of treatment with quinidine sulfate should generally be performed in a setting where facilities and personnel for monitoring and resuscitation are continuously available. Patients with symptomatic atrial fibrillation/ flutter should be treated with quinidine sulfate only after ventricular rate control ( e.g., with digitalis or β-blockers) has failed to provide satisfactory control of symptoms. Adequate trials have not identified an optimal regimen of quinidine sulfate for conversion of atrial fibrillation/flutter to sinus rhythm. In one reported regimen, the patient first receives two tablets (400 mg; 332 mg of quinidine base) of quinidine sulfate every six hours. If this regimen has not resulted in conversion after 4 or 5 doses, then the dose is cautiously increased. If, at any point during administration, the QRS complex widens to 130% of its pre-treatment duration; the QT C interval widens to 130% of its pre-treatment duration and is then longer than 500 ms; P waves disappear; or the patient develops significant tachycardia, symptomatic bradycardia, or hypotension, then quinidine sulfate is discontinued, and other means of conversion ( e.g., direct-current cardioversion) are considered. Reduction of Frequency of Relapse Into Atrial Fibrillation/Flutter In a patient with a history of frequent symptomatic episodes of atrial fibrillation/flutter, the goal of therapy with quinidine sulfate should be an increase in the average time between episodes. In most patients, the tachyarrhythmia will recur during therapy with quinidine sulfate, and a single recurrence should not be interpreted as therapeutic failure. Especially in patients with known structural heart disease or other risk factors for toxicity, initiation or dose-adjustment of treatment with quinidine sulfate should generally be performed in a setting where facilities and personnel for monitoring and resuscitation are continuously available. Monitoring should be continued for two or three days after initiation of the regimen on which the patient will be discharged. Therapy with quinidine sulfate should be begun with 200 mg (equivalent to 166 mg of quinidine base) every six hours. If this regimen is well tolerated, if the serum quinidine level is still well within the laboratory’s therapeutic range, and if the average time between arrhythmic episodes has not been satisfactorily increased, then the dose may be cautiously raised. The total daily dosage should be reduced if the QRS complex widens to 130% of its pretreatment duration; the QT C interval widens to 130% of its pretreatment duration and is then longer than 500 ms; P waves disappear; or the patient develops significant tachycardia, symptomatic bradycardia, or hypotension. Suppression of Ventricular Arrhythmias Dosing regimens for the use of quinidine sulfate in suppressing life-threatening ventricular arrhythmias have not been adequately studied. Described regimens have generally been similar to the regimen described just above for the prophylaxis of symptomatic atrial fibrillation/flutter. Where possible, therapy should be guided by the results of programmed electrical stimulation and/or Holter monitoring with exercise.