RYTHMODAN

What it is

Rythmodan contains disopyramide 100 mg per capsule. Disopyramide is an antiarrhythmic of Class Ia type, acting as a sodium channel blocker with membrane stabilising effect.

Approved indications

— Management of documented ventricular arrhythmias, such as sustained ventricular tachycardia, which are judged to be life threatening.

Dosing overview

The recommended dosage in adults with normal hepatic and renal function is 300 to 800 mg daily, with treatment initiated at 400–600 mg per day and a final maintenance dose of 300–400 mg per day achieved by progressively reducing the starting dose. The daily dose must be administered as no less than 3 equal divided doses. For patients with severe renal insufficiency (creatinine clearance less than 40 mL/minute), the recommended dosage regimen is a 200 mg loading dose followed by a 100 mg maintenance dose given approximately every half-life. Dosage should be reduced by 25% in patients with hepatic impairment.

Key safety warnings

Disopyramide may cause or worsen congestive heart failure or produce severe hypotension as a consequence of its negative inotropic properties. Proarrhythmia and cardiac decompensation are a special risk associated with antiarrhythmic drugs in patients with structural heart disease, and treatment should be given under strict supervision with cardiac function monitored. Because of its anticholinergic properties, disopyramide should not be used in patients with urinary retention unless adequate overriding measures are taken, and males with benign prostatic hypertrophy or prostatic adenoma are at particular risk. Disopyramide should not be used in patients with glaucoma. There is a risk of paralytic ileus occurring, especially in the elderly, and when disopyramide is taken with other anticholinergic medications. Significant lowering of blood glucose values has been reported during disopyramide administration, and blood glucose levels should be monitored in aged or malnourished patients, diabetics, and patients with renal insufficiency. QT interval should be monitored, as prolongation of the QT interval and worsening of the arrhythmia may occur, and if a QT prolongation of greater than 20% is observed, the medicine should be discontinued. Serum potassium must be monitored as potassium abnormalities may induce arrhythmias, and potassium imbalance should be corrected before and during treatment.

Contraindications

Rythmodan is contraindicated in cardiogenic shock; second or third degree atrioventricular block if no pacemaker is present; bundle branch block associated with first degree atrioventricular block; double block such as left posterior or anterior hemiblock and right bundle branch block; pre-existing long QT; severe sinus node dysfunction; cardiac insufficiency unless secondary to cardiac arrhythmia; concomitant use with other antiarrhythmics or other medicines liable to provoke ventricular arrhythmias or torsades de pointes; and known hypersensitivity to disopyramide.

PBS listing

Rythmodan 100 mg capsule is listed on the PBS with a restriction type of restricted and an ex-manufacturer price of A$11.60.

Regulatory history

Rythmodan 100 mg and 150 mg capsules were first listed on the ARTG on 30 August 1991.