SIGMAXIN

What it is

Sigmaxin contains digoxin. Digoxin is a cardiac glycoside with molecular haemodynamic, neurohumoral and electrophysiological effects contributing to its efficacy in heart failure. The primary action of digoxin is to reversibly inhibit the alpha subunit of sodium-potassium adenosine triphosphatase, resulting in inhibition of sodium-potassium exchange and allowing calcium to accumulate in cardiac myocytes, which is responsible for the positive inotropic effect of digoxin or increase in force of contraction.

Approved indications

— Congestive heart failure. — Atrial fibrillation, because digoxin depresses conduction in the atrioventricular bundle, producing a slower ventricular beat. — Paroxysmal atrial tachycardia.

Dosing overview

Dosage of Sigmaxin must be adjusted individually for each patient and the suggested doses are intended only as a guide. A stable therapeutic blood and tissue level can be achieved if the drug is started on an appropriate maintenance dosage regimen, but 5 to 7 days will elapse before an optimal effect is achieved; if there is no clinical urgency, this approach is preferred for outpatient and domiciliary digitalisation. For ambulatory patients with normal renal function, adults and children over 10 years receive 250 microgram as a single daily dose or, when required, up to 500 microgram daily in divided doses. The elderly require smaller doses of Sigmaxin because impairment of renal function is common and the sensitivity of the myocardium to the drug is thought to be increased; a usual dose is 125 microgram daily. The distribution of Sigmaxin into body fat is poor; dosage in obesity should be based on lean bodyweight and not total bodyweight.

Key safety warnings

Concurrent use of diuretics with Sigmaxin can predispose patients to toxicity reactions, due to the electrolyte disturbances caused by diuretics, primarily hypokalaemia but also hypomagnesaemia and, with thiazides, hypercalcaemia; periodic electrolyte determinations must be performed in patients receiving Sigmaxin and a diuretic and corrective measures undertaken if required. Hypokalaemia and hypomagnesaemia increase the risk of digitalis toxicity, and hypokalaemia can result from drugs, dialysis, mechanical suction of gastrointestinal secretions, malnutrition, diarrhoea, prolonged vomiting, old age, and long standing heart failure. Administering Sigmaxin to a patient with thyroid disease requires care; initial and maintenance doses should be reduced when thyroid function is subnormal, hyperthyroid patients may be less sensitive and require larger doses, while hypothyroid patients may be more sensitive and require smaller doses. Increased sensitivity of the myocardium to the effects of Sigmaxin and increased risk of digitalis-induced arrhythmias occurs with ischaemic heart disease, acute myocardial infarction, acute myocarditis, myxoedema, or severe pulmonary disease. Renal function impairment reduces volume of distribution and excretion of Sigmaxin, hence possibility of toxicity; dosage reduction may be required. Patients receiving digoxin should have their serum electrolytes and renal function assessed periodically; the frequency of assessments will depend on the clinical setting. Hypoxia increases risk of toxicity to digoxin.

Contraindications

Sigmaxin is contraindicated in intermittent complete heart block or second degree atrioventricular block especially if there is a history of Stokes-Adams attacks; ventricular tachycardia and ventricular fibrillation; arrhythmias caused by cardiac glycoside intoxication; supraventricular arrhythmias associated with an accessory atrioventricular pathway, as in Wolff-Parkinson-White syndrome, unless the electrophysiological characteristics have been evaluated; hypertrophic obstructive cardiomyopathy, unless there is concomitant atrial fibrillation and heart failure but even then, caution should be exercised; and hypersensitivity to digoxin, other digitalis glycosides, or any other constituent.

PBS listing

No information regarding PBS listing is provided in the source documents.

Regulatory history

Sigmaxin digoxin 62.5 microgram tablet and Sigmaxin digoxin 250 microgram tablet blister pack were first listed on the ARTG on 29 July 2002.