disopyramide phosphate: clinical use

Prescribing considerations

• Balance symptomatic benefit against proarrhythmia, particularly in structural heart disease.
• Negative inotropy can precipitate or worsen cardiac failure; life-threatening or haemodynamically significant arrhythmias should be initiated under hospital supervision.
• Review glaucoma risk, prostatic enlargement, constipation, myasthenia gravis, cognitive vulnerability and anticholinergic burden.
• Consider increased hypoglycaemia risk in older or malnourished people, those with diabetes and patients with cardiac failure.

Contraindications and cautions

• Hypersensitivity to disopyramide or an excipient
• Unpaced second- or third-degree atrioventricular block, specified conduction blocks, severe sinus-node dysfunction or pre-existing long-QT syndrome
• Severe heart failure unless secondary to the arrhythmia
• Concomitant antiarrhythmics or other medicines liable to provoke ventricular arrhythmias
• Renal or hepatic impairment with the selected prolonged-release formulation
• Use in children with the selected prolonged-release formulation

Monitoring

• Baseline and follow-up ECG, including QT interval and QRS duration
• Serum potassium, especially with potassium-lowering medicines
• Blood glucose throughout treatment, with closer attention in higher-risk patients
• Assessment for hypotension, heart failure, new arrhythmia and conduction block
• Consider intraocular-pressure assessment with a personal or family history of glaucoma

Clinical pharmacology

A class Ia sodium-channel blocker that slows cardiac conduction and increases atrial and ventricular effective refractory periods. It also has negative inotropic and anticholinergic activity and is probably metabolised through CYP3A.

Formulation and product differences

• The selected product is a prolonged-release matrix tablet designed for gradual release.
• It should be swallowed and not crushed or chewed.
• It contains sucrose and anhydrous glucose and is unsuitable for certain rare inherited sugar-intolerance disorders.
• The prolonged-release formulation is contraindicated in renal impairment, hepatic impairment and children.

Modified-release tablet

Route: Oral

Strengths: 250 mg