Disopyramide

How it works

It blocks cardiac fast sodium channels to slow conduction and prolong the action potential, and additionally has marked anticholinergic and negative inotropic properties.

Prescribing in practice

• It prolongs the QT interval and can be pro-arrhythmic, including torsade de pointes, so avoid in significant QT prolongation and with other QT-prolonging drugs.
• Its negative inotropic effect means it should be avoided in heart failure and significant left ventricular dysfunction.
• Pronounced antimuscarinic effects can cause urinary retention, dry mouth and worsen glaucoma, so use cautiously where these are a concern.

Monitoring

Monitor the ECG including QT interval, with attention to heart failure symptoms and anticholinergic effects.

Counselling the patient

• Report palpitations, fainting or marked dizziness.
• Expect possible dry mouth, blurred vision or difficulty passing urine.
• Tell your clinician about other heart-rhythm or QT-affecting medicines.

Evidence & guidelines

Class Ia antiarrhythmics carry a recognised pro-arrhythmic risk, and use of these older agents has declined in line with safety evidence from antiarrhythmic outcome studies.