Isorythm L.P. (Disopyramide Phosphate)

Disopyramide is a Class Ia antiarrhythmic that acts on cardiac electrical activity to treat several arrhythmic conditions.

• Ventricular arrhythmias: reduces the frequency and severity of ventricular premature beats and tachycardia.
• Atrial fibrillation: helps restore sinus rhythm and control ventricular response in persistent AF.
• Ventricular premature complexes: suppresses symptomatic ectopic ventricular activity.

• Disopyramide phosphate blocks fast sodium channels in cardiac myocytes, slowing phase 0 depolarization and prolonging the action potential duration. This lengthens the refractory period of myocardial tissue, decreasing the likelihood of premature impulses and stabilising abnormal conduction pathways. The drug also exhibits anticholinergic properties that may contribute to its electrophysiological effects.

Disopyramide may be associated with a range of adverse reactions, varying from mild to serious.

Common Side Effects

• Dry mouth: reduced salivary secretion causing discomfort.
• Constipation: slowed gastrointestinal motility.
• Blurred vision: transient visual disturbances.
• Dizziness: light‑headed sensation, especially on standing.

Serious or Rare Side Effects

• Proarrhythmia: new or worsening arrhythmias, including torsades de pointes.
• Severe hypotension: marked drop in blood pressure leading to syncope.
• Heart block: atrioventricular conduction delay or complete block.

When prescribing disopyramide, clinicians should observe several precautionary measures to minimise risk.

• Cardiac monitoring: perform baseline and periodic ECG to detect QT prolongation or new arrhythmias.
• Electrolyte balance: correct hypokalemia or hypomagnesemia before initiation.
• Renal/hepatic impairment: assess function and adjust dose if necessary.
• Concomitant drugs: review for interactions with other antiarrhythmics or CYP3A4 inhibitors.
• Store at room temperature: keep below 25 °C in the original container, protect from moisture and light.

Disopyramide interacts with several medicines; awareness of the interaction level guides clinical decisions.

Major Interactions (Avoid)

• Quinidine: additive antiarrhythmic effect may precipitate severe arrhythmias.
• Amiodarone: combined sodium channel blockade increases risk of proarrhythmia.
• Strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole): raise disopyramide plasma levels, heightening toxicity.

Moderate Interactions (Monitor Closely)

• Digoxin: may enhance vagal effects, requiring serum level monitoring.
• Warfarin: potential alteration of anticoagulant effect, monitor INR.
• Diuretics that cause electrolyte loss: monitor potassium and magnesium to avoid arrhythmia exacerbation.