Other anti-arrhythmic agents and cautions with disopyramide and quinidine
THE CONTEXT
These drugs have distinct roles in vagal bradycardia, supraventricular tachycardia and atrial fibrillation, with specific adverse effects and precautions.
Atropine and adenosine
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Atropine treats bradycardia and/or hypotension due to vagal overactivity. The intravenous dose is 0.6–3 mg. Adverse effects include dry mouth, thirst, blurred vision, and atrial and ventricular extrasystoles.
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Adenosine treats supraventricular tachycardia and aids diagnosis in unidentified tachycardia. Give 3 mg intravenously over 2 seconds, followed if necessary by 6 mg and then 12 mg at intervals of 1–2 minutes.
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Adenosine can cause flushing, dyspnoea and chest pain, and should be avoided in asthma.
Digoxin and sotalol
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Digoxin is used for rate control in atrial fibrillation. The intravenous loading dose totals 0.5–1 mg: 0.5 mg over 30 minutes, followed by 0.25–0.5 mg after 4–6 hours.
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The listed oral digoxin regimen is 0.5 mg repeated after 6 hours, followed by 0.0625–0.25 mg daily. Adverse effects include gastrointestinal disturbance, xanthopsia and arrhythmias.
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Sotalol also has class II activity as a β-blocker.
Disopyramide and quinidine
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Disopyramide causes anticholinergic adverse effects, including urinary retention, and can precipitate glaucoma. It can depress myocardial function and should be avoided in cardiac failure.
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Quinidine prevents atrial fibrillation and is occasionally used in Brugada syndrome. It is strongly pro-arrhythmic and can cause gastrointestinal upset.