• Sotalol prolongs the QT interval, and only specialists should co-prescribe drugs that prolong the QT interval. This is because of the risk of additive effects, which may lead to serious and potentially life-threatening torsades de pointes arrhythmias. Examples of drugs that are known to have a high risk of causing QT prolongation include:
• Antiarrhythmics, such as amiodarone, disopyramide, and quinidine.
• Antipsychotics, such as amisulpride, haloperidol, and droperidol.
• Antibiotics, such as erythromycin and clarithromycin.
• In addition, sotalol may interact with other drugs (in common with other beta-blockers).
• Verapamil and diltiazem
• The combination of a beta-blocker and verapamil should not be prescribed in primary care because bradycardia, asystole, severe hypotension, and heart failure can occur.
• The combination of a beta-blocker and diltiazem should not be prescribed in primary care because bradycardia and atrioventricular block can occur. Asystole and sudden death have also been reported.
• Combining a beta-blocker with either verapamil or diltiazem may be initiated in secondary care.
• Class I antiarrhythmics (for example quinidine and flecainide)
• The combination of a beta-blocker and a class I antiarrhythmic is not recommended in primary care because bradycardia and myocardial depression can occur. This combination may be initiated in secondary care.
• Class III antiarrhythmics (for example amiodarone)
• The combination of a beta-blocker and amiodarone should be prescribed with caution — monitor pulse and blood pressure and check for signs of worsening heart failure, as there is an increased risk of bradycardia, atrioventricular (AV) block, and myocardial depression.
• Digoxin
• Concomitant administration of a beta-blocker and digoxin can reduce heart rate and prolong AV conduction time, increasing the risk of AV block and bradycardia — monitor pulse carefully.
• Other drugs that reduce blood pressure (for example angiotensin-converting enzyme inhibitors)
• An additive hypotensive effect may occur — monitor for signs of hypotension (such as dizziness, light-headedness, and confusion).

These recommendations are based on the manufacturer's Summary of Product Characteristics [ABPI Medicines Compendium, 2007c; ABPI Medicines Compendium, 2007d; ABPI Medicines Compendium, 2007e; ABPI Medicines Compendium, 2010] and the British National Formulary [BNF 57, 2009].