Sotalol

Sotalol is a nonselective β-adrenoceptor antagonist which prolongs cardiac repolarisation independently of its antiadrenergic action (class III antiarrhythmic properties). The antiarrhythmic action of sotalol appears to arise predominantly from its class III properties, and the drug exhibits a broader antiarrhythmic profile than the conventional β-blockers. Sotalol is effective in controlling paroxysmal supraventricular tachycardias and the ventricular response to atrial fibrillation/flutter in Wolff-Parkinson- White syndrome, in maintaining sinus rhythm after cardioversion of atrial fibrillation/flutter, and in preventing initiation of supraventricular tachyarrhythmias following coronary artery bypass surgery. Sotalol shows promise in the control of nonmalignant and life-threatening ventricular arrhythmias, particularly those associated with ischaemic heart disease. It is effective in suppressing complex forms of ventricular ectopy, displaying superior antiectopic activity to propranolol and metoprolol. The acute efficacy of sotalol in preventing reinduction of sustained ventricular tachyarrhythmias and suppressing spontaneous episodes of these arrhythmias on Holter monitoring is translated into long term prophylactic efficacy against arrhythmia recurrence in approximately 55 to 85% of patients with refractory life-threatening ventricular arrhythmias. In addition, sotalol offers the advantage over the class I agents of reducing cardiac and all-cause mortality in the high risk population with life-threatening ventricular arrhythmias. The adverse effects of sotalol are primarily related to its β-blocking activity and its class III property of prolonging cardiac repolarisation. Sotalol is devoid of overt cardiodepressant activity in patients with mild or moderate left ventricular dysfunction. The overall arrhythmogenic potential is moderately low, but torsade de pointes may develop in conjunction with excessive prolongation of the QT interval due to bradycardia, hypokalaemia or high plasma concentrations of the drug. In summary, sotalol displays a broad spectrum of antiarrhythmic activity, is haemodynamically well tolerated, and confers a relatively low proarrhythmic risk. It is likely to prove particularly appropriate in the treatment and prophylaxis of life-threatening ventricular tachyarrhythmias. Sotalol is a nonselective, competitive β-adrenoceptor antagonist, devoid of intrinsic sympathomimetic or membrane-stabilising activity. It is unique among β-blockers in that it prolongs cardiac action potential duration and cardiac refractoriness without altering conduction velocity or the slope of phase 0 depolarisation (V̇max). This latter class III effect, which is attributable to potassium channel blockade, occurs in vitro at concentrations higher than those associated with β-blockade. In humans, the acute and chronic electrophysiological effects of intravenous (0.3 to 1.5 mg/kg) and oral (160 to 480 mg/day) sotalol can be attributed to a combination of β-blockade [as reflected in depression of sinus node function and slowing of atrioventricular (AV) nodal conduction] and class III activity (prolongation of atrial, AV nodal, accessory AV pathway and ventricular refractoriness, and ventricular repolarisation). At therapeutic dosages (160 to 480 mg/day), oral sotalol produces minimal QTc interval prolongation (⩽7%). Modest enhancement of the class III action of sotalol has, however, been noted on long term therapy. The effects of sotalol on cardiac repolarisation appear unrelated to its β-blocking action, since d-sotalol (which has 50-fold lower in vitro β-blocking potency than the l-isomer) is equally effective in prolonging action potential duration. Sotalol-induced prolongation of action potential duration tends to augment myocardial contractility in vitro, an effect which partly offsets the cardiodepressant effect of β-blockade. In humans, the pattern of haemodynamic effects of intravenous (0.125 to 2.0 mg/kg) and oral (160 to 1280 mg/day) sotalol differs from that of other β-blockers devoid of intrinsic sympathomimetic activity, comprising reductions in heart rate and systolic blood pressure, an increase in systemic vascular resistance, and minimal changes in cardiac output or left and right ventricular filling pressures. A reduction in left ventricular dP/dt in the absence of a concomitant decrease in preload following intravenous sotalol (0.1 to 0.5 mg/kg) is possibly indicative of intrinsic negative inotropy. While no significant deterioration in cardiac function has been noted on long term (⩽2 years) oral therapy with sotalol 320 to 640 mg/day in patients with mildly depressed left ventricular function, a marked cardiodepressant response to sotalol 320 to 640 mg/day has been observed in those with severely compromised left ventricular function and/or inadequate cardiac reserve. The oral bioavailability of sotalol approaches 100%, indicating negligible first-pass hepatic metabolism. Maximum plasma concentrations and area under the plasma concentration-time curve values are linearly related to oral dose over the range 80 to 640mg. The hydrophilic nature of the drug accounts for its low affinity for plasma proteins, limited tissue uptake and poor penetration of the blood-brain barrier. The volume of distribution following oral administration is 1.5 to 1.8 L/kg. Hepatic biotransformation of sotalol is limited, and no pharmacologically active metabolites have been identified. Elimination occurs predominantly via the renal route, with 75 to 90% of an oral or intravenous dose being recovered in the urine within 48 hours of administration. The plasma elimination half-life of sotalol is 6 to 15 hours on acute administration, and ranges from 10 to 18 hours at steady-state. The pharmacokinetic properties of sotalol are not significantly modified by obesity or hepatic impairment. Renal insufficiency is, however, a major cause of sotalol accumulation, and largely accounts for the observed reduction in plasma sotalol clearance in the elderly. The spectrum of antiarrhythmic activity of sotalol is wider than that of conventional β-blockers, and the drug is effective in suppressing both supraventricular and ventricular tachyarrhythmias. Under randomised, double-blind conditions, intravenous (1.0 to 1.5 mg/kg) and oral (320 mg/day) sotalol were highly effective in the acute termination and prophylaxis of spontaneous episodes of paroxysmal supraventricular tachycardias, particularly those with AV nodal or intra-atrial re-entrant mechanisms, but less effective against paroxysmal atrial fibrillation and flutter. By virtue of its effects on accessory AV pathways, sotalol slowed the ventricular response or converted to sinus rhythm re-entrant tachycardias and atrial fibrillation/flutter complicating the Wolff-Parkinson-White syndrome. Oral sotalol 80 to 1280 mg/day provided effective long term prophylaxis of recurrent paroxysmal supraventricular tachyarrhythmias: approximately 45 to 90% of patients remained free of recurrence of re-entrant tachycardia on prolonged (⩽47 months) therapy, while approximately 40 to 50% of patients remained in sinus rhythm at 6 months after cardioversion of atrial fibrillation. Sotalol 160 to 320 mg/day was as effective as quinidine 1200 mg/day in the long term prevention of recurrence of chronic atrial fibrillation after cardioversion, was better tolerated and, in the event of treatment failure, provided more effective control of the ventricular response. Acute postoperative administration of sotalol 120 to 240 mg/day significantly reduced the incidence of supraventricular tachyarrhythmias, especially atrial fibrillation, following coronary artery bypass graft surgery, proving more effective than metoprolol 150 mg/ day in this setting. Sotalol is effective in suppressing nonmalignant and life-threatening ventricular tachyarrhythmias, including ventricular fibrillation, particularly when associated with ischaemic heart disease. Sotalol 160 to 640 mg/day reduced ventricular ectopy, most notably higher grade ventricular arrhythmias (polymorphic and repetitive premature ventricular complexes, couplets and runs of nonsustained ventricular tachycardia); this action was maintained in the presence of mild left ventricular dysfunction and was sustained on long term (⩽2 years) therapy. The antiectopic action of sotalol 160 to 320 mg/day was superior to that of propranolol 120 to 240 mg/day and metoprolol 100 mg/day on short term (⩽4 weeks) administration to patients with frequent ventricular ectopy. Sotalol-induced suppression of ventricular ectopy appeared to be associated with a trend toward improved long term survival postmyocardial infarction. Oral sotalol 160 to 960 mg/day prevented reinduction of sustained ventricular tachycardia/fibrillation in 20 to 65% of patients with refractory life-threatening ventricular arrhythmias, and converted the ventricular tachycardia from a sustained to a nonsustained form in a further 5 to 27% of patients. A positive response to oral sotalol on acute electrophysiological testing or Holter monitoring appeared predictive of antiarrhythmic efficacy on long term therapy, with approximately 55 to 100% of initial responders remaining free of arrhythmia recurrence during long term (⩽6 years) follow-up. Additionally, the incidence of cardiac and all-cause mortality in patients with life-threatening ventricular tachyarrhythmias was significantly lower during long term treatment with sotalol than with class I agents. Sotalol 160 to 640 mg/day was of comparable efficacy to amiodarone 300 to 1200 mg/day in the long term (1 year) treatment of malignant ventricular arrhythmias. Analysis of pooled data from a total of 1288 patients with supraventricular or ventricular arrhythmias participating in 12 major controlled studies, indicates that the adverse effects of sotalol are essentially related to its β-adrenoceptor-blocking properties and its class III action of prolonging cardiac repolarisation. Dyspnoea, fatigue, bradycardia, asthenia and headache were the most common adverse effects of sotalol (≈ 10 to 20% of patients); aggravation of heart failure necessitated treatment withdrawal in 1.5% of patients. Factors predisposing to a deterioration in left ventricular function included a low baseline ejection fraction, and history of congestive heart failure, cardiomegaly or cardiomyopathy. The incidence of proarrhythmia possibly or probably attributable to sotalol treatment was 4.3%. Torsade de pointes, the most readily recognised drug-induced proarrhythmia, occurred in 1.9% of patients, and was frequently associated with an underlying history of life-threatening ventricular arrhythmia secondary to cardiomyopathy or myocardial infarction. Torsade de pointes has most commonly been reported in association with hypokalaemia, bradycardia or high plasma drug concentrations (e.g. as a consequence of over-dosage or renal failure) leading to excessive QT interval prolongation. Symptomatic cases of sotalol-induced torsade de pointes have generally been self-terminating or controlled by ventricular overdrive pacing or defibrillation, intravenous isoprenaline (isoproterenol) or magnesium sulphate infusion, or haemodialysis. Intravenous sotalol is well tolerated and effective in the treatment of arrhythmias at doses of approximately 1.0 to 2.0 mg/kg administered in conjunction with ECG and blood pressure monitoring. Oral dosages ranging from 160 to 480 mg/day are generally administered on a twice daily regimen. Dosage adjustment should not be performed more frequently than every 2 to 3 days, to a maximum of 480 mg/day. Although sotalol has been administered at oral dosages in excess of 480 mg/day, its safety at these higher dosages remains to be established. The concomitant use of sotalol with potassium-depleting diuretics requires caution, particularly in the absence of potassium supplementation, while concomitant therapy with drugs which prolong the QTc interval should be avoided. Caution is required in the use of sotalol in patients with markedly depressed left ventricular function or moderate to severe congestive heart failure. Sotalol dosing interval should be extended from the usual 12 hours to 24 to 48 hours in patients with impaired renal function, and in those with severe renal impairment sotalol dosage should be individualised.