Bretylium tosylate has a unique mode of action. It concentrates in the terminal sympathetic neurons, causing transient release of stored norepinephrine (noradrenaline) before blocking further release. The effect is of a chemical sympathectomy which also gives rise to its major side-effect of hypotension. It is used in patients with ventricular tachycardia refractory to other antiarrhythmic drugs, although it is being superseded by amiodarone which causes significantly less hypotension. Bretylium also has a unique action in that it may cause chemical cardioversion of ventricular fibrillation or facilitate cardioversion of ventricular fibrillation refractory to d.c. cardioversion. It is administered as an intravenous bolus of 5 to 10 mg/kg in emergency situations but is preferably given as an infusion over 30 min which can be repeated at intervals of 1 to 2 h or followed by an infusion of 1 to 2 mg/min. The drug is excreted renally with a half-life of 8 h.
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