Molecule

Drug Groups

approved

Description

Bretylium blocks the release of noradrenaline from the peripheral sympathetic nervous system, and is used in emergency medicine, cardiology, and other specialties for the acute management of ventricular tachycardia and ventricular fibrillation. The primary mode of action for bretylium is thought to be inhibition of voltage-gated K(+) channels. Recent evidence has shown that bretylium may also inhibit the Na,K-ATPase by binding to the extracellular K-site.

Indication

For use in the prophylaxis and therapy of ventricular fibrillation. Also used in the treatment of life-threatening ventricular arrhythmias, such as ventricular tachycardia, that have failed to respond to adequate doses of a first-line antiarrhythmic agent, such as lidocaine.

Pharmacology

Bretylium is a bromobenzyl quaternary ammonium compound which selectively accumulates in sympathetic ganglia and their postganglionic adrenergic neurons where it inhibits norepinephrine release by depressing adrenergic nerve terminal excitability. Bretylium also suppresses ventricular fibrillation and ventricular arrhythmias.

Toxicity

Oral, mouse: LD₅₀ = 400 mg/kg. In the presence of life-threatening arrhythmias, underdosing with bretylium probably presents a greater risk to the patient than potential overdosage. However, one case of accidental overdose has been reported in which a rapidly injected intravenous bolus of 30 mg/kg was given instead of an intended 10 mg/kg dose during an episode of ventricular tachycardia. Marked hypertension resulted, followed by protracted refractory hypotension. The patient expired 18 hours later in asystole, complicated by renal failure and aspiration pneumonitis. Bretylium serum levels were 8000 ng/mL.

Affected Organisms

Biotransformation

No metabolites have been identified following administration in man and laboratory animals.

Half Life

The terminal half-life in four normal volunteers averaged 7.8±0.6 hours (range 6.9-8.1). During hemodialysis, this patient's arterial and venous bretylium concentrations declined rapidly, resulting in a half-life of 13 hours.

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