Bretylol - General Information:Bretylol 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.
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Bretylol - Pharmacology:
Bretylol inhibits norepinephrine release by depressing adrenergic nerve terminal excitability. The mechanisms of the antifibrillatory and antiarrhythmic actions of bretylium are not established. In efforts to define these mechanisms, the following electrophysiologic actions of bretylium have been demonstrated in animal experiments: increase in ventricular fibrillation threshold, increase in action potential duration and effective refractory period without changes in heart rate, little effect on the rate of rise or amplitude of the cardiac action potential (Phase 0) or in resting membrane potential (Phase 4) in normal myocardium, decrease in the disparity in action potential duration between normal and infarcted regions, and increase in impulse formation and spontaneous firing rate of pacemaker tissue as well as increase ventricular conduction velocity.
Bretylol for patients
Hypotension: Administration of bretylium tosylate regularly results in postural hypotension, subjectively recognized by dizziness, light-headedness, vertigo or faintness. Some degree of hypotension is present in about 50% of patients while they are supine. Hypotension may occur at doses lower than those needed to suppress arrhythmias.
Patients should be kept in the supine position until tolerance to the hypotensive effect of bretylium develops. Tolerance occurs unpredictably but may be present after several days.
Patients over 65 years may be at increased risk of developing orthostatic hypotension, especially when the recommended rate of intravenous infusion is exceeded.
Hypotension with supine systolic pressure greater than 75 mm Hg need not be treated unless there are associated symptoms. If supine systolic pressure falls below 75 mm Hg, an infusion of dopamine or norepinephrine may be used to raise blood pressure. When catecholamines are administered, a dilute solution should be employed and blood pressure monitored dosely because the pressor effects of the catecholamines are enhanced by bretylium. Volume expansion with blood or plasma and correction of dehydration should be carried out where appropriate.
Transient hypertension and increased frequency of arrhythmias: Due to the initial release of norepinephrine from adrenergic postganglionic nerve terminals by bretylium, transient hypertension or increased frequency of premature ventricular contractions and other arrhythmias may occur in some patients.
Caution during use with digitalis glycosides: The initial release of norepinephrine caused by bretylium may aggravate digitalis toxicity. When a life-threatening cardiac arrhythmia occurs in a digitalized patient, bretylium should be used only if the etiology of the arrhythmia does not appear to be digitalis toxicity and other antiarrhythmic drugs are not effective. Simultaneous initiation of therapy with digitalis glycosides and bretylium should be avoided.
Patients with fixed cardiac output: In patients with fixed cardiac output (i.e., severe aortic stenosis or severe pulmonary hypertension) bretylium should be avoided since severe hypotension may result from a fall in peripheral resistance without a compensatory increase in cardiac output. If survival is threatened by the arrhythmia, bretylium tosylate may be used but vasoconstrictive catecholamines should be given promptly if severe hypotension occurs.
Hyperthermia: In a small number of patients, hyperthermia, characterized by temperature in excess of 106°F, has been reported in association with bretylium tosylate administration. Temperature rise can begin within one hour or later after administration of drug, and reach a peak within 1 to 3 days. If hyperthermia is suspected or diagnosed, bretylium should be discontinued and appropriate treatment instituted immediately.
Digitalis toxicity may be aggravated by the initial release of norepinephrine caused by Bretylium Tosylate Injection.
The pressor effects of catecholamines such as dopamine or norepinephrine are enhanced by Bretylium Tosylate. When catecholamines are administered, dilute solutions should be used and blood pressure should be monitored closely.
Although there is little published information on concomitant administration of lidocaine and Bretylium Tosylate, these drugs are often administered concurrently without any evidence of interactions resulting in adverse effects or diminished efficacy.
There are no contraindications to use in treatment of ventricular fibrillation or life-threatening refractory ventricular arrhythmias.
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