Propranolol
Pharmacology. Propranolol is a nonselective beta-adrenergic blocker that acts on beta1 receptors in the myocardium and beta2 receptors in the lung, vascular smooth muscle, and kidney. Within the myocardium, propranolol depresses the heart rate, conduction velocity, myocardial contractility, and automaticity. Although propranolol is effective orally, for toxicologic emergencies it usually is administered by the intravenous route. After intravenous injection, the onset of action is nearly immediate and the duration of effect is 10 minutes to 2 hours, depending on the cumulative dose. The drug is eliminated by hepatic metabolism, with a half-life of about 2–3 hours. Propranolol also has antagonistic properties at the serotonin (5-HT1A) receptor and has been used to treat serotonin syndrome with mixed success (anecdotal case reports).
Indications
To control excessive sinus tachycardia or ventricular arrhythmias caused by catecholamine excess (eg, theophylline or caffeine), sympathomimetic drug intoxication (eg, amphetamines, pseudoephedrine, or cocaine), excessive myocardial sensitivity (eg, chloral hydrate, freons, or chlorinated and other hydrocarbons), or thyrotoxicosis.
To control hypertension in patients with excessive beta1-mediated increases in heart rate and contractility; used in conjunction with a vasodilator (eg, phentolamine) in patients with mixed alpha- and beta-adrenergic hyperstimulation.
To raise diastolic blood pressure in patients with hypotension caused by excessive beta2-mediated vasodilation (eg, theophylline or metaproterenol).
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