Prazosin

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

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Synonyms / Brand Names: PRAZOSIN^®, MINPRESS^®

Overview

Prazosin, trade names Minipress® and Hypovase®, is a medication used to treat high blood pressure (hypertension). It belongs to the class of alpha-adrenergic blockers, which lower blood pressure by relaxing blood vessels. Specifically, prazosin is selective for the alpha-1 receptors on vascular smooth muscle. These receptors are responsible for the vasoconstrictive action of norepinephrine, which in turn raises blood pressure. By blocking these receptors, prazosin reduces blood pressure.

Other features which add to the therapeutic value of Prazosin

1) The drug is orally active.

2) Unlike other less selective alpha blockers, which also block presynaptic alpha-2 receptors, it doesn't prevent inhibition of noradrenaline release. uninhibited noradrenaline release causes increased reflex tachycardia through the sympathetic baroreflex response that increases cardiac output, prazosin has a minimal effect on cardiac function due to its alpha-1 receptor selectivity.

3) Prazosin is also useful in treating urinary hesitancy associated with prostatic hyperplasia by blocking alpha-1 receptors, which control constriction of both the prostate and ureters.

Side effects of prazosin include orthostatic hypotension, syncope, and nasal congestion. The orthostatic hypotension and syncope are associated with the body's poor ability to control blood pressure without active alpha-adrenergic receptors. Patients on prazosin should be told not to stand up too quickly, since their poor baroreflex may cause them to faint as all their blood rushes to their feet. The nasal congestion is due to dilation of vessels in the nasal mucosa. One phenomenon associated with prazosin is known as the "first dose response", in which the side effects of the drug, especially orthostatic hypotension, are especially pronounced after the first dose. Another Common Side effect of Prazosin(And Doxazosin) is Priapism.[2][3].

This medication has shown to be effective in treating severe nightmares in children, associated with PTSD symptoms.

Category

ِAlpha adrenergic blocker.

FDA Package Insert

MINIPRESS^®

Indications and Usage | Dosage and Administration | Dosage Forms and Strengths | Contraindications | Warnings and Precautions | Adverse Reactions | Drug Interactions | Use in Specific Populations | Overdosage | Description | Clinical Pharmacology | Nonclinical Toxicology | Clinical Studies | How Supplied/Storage and Handling | Patient Counseling Information | Labels and Packages

Mechanism of Action

The exact mechanism of the hypotensive action of prazosin is unknown. Prazosin causes a decrease in total peripheral resistance and was originally thought to have a direct relaxant action on vascular smooth muscle. Recent animal studies, however, have suggested that the vasodilator effect of prazosin is also related to blockade of postsynaptic alpha-adrenoceptors. The results of dog forelimb experiments demonstrate that the peripheral vasodilator effect of prazosin is confined mainly to the level of the resistance vessels (arterioles). Unlike conventional alpha-blockers, the antihypertensive action of prazosin is usually not accompanied by a reflex tachycardia. Tolerance has not been observed to develop in long term therapy.