Prazosin
Prazosin is an alpha-blocker that causes a decrease in total peripheral resistance and is used to treat hypertension.
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Summary

Prazosin is an alpha-blocker that causes a decrease in total peripheral resistance and is used to treat hypertension.

Brand Names

Minipress, Minizide

Generic Name

Prazosin

DrugBank Accession Number

DB00457

Background

Prazosin is a drug used to treat hypertension. Prazosin is marketed by Pfizer and was initially approved by the FDA in 1988.16 It belongs to the class of drugs known as alpha-1 antagonists.

Recently, many studies have evaluated the benefits of this drug in controlling the symptoms of post-traumatic stress disorder (PTSD) and associated nightmares.4,5,6

Type

Small Molecule

Groups

Approved

Structure

Weight

Average: 383.4011

Monoisotopic: 383.159354185

Chemical Formula

C19H21N5O4

Synonyms

1-(4-Amino-6,7-dimethoxy-2-quinazolinyl)-4-(2-furanylcarbonyl)piperazine

2-(4-(2-Furoyl)piperazin-1-yl)-4-amino-6,7-dimethoxyquinazoline

Prazosin

Prazosina

Prazosine

Prazosinum

External IDs

CP-122991

Indication

This drug is indicated for the treatment of hypertension (high blood pressure). Prazosin can be given alone or given with other blood pressure-lowering drugs, including diuretics or beta-adrenergic blocking agents Label.

Prazosin does not negatively impact lung function, and therefore may be used to manage hypertension in patients who are asthmatic or patients with chronic obstructive lung disease (COPD)8.

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Associated Conditions

Indication TypeIndicationCombined Product DetailsApproval LevelAge GroupPatient CharacteristicsDose FormTreatment ofAgitation••• •••••Symptomatic treatment ofBenign prostatic hyperplasia••• •••••Management ofHigh blood pressure (hypertension)•••••••••••••••••••Management ofHypertension••••••••••••Treatment ofHypertension (htn)••••••••••••

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Pharmacodynamics

Effects on blood pressure

The pharmacodynamic and therapeutic effect of this drug includes is a decrease in blood pressure as well as clinically significant decreases in cardiac output, heart rate, blood flow to the kidney, and glomerular filtration rate. The decrease in blood pressure may occur in both standing and supine positions Label.

Many of the above effects are due to vasodilation of blood vessels caused by prazosin, resulting in decreased peripheral resistance 7, Label. Peripheral resistance refers to the level resistance of the blood vessels to blood that flows through them. As the blood vessels constrict (narrow), the resistance increases and as they dilate (widen), and peripheral resistance decreases, lowering blood pressure 14,17.

Effects on sleep disturbance related to post-traumatic stress disorder (PTSD)

Some studies have suggested that this drug improves sleep in patients suffering from insomnia related to nightmares and post-traumatic stress disorder, caused by hyperarousal 5,6. This effect likely occurs through the inhibition of adrenergic stimulation found in states of hyperarousal 13.

Mechanism of action

Alpha-adrenergic receptors are essential for the regulation of blood pressure in humans. Two types of alpha receptors, alpha 1 and alpha 2, both play a role in regulating blood pressure. Alpha-1 receptors are postsynaptic (located after the nerve junction, or space between a nerve fiber and target tissue). In this case, the target tissue is the vascular smooth muscle 18. These receptors, when activated, increase blood pressure 9.

Prazosin inhibits the postsynaptic alpha-1 adrenoceptors. This inhibition blocks the vasoconstricting (narrowing) effect of catecholamines (epinephrine and norepinephrine) on the vessels, leading to peripheral blood vessel dilation. Through blood vessel constriction by adrenergic receptor activation, epinephrine and norepinephrine normally act to increase blood pressure 10.

TargetActionsOrganismAAlpha-1A adrenergic receptor

antagonist

HumansAAlpha-1B adrenergic receptor

antagonist

HumansAAlpha-1D adrenergic receptor

antagonist

HumansUPotassium voltage-gated channel subfamily H member 2

inhibitor

HumansUAlpha-2A adrenergic receptor

binder

HumansUAlpha-2B adrenergic receptor

binder

HumansUAlpha-1 adrenergic receptorsNot AvailableHumans

Absorption

After administration of an oral dose, peak plasma concentrations are attained at approximately 3 hours Label. There is a linear association between the prazosin dose given and plasma concentration at steady state 11.

Volume of distribution

About 0.6 L/kg 11.

Protein binding

Highly bound to proteins Label with 97% binding to albumin and alpha 1-acid glycoprotein 11. Prazosin is thought to be mostly (about 80-90%) bound to albumin 15.

Metabolism

In animals, prazosin hydrochloride is heavily metabolized. This occurs through liver demethylation and conjugation Label. Some studies in humans or human cells in vitro show similar prazosin metabolism 7,12.

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Prazosin

6-O-demethyl prazosin + 7-O-demethyl prazosin

Glucuronide conjugate

2,4-diamino-6,7-dimethoxyquinazoline + 2-(l-Piperazinyl)- 4-amino-6,7 - dimethoxyquinazoline

Route of elimination

This drug is mainly excreted in the bile and the feces Label.

Half-life

Clearance

Adverse Effects

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Toxicity

TDLO, LD50: Oral TDLO (human): 285 μg/kg; Oral TDLO (woman): 10 μg/kg MSDS.

Oral LD50 (rat): 1950 mg/kg; Intraperitoneal LD50 (rat): 102 mg/kg MSDS.

Overdose information

Accidental ingestion of at least 50 mg of prazosin by a two-year-old child led to severe drowsiness with depressed reflexes. There was no fall in blood pressure, and the child recovered without complication Label.

Use in pregnancy

There are no adequate and well-controlled studies determining the safety of prazosin use during pregnancy. It is considered a pregnancy category C drug. Prazosin should be used during pregnancy only in cases where the benefit outweighs the possible risk to the mother and fetus Label. In specific cases where blood pressure control was emergent during pregnancy, prazosin has been used and no effects on the fetus or neonate were reported Label.

Use in nursing

This drug is found excreted in small concentrations in human milk. This drug should be used with caution when used during nursing Label.

Pathways

Not Available

Pharmacogenomic Effects/ADRs

Not Available