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Prazosin: Wikis


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Systematic (IUPAC) name
CAS number 19216-56-9
ATC code C02CA01
PubChem 4893
DrugBank APRD00020
ChemSpider 4724
Chemical data
Formula C19H21N5O4 
Mol. mass 383.401 g/mol
Pharmacokinetic data
Bioavailability ~60%
Protein binding 97%
Half life 2–3 hours
Therapeutic considerations
Pregnancy cat.  ?
Legal status POM (UK)
Routes Oral
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Prazosin, trade names Minipress,Vasoflex and Hypovase, is a sympatholytic drug 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 would normally raise blood pressure. By blocking these receptors, prazosin reduces blood pressure.



Prazosin is orally active and has a minimal effect on cardiac function due to its alpha-1 receptor selectivity. However, when prazosin is initially started, heart rate and contractility go up in order to maintain the pre-treatment blood pressures. This is because the body has reached homeostasis at this abnormally high blood pressure. The blood pressure lowering effect is apparent however when prazosin is taken for longer periods of time. The heart rate and contractility go back down over time and blood pressure decreases.

The antihypertensive characteristics of prazosin make it a second-line choice for the treatment of high blood pressure.[1]

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. Although not a first line choice for either hypertension or prostatic hyperplasia, it is a choice for patients who present with both problems concomitantly.[1]

This medication has shown to be effective in treating severe nightmares in children, associated with PTSD symptoms.[2] Also veterans have been treated successfully at the Oregon VA for sleep disturbance related to PTSD. Doses are lower for this purpose than for control of blood pressure.[2]

Side effects

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 and fainting, are especially pronounced after the first dose.

Another common side effect of prazosin (and doxazosin) is priapism.[3][4]

Prazosin in management of PTSD

Prazosin has been reported to be useful in management of nightmares in military personnel suffering from post-combat stresses. It remains uncertain how effective prazosin may be in treating other aspects of PTSD (posttraumatic stress disorder).[5]

Prazosin in scorpion stings

Since 1983 prazosin has revolutionized the management of severe scorpion stings.[6]


  1. ^ a b Shen, Howard (2008). Illustrated Pharmacology Memory Cards: PharMnemonics. Minireview. p. 13. ISBN 1-59541-101-1. 
  2. ^ a b Department of Veteran Affairs (March 30, 2008). "Drug Helps PTSD Nightmares". Press release. Retrieved 2009-03-16. 
  3. ^ Bhalla AK, Hoffbrand BI, Phatak PS, Reuben SR (October 1979). "Prazosin and priapism". Br Med J 2 (6197): 1039. doi:10.1136/bmj.2.6197.1039. PMID 519276. 
  4. ^ Avisrror MU, Fernandez IA, Sánchez AS, García-Pando AC, Arias LM, del Pozo JG (January 2000). "Doxazosin and priapism". J. Urol. 163 (1): 238. doi:10.1016/S0022-5347(05)68018-4. PMID 10604360. 
  5. ^ "Blood pressure pill slays nightmares", Fontaine, Scott, Washington Post, December 31, 2009, downloaded 2009 December 31
  6. ^ Bawaskar HS, Bawaskar PH (January 2007). "Utility of scorpion antivenin vs prazosin in the management of severe Mesobuthus tamulus (Indian red scorpion) envenoming at rural setting". J Assoc Physicians India 55: 14–21. PMID 17444339. 
  5. Department of Veteran Affairs (March 30, 2008). "Drug Helps PTSD Nightmares". Press release. Retrieved 2009-03-16.

Department of Veteran Affairs (March 30, 2008). "Drug Helps PTSD Nightmares". Press release. Retrieved 2009-03-16. 

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