prazosin

[P(IPE)RAZ(INE) + perhaps alteration of OX(Y)- + (quinazol)in(e), one of its constituents.]

Brand names: Minipress®

Chemical formula:

Drug Forms:
• Prazosin capsules (below)
• Prazosin Hydrochloride Oral capsule

Español:
• Cápsulas de prazosín
• Prazosín Clorhidrato, Cápsula oral

Prazosin capsules

What are prazosin capsules?

PRAZOSIN (Minipress®) is an antihypertensive. Prazosin lowers, but does not cure, high blood pressure. It works by relaxing the blood vessels. Prazosin is sometimes used for prostate problems. Generic prazosin capsules are available.

What should I tell my health care provider before I take this medicine?

They need to know if you have any of the following conditions:
• angina
• kidney disease
• an unusual or allergic reaction to prazosin, other medicines, foods, dyes, or preservatives
• pregnant or trying to get pregnant
• breast-feeding

How should I take this medicine?

Take prazosin capsules by mouth. Follow the directions on the prescription label. Swallow the capsules with a drink of water. Taking the capsules with food can help to reduce side effects. Take your doses at regular intervals. Do not take your medicine more often than directed. Do not stop taking except on your prescriber's advice.

Contact your pediatrician or health care professional regarding the use of this medicine in children. Special care may be needed.

What if I miss a dose?

What drug(s) may interact with prazosin?

Do not take prazosin if you are taking the following medications:
• other alpha-blockers such as alfuzosin, doxazosin, phentolamine, phenoxybenzamine, tamsulosin, terazosin

Prazosin may also interact with the following medications:
• medicines for colds and breathing difficulties
• medicines for high blood pressure
• monoamine oxidase inhibitors (Azilect®, Eldepryl®, Emsam®, Marplan®, Nardil®, Parnate®, Zelapar™)
• sildenafil (doses of sildenafil higher than 25 mg should be taken at least 4 hours apart from taking prazosin)
• tadalafil
• vardenafil
• water pills

Tell your prescriber or health care professional about all other medicines you are taking, including nonprescription medicines, nutritional supplements, or herbal products. Also tell your prescriber or health care professional if you are a frequent user of drinks with caffeine or alcohol, if you smoke, or if you use illegal drugs. These may affect the way your medicine works. Check with your prescriber or health care professional before stopping or starting any of your medicines.

What should I watch for while taking prazosin?

Check your blood pressure regularly. Ask your prescriber or health care professional what your blood pressure should be and when you should contact him or her.

You may feel drowsy or dizzy. Do not drive, use machinery, or do anything that requires mental alertness until you know how prazosin affects you. To reduce the risk of dizzy or fainting spells, do not sit or stand up quickly. Avoid alcoholic drinks; they can make you more drowsy, and can increase flushing and rapid heartbeats. Taking initial doses of prazosin at bedtime can lessen the effects of drowsiness and dizziness, but be careful if you have to get up during the night. Drowsiness and dizziness are more likely to occur after the first dose, after an increase in dose, or during hot weather or exercise. These effects can decrease once your body adjusts to this medicine.

Although extremely rare in men taking prazosin, contact you health care provider immediately if you experience prolonged and painful erection of the penis which is unrelated to sexual activity (priapism). If not brought to immediate medical attention, priapism can lead to permanent erectile dysfunction (impotence).

Your mouth may get dry. Chewing sugarless gum or sucking hard candy, and drinking plenty of water, will help.

Do not take nonprescription medicine for weight-loss without asking your prescriber or health care professional. Also, do not take cough and cold, hay fever or sinus medications without asking your prescriber or health care professional.

If you are going to have surgery, tell your prescriber or health care professional that you are taking prazosin.

What side effects may I notice from taking prazosin?

Side effects that you should report to your prescriber or health care professional as soon as possible:
Rare or uncommon:
• difficulty breathing, shortness of breath
• prolonged painful erection of the penis (priapism)
More common:
• blurred vision
• fainting spells, lightheadedness
• irregular heartbeat, palpitations or chest pain
• mental depression
• swelling of the legs and ankles
• vomiting

Side effects that usually do not require medical attention (report to your prescriber or health care professional if they continue or are bothersome):
• constipation or diarrhea
• drowsiness or dizziness
• dry mouth
• headache
• nausea
• sexual difficulties (impotence)
• stomach pain
• unusual weakness or tiredness

Where can I keep my medicine?

Keep out of the reach of children in a container that small children cannot open.

Store at room temperature between 15 and 30 degrees C (59 and 86 degrees F). Protect from light. Keep container tightly closed. Throw away any unused medicine after the expiration date.

Last updated: 7/1/2002

Important Disclaimer: The drug information provided here is for educational purposes only. It is intended to supplement, not substitute for, the diagnosis, treatment and advice of a medical professional. This drug information does not cover all possible uses, precautions, side effects and interactions. It should not be construed to indicate that this or any drug is safe for you. Consult your medical professional for guidance before using any prescription or over the counter drugs.

A postsynaptic α-adrenergic receptor blocker that acts as a peripheral vasodilator; used as the hydrochloride salt in the treatment of congestive heart failure.

Prazosin

Systematic (IUPAC) name
2-[4-(2-furoyl)piperazin-1-yl]-6,7-dimethoxyquinazolin-4-amine
Identifiers
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%
Metabolism	?
Half life	2–3 hours
Excretion	?
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.

Contents 1 Use 2 Side effects 3 Prazosin in scorpion stings 4 References

Use

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 scorpion stings

Since 1983 prazosin has revolutionized the management of severe scorpion stings.^[5]

References

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. http://www.research.va.gov/news/press_releases/ptsd-033007.cfm. 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. http://linkinghub.elsevier.com/retrieve/pii/S0022-5347(05)68018-4. 
5. ^ 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. http://www.research.va.gov/news/press_releases/ptsd-033007.cfm. Retrieved 2009-03-16. 

v • d • e Sympatholytic (and closely related) antihypertensives (C02) Sympatholytics (antagonize α-adrenergic vasoconstriction) Central α2 agonist Clonidine • Guanfacine • Methyldopa # Guanidine derivatives: Betanidine • Guanethidine • Guanoxan • Debrisoquine • Guanoclor • Guanazodine • Guanoxabenz Imidazoline receptor agonist Moxonidine • Rilmenidine Ganglion-blocking/nicotinic antagonist Mecamylamine • Trimethaphan Peripheral Indirect MAOI Pargyline Adrenergic uptake inhibitor Rescinnamine • Reserpine Tyrosine hydroxylase inhibitor Metirosine Direct α1 blockers Prazosin • Indoramin • Trimazosin • Doxazosin • Urapidil Non-selective α blocker Phentolamine Other antagonists Serotonin antagonist Ketanserin Endothelin antagonist (for PH) dual (Bosentan) • selective (Ambrisentan, Sitaxentan) #WHO-EM. ‡Withdrawn from market. CLINICAL TRIALS: †Phase III. §Never to phase III

v • d • e Adrenergics Receptor Ligands α α1 Agonists: Amidephrine • Cirazoline • Dopamine • Epinephrine (Adrenaline) • Etilefrine • Isoprenaline • Levonordefrin • Metaraminol • Methoxamine • Methyldopa • Norepinephrine (Noradrenaline) • Oxymetazoline • Phenylephrine Antagonists: Alfuzosin • Arotinolol • Carvedilol • Doxazosin • Indoramin • L-765,314 • Labetalol • Moxisylyte • Nantenine • Phentolamine • Phenoxybenzamine • Prazosin • Silodosin • Tamsulosin • Terazosin • Tolazoline • Trimazosin • Urapidil α2 Agonists: (R)-3-Nitrobiphenyline • 4-NEMD • Amitraz • Apraclonidine • Brimonidine • Clonidine • Detomidine • Dexmedetomidine • Dopamine • Epinephrine (Adrenaline) • Etilefrine • Guanabenz • Guanfacine • Guanethidine • Guanoxabenz • Levonordefrin • Lofexidine • Medetomidine • Methyldopa • Norepinephrine (Noradrenaline) • Octopamine • Romifidine • Tizanidine • Tolonidine • Xylazine • Xylometazoline Antagonists: 1-PP • Atipamezole • BRL-44408 • Buspirone • Cirazoline • Efaroxan • Gepirone • Idazoxan • Ipsapirone • Mianserin • Mirtazapine • NAN-190 • Phentolamine • Phenoxybenzamine • Rauwolscine • SB-269,970 • Setiptiline • Spiroxatrine • Tandospirone • Tolazoline • Yohimbine α? Agonists: Anisodamine • Ephedrine • Ergotamine • Indanidine • Mephentermine • Midodrine • Mivazerol • Naphazoline • Phenylpropanolamine • Pseudoephedrine • Rilmenidine • Synephrine • Talipexole • Tetrahydrozoline β β1 Agonists: Denopamine • Dobutamine • Dopamine • Epinephrine (Adrenaline) • Etilefrine • Levonordefrin • Methyldopa • Norepinephrine (Noradrenaline) Antagonists: Acebutolol • Alprenolol • Amosulalol • Arotinolol • Atenolol • Bupranolol • Carvedilol • Celiprolol • Betaxolol • Bisoprolol • Dichloroisoprenaline • Esmolol • Labetalol • Metipranolol • Metoprolol • Nadolol • Nebivolol • Oxprenolol • Penbutolol • Pindolol • Practolol • Pronethalol • Propranolol • Sotalol • Tertatolol • Timolol • Tilisolol • Xamoterol β2 Agonists: Arformoterol • Bambuterol • Bitolterol • Carbuterol • Clenbuterol • Dopamine • Dopexamine • Epinephrine (Adrenaline) • Etilefrine • Fenoterol • Formoterol • Hexoprenaline • Indacaterol • Levonordefrin • Levosalbutamol • Methyldopa • Norepinephrine (Noradrenaline) • Orciprenaline • Pirbuterol • Procaterol • Reproterol • Rimiterol • Ritodrine • Salbutamol (Albuterol) • Salmeterol • Terbutaline • Tulobuterol Antagonists: Alprenolol • Amosulalol • Arotinolol • Bupranolol • Butaxamine • Carvedilol • Dichloroisoprenaline • ICI 118551 • Labetalol • Metipranolol • Nadolol • Oxprenolol • Penbutolol • Pindolol • Pronethalol • Propranolol • Sotalol • Tertatolol • Timolol • Tilisolol β3 Agonists: Amibegron • Arotinolol • Dopamine • Epinephrine (Adrenaline) • Etilefrine • Labetalol • Levonordefrin • Methyldopa • Norepinephrine (Noradrenaline) • Solabegron Antagonists: Carvedilol • SR 59230A β? Agonists: Arbutamine • BAAM • Befunolol • Broxaterol • Buphenine • Cimaterol • Ephedrine • Higenamine • Isoetarine • Isoxsuprine • Mabuterol • Methoxyphenamine • Oxyfedrine • Prenalterol • Pseudoephedrine • Ractopamine • Tretoquinol • Zilpaterol • Zinterol Reuptake Inhibitors Plasmalemmal NET Inhibitors Norepinephrine Reuptake Inhibitors: Atomoxetine (Tomoxetine) • Ciclazindol • Mazindol • Nisoxetine • Reboxetine • Tandamine • Tapentadol • Viloxazine; Norepinephrine-Dopamine Reuptake Inhibitors: Amineptine • Bupropion (Amfebutamone) • Fencamine • Fencamfamine • Lefetamine • LR-5182 • Manifaxine • Methylphenidate • Nomifensine • O-2172 • Radafaxine; Serotonin-Norepinephrine Reuptake Inhibitors: Bicifadine • Desvenlafaxine • Duloxetine • Milnacipran • Sibutramine • Tramadol • Venlafaxine; Serotonin-Norepinephrine-Dopamine Reuptake Inhibitors: Brasofensine • Diclofensine • DOV-102,677 • DOV-21,947 • DOV-216,303 • JNJ-7925476 • JZ-IV-10 • Methylnaphthidate • Naphyrone • NS-2359 • PRC200-SS • SEP-225,289 • SEP-227,162 • Tesofensine; Tricyclic Antidepressants: Amitriptyline • Butriptyline • Cianopramine • Clomipramine • Desipramine • Dosulepin • Doxepin • Imipramine • Lofepramine • Nortriptyline • Protriptyline • Trimipramine; Tetracyclic Antidepressants: Amoxapine • Maprotiline • Mianserin • Oxaprotiline; Others: Cocaine • Nefazodone • Nefopam • Ziprasidone TRPC6 Activators Adhyperforin • Hyperforin Vesicular VMAT Inhibitors Ibogaine • Reserpine • Tetrabenazine Releasing Agents Oxazolines: 4-Methylaminorex (4-MAR, 4-MAX) • Aminorex • Clominorex • Cyclazodone • Fenozolone • Fluminorex • Pemoline • Thozalinone; Phenethylamines (also Amphetamines, Cathinones, Phentermines, etc): 2-Hydroxyphenethylamine (2-OH-PEA) • 4-Methylamphetamine (4-MA) • 4-Methylmethamphetamine (4-MMA) • Alfetamine • Amphetamine (Dextroamphetamine, Levoamphetamine) • Amphetaminil • Amfepentorex • β-Methylphenethylamine (β-Me-PEA) • Benzodioxolylbutanamine (BDB) • Benzodioxolylhydroxybutanamine (BOH) • Benzphetamine • Buphedrone • Butylone • Cathine • Cathinone • Clobenzorex • Clortermine • Diethylcathinone (Diethylpropion, Amfepramone) • Dimethoxyamphetamine (DMA) • Dimethoxymethamphetamine (DMMA) • Dimethylamphetamine • Dimethylcathinone (Dimethylpropion, Metamfepramone) • Ephedrine (EPH) • Ethcathinone (Ethylpropion) • Ethylamphetamine • Ethylbenzodioxolylbutanamine (EBDB) • Ethylone • Fenethylline • Fenproporex • Flephedrone • Fludorex • Furfenorex • Hordenine • Indanorex • Indanylamphetamine (IAP) • Lisdexamfetamine • Lophophine (Homomyristicylamine) • Mefenorex • Mephedrone • Mephentermine • Methamphetamine (Desoxyephedrine, Methedrine; Dextromethamphetamine, Levomethamphetamine) • Methcathinone (Methylpropion) • Methedrone • Methoxymethylenedioxyamphetamine (MMDA) • Methoxymethylenedioxymethamphetamine (MMDMA) • Methylbenzodioxolylbutanamine (MBDB) • Methylenedioxyamphetamine (MDA; Tenamfetamine) • Methylenedioxyethylamphetamine (MDEA) • Methylenedioxyhydroxyamphetamine (MDOH) • Methylenedioxymethamphetamine (MDMA) • Methylenedioxymethylphenethylamine (MDMPEA; Homarylamine) • Methylenedioxyphenethylamine (MDPEA; Homopiperonylamine) • Methylone • Naphthylamphetamine (NAP) • Ortetamine • Oxaflozane • Parabromoamphetamine (PBA) • Parachloroamphetamine (PCA) • Parafluoroamphetamine (PFA) • Parafluoromethamphetamine (PFMA) • Parahydroxyamphetamine (PHA) • Paraiodoamphetamine (PIA) • Paramethoxyamphetamine (PMA) • Paramethoxyethylamphetamine (PMEA) • Paramethoxymethamphetamine (PMMA) • Paredrine (Norpholedrine, Oxamphetamine) • Phendimetrazine • Phenethylamine (PEA) • Phenmetrazine • Pholedrine • Phenpentermine • Phenpromethamine • Phentermine • Phenylpropanolamine (PPA) • Propylamphetamine • Pseudoephedrine (PSE) • Tiflorex (Flutiorex) • Tyramine (TRA) • Xylopropamine • Zylofuramine; Piperazines: 2,5-Dimethoxy-4-bromobenzylpiperazine (2C-B-BZP) • Benzylpiperazine (BZP) • Methoxyphenylpiperazine (MeOPP; Paraperazine) • Methylbenzylpiperazine (MBZP) • Methylenedioxybenzylpiperazine (MDBZP; Piperonylpiperazine) • Parafluorophenylpiperazine (pFPP; Fluoperazine); Others: 2-Aminoindane (2-AI) • 2-Aminotetralin (2-AT) • 2-Benzylpiperidine (2-BP) • 4-Benzylpiperidine (4-BP) • Clofenciclan • Cyclopentamine • Cypenamine • Cyprodenate • Feprosidnine • Gilutensin • Heptaminol • Hexacyclonate • Isometheptene • Methylhexanamine • Octodrine • Phthalimidopropiophenone • Propylhexedrine (PHX) • Tuaminoheptane (Tuamine) Enzyme Inhibitors Anabolism PAH Inhibitors 3,4-Dihydroxystyrene TH Inhibitors 3-Iodotyrosine • Aquayamycin • Bulbocapnine • Metirosine • Oudenone AAAD Inhibitors Benserazide • Carbidopa DBH Inhibitors Disulfiram • Nepicastat • Tropolone PNMT Inhibitors CGS-19281A • SKF-64139 • SKF-7698 Catabolism MAO Inhibitors Nonselective: Etryptamine • Furazolidone • Hydralazine • Iproclozide • Iproniazid • Isocarboxazid • Isoniazid • Linezolid • Mebanazine • Metryptamine • Nialamide • Phenelzine • Pheniprazine • Phenoxypropazine • Pivalylbenzhydrazine • Procarbazine • Safrazine • Tranylcypromine; MAO-A Selective: Befloxatone • Brofaromine • Cimoxatone • Clorgiline • Harmala Alkaloids (Harmine, Harmaline, Tetrahydroharmine, etc) • Minaprine • Moclobemide • Pirlindole • Toloxatone • Tyrima; MAO-B Selective: Lazabemide • Pargyline • Rasagiline • Selegiline * Note that MAO-B inhibitors also influence norepinephrine/epinephrine levels since they inhibit the breakdown of their precursor dopamine. COMT Inhibitors Entacapone • Tolcapone Others Precursors L-Phenylalanine → L-Tyrosine → L-DOPA (Levodopa) → Dopamine • L-DOPS (Droxidopa) Cofactors Ferrous Iron (Fe2+) • S-Adenosyl-L-Methionine • Vitamin B3 (Niacin, Nicotinamide → NADPH) • Vitamin B6 (Pyridoxine, Pyridoxamine, Pyridoxal → Pyridoxal Phosphate) • Vitamin B9 (Folic Acid → Tetrahydrofolic Acid) • Vitamin C (Ascorbic Acid) • Zinc (Zn2+) Others Activity Enhancers: Benzofuranylpropylaminopentane (BPAP) • Phenylpropylaminopentane (PPAP); Release Blockers: Bretylium • Guanethidine

Department of Veteran Affairs (March 30, 2008). "Drug Helps PTSD Nightmares". Press release. http://www.research.va.gov/news/press_releases/ptsd-033007.cfm. Retrieved 2009-03-16. 

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