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Medication Safety Issues
Sound-alike/look-alike issues:
Prazosin may be confused with predniSONE
International issues:
Prazac® [Denmark] may be confused with Prozac® which is a brand name for fluoxetine in the U.S.
Prazepam [multiple international markets] may be confused with prazosin.
Pronunciation
(PRAZ oh sin )
U.S. Brand Names
Index Terms
Generic Available
Yes
Canadian Brand Names
Pharmacologic Category
Pharmacologic Category Synonyms
Use: Labeled Indications
Treatment of hypertension
Use: Unlabeled/Investigational
Post-traumatic stress disorder (PTSD); benign prostatic hyperplasia; Raynaud's syndrome
Pregnancy Risk Factor
C
Lactation
Excretion in breast milk unknown/use caution
Contraindications
Hypersensitivity to quinazolines (doxazosin, prazosin, terazosin) or any component of the formulation; concurrent use with phosphodiesterase-5 (PDE-5) inhibitors including sildenafil (>25 mg), tadalafil, or vardenafil
Warnings/Precautions
Concerns related to adverse effects:
• Angina: Discontinue if symptoms of angina occur or worsen.
• Orthostatic hypotension/syncope: May cause significant orthostatic hypotension and syncope, especially with first dose; anticipate a similar effect if therapy is interrupted for a few days, if dosage is rapidly increased, or if another antihypertensive drug (particularly vasodilators) or a PDE-5 inhibitor is introduced. Patients should be cautioned about performing hazardous tasks when starting new therapy or adjusting dosage upward.
Disease-related concerns:
• Prostate cancer: Should rule out prostatic carcinoma before beginning therapy.
Special populations:
• Pediatrics: Safety and efficacy have not been established in children.
Adverse Reactions
>10%: Central nervous system: Dizziness (10%)
1% to 10%:
Cardiovascular: Palpitation (5%), edema, orthostatic hypotension, syncope (1%)
Central nervous system: Headache (8%), drowsiness (8%), vertigo, depression, nervousness
Dermatologic: Rash (1% to 4%)
Endocrine & metabolic: Decreased energy (7%)
Gastrointestinal: Nausea (5%), vomiting, diarrhea, constipation
Genitourinary: Urinary frequency (1% to 5%)
Neuromuscular & skeletal: Weakness (7%)
Ocular: Blurred vision, reddened sclera, xerostomia
Respiratory: Dyspnea, epistaxis, nasal congestion
<1% (Limited to important or life-threatening): Abdominal discomfort, alopecia, angina, bradycardia, cataracts (both development and disappearance have been reported), hallucinations, impotence, incontinence, lichen planus, liver function abnormalities, MI, narcolepsy (worsened), pancreatitis, paresthesia, pigmentary mottling and serous retinopathy, priapism, pruritus, tachycardia, tinnitus
Postmarketing and/or case reports: Allergic reaction, cataplexy, enuresis, eye pain, gynecomastia, leukopenia, systemic lupus erythematosus, urticaria, vasculitis
Drug Interactions
Beta-Blockers: May enhance the orthostatic effect of Alpha1-Blockers. The risk associated with ophthalmic products is probably less than systemic products. Exceptions: Levobunolol; Metipranolol. Risk D: Consider therapy modification
Calcium Channel Blockers: Alpha1-Blockers may enhance the hypotensive effect of Calcium Channel Blockers. Risk C: Monitor therapy
Dabigatran Etexilate: P-Glycoprotein Inducers may decrease the serum concentration of Dabigatran Etexilate. Risk C: Monitor therapy
Diazoxide: May enhance the hypotensive effect of Antihypertensives. Risk C: Monitor therapy
Herbs (Hypertensive Properties): May diminish the antihypertensive effect of Antihypertensives. Risk C: Monitor therapy
Herbs (Hypotensive Properties): May enhance the hypotensive effect of Antihypertensives. Risk C: Monitor therapy
Methylphenidate: May diminish the antihypertensive effect of Antihypertensives. Risk C: Monitor therapy
P-Glycoprotein Substrates: P-Glycoprotein Inducers may decrease the serum concentration of P-Glycoprotein Substrates. P-glycoprotein inducers may also further limit the distribution of p-glycoprotein substrates to specific cells/tissues/organs where p-glycoprotein is present in large amounts (e.g., brain, T-lymphocytes, testes, etc.). Risk C: Monitor therapy
Phosphodiesterase 5 Inhibitors: May enhance the hypotensive effect of Alpha1-Blockers. Risk D: Consider therapy modification
Prostacyclin Analogues: May enhance the hypotensive effect of Antihypertensives. Risk C: Monitor therapy
RiTUXimab: Antihypertensives may enhance the hypotensive effect of RiTUXimab. Risk D: Consider therapy modification
Ethanol/Nutrition/Herb Interactions
Ethanol: Avoid ethanol (may increase vasodilation).
Food: Food has variable effects on absorption.
Herb/Nutraceutical: Avoid dong quai if using for hypertension (has estrogenic activity). Avoid ephedra, yohimbe, ginseng (may worsen hypertension). Avoid saw palmetto (due to limited experience with this combination). Avoid garlic (may have increased antihypertensive effect).
Storage
Store in airtight container. Protect from light.
Mechanism of Action
Competitively inhibits postsynaptic alpha-adrenergic receptors which results in vasodilation of veins and arterioles and a decrease in total peripheral resistance and blood pressure
Pharmacodynamics/Kinetics
Onset of action: BP reduction: ?2 hours
Maximum decrease: 2-4 hours
Duration: 10-24 hours
Distribution: Hypertensive adults: Vd: 0.5 L/kg
Protein binding: 92% to 97%
Metabolism: Extensively hepatic
Bioavailability: 43% to 82%
Half-life elimination: 2-4 hours; prolonged with congestive heart failure
Excretion: Urine (6% to 10% as unchanged drug)
Dosage
Oral:
Children (unlabeled use): Initial: 0.05-0.1 mg/kg/day in 3 divided doses; maximum: 0.5 mg/kg/day
Adults:
Hypertension: Initial: 1 mg/dose 2-3 times/day; usual maintenance dose: 3-15 mg/day in divided doses 2-4 times/day; maximum daily dose: 20 mg
Hypertensive urgency: 10-20 mg once, may repeat in 30 minutes
PTSD (unlabeled use): Initial: 2 mg at bedtime; titrate as tolerated to 10-15 mg at bedtime
Raynaud's (unlabeled use): 0.5-3 mg twice daily
Benign prostatic hyperplasia (unlabeled use): 2 mg twice daily
Monitoring Parameters
Blood pressure, standing and sitting/supine
Test Interactions
Increased urinary VMA 17%, norepinephrine metabolite 42%
Patient Education
Inform prescriber of all prescriptions, OTC medications, or herbal products you are taking, and any allergies you have. Do not take any new medication during therapy unless approved by prescriber. Take as directed, at same time each day, with or without meals; do not skip dose or discontinue without consulting prescriber. Avoid alcohol. Follow recommended diet and exercise program. May cause drowsiness, dizziness, or impaired judgment (use caution when driving or engaging in tasks that require alertness until response to drug is known); postural hypotension (use caution when rising from sitting or lying position or when climbing stairs); or dry mouth or nausea (frequent mouth care or sucking lozenges may help). Report increased nervousness or depression; sudden weight gain (weigh yourself in the same clothes at the same time of day once a week); palpitations or rapid heartbeat; respiratory difficulty; muscle weakness, fatigue, or pain; vision changes or hearing; rash; changes in urinary pattern (void before taking medications); or other persistent side effects. Pregnancy/breast-feeding precautions: Inform prescriber if you are or intend to become pregnant. Consult prescriber if breast-feeding.
Geriatric Considerations
Adverse effects such as dry mouth and urinary problems can be particularly bothersome in elderly.
Anesthesia and Critical Care Concerns/Other Considerations
Alpha1 blockers do not affect renal blood flow or glomerular filtration. Orthostatic hypotension, compared to newer alpha-blockers, is more of a concern.
Cardiovascular Considerations
An alpha1 blocker may be used in combination with other agents for the treatment of hypertension or alone in select patients who fail to respond or have contraindications to other agents. Patients with BPH may derive an extra benefit from therapy. Recently, the doxazosin treatment arm of ALLHAT (Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial) was prematurely stopped due to a significantly higher incidence (25%) of cardiovascular events, particularly heart failure events, compared to the diuretic (chlorthalidone) treatment arm. This unfavorable difference was also present when doxazosin was compared to the amlodipine and lisinopril treatment arms. This study does not address cardiovascular outcomes when doxazosin is combined with other antihypertensive medications. Consideration should be given to the ALLHAT results when considering the use of an alpha1 blocker for treatment of hypertension.
Dental Health: Effects on Dental Treatment
Key adverse event(s) related to dental treatment: Significant xerostomia (normal salivary flow resumes upon discontinuation). Significant orthostatic hypotension is a possibility; monitor patient when getting out of dental chair.
Dental Health: Vasoconstrictor/Local Anesthetic Precautions
No information available to require special precautions
Mental Health: Effects on Mental Status
Dizziness is common; may cause drowsiness or nervousness; may rarely cause nightmares
Mental Health: Effects on Psychiatric Treatment
Concurrent use with low potency antipsychotics and TCAs may increase risk of postural hypotension
Nursing: Physical Assessment/Monitoring
Assess potential for interactions with other pharmacological agents and herbal products patient may be taking (eg, anything that may affect blood pressure [beta-blockers, diuretics, ACE inhibitors, calcium channel blockers, dong quai] and any PDE-5 inhibitors [sildenafil, tadalafil, vardenafil]). Evaluate therapeutic effectiveness (cardiac status and blood pressure) and adverse reactions (eg, orthostatic hypotension, rash, drowsiness, nausea, vomiting) at beginning of therapy and on a regular basis with long-term therapy. When discontinuing, monitor blood pressure and taper dose slowly over 1 week or more. Teach patient proper use, possible side effects/appropriate interventions, and adverse symptoms to report.
Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Capsule, as hydrochloride: 1 mg, 2 mg, 5 mg
Pricing: U.S. (www.drugstore.com)
Capsules (Minipress)
1 mg (60): $29.99
2 mg (60): $60.42
5 mg (60): $101.17
Capsules (Prazosin HCl)
1 mg (60): $17.99
2 mg (60): $22.99
5 mg (60): $33.99
References
Chobanian AV, Bakris GL, Black HR, et al, “The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: The JNC 7 Report,” JAMA, 2003, 289(19):2560-71.
"Major Cardiovascular Events in Hypertensive Patients Randomized to Doxazosin vs Chlorthalidone: The Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT). ALLHAT Collaborative Research Group," JAMA, 2000, 283(15):1967-75.
National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents, “The Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents,” Pediatrics, 2004, 114(2 Suppl):555-76.
Peskind ER, Bonner LT, Hoff DJ, et al, “Prazosin Reduces Trauma-Related Nightmares in Older Men With Chronic Posttraumatic Stress Disorder,” J Geriatr Psychiatry Neurol, 2003, 16(3):165-71.
Raskind MA, Dobie DJ, Kanter ED, et al, “The Alpha1-Adrenergic Antagonist Prazosin Ameliorates Combat Trauma Nightmares in Veterans With Posttraumatic Stress Disorder: A Report of 4 Cases,” J Clin Psychiatry, 2000, 61(2):129-33.
Raskind MA, Peskind ER, Kanter ED, et al, “Reduction of Nightmares and Other PTSD Symptoms in Combat Veterans by Prazosin: A Placebo-Controlled Study,” Am J Psychiatry, 2003, 160(2):371-3.
Raskind MA, Thompson C, Petrie EC, et al, “Prazosin Reduces Nightmares in Combat Veterans With Posttraumatic Stress Disorder,” J Clin Psychiatry, 2002, 63(7):565-8.
Raskind MA, Peskind ER, Hoff DJ, et al, “A Parallel Group Placebo Controlled Study of Prazosin for Trauma Nightmares and Sleep Disturbance in Combat Veterans With Post-traumatic Stress Disorder,” Biol Psychiatry, 2007, 61(8):928-34.
International Brand Names
Lexi-Comp.com
Last full review/revision September 2008
Content last modified September 2008
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