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Prazosin


Pronunciation

 (PRA zoe sin)


U.S. Brand Names

 Minipress®


Synonyms

 Furazosin; Prazosin Hydrochloride


Generic Available

 Yes


Canadian Brand Names

 Apo-Prazo®; Minipress™; Novo-Prazin; Nu-Prazo


Use

 Treatment of hypertension


Use - Unlabeled/Investigational

 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

 May cause significant orthostatic hypotension and syncope, especially with first dose. Risk is increased at doses >1 mg, hypovolemia, or in patients receiving concurrent beta-blocker therapy. Anticipate a similar effect if therapy is interrupted for a few days, if dosage is rapidly increased, or if another antihypertensive drug is introduced.


Adverse Reactions

>10%: Central nervous system: Dizziness (10%)

1% to 10%:

Cardiovascular: Palpitations (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


Overdosage/Toxicology

 Symptoms of overdose include hypotension and drowsiness. Treatment is otherwise supportive and symptomatic.


Drug Interactions

ACE inhibitors: Hypotensive effect may be increased.

Beta-blockers: Hypotensive effect may be increased.

Calcium channel blockers: Hypotensive effect may be increased.

NSAIDs may reduce antihypertensive efficacy.

Sildenafil, tadalafil, vardenafil: Blood pressure-lowering effects are additive. Use of tadalafil or vardenafil is contraindicated by the manufacturer. Use sildenafil with extreme caution (dose 25 mg).

Tricyclic antidepressants (TCAs) and low-potency antipsychotics: May increase risk of orthostasis.


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).


Stability

 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: Initial: 5 mcg/kg/dose (to assess hypotensive effects); usual dosing interval: every 6 hours; increase dosage gradually up to maximum of 25 mcg/kg/dose every 6 hours

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

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 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.


Nursing Implications

 Syncope may occur (usually within 90 minutes of the initial dose)


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

 Prazosin can be used alone or in combination with other antihypertensive agents. Patients with BPH may derive benefit from therapy. Orthostatic hypotension, compared to newer alpha-blockers, is more of a concern.


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


Dosage Forms

 Capsule, as hydrochloride: 1 mg, 2 mg, 5 mg


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.


International Brand Names

 Adversuten® (DE, RO); Alphapress® (BD); Alphavase® (GB); Alpress® (FR); Apo-Prazo® (CA, TR); Atodel® (CY, TH); Chem mart Prazosin® (AU); DBL Prazosin® (AU); Decliten® (AR); Deprazolin® (CZ); duramipress® (DE); GenRX Prazosin® (AU); Healthsense Prazosin® (AU); Hexapress® (DK); Huma-Prazin® (HU); Hypotens® (IL); Hypovase® (GB, IE); Hyprosin® (NZ); Kentovase (GB); Lopress® (TH); Minipres® (AR, CL, ES, MX); Minipress® (AT, AU, BE, BR); Minipress™ (CA); Minipress® (CH, CO, CZ, DE, DO, EG, FR, HU, ID, IN, JO, JP, KW, LB, LU, NL, PL, SG, TH, TR, YU, ZA); Minipress R® (RO); Novo-Prazin (CA); Nu-Prazo (CA); Parabowl® (TH); Peripress® (DK, FI); Polpressin® (PL, RU); Polypress® (TH); Prasig® (AU); Pratsiol® (AU, FI, HK, NZ, TR, ZA); Prazac® (DK); Prazosin Atid® (DE); Prazosin-BC (AU); Prazosin® (GB); Prazosin Heumann® (DE); Prazosin-Hexal® (LU); Prazosin-ratiopharm® (DE); Pressin® (AU, TH); Sinozzard® (MX); Terry White Chemists Prazosin® (AU); Vasoflex® (HR, SI)


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