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Prazosin: Drug information

Prazosin: Drug information
(For additional information see "Prazosin: Patient drug information" and see "Prazosin: Pediatric drug information")

For abbreviations, symbols, and age group definitions used in Lexicomp (show table)
Brand Names: US
  • Minipress
Brand Names: Canada
  • APO-Prazo;
  • Minipress;
  • TEVA-Prazosin
Pharmacologic Category
  • Alpha 1 Blocker;
  • Antihypertensive
Dosing: Adult
Hypertension, chronic

Hypertension, chronic (alternative agent):

Note: Not recommended for initial management but may be considered as additional therapy for resistant hypertension in patients who do not respond adequately to combination therapy with preferred agents (ACC/AHA [Whelton 2018]).

Oral: Initial: 1 mg 2 or 3 times daily; titrate as needed based on patient response up to 20 mg/day in 2 or 3 divided doses (ACC/AHA [Whelton 2018]).

PTSD-related nightmares and sleep disruption

PTSD-related nightmares and sleep disruption (off-label use):

Oral: Initial: 1 mg at bedtime; after 2 to 3 days increase dose to 2 mg at bedtime, then adjust dosage based on response and tolerability in 1 to 5 mg increments every 7 days up to a maximum of 15 mg/day. Titration as rapid as every 2 to 3 days has been evaluated (Singh 2016). Usual dose range: 3 to 15 mg at bedtime (APA [Benedek 2009]). Civilian patients, especially females, may require lower doses (Taylor 2008).

Raynaud phenomenon

Raynaud phenomenon (alternative agent) (off-label use):

Note: Effects may be transient and may become less effective over several weeks; consider an alternative agent (Wigley 2002).

Oral: Initial: 0.5 to 1 mg once daily (at bedtime) or 0.5 mg twice daily; gradually adjust dose based on response and tolerability up 12 mg/day in 2 to 3 divided doses (Nielson 1983; Russell 1985; Wigley 2002; Wollersheim 1988).

Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.

Dosing: Kidney Impairment: Adult

There are no dosage adjustments provided in the manufacturer’s labeling. It has been recommended to initiate at low dosages; titrate cautiously (Aronoff 2007).

Dosing: Hepatic Impairment: Adult

There are no dosage adjustments provided in the manufacturer’s labeling.

Dosing: Pediatric

(For additional information see "Prazosin: Pediatric drug information")

Hypertension

Hypertension: Limited data available:

Note: Not recommended first-line therapy; reserve for patients not responsive to therapeutic trials of 2 or more preferred agents (eg, ACE inhibitor, ARB, calcium channel blocker, or thiazide diuretic) (AAP [Flynn 2017]).

Children and Adolescents: Oral: Initial: 0.05 to 0.1 mg/kg/day in divided doses every 8 hours; may titrate up to 0.5 mg/kg/day in divided doses 3 times daily; maximum daily dose: 20 mg/day (NHBPEP 2004; NHLBI 2011).

Scorpion envenomation

Scorpion envenomation: Limited data available; multiple regimens reported:

Note: Dosing based on small studies and case series/reports that describe positive effects of prazosin in the management of the sympathetic stimulatory cardiovascular effects of scorpion envenomation, usually due to stings from non-Centruroides species typically found outside North America (eg, India [M. tamulus], Africa [L. quinquestriatus], Middle East [A. crassicauda]) (Abdel Baseer 2021; Isbister 2014; Rodrigo 2017). Scorpion antivenom has been used in conjunction with prazosin, and the combination was reported to be more beneficial than antivenom alone in some instances (Pandi 2014; Rodrigo 2017).

Weight-directed dosing: Infants ≥4 months, Children, and Adolescents: Oral: 0.03 mg/kg/dose every 3 to 6 hours; reported administration schedule for dosing interval and length of therapy are variable; in general, therapy continued until extremities were warm and dry (Bosnak 2009; Gupta 2010; Kumar 2015; Pandi 2014).

Fixed dosing:

Infants >6 months and Children <12 years: Oral: 0.25 mg every 3 hours until extremities are warm and dry (Bawaskar 2011; Isbister 2014).

Children ≥12 years and Adolescents:

≤20 kg: Oral: 0.25 to 0.5 mg every 3 hours until extremities are warm and dry (Bawaskar 2011; Natu 2010).

>20 kg: Oral: 0.25 to 1 mg every 3 hours until extremities are warm and dry (Bawaskar 2011; Isbister 2014; Natu 2010).

Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.

Dosing: Kidney Impairment: Pediatric

There are no dosage adjustments provided in the manufacturer's labeling. Based on experience in adults, initiation at lower dosages suggested; titrate cautiously (Aronoff 2007).

Dosing: Hepatic Impairment: Pediatric

There are no dosage adjustments provided in the manufacturer's labeling.

Dosing: Older Adult

Avoid use for hypertension treatment (Beers Criteria [AGS 2019]). Refer to adult dosing for other indications.

Dosage Forms: US

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Capsule, Oral:

Minipress: 1 mg, 2 mg, 5 mg

Generic: 1 mg, 2 mg, 5 mg

Generic Equivalent Available: US

Yes

Dosage Forms: Canada

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Tablet, Oral:

Minipress: 1 mg [contains fd&c yellow #6 (sunset yellow)]

Minipress: 2 mg, 5 mg

Generic: 1 mg, 2 mg, 5 mg

Administration: Pediatric

Oral: Administer without regard to meals at the same time each day.

Use: Labeled Indications

Hypertension, chronic: Management of hypertension. Note: Alpha blockers are not recommended as first line therapy (ACC/AHA [Whelton 2018]).

Use: Off-Label: Adult

Posttraumatic stress disorder related nightmares and sleep disruption; Raynaud phenomenon

Medication Safety Issues
Sound-alike/look-alike issues:

Prazosin may be confused with predniSONE

Older Adult: High-Risk Medication:

Beers Criteria: Prazosin is identified in the Beers Criteria as a potentially inappropriate medication for hypertension in patients 65 years and older due to its high risk of orthostatic hypotension. Avoid use for hypertension treatment (alternative agents have superior risk-benefit profiles) (Beers Criteria [AGS 2019]).

Adverse Reactions (Significant): Considerations
Floppy iris syndrome

Intraoperative floppy iris syndrome (IFIS) has been reported in patients with current or prior use of alpha-1 blockers undergoing cataract surgery (Ref). Studies report significantly higher surgical complication rates for patients who experience IFIS (Ref).

Mechanism: Not completely established; may be related to a combination of the pharmacologic action (ie, inhibition of the iris dilator smooth muscle contraction) and long-term smooth muscle atrophy from accumulation in iris pigment epithelial cells (Ref).

Onset: Varied; may occur with current (within a few days to months of initiation) or prior use (years following discontinuation) (Ref). A minimum 3-month duration of alpha-1 blocker use has been proposed as a risk for IFIS (Ref).

Risk factors:

• Individual alpha-1 blocker (risk highest with tamsulosin) (Ref)

• Hypertension (Ref)

• Males (Ref)

• Older age (Ref)

• Decreased preoperative dilated pupil diameter (Ref)

Orthostatic hypotension

Prazosin is associated with orthostatic hypotension, which can manifest as dizziness and vertigo (Ref). One study suggests that orthostatic hypotension may be transient (Ref).

Mechanism: Dose-related; related to the pharmacologic action (ie, inhibition of vascular smooth muscle contraction and vasodilation) (Ref).

Onset: Varied; “first dose” orthostatic hypotension may occur 30 minutes to 3 hours after dose (Ref). However, has also occurred months after initiation (Ref).

Risk factors:

• Individual alpha-1 blocker (risk lowest with tamsulosin) (Ref)

• First dose or redose after dose interruption (Ref)

• Rapid increase in dose

• Concurrent medications that cause orthostatic hypotension (eg, antihypertensives, nitrates, phosphodiesterase-5 inhibitors) (Ref)

• Females >65 years of age (Ref)

• Alcohol use (Ref)

Adverse Reactions

The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.

1% to 10%:

Cardiovascular: Edema (1% to 4%), orthostatic hypotension (1% to 4%), palpitations (5%), syncope (1% to 4%)

Dermatologic: Skin rash (1% to 4%)

Gastrointestinal: Constipation (1% to 4%), diarrhea (1% to 4%), nausea (5%), vomiting (1% to 4%), xerostomia (1% to 4%)

Genitourinary: Urinary frequency (1% to 4%)

Nervous system: Asthenia (7%), depression (1% to 4%), dizziness (10%), drowsiness (8%), fatigue (7%), headache (8%), nervousness (1% to 4%), vertigo (1% to 4%)

Ophthalmic: Blurred vision (1% to 4%), injected sclera (1% to 4%)

Respiratory: Dyspnea (1% to 4%), epistaxis (1% to 4%), nasal congestion (1% to 4%)

<1%:

Cardiovascular: Tachycardia

Dermatologic: Alopecia, diaphoresis, lichen planus, pruritus

Gastrointestinal: Abdominal distress, abdominal pain, pancreatitis

Genitourinary: Impotence, priapism, urinary incontinence

Hematologic & oncologic: Positive ANA titer

Hepatic: Abnormal hepatic function tests

Nervous system: Hallucination, paresthesia

Neuromuscular & skeletal: Arthralgia

Otic: Tinnitus

Miscellaneous: Fever

Postmarketing:

Cardiovascular: Angina pectoris (including exacerbation of angina pectoris) (Charness 1979), bradycardia (Ball 1994), flushing, vasculitis

Dermatologic: Urticaria (Ruzicka 1983)

Endocrine & metabolic: Gynecomastia

Nervous system: Insomnia, malaise, narcolepsy (exacerbation), pain

Ophthalmic: Cataract, eye pain, intraoperative floppy iris syndrome (cataract surgery) (Issa 2008), retinal pigment changes (mottled), retinopathy (serous)

Contraindications

Known sensitivity to quinazolines, prazosin, or any component of the formulation

Warnings/Precautions

Concerns related to adverse effects:

• Angina: Discontinue if symptoms of angina occur or worsen.

• CNS depression: May cause CNS depression, which may impair physical or mental abilities; patients must be cautioned about performing tasks that require mental alertness (eg, operating machinery or driving).

• Floppy iris syndrome: Intraoperative floppy iris syndrome has been observed in cataract surgery patients who were on or were previously treated with alpha1-blockers; modification to surgical technique may be necessary. There appears to be no benefit in discontinuing alpha1-blockers prior to surgery.

• Orthostatic hypotension/syncope: May cause significant orthostatic hypotension and syncope with sudden loss of consciousness, especially within 30 to 90 minutes of the 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 beta-blocker) or a phosphodiesterase 5 (PDE 5) inhibitor (eg, sildenafil, tadalafil, vardenafil) is introduced. Severe tachycardia (120 to 160 beats/minute) has occasionally been reported prior to a syncopal episode. Patients should be cautioned about alcohol use and performing hazardous tasks when starting new therapy or adjusting dosage upward.

• Priapism: Priapism and prolonged erections have been reported; seek immediate medical assistance for erections lasting longer than 4 hours.

Disease-related concerns:

• Heart failure: In a scientific statement from the American Heart Association, prazosin has been determined to be an agent that may exacerbate underlying myocardial dysfunction (magnitude: moderate) (AHA [Page 2016]).

• Prostate cancer: Should rule out prostatic carcinoma before beginning therapy.

Metabolism/Transport Effects

None known.

Drug Interactions

Note: Interacting drugs may not be individually listed below if they are part of a group interaction (eg, individual drugs within “CYP3A4 Inducers [Strong]” are NOT listed). For a complete list of drug interactions by individual drug name and detailed management recommendations, use the Lexicomp drug interactions program by clicking on the “Launch drug interactions program” link above.

Alpha-/Beta-Agonists: Alpha1-Blockers may diminish the vasoconstricting effect of Alpha-/Beta-Agonists. Similarly, Alpha-/Beta-Agonists may antagonize Alpha1-Blocker vasodilation. Risk C: Monitor therapy

Alpha1-Agonists: Alpha1-Blockers may diminish the vasoconstricting effect of Alpha1-Agonists. Similarly, Alpha1-Agonists may antagonize Alpha1-Blocker vasodilation. Risk C: Monitor therapy

Alpha1-Blockers: May enhance the antihypertensive effect of other Alpha1-Blockers. Risk X: Avoid combination

Amifostine: Blood Pressure Lowering Agents may enhance the hypotensive effect of Amifostine. Management: When used at chemotherapy doses, hold blood pressure lowering medications for 24 hours before amifostine administration. If blood pressure lowering therapy cannot be held, do not administer amifostine. Use caution with radiotherapy doses of amifostine. Risk D: Consider therapy modification

Amphetamines: May diminish the antihypertensive effect of Antihypertensive Agents. Risk C: Monitor therapy

Antipsychotic Agents (Second Generation [Atypical]): Blood Pressure Lowering Agents may enhance the hypotensive effect of Antipsychotic Agents (Second Generation [Atypical]). Risk C: Monitor therapy

Barbiturates: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy

Benperidol: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy

Beta-Blockers: May enhance the orthostatic hypotensive effect of Alpha1-Blockers. The risk associated with ophthalmic products is probably less than systemic products. Risk C: Monitor therapy

Brigatinib: May diminish the antihypertensive effect of Antihypertensive Agents. Brigatinib may enhance the bradycardic effect of Antihypertensive Agents. Risk C: Monitor therapy

Brimonidine (Topical): May enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy

Bromperidol: May diminish the hypotensive effect of Blood Pressure Lowering Agents. Blood Pressure Lowering Agents may enhance the hypotensive effect of Bromperidol. Risk X: Avoid combination

Calcium Channel Blockers: Alpha1-Blockers may enhance the hypotensive effect of Calcium Channel Blockers. Risk C: Monitor therapy

Dapoxetine: May enhance the orthostatic hypotensive effect of Alpha1-Blockers. Risk C: Monitor therapy

Dexmethylphenidate: May diminish the therapeutic effect of Antihypertensive Agents. Risk C: Monitor therapy

Diazoxide: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy

DULoxetine: Blood Pressure Lowering Agents may enhance the hypotensive effect of DULoxetine. Risk C: Monitor therapy

Flunarizine: May enhance the therapeutic effect of Antihypertensive Agents. Risk C: Monitor therapy

Herbal Products with Blood Pressure Increasing Effects: May diminish the antihypertensive effect of Antihypertensive Agents. Risk C: Monitor therapy

Herbal Products with Blood Pressure Lowering Effects: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy

Hypotension-Associated Agents: Blood Pressure Lowering Agents may enhance the hypotensive effect of Hypotension-Associated Agents. Risk C: Monitor therapy

Levodopa-Containing Products: Blood Pressure Lowering Agents may enhance the hypotensive effect of Levodopa-Containing Products. Risk C: Monitor therapy

Loop Diuretics: May enhance the hypotensive effect of Antihypertensive Agents. Risk C: Monitor therapy

Lormetazepam: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy

Methylphenidate: May diminish the antihypertensive effect of Antihypertensive Agents. Risk C: Monitor therapy

Molsidomine: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy

Nicorandil: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy

Nitroprusside: Blood Pressure Lowering Agents may enhance the hypotensive effect of Nitroprusside. Risk C: Monitor therapy

Obinutuzumab: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Management: Consider temporarily withholding blood pressure lowering medications beginning 12 hours prior to obinutuzumab infusion and continuing until 1 hour after the end of the infusion. Risk D: Consider therapy modification

Pentoxifylline: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy

Pholcodine: Blood Pressure Lowering Agents may enhance the hypotensive effect of Pholcodine. Risk C: Monitor therapy

Phosphodiesterase 5 Inhibitors: May enhance the hypotensive effect of Alpha1-Blockers (Nonselective). Management: Ensure patient is stable on one agent prior to initiating the other, and always initiate combination using the lowest possible dose of the drug being added. When tadalafil is used for treatment of BPH, concurrent alpha 1-blockers are not recommended. Risk D: Consider therapy modification

Prostacyclin Analogues: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy

Quinagolide: May enhance the hypotensive effect of Blood Pressure Lowering Agents. Risk C: Monitor therapy

Rilmenidine: Alpha1-Blockers may enhance the hypotensive effect of Rilmenidine. Risk C: Monitor therapy

Food Interactions

Food has variable effects on absorption. Management: Administer without regard to food.

Pregnancy Considerations

Prazosin crosses the placenta and its pharmacokinetics may be slightly altered during pregnancy (Bourget 1995; Rubin 1983); bioavailability was increased, time to peak serum concentration, and elimination rates were longer in women during the third trimester (Rubin 1983). Limited use in pregnant women has not demonstrated any fetal abnormalities or adverse effects (maternal treatment started after the first trimester) (Dommisse 1983; Lubbe 1981).

Chronic maternal hypertension may increase the risk of birth defects, low birth weight, preterm delivery, stillbirth, and neonatal death. Actual fetal/neonatal risks may be related to duration and severity of maternal hypertension. Untreated hypertension may also increase the risks of adverse maternal outcomes, including gestational diabetes, myocardial infarction, preeclampsia, stroke, and delivery complications (ACOG 203 2019).

Agents other than prazosin are more commonly used to treat hypertension in pregnancy (ACOG 203 2019; ESC [Regitz-Zagrosek 2018]); use of prazosin should be considered in consult with subspecialists (ACOG 203 2019). Females with preexisting hypertension may continue their medication during pregnancy unless contraindications exist (ESC [Regitz-Zagrosek 2018]). Although rare, use of prazosin for the treatment of hypertension due to a pheochromocytoma during pregnancy has been described (Mazza 2014).

Breastfeeding Considerations

Prazosin is present in breast milk.

The manufacturer recommends that caution be exercised when administering prazosin to breastfeeding women.

Monitoring Parameters

Blood pressure, standing and sitting/supine

Hypertension: The 2017 Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults (ACC/AHA [Whelton 2018]):

Confirmed hypertension and known CVD or 10-year ASCVD risk ≥10%: Target blood pressure <130/80 mm Hg is recommended

Confirmed hypertension without markers of increased ASCVD risk: Target blood pressure <130/80 mm Hg may be reasonable

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

Pharmacokinetics

Onset of action: Antihypertensive: Within 2 hours; Peak effect: 2 to 4 hours

Duration of action: 10 to 24 hours

Distribution: Vd: 0.5 L/kg

Protein binding: Highly bound (97%)

Metabolism: Extensively hepatic via demethylation and conjugation

Bioavailability: 43% to 82%

Half-life elimination: 2 to 3 hours, prolonged with CHF

Time to peak, plasma: ~3 hours

Excretion: Feces; urine (6% to 10% as unchanged drug)

Pricing: US

Capsules (Minipress Oral)

1 mg (per each): $2.75

2 mg (per each): $3.83

5 mg (per each): $6.53

Capsules (Prazosin HCl Oral)

1 mg (per each): $0.50 - $1.81

2 mg (per each): $0.55 - $2.52

5 mg (per each): $1.00 - $5.41

Disclaimer: A representative AWP (Average Wholesale Price) price or price range is provided as reference price only. A range is provided when more than one manufacturer's AWP price is available and uses the low and high price reported by the manufacturers to determine the range. The pricing data should be used for benchmarking purposes only, and as such should not be used alone to set or adjudicate any prices for reimbursement or purchasing functions or considered to be an exact price for a single product and/or manufacturer. Medi-Span expressly disclaims all warranties of any kind or nature, whether express or implied, and assumes no liability with respect to accuracy of price or price range data published in its solutions. In no event shall Medi-Span be liable for special, indirect, incidental, or consequential damages arising from use of price or price range data. Pricing data is updated monthly.

Brand Names: International
  • Alphapress (BD);
  • Alpress (FR);
  • Apo-Prazo (HK);
  • Atodel (MY, PH, TR);
  • CP-Prazo (HK);
  • Cyber (IN);
  • Czopress (IN);
  • Damin (TW);
  • Decliten (AR);
  • Deprazolin (CZ);
  • Hypotens (IL);
  • Hypovase (GB, IE);
  • Hyprosin (NZ);
  • Lopress (TH);
  • Minecin (KR);
  • Minipres (BZ, CR, EC, ES, GT, MX, NI, PA, SV, VE);
  • Minipres Retard (AR);
  • Minipres SR (CO);
  • Minipress (AE, AT, AU, BB, BE, BF, BG, BH, BJ, BM, BS, BZ, CI, CY, EG, ET, FR, GH, GM, GN, GR, GY, HN, ID, IL, IQ, IR, JM, JO, JP, KE, KW, LB, LR, LU, LY, MA, ML, MR, MU, MW, MY, NE, NG, NL, OM, PK, PL, RO, SA, SC, SD, SG, SL, SN, SR, SY, TH, TN, TR, TT, TW, TZ, UG, YE, ZM, ZW);
  • Minipress SR (BR);
  • Minipress XL (IN, LK);
  • Minison (MY, TW);
  • Mizosin (HK, MY, SG);
  • Polpressin (PL);
  • Polypress (TH);
  • Pratisol (NZ, TW);
  • Pratsiol (BG, FI);
  • Praxin (PY, UY);
  • Prazolin (LK);
  • Prazon (HK);
  • Prazopress (BD);
  • Tenosin (BD);
  • Variprex (ZW)


For country code abbreviations (show table)
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