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: Limited data available:
Weight-directed: Infants ≥4 months, Children, and Adolescents: Oral: 0.03 mg/kg/dose; second dose has been administered at 3 or 6 hours after initial dose; subsequent doses every 3 to 6 hours; therapy has been continued for 48 hours or until extremities are warm and dry (Bosnak 2009; Gupta 2010; Pandi 2014)
Fixed dosing: Infants >6 months, Children, and Adolescents: Oral: 0.25 mg every 3 hours until extremities are warm and dry (Bawaskar 2010)
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
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).
There are no dosage adjustments provided in the manufacturer's labeling.
(For additional information see "Prazosin: Drug information")
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 (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 (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.
There are no dosage adjustments provided in the manufacturer’s labeling. It has been recommended to initiate at low dosages; titrate cautiously (Aronoff 2007).
There are no dosage adjustments provided in the manufacturer’s labeling.
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
Yes
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
Oral: Administer without regard to meals at the same time each day.
Store at 20°C to 25°C (68°F to 77°F). Protect from moisture and light.
Treatment of hypertension alone or in combination with diuretics or beta-blockers (FDA approved in adults); has also been used in the management of the sympathetic stimulatory cardiovascular effects of scorpion envenomation usually due to non-Centruroides species stings (typically found outside North America)
Prazosin may be confused with predniSONE
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]).
The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.
>4%:
Cardiovascular: Palpitations (5%)
Central nervous system: Dizziness (10%), drowsiness (8%), headache (8%), fatigue (7%)
Gastrointestinal: Nausea (5%)
Neuromuscular & skeletal: Weakness (7%)
1% to 4%:
Cardiovascular: Edema, orthostatic hypotension, syncope
Central nervous system: Depression, nervousness, vertigo
Dermatologic: Skin rash
Gastrointestinal: Constipation, diarrhea, vomiting, xerostomia
Genitourinary: Urinary frequency
Ophthalmic: Blurred vision, injected sclera
Respiratory: Dyspnea, epistaxis, nasal congestion
<1%, postmarketing, and/or case reports: Abdominal distress, abnormal hepatic function tests, alopecia, angina pectoris, arthralgia, bradycardia, cataplexy, cataract (both development of cataract and disappearance have been reported), diaphoresis, eye pain, fever, flushing, gynecomastia, hallucination, hypersensitivity reaction, impotence, insomnia, leukopenia, lichen planus, malaise, myocardial infarction, narcolepsy (worsened), pain, pancreatitis, paresthesia, positive ANA titer, priapism, pruritus, retinal pigment changes (mottled), retinopathy (serous), systemic lupus erythematosus, tachycardia, tinnitus, urinary incontinence, urticaria, vasculitis
Known sensitivity to quinazolines, prazosin, or any component of the formulation
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.
None known.
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
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
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 has variable effects on absorption. Management: Administer without regard to food.
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).
Blood pressure (standing and sitting or supine)
Competitively inhibits postsynaptic alpha-adrenergic receptors which results in vasodilation of veins and arterioles and a decrease in total peripheral resistance and blood pressure
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)
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
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