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 (Ref).
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 (Ref).
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 (Ref). Usual dose range: 3 to 15 mg at bedtime (Ref). Civilian patients, especially females, may require lower doses (Ref).
Raynaud phenomenon (alternative agent) (off-label use):
Note: Effects may be transient and may become less effective over several weeks; consider an alternative agent (Ref).
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 (Ref).
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
The renal dosing recommendations are based upon the best available evidence and clinical expertise. Senior Editorial Team: Bruce Mueller, PharmD, FCCP, FASN, FNKF; Jason A. Roberts, PhD, BPharm (Hons), B App Sc, FSHP, FISAC; Michael Heung, MD, MS.
Altered kidney function:
eGFR ≥60 mL/minute/1.73 m2: No dosage adjustment necessary (Ref).
eGFR <60 mL/minute/1.73 m2: Although pharmacokinetic parameters are not significantly altered, BP-lowering effects may be exaggerated in patients with kidney impairment; begin at low dosages; titrate cautiously (Ref).
Hemodialysis, intermittent (thrice weekly): Unlikely to be dialyzed (highly protein bound): Although pharmacokinetic parameters are not significantly altered, BP-lowering effects may be exaggerated in patients with kidney impairment; begin at low dosages; titrate cautiously (Ref).
Peritoneal dialysis: Unlikely to be dialyzed (highly protein bound): Although pharmacokinetic parameters are not expected to be significantly altered, BP-lowering effects may be exaggerated in patients with kidney impairment; begin at low dosages; titrate cautiously (Ref).
CRRT: Although pharmacokinetic parameters are not expected to be significantly altered, BP-lowering effects may be exaggerated in patients with kidney impairment; begin at low dosages; titrate cautiously (Ref).
PIRRT (eg, sustained, low-efficiency diafiltration): Although pharmacokinetic parameters are not expected to be significantly altered, BP-lowering effects may be exaggerated in patients with kidney impairment; begin at low dosages; titrate cautiously (Ref).
There are no dosage adjustments provided in the manufacturer’s labeling.
Avoid use for hypertension treatment (Ref). Refer to adult dosing for other indications.
(For additional information see "Prazosin: Pediatric drug information")
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) (Ref).
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 (Ref).
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]) (Ref). Scorpion antivenom has been used in conjunction with prazosin, and the combination was reported to be more beneficial than antivenom alone in some instances (Ref).
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 (Ref).
Fixed dosing:
Infants >6 months and Children <12 years: Oral: 0.25 mg every 3 hours until extremities are warm and dry (Ref).
Children ≥12 years and Adolescents:
≤20 kg: Oral: 0.25 to 0.5 mg every 3 hours until extremities are warm and dry (Ref).
>20 kg: Oral: 0.25 to 1 mg every 3 hours until extremities are warm and dry (Ref).
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 (Ref).
There are no dosage adjustments provided in the manufacturer's labeling.
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)
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)
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)
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.
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
Capsules (Minipress Oral)
1 mg (per each): $2.78
2 mg (per each): $3.87
5 mg (per each): $6.59
Capsules (Prazosin HCl Oral)
1 mg (per each): $0.07 - $1.81
2 mg (per each): $0.10 - $2.52
5 mg (per each): $0.15 - $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.
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.
Hypertension, chronic: Management of hypertension. Note: Alpha blockers are not recommended as first line therapy (ACC/AHA [Whelton 2018]).
Posttraumatic stress disorder related nightmares and sleep disruption; Raynaud phenomenon
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 2023]).
None known.
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
Antihypertensive Agents: May enhance the hypotensive effect of Prazosin. 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
Arginine: May enhance the hypotensive effect of Blood Pressure Lowering Agents. 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
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
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-Foslevodopa: Blood Pressure Lowering Agents may enhance the hypotensive effect of Levodopa-Foslevodopa. 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 has variable effects on absorption. Management: Administer without regard to food.
Medications considered acceptable for the treatment of chronic hypertension during pregnancy may generally be continued in patients trying to conceive. Prazosin is not considered a preferred agent for use in pregnant patients; consider transitioning to a preferred agent in patients planning to become pregnant (ACC/AHA [Whelton 2018]; ACOG 2019; NICE 2019).
Prazosin crosses the placenta (Bourget 1995).
Chronic maternal hypertension is associated with adverse events in the fetus/infant. Chronic maternal hypertension may increase the risk of birth defects, low birth weight, premature delivery, stillbirth, and neonatal death. Actual fetal/neonatal risks may be related to the duration and severity of maternal hypertension. Untreated chronic hypertension may also increase the risks of adverse maternal outcomes, including gestational diabetes, preeclampsia, delivery complications, stroke, and myocardial infarction (ACOG 2019).
Due to pregnancy-induced physiologic changes, some pharmacokinetic properties of prazosin may be altered (Bourget 1995; Rubin 1983).
Patients with preexisting hypertension may continue their medication during pregnancy unless contraindications exist (ESC [Regitz-Zagrosek 2018]). When treatment of chronic hypertension during pregnancy is initiated during pregnancy, agents other than prazosin may be preferred (ACOG 2019; ESC [Cífková 2020]; ESC [Regitz-Zagrosek 2018]; SOGC [Magee 2022]); if needed, use of prazosin should be considered in consult with subspecialists (ACOG 2019).
Untreated hypertension due to a pheochromocytoma during pregnancy is associated with a high rate of maternal and fetal mortality therefore treatment is recommended (ESC [Cífková 2020]). Case reports describe the use of prazosin as part of combination therapy for the treatment of hypertension due to pheochromocytoma in pregnant patients (Agrawal 2022). Prazosin may be an alternative option for the treatment of hypertension due to pheochromocytoma during pregnancy (Pacu 2021).
Prazosin is present in breast milk.
The manufacturer recommends that caution be exercised when administering prazosin to lactating patients.
Blood pressure.
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)
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