Dosing & Uses
Dosage Forms & Strengths
capsule
- 1mg
- 2mg
- 5mg
Hypertension
Initial: 1 mg PO q8-12hr
Maintenance: 6-15 mg/day divided 2 or 3 times daily; alternatively, 1-5 mg PO BID; may increase dose to 20 mg/day in divided doses; some patients may benefit from up to 40 mg/day in divided doses
PTSD-Related Nightmares & Sleep Disruption (Off-label)
Initial: 1 mg PO qHS
Maintenance: 1 mg PO qHS initially; may increase dose to 2 mg qHS; adjust dose based on response and tolerability in 1-2 mg increments q7days; not to exceed 15 mg/day
Benign Prostate Hypertrophy (Off-label)
Initial: 0.5 mg PO q12hr
Maintenance: 2 mg PO q12hr
Raynaud Phenomenon (Off-label)
0.5-1 mg PO qDay (HS) or 0.5 mg PO BID; adjust dose based on response and tolerability up to 12 mg/day divided BID/TID
Administration
Give first dose and subsequent increases at bedtime to avoid syncope
Okay with food
Interactions
Interaction Checker
No Results
Contraindicated
Serious - Use Alternative
Significant - Monitor Closely
Minor
Adverse Effects
1-10%
Dizziness (10%)
Drowsiness (8%)
Headache (8%)
Weakness (7%)
Asthenia (6.5%)
Nausea (5%)
Palpitation (5%)
Frequency Not Defined (Selected)
Edema
Orthostatic hypotension
Syncope
Fever
Rash
Abdominal discomfort/pain
Diarrhea
Vomiting
Abnormal liver function tests
Impotence
Pancreatitis
Urinary incontinence
Warnings
Contraindications
Hypersensitivity
Cautions
Risk of syncope; has no relation to plasma prazosin concentration; if syncope occurs, place patient in the recumbent position and treat supportively as necessary
Discontinue if angina symptoms occur or worsen
May cause CNS depression, which may impair physical or internal abilities; use caution when performing tasks that require mental alertness
May impair ability to drive/perform hazardous tasks due to dizziness
History of narcolepsy - May exacerbate
Cataract surgery - Linked to intraoperative floppy iris syndrome
Concomitant administration with PDE-5 inhibitor (eg, sildenafil) can result in additive blood pressure-lowering effects and symptomatic hypotension; initiate PDE-5 inhibitor therapy at lowest dose
First dose effect may occur, causing a sudden and drastic fall in blood pressure after administration of the first dose.
May exacerbate heart failure
Prolonged erections and priapism reported with alpha-1 blockers including prazosin in post marketing experience; if erection persists > 4 hours, seek immediate medical assistance
May cause significant orthostatic hypotension and syncope with sudden loss of consciousness, especially 30-90 min of first dose; may also occur if therapy interrupted for a few days, if dosage rapidly increased or if another antihypertensive drug, like a beta-blocker or vasodilator, or a phosphodiesterase 5 inhibitor is introduced
Prostatic carcinoma should be ruled out before initiating therapy
Geriatric considerations
- Avoid use for hypertension; high risk of orthostatic hypotension (Beers criteria)
- May cause significant orthostatic hypotension and syncope; consider lower initial dose; titrate to response
- Adverse effects such as dry mouth and urinary complications can be bothersome in the elderly
Pregnancy & Lactation
Pregnancy category: C
Lactation: Excreted in breast milk; use caution
Pregnancy Categories
A:Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B:May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C:Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D:Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X:Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA:Information not available.
Pharmacology
Mechanism of Action
Alpha-1 blocker inhibits postsynaptic alpha-adrenergic receptors, causing arterial and venous dilation and a subsequent decrease in blood pressure
Absorption
Bioavailability: 43-82%
Onset: ~2 hr
Duration: 10-24 hr
Peak effect: 2-4 hr
Peak plasma time: 2-3 hr
Distribution
Protein bound: 97%
Metabolism
Hepatic metabolization (extensive)
Elimination
Half-life elimination: 2-3 hr
Excretion: Urine (6-10%); rest in feces (via bile)
Images
Patient Handout
Formulary
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Adding plans allows you to:
- View the formulary and any restrictions for each plan.
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- Compare formulary status to other drugs in the same class.
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