prazosin (Rx)

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

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 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.

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)