Dosing and uses of Minipress, Prazin (prazosin)
Adult dosage forms and strengths
capsule
- 1mg
- 2mg
- 5mg
Hypertension
Initial: 1 mg PO q8-12hr
Maintenance: 2-20 mg/day PO divided q8-12hr
PTSD-Related Nightmares & Sleep Disruption
Initial: 1 mg PO qHs
Maintenance: 2-15 mg PO qHs
Benign Prostate Hypertrophy (Off-label)
Initial: 0.5 mg PO q12hr
Maintenance: 2 mg PO q12hr
Raynaud Phenomenon (Off-label)
1-5 PO q12hr
Administration
Give first dose and subsequent increases at bedtime to avoid syncope
Okay with food
Pediatric dosage forms and strengths
capsule
- 1mg
- 2mg
- 5mg
Hypertension (Off-label)
Initial: 0.05-0.1 mg/kg/day PO divided q8hr
Titrate to 0.5 mg/kg/day; not to exceed 20 mg/day
Administration
Okay with food
Minipress, Prazin (prazosin) adverse (side) 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
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
Rule out prostate cancer before initiating therapy
Hypotension/syncope may occur with first few doses or with increase in dose; minimize effect by using small first dose at bedtime; increase dose slowly
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 and 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 of Minipress, Prazin (prazosin)
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)
