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Minipress, Prazin (prazosin) dosing, indications, interactions, adverse effects, and more

Adverse Effects
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
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
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