Prazosin

Prazosin is a prescription drug indicated for the treatment of hypertension, to lower blood pressure. Lowering blood pressure reduces the risk of fatal and nonfatal cardiovascular events, primarily strokes and myocardial infarctions. These benefits have been seen in controlled trials of antihypertensive drugs from a wide variety of pharmacologic classes, including this drug.

• Prazosin can be used alone or in combination with other antihypertensive drugs such as diuretics or beta-adrenergic blocking agents.
• Prazosin is available under the following different brand names: Minipress, Prazin, and Prazo.

Adult and Pediatric Dosage:

Capsule

• 1 mg
• 2 mg
• 5 mg

Dosing Considerations – Should be Given as Follows:

Hypertension

Adult:

• Initial: 1 mg orally every 8-12 hours
• Maintenance: 6-15 mg/day divided 2 or 3 times daily; alternatively, 1-5 mg orally twice daily; may increase the dose to 20 mg/day in divided doses; some patients may benefit from up to 40 mg/day in divided doses

Pediatric: (off label)

• Initial: 0.05-0.1 mg/kg/day orally divided every 8 hours
• Titrate to 0.5 mg/kg/day; not to exceed 20 mg/day

PTSD-Related Nightmares and Sleep Disruption (off label)

• Initial: 1 mg orally at bedtime
• Maintenance: 1 mg orally at bedtime initially; may increase the dose to 2 mg at bedtime; adjust dose based on response and tolerability in 1-2 mg increments every 7 days; not to exceed 15 mg/day

Benign Prostate Hypertrophy (off label)

• Initial: 0.5 mg orally every 12 hours
• Maintenance: 2 mg orally every 12 hours

Raynaud Phenomenon (off label)

• 0.5-1 mg orally each day (at bedtime) or 0.5 mg orally twice daily; adjust dose based on response and tolerability up to 12 mg/day divided twice daily/three times daily

Administration

Adult:

• Give first dose and subsequent increases at bedtime to avoid syncope
• Okay with food

Pediatric:

• Okay with food

Side effects of prazosin include:

• dizziness
• drowsiness
• headache
• weakness
• nausea
• strong irregular heartbeat
• swelling
• dizziness upon standing
• fainting
• fever
• rash
• abdominal discomfort/pain
• diarrhea
• vomiting
• constipation
• shortness of breath
• spinning sensation (vertigo)
• depression
• nervousness
• urinary frequency
• blurred vision
• reddened whites of the eye
• nosebleed
• dry mouth
• nasal congestion
• fast heart rate
• numbness and tingling
• hallucinations
• itching
• hair loss
• white lesions in the mouth
• prolonged erection
• ringing in the ears (tinnitus)
• sweating
• positive autoimmune disease test (ANA titer)
• joint pain
• abnormal liver function tests
• impotence
• pancreatitis
• urinary incontinence
• fluid buildup under the retina
• cataracts
• falling asleep whenever relaxing
• flushing
• allergic reaction
• feeling unwell (malaise)
• pain
• chest pain
• low blood pressure (hypotension)
• enlarged breasts in men (gynecomastia)
• slow heart rate
• insomnia
• hives
• inflammation of blood vessels
• eye pain
• small pupil syndrome/intraoperative floppy iris syndrome (IFIS)

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

• Prazosin has no known severe interactions with other drugs.
• Serious interactions of prazosin include:
  • sildenafil
  • tamsulosin
  • vardenafil
  • Yohimbe
  • Prazosin has moderate interactions with at least 96 different drugs.
• Moderate interactions of prazosin include:
  • brimonidine
  • butcher's broom
  • ethanol
  • lofexidine
  • phenylephrine
  • phenylephrine (orally)
  • tizanidine
  • treprostinil

This information does not contain all possible interactions or adverse effects. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns, or for more information about this medicine.

Warnings

This medication contains prazosin. Do not take Minipress, Prazosin, or Prazo if you are allergic to prazosin or any ingredients contained in this drug.

Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately

Contraindications

• Hypersensitivity

Effects of Drug Abuse

• No information available

Short-Term Effects

• See "What Are Side Effects Associated with Using Prazosin?"

Long-Term Effects

• See "What Are Side Effects Associated with Using Prazosin?"

Cautions

• The risk of syncope; has no relation to plasma prazosin concentration; if syncope occurs, place the patient in the recumbent position and treat supportively as necessary
• Discontinue if angina symptoms occur or worsen
• May cause central nervous system depression, which may impair physical or internal abilities; use caution when performing tasks that require mental alertness
• May impair the 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 (sildenafil) can result in additive blood pressure-lowering effects and symptomatic hypotension; initiate PDE-5 inhibitor therapy at the 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 the erection persists over 4 hours, seek immediate medical assistance
• May cause significant orthostatic hypotension and syncope with the sudden loss of consciousness, especially 30-90 min of the 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 the dry mouth and urinary complications can be bothersome in the elderly

Pregnancy and Lactation

• Use prazosin during pregnancy with caution if benefits outweigh risks
• Animal studies show risk and human studies are not available, or neither animal nor human studies were done
• Prazosin is excreted in breast milk; use caution if breastfeeding
• Consult your physician