Prazosin (Minipress) is an alpha receptors blocker that inhibits the postsynaptic alpha-adrenergic receptors resulting in vasodilation. It is used as a second line of treatment in the management of hypertension.

It is also used as an off-label medicine for the treatment of:

• nightmares (post-traumatic stress disorder)
• Benign prostatic hyperplasia
• sleep disorders
• Raynaud phenomenon

Prazosin dose in Adults

Prazosin dose in the treatment of Hypertension:

• 1 mg two or three times a day.
• The dose is titrated up to a maximum dose of 20 mg per day in two or three divided doses.
• Rarely, a daily dose of 40 mg may be required.

• Concomitant diuretics or other antihypertensives:

  • The dose should be reduced to 1 - 2 mg three times a day if a concomitant diuretic or other antihypertensive drug is used.

Prazosin dose in the treatment of nightmares and sleep disruption:

• 1 mg at bedtime.
• The dose may be increased to 2 mg at bedtime after 2 to 3 days.
• The dose should be adjusted in increments of 1 - 5 mg at weekly intervals up to a maximum of 15 mg per day based on the patients' response and tolerability.
• The usual dose is 3 - 15 mg per day.

Prazosin dose in the treatment of Raynaud phenomenon:

• 0.5 to 1 mg orally once a day at bedtime or 0.5 mg two times a day.
• The dose is gradually adjusted up to a maximum of 12 mg/day in 2 - 3 divided doses based on the patients' response and tolerability.

Prazosin dose in Childrens

Prazosin dose in the treatment of Hypertension:

• Children and Adolescents:
  • 0.05 to 0.1 mg/kg/day in three divided doses administered every 8 hours.
  • The dose may be titrated up to 0.5 mg/kg/day in three divided doses to a maximum daily dose of 20 mg/day.
  • It should not be used as a first-line of treatment. Other preferred therapies like ACE-I, ARBs, calcium channel blockers and thiazide diuretics should be used as the first line of treatment.

Dose in the treatment of scorpion envenomation:

• Weight-directed:

  • Infants ≥4 months, Children, and Adolescents:
    • 0.03 mg/kg/dose.
    • The second dose should be administered at 3 or 6 hours after the first dose.
    • Subsequent doses may be administered every 3 to 6 hours for 48 hours or until the extremities are warm and dry.

• Fixed dosing:

  • Infants >6 months, Children, and Adolescents:
    • 0.25 mg orally three hourly until extremities are warm and dry.

Prazosin pregnancy Risk Category: C

• Prazosin crosses a placental barrier, and adverse fetal events were observed in animal studies.
• Its use for a short time does not cause harm to the fetus.
• Prazosin can be used to treat hypertension that is not treated.
• This is because it may be more harmful to the mother and the baby than other treatments.

Prazosin use during breastfeeding:

• Breastmilk contains small amounts of the drug.
• It should be used with caution by women who are breastfeeding.

Prazosin dose in Kidney Disease:

The manufacturer has not recommended any adjustment in the dose. It should be initiated at lower doses and titrated cautiously

Prazosin dose in Liver Disease:

The manufacturer has not recommended any adjustment in the dose.

Common Side Effects of Prazosin Include:

• Cardiovascular:

  • Palpitations

• Central Nervous System:

  • Dizziness
  • Drowsiness
  • Headache
  • Decreased Energy

• Gastrointestinal:

  • Nausea

• Neuromuscular & Skeletal:

  • Weakness

Less Common Side Effects Of Prazosin Include:

• Cardiovascular:

  • Edema
  • Orthostatic Hypotension
  • Syncope

• Central Nervous System:

  • Depression
  • Nervousness
  • Vertigo

• Dermatologic:

  • Skin Rash

• Gastrointestinal:

  • Constipation
  • Diarrhea
  • Vomiting
  • Xerostomia

• Genitourinary:

  • Urinary Frequency

• Ophthalmic:

  • Blurred Vision
  • Injected Sclera

• Respiratory:

  • Dyspnea
  • Epistaxis
  • Nasal Congestion

Contraindication to Prazosin Include:

Allergy to Quinazolines, Prazosin or any component of the formulation

Warnings and precautions

• Angina
  • Angina symptoms may be present or patients may notice an increase in the severity of ischemic heart disease.
  • Both cases should be treated immediately with prazosin.
• CNS depression:
  • It is possible to develop CNS depression.
  • Patients who are required to be alert for driving or operating heavy machinery should be cautious about taking the drug.
• Floppy iris syndrome:
  • Intraoperative floppy Iris Syndrome may occur in patients who have undergone cataract surgery.
  • Although the surgical procedure can be altered, it is possible to discontinue prazosin before the surgery.
• Orthostatic hypotension, syncope
  • Symptoms such as syncope or postural hypotension can occur after the first dose, and even after adjustment.
  • Patients who are taking antihypertensive medications (especially beta-blockers and vasodilators) or phosphodiesterase inhibitors, such as sildenafil, Tadalafil and Vardenafil, may experience syncopal attacks.
  • A syncopal attack can precede severe tachycardia. Patients should be aware of the possibility of an attack before increasing the dose.
• Priapism
  • It is possible to have prolonged erections. If the erection lasts longer than four hours, patients should seek medical attention.
• Heart failure:
  • Prazosin may exacerbate heart failure.
• Prostate cancer:
  • Before initiating treatment, patients with symptoms must first rule out prostate cancer.

Prazosin: Drug Interaction

Note: Drug Interaction Categories:

• Risk Factor C: Monitor When Using Combination
• Risk Factor D: Consider Treatment Modification
• Risk Factor X: Avoid Concomitant Use

Monitor:

Blood pressure (and postural hypotension) The 2017 Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults recommend the following targets:

• Confirmed hypertension and known cardiovascular disease or a 10-year ASCVD risk is greater than 10%:

  • Target blood pressure of less than 130/80 mm Hg is recommended

• Confirmed hypertension without markers of increased ASCVD risk:

  • Target blood pressure of less than 130/80 mm Hg may be reasonable

How to administer Prazosin (minipress)?

Administer the drug without regard to meals at the same time each day.

Mechanism of action of Prazosin (minipress):

It inhibits postsynaptic alpha adrenergic receptors competitively. The inhibition of the alpha-adrenergic receptors causes vasodilation and arterioles to dilate and decreases total peripheral resistance and blood pressure.

The antihypertensive effect is noticed within 2 hours with a peak effect in 2 - 4 hours

The duration of action is 10 to 24 hours

Distribution: V : 0.5 L/kg

Protein binding: Highly protein-bound (97%)

Metabolism: It is extensively metabolized via the liver via demethylation and conjugation

Bioavailability: 43% to 82%

Half-life elimination: 2 - 3 hours and prolonged in patients with CHF

The time to reach peak plasma concentration is about 3 hours

Excretion is primarily in the feces and minimally in the urine (6% to 10% as unchanged drug)

International Brands of Prazosin:

• Minipress
• APO-Prazo
• TEVA-Prazosin
• Alphapress
• Atodel
• Damin
• Deprazolin
• Hypotens
• Hypovase
• Hyprosin
• Lopress
• Minecin
• Minipres
• Minipres Retard
• Minipres SR
• Minipress
• Minipress SR
• Minipress XL
• Minison
• Mizosin
• Peripress
• Polpressin
• Polypress
• Pratisol
• Pratsiol
• Praxin
• Prazolin
• Prazopress
• Sinetens
• Tenosin
• Variprex

Prazosin Brands in Pakistan: