Prazosin selectively blocks alpha-1 adrenergic receptors, which are located in the smooth muscle of blood vessels and the prostate. The mechanism of action involves:

1. Vasodilation:
   • By inhibiting alpha-1 receptors in blood vessels, prazosin causes relaxation of vascular smooth muscle, leading to vasodilation and a reduction in peripheral vascular resistance.
   • This results in a decrease in blood pressure, making it effective for hypertension.
2. Prostate and Bladder Neck Relaxation:
   • In the prostate and bladder neck, prazosin reduces the tone of smooth muscles, decreasing resistance to urine flow and alleviating BPH symptoms.
3. Selectivity:
   • Prazosin’s selective action on alpha-1 receptors minimizes its effects on alpha-2 receptors, reducing the risk of reflex tachycardia (unlike non-selective alpha-blockers).

Prazosin is approved for the following conditions:

1. Hypertension:
   • Management of mild to moderate hypertension, either as monotherapy or in combination with other antihypertensive agents.
2. Benign Prostatic Hyperplasia (BPH):
   • Treatment of lower urinary tract symptoms (LUTS) associated with BPH, such as:
     • Difficulty starting urination
     • Weak urine stream
     • Frequent urination (especially at night)
     • Incomplete bladder emptying
3. Off-Label Uses:
   • PTSD-Related Nightmares: Prazosin is used to reduce the frequency and severity of nightmares in patients with post-traumatic stress disorder.
   • Raynaud's Phenomenon: Prazosin may be used to improve blood flow in patients with Raynaud's phenomenon.
   • Congestive Heart Failure (CHF): Occasionally used to reduce afterload in CHF patients.

The dosage of prazosin varies depending on the indication and patient response. Below are general guidelines:

1. Hypertension:
   • Initial Dose: 0.5–1 mg taken orally 2–3 times daily.
   • Maintenance Dose: Gradually increase to 6–15 mg daily in divided doses, based on blood pressure response.
   • Maximum Dose: 20 mg per day.
2. Benign Prostatic Hyperplasia (BPH):
   • Initial Dose: 0.5 mg taken orally twice daily.
   • Maintenance Dose: Gradually increase to 2–5 mg twice daily, based on symptom relief and tolerability.
3. Off-Label Uses (e.g., PTSD-Related Nightmares):
   • Initial Dose: 1 mg taken orally at bedtime.
   • Maintenance Dose: Gradually increase to 3–15 mg daily, based on response and tolerability.
4. Administration:
   • Prazosin should be taken with food to enhance absorption and reduce the risk of side effects.
   • Swallow the tablet whole; do not crush or chew.

Prazosin is generally well-tolerated, but some side effects may occur. These include:

1. Common Side Effects:
   • Dizziness
   • Headache
   • Fatigue
   • Nausea
   • Palpitations
2. Less Common Side Effects:
   • Orthostatic hypotension (dizziness upon standing)
   • Nasal congestion
   • Dry mouth
3. Rare but Serious Side Effects:
   • Priapism: Prolonged and painful erection. This is a medical emergency and requires immediate treatment.
   • Severe Hypotension: Rare cases of significant blood pressure drops.
   • Syncope (Fainting): Especially during the initial dose or dose escalation.

1. Contraindications:
   • Hypersensitivity to prazosin or any component of the formulation.
   • Severe hepatic impairment.
2. Warnings:
   • Orthostatic Hypotension: Patients should be cautious when standing up quickly, especially during the initial dose or dose escalation.
   • First-Dose Effect: The first dose or any dose increase may cause a significant drop in blood pressure, leading to dizziness or fainting. The initial dose should be taken at bedtime.
   • Pregnancy and Lactation: Prazosin is not indicated for use in women unless the benefits outweigh the risks.
3. Monitoring:
   • Monitor for signs of hypotension, especially in patients taking antihypertensive medications.
   • Regular assessment of BPH symptoms and urinary flow.
   • Blood pressure monitoring in patients with hypertension.

Prazosin interacts with several medications, including:

1. Other Alpha-Blockers (e.g., doxazosin): Increased risk of hypotension.
2. Antihypertensive Medications: May cause additive hypotensive effects.
3. Phosphodiesterase-5 Inhibitors (e.g., sildenafil): May cause additive hypotensive effects.
4. Diuretics: May enhance the hypotensive effects of prazosin.
5. Alcohol: May enhance the hypotensive effects of prazosin.

Prazosin is available under its generic name as well as brand names. Some common formulations include:

• Generic Name: Prazosin hydrochloride
• Brand Names: Minipress (commonly used in the US and UK), and others depending on the region.