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

1. Smooth Muscle Relaxation:
   • In the prostate and bladder neck, terazosin reduces the tone of smooth muscles, decreasing resistance to urine flow and alleviating BPH symptoms.
   • In blood vessels, terazosin causes vasodilation, reducing peripheral vascular resistance and lowering blood pressure.
2. Improved Urine Flow:
   • By relaxing the prostate and bladder neck, terazosin improves symptoms such as difficulty starting urination, weak stream, and incomplete bladder emptying.
3. Blood Pressure Reduction:
   • Terazosin’s vasodilatory effects help lower blood pressure, making it useful in the management of hypertension.

Terazosin is approved for the following conditions:

1. 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
2. Hypertension:
   • Management of mild to moderate hypertension, either as monotherapy or in combination with other antihypertensive agents.

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

1. Benign Prostatic Hyperplasia (BPH):
   • Initial Dose: 1 mg taken orally at bedtime.
   • Maintenance Dose: Gradually increase to 2–10 mg once daily, based on symptom relief and tolerability.
   • Maximum Dose: 10 mg per day.
2. Hypertension:
   • Initial Dose: 1 mg taken orally at bedtime.
   • Maintenance Dose: Gradually increase to 2–20 mg once daily or in divided doses, based on blood pressure response.
   • Maximum Dose: 20 mg per day.
3. Administration:
   • Terazosin should be taken at the same time each day, preferably at bedtime, to minimize the risk of orthostatic hypotension.
   • Swallow the tablet whole; do not crush or chew.

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

1. Common Side Effects:
   • Dizziness
   • Headache
   • Fatigue
   • Nausea
   • Nasal congestion
2. Less Common Side Effects:
   • Orthostatic hypotension (dizziness upon standing)
   • Palpitations
   • Peripheral edema (swelling in the legs)
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 terazosin 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: Terazosin is not indicated for use in women.
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.

Terazosin 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 terazosin.
5. Alcohol: May enhance the hypotensive effects of terazosin.

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

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