Silodosin selectively blocks alpha-1A adrenergic receptors, which are primarily located in the smooth muscle of the prostate, bladder neck, and urethra. The mechanism of action involves:

1. Smooth Muscle Relaxation:
   • By inhibiting alpha-1A receptors, silodosin reduces the tone of the smooth muscles in the prostate and bladder neck.
2. Improved Urine Flow:
   • This relaxation decreases resistance to urine flow, alleviating symptoms such as difficulty starting urination, weak stream, and incomplete bladder emptying.
3. Selectivity:
   • Silodosin’s high selectivity for alpha-1A receptors minimizes its effects on blood vessels, reducing the risk of hypotension compared to non-selective alpha-blockers.

Silodosin is approved for the following condition:

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

The dosage of silodosin is standardized, but adjustments may be made based on patient response and tolerability. Below are general guidelines:

1. Adults:
   • Standard Dose: 8 mg taken orally once daily, preferably with a meal.
   • Administration: Swallow the capsule whole; do not crush or chew.
2. Special Populations:
   • Elderly: No dose adjustment is required.
   • Renal Impairment: Use with caution in patients with moderate renal impairment (CrCl 30–50 mL/min). Avoid use in severe renal impairment (CrCl < 30 mL/min).
   • Hepatic Impairment: No dose adjustment is needed for mild to moderate impairment. Avoid use in severe hepatic impairment.

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

1. Common Side Effects:
   • Retrograde ejaculation (abnormal ejaculation into the bladder)
   • Dizziness
   • Nasal congestion
   • Diarrhea
   • Orthostatic hypotension (dizziness upon standing)
2. Less Common Side Effects:
   • Headache
   • Nausea
   • Fatigue
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 silodosin or any component of the formulation.
   • Severe renal impairment (CrCl < 30 mL/min).
   • Severe hepatic impairment.
2. Warnings:
   • Orthostatic Hypotension: Patients should be cautious when standing up quickly, especially during the initial dose or dose escalation.
   • Pregnancy and Lactation: Silodosin is not indicated for use in women.
   • Cataract Surgery: Inform the ophthalmologist about silodosin use due to the risk of intraoperative floppy iris syndrome (IFIS).
3. Monitoring:
   • Monitor for signs of hypotension, especially in patients taking antihypertensive medications.
   • Regular assessment of BPH symptoms and urinary flow.

Silodosin 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. Strong CYP3A4 Inhibitors (e.g., ketoconazole, ritonavir): Increase silodosin levels, increasing the risk of side effects. Concurrent use is contraindicated.
4. Phosphodiesterase-5 Inhibitors (e.g., sildenafil): May cause additive hypotensive effects.
5. Alcohol: May enhance the hypotensive effects of silodosin.

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

• Generic Name: Silodosin
• Brand Names: Rapaflo (commonly used in the US), Urief (commonly used in the UK and Europe), and others depending on the region.