Rx Insights: Alpha-Adrenergic Blockers (α-Blockers)

Alpha-adrenergic blockers are drugs that inhibit the action of norepinephrine and epinephrine on alpha-adrenergic receptors, leading to relaxation of smooth muscle in blood vessels and certain organs. By blocking α₁-receptors, they cause vasodilation, which helps lower blood pressure and reduce the workload on the heart. These agents are commonly used in the management of hypertension, benign prostatic hyperplasia (BPH), and certain cases of pheochromocytoma. Examples include prazosin, doxazosin, and tamsulosin.

Rx Insights: Alpha-Adrenergic Blockers (α-Blockers)

💊 Drug Class: 

Adrenergic antagonists that block α₁ or both α₁ and α₂ receptors, leading to vasodilation and smooth muscle relaxation.

🧬 Mechanism of Action: 

α₁ blockade: relaxes vascular smooth muscle → ↓ peripheral resistance → ↓ BP.

Bladder neck & prostate relaxation: improves urinary flow in BPH.

α₂ blockade (in some drugs): enhances norepinephrine release.

💊 Common Drugs: 

Selective α₁ blockers: Prazosin, Terazosin, Doxazosin, Tamsulosin, Alfuzosin, Silodosin.

Non-selective α blockers: Phentolamine, Phenoxybenzamine.

✅ Indications: 

Hypertension (adjunct or resistant cases).

Benign Prostatic Hyperplasia (BPH).

Pheochromocytoma (phenoxybenzamine, phentolamine).

Raynaud’s phenomenon.

⚠️ Side Effects: 

First-dose hypotension (“first-dose effect”).

Dizziness, postural hypotension, headache.

Reflex tachycardia.

Nasal congestion.

Retrograde ejaculation (esp. tamsulosin).

🚫 Contraindications: 

History of orthostatic hypotension.

Severe liver impairment (for some agents).

Caution in elderly (fall risk due to hypotension).

🔍 Monitoring: 

Blood pressure (supine & standing).

Heart rate (for reflex tachycardia).

Symptoms of dizziness or syncope.

Urinary symptoms in BPH patients.

💊 Major Drug Interactions: 

1. PDE-5 inhibitors (sildenafil, tadalafil) → severe hypotension.

2. Other antihypertensives (β-blockers, diuretics) → additive BP lowering.

3. Clonidine withdrawal while on α-blockers → rebound hypertension.

💡 Clinical Tips: 

Give first dose at bedtime to reduce syncope risk.

Tamsulosin, Silodosin, Alfuzosin are uroselective → preferred for BPH.

Phenoxybenzamine (irreversible) used for pheochromocytoma pre-op.

Avoid abrupt discontinuation → rebound hypertension possible.