How Do Alpha Blockers Work?

Alpha blockers, also known as alpha-adrenergic antagonists, are used to treat conditions such as high blood pressure, benign prostatic hyperplasia (age-associated prostate gland enlargement that can cause urination difficulty), and Raynaud’s disease, which is a rare circulatory disorder affecting hands and feet. Alpha blockers affect the sympathetic nervous system and work by inhibiting alpha receptors. Alpha receptors are of two types: alpha receptor 1 and alpha receptor 2.

Alpha 1 receptors are present on the vascular smooth muscle of the skin, sphincters of the gastrointestinal system, kidney, and brain. They cause constriction of the vessels when activated by catecholamines (hormones made by your adrenal glands) such as epinephrine and norepinephrine, leading to a decrease in the blood flow and an increase in blood pressure.

Alpha 2 receptors are present on the peripheral nerve endings. These receptors inhibit the release of norepinephrine when activated. This is a feedback mechanism to maintain the levels of norepinephrine, which maintains the blood flow by constriction and dilation of the blood vessels.

Alpha blockers are divided into three types:

• Nonselective alpha blockers (alpha 1 and alpha 2)

These alpha blockers widen the blood vessels by blocking both alpha 1 and alpha 2 receptors. The blocking of alpha 1 receptors causes the widening of the blood vessels by inhibiting the action of catecholamines that cause vasoconstriction. The blocking of alpha 2 receptors increases the release of norepinephrine. This reduces the force of the vasodilation caused by the blocking of alpha 1 receptors. These drugs are used in conditions that increase sympathetic activity such as stress and to treat pheochromocytoma (a rare, usually noncancerous (benign) tumor that develops in an adrenal gland).

• Selective alpha-1 blockers

These alpha blockers inhibit norepinephrine from activating the alpha 1 receptors, causing widening of the blood vessels. This increases the free flow of blood and decreases blood pressure. These receptors also cause relaxation of the smooth muscle in the prostate and improve urine flow in patients with benign prostatic hyperplasia.

• Selective alpha-2 blockers

These alpha blockers work by inhibiting alpha 2 receptors and cause negative feedback of norepinephrine, stimulating the sympathetic nervous system.

Alpha blockers are used to treat the following:

• Benign prostate hyperplasia
• High blood pressure
• Pheochromocytoma
• Heart failure
• Dermal necrosis
• Raynaud’s phenomenon
• Improve systemic oxygen delivery and stabilize the pulmonary flow

• Postural hypotension (a form of low blood pressure that happens when you stand up from sitting or lying down)
• Dizziness and faintness
• Headache
• Tachycardia (a heart rate over 100 beats per minute)
• Nasal stuffiness
• Peripheral edema
• Decreased ejaculation

The information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Drug names include:

• Dibenzyline
• Hytrin
• Minipress
• OraVerse
• Phenoxybenzamine
• Phentolamine
• Prazin
• Prazo
• Prazosin
• Regitine
• Terazosin