Beta-blocker

Beta-blocker

Beta-blockers, also known as beta-adrenergic blocking agents, are a class of medications that are primarily used to manage abnormal heart rhythms, protect the heart from a second heart attack after a first heart attack (secondary prevention), and treat hypertension. They work by blocking the effects of the hormone epinephrine, also known as adrenaline, and slowing the heart's rate, thereby reducing blood pressure.

Mechanism of Action

Beta-blockers exert their effects by blocking the beta-adrenergic receptors in the heart and blood vessels. These receptors are part of the sympathetic nervous system, which is responsible for the "fight or flight" response. By inhibiting these receptors, beta-blockers reduce the heart rate, decrease cardiac output, and lower blood pressure.

There are three main types of beta-adrenergic receptors:

• Beta-1 receptors: Primarily located in the heart. Blocking these receptors reduces heart rate and force of contraction.
• Beta-2 receptors: Found in the lungs, gastrointestinal tract, liver, uterus, vascular smooth muscle, and skeletal muscle. Blocking these receptors can lead to bronchoconstriction and vasoconstriction.
• Beta-3 receptors: Found in adipose tissue and involved in the regulation of lipolysis.

Clinical Uses

Beta-blockers are used in the treatment of various cardiovascular conditions, including:

• Hypertension
• Angina pectoris
• Myocardial infarction (heart attack)
• Heart failure
• Arrhythmias, such as atrial fibrillation
• Migraine prophylaxis
• Anxiety

Common Beta-blockers

Some commonly prescribed beta-blockers include:

• Propranolol: A non-selective beta-blocker used for hypertension, angina, and anxiety.
• Atenolol: A selective beta-1 blocker used for hypertension and angina.
• Metoprolol: A selective beta-1 blocker used for hypertension, angina, and heart failure.
• Carvedilol: A non-selective beta-blocker with alpha-blocking activity, used for heart failure and hypertension.
• Bisoprolol: A selective beta-1 blocker used for hypertension and heart failure.

Side Effects

Common side effects of beta-blockers include:

• Fatigue
• Cold hands and feet
• Weight gain
• Depression
• Sleep disturbances

Less common but serious side effects can include:

• Bradycardia (slow heart rate)
• Hypotension (low blood pressure)
• Bronchospasm, especially in patients with asthma
• Heart block

Contraindications

Beta-blockers are contraindicated in patients with:

• Severe asthma or COPD
• Severe bradycardia
• Second or third-degree heart block
• Uncontrolled heart failure

See Also

• Adrenergic receptor
• Sympathetic nervous system
• Antihypertensive drug