Beta-blockers are a class of drugs targeting beta receptors found in the different parts of the body such as heart muscle, smooth muscles, blood vessels, airways, kidneys and other tissues. Beta-blockers reduce heart rate and thus decrease its oxygen demand.
Beta-blockers work by inhibiting the release of adrenaline and noradrenaline and reducing response to stress. Noradrenaline is a chemical released by stimulated nerve endings. It transmits signals from nerve endings to muscles, blood vessels and heart.
When are beta-blockers used?
Beta-blockers are commonly used in many different conditions like:
- Angina - dull chest discomfort due to restricted blood supply to the heart muscle
- Heart attack - sudden blockage of blood supply to a part of the heart muscle due blood clot
- Heart failure - heart is unable to pump adequate blood volume around the body
- Cardiac arrhythmias, including atrial fibrillation - fast and irregular heart beat
- Hypertension - abnormally high blood pressure (140/90 mmHg or above)
Less commonly these agents are used in anxiety, overactive thyroid (thyrotoxicosis), glaucoma and tremors.
Classification of beta-blockers
Beta blockers are non selective, ie without preference to any subtype of beta receptors (carvedilol, labetalol, propranolol, sotalol) or cardioselective, working mainly on heart tissue (atenolol, bisoprolol, metoprolol, nebivolol). Carvedilol, bisoprolol and sustained-release metoprolol can be used in heart failure patients.
Beta-blockers should not be stopped suddently due to the risk of rebound phenomenon (sudden deterioration in symptoms).
Beta blockers are contraindicated in asthma. Side effects include:
- dizziness and lightheadedness
- excessive fatigue
- bradycardia (slow heart beat)
- cold hands and feet
- slow heartbeat