Beta-blockers are used to treat several conditions, usually by regulating heart activity.
Also called beta-adrenoreceptor blocking agents, these medications bind to beta receptors present on the cells of the heart, arteries, kidneys and other tissues that are stimulated by the stress hormones (e.g. adrenaline and noradrenaline).
Beta blockers are often used to treat high blood pressure, angina, heart attack and atrial fibrillation. Less common indications include migraine, tremor and anxiety.
Examples of drugs in this class include acebutolol, atenolol, bisoprolol, carvedilol, celiprolol, labetalol, metoprolol, nadolol, nebivolol, oxprenolol, pindolol and timolol.
Mechanism of action
The sympathetic nervous system is part of the autonomic nervous system that controls various vital functions of the body including heart rate and blood pressure.
The two main beta receptors that are targeted by beta blockers are the beta 1 receptor and the beta 2 receptor. A large number of beta 1 receptors are present on the heart and kidney cells, while the beta 2 receptor is the predominant regulator of vascular and nonvascular smooth muscles.
Some beta blockers are selective and block the beta 1 receptor more than the beta 2 receptor. These are called cardioselective agents. Nonselective beta blockers are those that bind to both types of receptors.
Some of the effects of using beta blockers to block these receptors include:
Effects on the kidney - Blocking of the beta 1 receptors on the kidneys prevents the release of renin from juxta-glomerular cells. This suppresses the renin-angiotensin-aldosterone system, helping to regulate blood pressure as well as fluid and electrolyte balance.
Effects on the heart - Beta 1 receptors are present on the sino-atrial node, which is responsible for generating the impulses that make the heart beat. Blocking the sino-atrial node therefore reduces heart rate.
Uses of beta blockers
Some examples of the conditions beta blockers are used to treat include high blood pressure, angina, heart failure, cardiac arrhythmias and atrial fibrillation, anxiety, severely overactive thyroid (thyrotoxicosis), glaucoma and migraine.
Beta blockers can be taken in the form of capsules, a solution, eye drops or by injection and are usually eliminated from the body via the liver or kidney.
Beta blockers that are soluble in fats such as labetalol, metoprolol, pindolol and propranolol are excreted by the liver, while those that are soluble in water such as atenolol are cleared by the kidney. Fat soluble drugs have a short duration of action, while water soluble drugs have a longer duration of action.
Some of the side effects of beta blockers are more common than others.
Some examples of more common side effects are given below:
- Cold extremities (hands and feet)
- Slow heartbeat
- Blurred vision
- Diarrhea and nausea
Some examples of the less common side effects include:
- Loss of libido