Beta-Blockers

What are beta-blockers and how do they work?

Beta-blockers are drugs that are used to treat a variety of conditions. Their full correct name is 'beta-adrenoceptor blocking drugs', but they are commonly just called beta-blockers. There are several types of beta-blocker. They include: acebutolol, atenolol, betaxolol, bisoprolol, carvedilol, celiprolol, co-tenidone, esmolol, labetalol, metoprolol, nadolol, nebivolol, oxprenolol, pindolol, sotalol, propranolol, timolol. Each type has one or more brand names.

Beta-blockers work by blocking the transmission of certain nerve impulses.

The ends of some nerves release a chemical (neurotransmitter) called noradrenaline when the nerve is stimulated. This chemical then stimulates beta-adrenergic receptors. These receptors are tiny structures which occur on cells in various parts of the body including the heart, brain, and blood vessels. When these receptors are stimulated, they cause various effects. For example, nerve impulses to the heart can stimulate beta-adrenergic receptors on heart cells. This causes an increase in the force and rate of the heart beat.

The beta-adrenergic receptors are also stimulated by adrenaline, a hormone which circulates in the bloodstream. Adrenaline is made in the adrenal gland. The blood level of adrenaline can vary. For example, you may release a lot of adrenaline into the bloodstream when you are frightened or anxious which can cause an increase in your heart rate and other effects.

The beta-blocker drug 'sits' on beta-adrenergic receptors and stops ('blocks') the receptor from being stimulated. So, for example, if beta-receptors in the heart are blocked, the force and rate of the heart beat is reduced.

Which conditions are treated with beta-blockers?

Heart and blood vessel conditions

Because of their effect on the heart cells, beta-blockers may be used to:

• Prevent angina pains.
• Reduce the risk of a further heart attack if you have already had one.
• Control certain abnormal heart rhythms (arrhythmias).
• Help to treat heart failure.
• Lower blood pressure.

Other conditions

Because beta-receptors are found in other parts of the body, beta-blockers are also used for various other conditions. These include:

• Glaucoma. Beta-blocker eye drops reduce the fluid that you make in the front chamber of the eye. This reduces the pressure in the eye.
• Anxiety. Beta-blockers do not reduce anxiety itself, but can reduce some of the symptoms caused by anxiety. For example, they can reduce shaking (tremor) and a fast heart rate.
• Overactive thyroid gland. Beta-blockers can help to reduce the symptoms such as tremor, and slow down a fast heart rate.
• Migraine. Beta-blockers can reduce the number of migraine attacks if the attacks occur frequently.

What are the possible side-effects?

Most people who take beta-blockers have no side-effects, or only minor ones. However, because of their action in various parts of the body, some people have unwanted effects. For example:

• Sometimes the heart rate can go too slow. This can make you dizzy or feel faint.
• If you have asthma or are prone to 'bronchospasm' (sudden narrowing of the airways) you should not take beta-blockers. This is because beta-blockers may narrow the airways and make breathing symptoms worse. (There are some exceptions in certain circumstances when a beta-blocker is prescribed under the careful supervision of a doctor.)
• If you have diabetes you need to be aware that beta-blockers may dull the warning signs of a low blood sugar level (hypo). For example, you may not develop palpitations or tremor which tend to occur as the blood sugar is going too low.
• Some people develop cool hands and feet when taking beta-blockers. This is because they can constrict (narrow) small blood vessels and reduce the circulation to the skin of the hands and feet.
• Tiredness, depression, impotence, vivid dreams, nightmares and other sleeping problems occur in some people.
• There is some evidence to suggest that beta-blockers may provoke type 2 diabetes to develop in some people

The above is not a full list of possible side-effects - but mentions the main ones that may occur. Read the information leaflet that comes with your particular brand for a full list of possible side-effects and cautions.

Other considerations

Do not stop a beta-blocker suddenly without first consulting a doctor. When you take a beta-blocker regularly, the body becomes used to it. So, suddenly stopping it can sometimes cause problems such as palpitations, a rise in blood pressure, or a recurrence of angina pains. If you do need to stop a beta-blocker then your doctor may advise a gradual reduction in dose.