What are calcium-channel blockers?

Calcium-channel blockers (sometimes called calcium-antagonists) are a group of drugs that affect the way calcium passes into certain muscle cells. They are used to treat various conditions including high blood pressure, angina, Raynaud's phenomenon, and some arrhythmias (abnormal heart rhythms).

Calcium-channel blockers can be used alone. However, Calcium-channel blockers are often combined with another drugs (such as a beta-blocker) to treat high blood pressure or angina when one drug alone has not worked so well.

How do calcium-channel blockers work?

The heart is mainly made of special muscle cells which contract to pump blood into the arteries (blood vessels). The walls of the arteries also contain 'smooth' muscle cells. When these contract the artery narrows. The heart muscle cells and smooth muscle cells need calcium to contract. Calcium passes into these cells via tiny 'channels'.

Calcium-channel blockers reduce the amount of calcium that goes into these muscle cells. This causes these muscle cells to relax. So, the effects of these drugs are:

    * To widen the arteries which:
          o Reduces the blood pressure.
          o Helps to ease angina by widening the coronary arteries.
          o Can ease symptoms of Raynaud's phenomenon. In this condition you have cold and painful fingers and toes caused by narrowing of the arteries in the hands and feet.
    * To reduce the force and rate of the heartbeat. This helps to prevent angina pains.

Different types of calcium-channel blockers

Different types of calcium-channel blockers differ in their main sites of action in the body. Therefore, different types of Calcium-channel blockers are used for different conditions.

What are the possible side-effects?

Most people who take calcium-channel blockers have no side-effects, or only minor ones. Because of calcium-channel blockers action to relax and widen arteries, some people develop flushing and headache. These tend to ease over a few days if you continue to take the tablets. Mild ankle swelling is also quite common, particularly with dihydropyridine calcium-channel blockers.

Other side-effects of calcium-channel blockers are uncommon and include: feeling sick, palpitations, tiredness, dizziness, and rashes. This is not a complete list of all possible known side-effects. Read the information leaflet that comes with your particular brand for a full list of possible side-effects. But be optimistic: don't necessarily be put off taking these tablets. Serious side effects are rare, and it's wise not to stop them without speaking to your doctor.
Other considerations

Some people who suddenly stop taking calcium-channel blockers have a 'rebound' flare up of angina. Therefore, it is best not to stop taking calcium-channel blockers without first consulting a doctor.

If you are taking a calcium-channel blocker, do not drink grapefruit juice. This can interact with calcium-channel blockers and alter its effect.