Calcium-Channel Blockers

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).

A calcium-channel blocker can be used alone. However, one is often combined with another drug (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:
  • Reduces the blood pressure.
  • Helps to ease angina by widening the coronary arteries.
  • 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 are used for different conditions.

Verapamil

This is commonly used to treat angina and high blood pressure. It is also used to treat certain arrhythmias (when the heart rate is abnormally fast). This is because it also blocks calcium going into the special conducting cells in the heart and so it can slow the heart rate. You should not take verapamil in addition to a beta-blocker drug.

Diltiazem

This is used to treat angina and high blood pressure. Unlike verapamil it is not used to treat arrhythmias. It can be used in addition to a beta-blocker if this combination is necessary.
As a rule, you should not take verapamil or diltiazem if you have heart failure. This is because they 'relax' the heart, and can make heart failure worse.

Dihydropyridine calcium-channel blockers

These include amlodipine, felodipine, isradipine, lacidipine, lercanidipine, nicardipine, nifedipine, and nimodipine. These have more effect of relaxing blood vessels, and less effect of relaxing the heart muscle than verapamil or diltiazam. Most are used to treat high blood pressure or angina. But, isradipine, lacidipine, and lercanidipine are only used to treat high blood pressure. Nifedipine is also used to treat Raynaud's phenomenon.

As they do not affect heart muscle much, dihydropyridine calcium-channel blockers are not useful for arrhythmias. They are also unlikely to make heart failure worse. You can take one of these in addition to a beta-blocker. In fact, a dihydropyridine calcium-channel blocker in addition to a beta-blocker drug is commonly used to prevent angina pains if either does not work well enough alone.

What are the possible side-effects?

Most people who take calcium-channel blockers have no side-effects, or only minor ones. Because of their 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.

Constipation is quite a common side-effect, especially with verapamil. You can often deal with this by increasing the amount of fibre that you eat, and increasing the amount of water and other fluids that you drink.

Other side-effects 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 a calcium-channel blocker have a 'rebound' flare up of angina. Therefore, it is best not to stop taking these drugs without first consulting a doctor.

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