Bloqueadores dos canais de cálcio

How do calcium channel blockers work?

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

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 medicines are:

• To widen the arteries, which:
  

  • Reduces the a pressão arterial.

  • Helps to treat angina by widening the coronary arteries.

  • Can ease symptoms of fenômeno de Raynaud. 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 heart rate. This helps to prevent angina, including the associated dor no peito.

When a pregnant woman goes into labour too early, calcium-channel blockers stop the muscles of the womb (uterus) from contracting.

Different types of calcium channel blockers differ in the main sites of action in the body:

Dihydropyridine calcium-channel blockers

Isso inclui:

• Amlodipine.

• Felodipine.

• Lacidipine.

• Lercanidipine.

• Nicardipine.

• Nifedipine.

• Nimodipine.

Most are used to treat high blood pressure or angina. (Lacidipine and lercanidipine are only used to treat high blood pressure.) Nifedipine is also used to treat Raynaud's phenomenon.

As they have very little effect on the special conducting cells in the heart, this type of calcium-channel blocker is not useful for arrhythmias. It is unlikely to make heart failure worse. It is safe to take with a beta-blocker.

Calcium channel blockers are most often used for treating pressão alta (hipertensão) or angina. If you need more than one blood pressure medication, a doctor may prescribe a calcium channel blocker in combination with one or two other medicines, such as an inibidor da ECA ou diuretic.

If you’ve been prescribed a calcium channel blocker for angina, you may also receive other medications, such as a beta-bloqueador ou nitrate, to help control your symptoms.

As a rule, you should not take verapamil or diltiazem if you have heart disease ou insuficiência cardíaca. This is because they have an effect on the heart muscle that makes it 'relax' and can make heart failure worse.

Most people who take calcium channel blockers have no side-effects, or only minor ones. Because their action is to relax and widen blood vessels (arteries), some people develop flushing and dor de cabeça. 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.

Constipação is quite a common side-effect of calcium channel blockers, 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:

• Sentindo-se mal.

• Palpitações.

• Cansaço.

• Tontura.

• Erupções cutâneas.

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. However, be optimistic - don't necessarily be put off taking these tablets. Serious side-effects are rare and it's wise not to stop calcium channel blockers without speaking with your doctor.

Hypertension is generally treated for life, as the medications only work while you are taking them. However, if you can change a significant risk factor, then your blood pressure might fall naturally and you might not need the drugs any more. So, for example, if you drink a lot of alcohol and manage to stop, or you have obesity and manage to lose a lot of weight, you might be able to come off the medications. If you do have a lifestyle change like this and start to feel dizzy then get your blood pressure checked, both sitting and standing, as it may be that it is now too low and you need to stop some of the tablets. It is probably less common to be able to stop calcium channel blockers which are taken for angina.