Calcium-channel blockers

Why would I take calcium-channel blockers?

Your GP may prescribe calcium-channel blockers if you have:

  • angina
  • high blood pressure (hypertension)
  • disturbance of the normal heart rhythm (arrhythmia)
  • Raynaud's phenomenon (pale, cold hands and feet caused by narrowing of the arteries that supply them with blood)

If you get cluster headaches (severe headaches usually affecting the area around one eye or temple), you may be prescribed a particular type of calcium-channel blocker called verapamil to try to prevent them.

If you have angina, your GP will usually only prescribe a calcium-channel blocker if beta-blockers (a different type of heart medicine) haven’t worked well enough alone or if there is a reason why you can't take them.

What are the main types of calcium-channel blocker?

There are three main types of calcium-channel blockers.

  • The phenylalkylamines mainly affect the heart, reducing how hard it can work. You may be prescribed these to treat angina, high blood pressure and arrhythmia. These medicines aren’t suitable if you have heart failure or if you are taking beta-blockers, which also stop your heart working so hard. This group includes verapamil.
  • The dihydropyridines mainly affect the arteries, causing them to become wider, which lowers blood pressure. This group includes most of the other commonly used calcium-channel blockers, such as amlodipine and nifedipine.
  • The benzothiazepines affect both the heart and the arteries. These can be used to treat angina or high blood pressure. This group includes diltiazem.

Individual calcium-channel blockers work in different ways, so one that is taken to treat a certain condition may not be suitable for another.

How do calcium-channel blockers work?

Effect on the heart

Your heartbeat is controlled by special cells that generate electrical impulses, acting like pacemakers to regulate how often your heart beats. These electrical impulses flow from cell to cell within the heart and are converted into chemical signals.

One of these chemical signals is a rising level of calcium inside the muscle cell. This causes the muscle to contract.

Calcium-channel blockers slow down the amount of calcium that can get into heart muscle cells and so reduce how fast and strongly it can contract. This effect can help with the symptoms of angina and irregular heart rhythms, but this can vary depending on the type of medicine you’re prescribed.

Effect on blood vessels

The arteries that carry blood from your heart to the rest of your body have walls that contain a special type of muscle called smooth muscle, which controls the width of the arteries.

As the level of calcium inside muscle cells increases, the muscle contracts and the artery narrows. This raises your blood pressure because your blood is squeezed into a smaller space.

When calcium channels are blocked calcium can’t enter the cells so there is no signal to contract. Instead, the muscle cells in the blood vessels relax, causing the arteries to widen (this is called vasodilation). This helps to lower your blood pressure. Calcium-channel blockers also prevent angina by widening the coronary arteries that supply the heart and allowing more oxygen to reach the heart muscle cells.

How to take calcium-channel blockers

Calcium-channel blockers are only available on prescription. They usually come as tablets or capsules that you take once or twice a day. Long-acting versions, which are sometimes called 'modified release', are also available.

It’s important that you make sure you always have a prescription for the same brand of calcium-channel blocker because different brands aren’t necessarily absorbed by your body in the same way.

Don’t stop taking a calcium-channel blocker suddenly because this may make angina worse. Your GP will tell you how to reduce your calcium-channel blockers gradually if you need to stop taking them.

Always ask your GP for advice and read the patient information leaflet that comes with your medicine.

Special care

Your GP may not prescribe calcium-channel blockers if you’re pregnant or breastfeeding, have recently had a heart attack or certain other conditions, or are taking beta-blockers. Talk to your GP for more advice.

Side-effects of calcium-channel blockers

Side-effects are the unwanted effects of taking a medicine. This section doesn’t include every possible side-effect of calcium-channel blockers. Please read the patient information leaflet that comes with your medicine for more information.

Calcium-channel blockers can cause a drop in your blood pressure. This can make you feel dizzy when you stand up. To help prevent this, make sure you get up slowly when you stand up from lying or sitting down, and stay next to your bed or chair until you're sure that you aren’t feeling dizzy. Don’t drive or do anything else that needs you to be alert until you know how you react to your medicine.

Calcium-channel blockers slow down your heart (especially the medicines verapamil and diltiazem) and can cause headaches, constipation, flushing of your face and fluid retention, especially around your ankles.

Interactions of calcium-channel blockers with other medicines

Some calcium-channel blockers can be affected if you eat grapefruit or drink grapefruit juice so that the medicine is absorbed by your body at a different rate. Check with your GP or pharmacist whether you can still have grapefruit with the type of calcium-channel blocker you have been prescribed.

Also check with your GP or pharmacist before you take any other medicines or herbal remedies at the same time as a calcium-channel blocker.

Names of common calcium-channel blockers

The main types of calcium-channel blockers are shown in the table.

All medicines have a generic name. Many medicines also have one or more brand names. Generic names are written in lower case, whereas brand names start with a capital letter. 

Generic names Examples of common brand names
amlodipine Exforge (in combination with valsartan), Istin
diltiazem Adizem-SR, Adizem-XL, Angitil SR, Angitil XL, Calcicard CR, Dilcardia SR, Dilzem SR, Dilzem XL, Slozem, Tildiem, Tildiem LA, Tildiem Retard, Viazem XL, Zemtard
felodipine Cardioplen XL, Felogen XL, Felotens XL, Keloc SR, Neofel XL, Parmid XL, Plendil, Vascalpha
isradipine

Prescal

lacidipine Motens
lercanidipine

Zanidip

nicardipine Cardene, Cardene SR, Nicardipine
nifedipine Adalat, Adalat LA, Adalat Retard, Adipine MR, Adipine XL, Coracten SR, Coracten XL, Fortipine LA 40, Nifedipress MR, Tensipine MR, Valni XL
nimodipine Nimotop
verapamil Cordilox, Securon, Half Securon SR, Securon SR, Univer, Verapress MR, Vertab SR 240

What is the difference between XL and SR forms of a medicine?

Answer

XL means extended release and SR means sustained release. XL forms of calcium-channel blockers last for longer in your body than SR forms. This means you need to take them less often.

Explanation

Some types of tablets or capsules are designed specifically to be broken down slowly in your body, so that the medicine takes longer to get into your bloodstream. This means your body receives a steady, continuous dose of the medicine, and its effects last for longer than those of an ordinary tablet. Different forms may release the active medicine into your bloodstream at different rates.

The SR form of calcium-channel blockers has been modified to release the medicine over a few hours, for example, the medicine might be in granule form rather than powder form. You will usually take them twice daily. Different brands of medicine may use the terms MR (modified release), CR (controlled release) or Retard, but these all mean the same as SR.

The XL form of calcium-channel blockers is designed to stay in your body even longer – usually more than 24 hours. This means you may only have to take your medicine once a day. Different brands of medicine may use the term LA (long-acting) instead of XL.

Diltiazem and nifedipine are examples of calcium-channel blockers that have a number of different slow-release forms.

You must swallow these types of medicine whole and not chew, crush or break them up, as this makes their slow-release mechanism ineffective. It can be dangerous if all the medicine is released into your body at once.

Don’t take a different brand of calcium-channel blocker to the one that has been prescribed for you, as different brands can be released into your body at slightly varying rates.

I have forgotten to take a tablet - what can I do?

Answer

This depends on the exact type of calcium-channel blocker you’re taking, and how late you are with taking your medicine.

Explanation

First, check the patient information leaflet that comes with your medicine to find out what you need to do if you miss a dose of your medicine. Usually, you will just need to take your medicine as soon as you remember. But, if it's nearly time for your next dose, you should miss a dose and just take the next one at the usual time. Never take a double dose to make up for one that you have forgotten because it can be dangerous to have a high level of the medicine in your body.

With some medicines, you must not take the missed tablet/capsule if you are more than four hours late taking the dose. All medicines are different, so it's important that you check the patient information leaflet. If you’re still unsure, speak to your pharmacist or GP.

Never stop taking your calcium-channel blockers unless your GP tells you to. Calcium-channel blockers need to be stopped gradually because stopping them suddenly can cause pain and tightness in your chest (angina). 

Can I carry on taking my calcium-channel blocker if I become pregnant?

Answer

You may need to stop taking your calcium-channel blocker if you become pregnant. However, talk to your GP before stopping any medicines – he or she will tell you if you need to change your medicine.

Explanation

Some calcium-channel blockers aren’t advised for women who are pregnant. Tell your GP if you’re trying for a baby or have become pregnant.

In particular, diltiazem can be harmful to your unborn baby. It shouldn't be taken during pregnancy or if you're trying for a baby. Your GP might prescribe a different medicine instead. Other calcium-channel blockers, such as nifedipine and verapamil, are also thought to be best avoided while pregnant, but you may need to keep taking them for your own health. If you’re taking these medicines, your GP will weigh up the risk of harm to your baby against your need for the medicine.

If you usually take calcium-channel blockers for high blood pressure and want to try for a baby or you become pregnant, your GP may suggest you switch to a different type of medicine, such as a beta-blocker or a medicine called methyldopa.

You may also need to carry on taking alternative medicines to calcium-channel blockers while you’re breastfeeding, as the medicines can get into your breast milk.