There are three main types of calcium-channel blockers.
- The phenylalkylamines mainly affect your 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’re taking beta-blockers. This group includes verapamil.
- The dihydropyridines mainly affect your arteries, causing them to become wider, which lowers blood pressure. They are used to treat Raynaud’s phenomenon. This group includes most of the other commonly used calcium-channel blockers, such as amlodipine and nifedipine.
- The benzothiazepines affect both your heart and your 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.
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.
Effect on blood vessels
Arteries carry blood from your heart to the rest of your body. They 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 your heart. This allows more oxygen to reach the heart muscle cells.
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 always have a prescription for the same brand of calcium-channel blocker. This is 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.
Your GP may not prescribe calcium-channel blockers if you’ve recently had a heart attack or taking beta-blockers. Or, if you’re pregnant or breastfeeding. Talk to your GP for more advice.
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. Also 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 can slow down your heart (especially verapamil) and can cause headaches, constipation, flushing of your face and fluid retention, especially around your ankles.
Other possible side-effects include:
- feeling sick
Some calcium-channel blockers can be affected if you eat grapefruit or drink grapefruit juice. This can cause the medicine to be absorbed by your body at a different rate. Check with your pharmacist to see if you can still have grapefruit with your calcium-channel blocker.
Calcium-channel blockers can also interact with other medicines, including some other heart medicines and certain antibiotics. Always check with your GP or pharmacist before you take any other medicines or herbal remedies at the same time as a calcium-channel blocker.
The main types of calcium-channel blockers are shown in the table below.
All medicines have a generic name. Many medicines also have one or more brand names. Generic names are written in lower case, 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 X, Parmid XL, Plendil, Triapin (in combination with ramipril), Vascalpha isradipine
lacidipine Motens lercanidipine
nicardipine Cardene, Cardene SR nifedipine Adalat, Adalat LA, Adalat Retard, Adipine MR, Adipine XL, Beta-Adalat (in combination with atenolol), Coracten SR, Coracten XL, Fortipine LA 40, Nifedipress MR, Tenif (in combination with atenolol), Tensipine MR, Valni XL nimodipine Nimotop verapamil Cordilox, Securon, Half Securon SR, Securon SR, Univer, Verapress MR, Vertab SR 240
What's the difference between XL and SR forms of a medicine?
XL means extended or prolonged 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.
Some types of tablets or capsules are designed to be broken down slowly in your body. This means that the medicine takes longer to get into your bloodstream. This gives you a steady, continuous dose of the medicine, so its effects last for longer than 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), LA (long acting) 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.
Diltiazem and nifedipine are examples of calcium-channel blockers that have a number of different slow-release forms.
You must swallow these formulations whole and not chew or crush 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. Different brands can be released into your body at slightly varying rates.
I've forgotten to take a tablet – what can I do?
This depends on the exact type of calcium-channel blocker you’re taking, and how late you are with taking your medicine.
First, check the patient information leaflet that comes with your medicine. This will explain 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 may need to miss a dose. You then take the next one at the usual time. Never take a double dose to make up for one that you have forgotten. 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’re 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?
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.
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, also aren’t advised if you’re pregnant. However you may need to keep taking them for your own health. Your GP will weigh up the risk of harm to your baby with your need for the medicine.
If you take calcium-channel blockers for high blood pressure and want to have a baby or become pregnant, your GP may suggest you switch. He or she may prescribe a beta-blocker or a medicine called methyldopa instead.
You may also need to carry on taking alternative medicines to calcium-channel blockers while you’re breastfeeding. This is because they can get into your breast milk.
- Joint Formulary Committee. British National Formulary (online) London: BMJ group and Pharmaceutical Press. www.medicinescomplete.com, accessed 28 October 2013 (online version)
- Raynaud’s phenomenon. NICE Clinical Knowledge Summaries. cks.nice.org.uk, published June 2009
- Headache – cluster. NICE Clinical Knowledge Summaries. cks.nice.org.uk, published November 2012
- Koeppen B and Stanton B. Berne & Levy Physiology. 6th ed. St Louis: Mosby, 2009:302
- Rang HP, Dale MM, Ritter JM et al. Rang and Dale’s Pharmacology. 6th ed. Churchill Livingstone Elsevier. 2007: 295
- Hypertension. Medscape. www.emedicine.medscape.com, published 7 October 2013
- Verapamil tablets BP 80mg summary of product characteristics. electronic Medicines Compendium (eMC). www.medicines.org.uk, published 23 March 2011
- MHRA guideline for the naming of medicinal products and braille requirements for name on label. Medicines and Healthcare Products Regulatory Agency. www.mhra.gov.uk, accessed 28 October 2013
- Hypertension in pregnancy: the management of hypertensive disorders during pregnancy. National Institute for Health and Care Excellence (NICE) 2010. www.nice.org.uk
- Securon SR/Half Securon SR patient information leaflet. electronic Medicines Compendium (eMC). www.medicines.org.uk, published January 2013
- Adizem-SR capsules patient information leaflet. electronic Medicines Compendium (eMC) www.medicines.org.uk, published September 2010
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