If the blood vessels on your heart get furred up, it can cause angina. If a medicine can widen the blood vessels, more blood can get through and make the angina better for a while. These medicines are called nitrates. They can be taken as a short-acting form, for when angina comes on; or they can be taken as a long-acting form to try to prevent angina.
What are nitrate medicines?
Nitrate medicines include glyceryl trinitrate (GTN), isosorbide dinitrate and isosorbide mononitrate. Each has various brand names. Nitrate drugs do not alter the underlying cause of angina. (Angina is usually caused by narrowing of the heart arteries due to a build-up of a fatty substance called atheroma. See separate leaflet called Angina.) However, nitrate medicines are good at easing and preventing angina pains.
How do nitrates work?
Nitrates work by relaxing the walls of blood vessels, which makes them slightly wider. By relaxing the blood vessels on the surface of the heart, the heart can get more blood flow and oxygen. That helps to treat angina, which is caused by not enough blood flow getting to the heart.
Nitrates also relax other blood vessels in the body, which takes the strain off the heart a little.
Short-acting nitrate preparations
Glyceryl trinitrate (GTN) tablets or sprays
GTN is commonly used to ease angina pains. Many people who have angina always carry their GTN spray or tablets with them. You take a dose under your tongue as required when a pain develops. GTN is absorbed quickly into the bloodstream from under the tongue. A dose works to ease the pain within a minute or so. If the first dose does not work, take a second dose after five minutes. (If the pain persists for 15 minutes despite taking GTN then call an ambulance.)
GTN tablets go off after a few weeks. Therefore, you need a fresh supply of tablets every eight weeks, and return any unused tablets to the pharmacist. You may prefer to use a GTN spray which has a much longer shelf life than tablets.
Some people with angina take a GTN tablet or a spray before certain types of exercise. For example, before climbing stairs. They know a pain is likely to develop with the exercise, but a dose of GTN is likely to prevent it.
Isosorbide dinitrate is sometimes used as an alternative to GTN for the immediate relief of angina pains when they develop. Again, it comes in tablet and spray form.
Long-acting nitrate preparations
If you have frequent angina pains, you are likely to be prescribed one or more medicines which aim to prevent the pains from developing. You need to take these each day as prescribed. Several groups of medicines can prevent angina pains and these include beta-blockers, calcium antagonists and long-acting nitrates.
Isosorbide mononitrate is a long-acting form of isosorbide dinitrate and works in the same way as the other nitrates: it relaxes the walls of the blood vessels and so boosts the blood flow.
All the nitrates (GTN, isosorbide dinitrate, and isosorbide mononitrate) come in long-acting preparations. A long-acting preparation takes longer to start working, so is not much use for immediate pain relief. But, it works for much longer after each dose than a short-acting preparation (which loses its effect after 20 minutes or so). Some preparations are slow-release or modified-release tablets. When you swallow these they gradually release a steady amount of nitrate which is absorbed into the body. Some preparations come as skin patches or ointments which release a steady amount of nitrate into the bloodstream through the skin.
Can my body get used to my nitrate medication?
If nitrate stays in your bloodstream all the time, your body becomes used to it and the nitrate then has much less of an effect. To overcome this tolerance the dose schedule aims to leave your blood free of nitrate, or with very low levels of it, for a few hours each day. This is why the slow-release tablets may not be prescribed at equal intervals throughout the day. This can result in your body being free of nitrate in the early hours when you are asleep.
What are the possible side-effects of nitrates?
Common side-effects include:
- A throbbing headache.
- A flushed face.
- Lightheadedness (from the nitrate causing low blood pressure).
- Feeling slightly nauseous.
- With the spray under the tongue: a slight burning or tingling sensation under the tongue.
Thankfully these side-effects are unpleasant but not serious. Often they get better once you've been using the medicine for a few weeks.
When should I not take a nitrate medication?
- You should not take nitrates if you have various other disorders. For example: hypertrophic obstructive cardiomyopathy, aortic stenosis, constrictive pericarditis, mitral stenosis or closed-angle glaucoma. (This is the less common form of glaucoma. Nitrates are fine if you have the more common type of glaucoma called open-angle glaucoma.) This is because the nitrate medicine can make these conditions worse.
Are there other medications I shouldn't take if I'm already on a nitrate?
- Nitrates interfere with some other medicines, which may cause problems. In particular, you should not take sildenafil (Viagra®) or similar medicines used for erectile dysfunction (impotence) if you are taking a nitrate. This is because the combination of the medicines could make your blood pressure go far too low, which can be dangerous.
Will my nitrate medicine stop me having a heart attack?
Although they help with the symptoms of chest pain from the blood vessels getting furred up, they don't change the underlying reason for the chest pains. So although they can make you feel better, they don't prevent heart attacks.
How do I report a side-effect to my medicine?
If you think you have had a side-effect to one of your medicines you can report this on the Yellow Card Scheme. You can do this online at the following web address: www.mhra.gov.uk/yellowcard.
The Yellow Card Scheme is used to make pharmacists, doctors and nurses aware of any new side-effects that medicines or any other healthcare products may have caused. If you wish to report a side-effect, you will need to provide basic information about:
- The side-effect.
- The name of the medicine which you think caused it.
- The person who had the side-effect.
- Your contact details as the reporter of the side-effect.
It is helpful if you have your medication - and/or the leaflet that came with it - with you while you fill out the report.
Further reading and references
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