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 are commonly used to ease angina pains.
- 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, long acting nitrate preparations help to prevent the pains from developing.
- Isosorbide mononitrate iworks 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).
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.