How do nitrates work?

Nitrates (also known as nitric oxide) work by relaxing the walls of blood vessels, which makes them slightly wider. In angina they work by relaxing the walls of veins that return blood to the heart. This lowers the pressure of that blood and means the heart doesn't have to work as hard. They also make the blood vessels that supply the heart muscle widen 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 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 dinitrato, e mononitrato de isossorbida) 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.

• You may feel dizzy.

• 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.

• You should not take nitrates if you have various other disorders. For example: hypertrophic obstructive cardiomyopathy, estenose aórtica, pericardite constritiva, estenose mitral ou 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.

• 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.

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 dores no peito. So although they can make you feel better, they don't prevent heart attacks.

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 www.mhra.gov.uk/yellowcard.