Isosorbide dinitrate (Isoket Retard)

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Isosorbide dinitrate helps to prevent angina pain.

The most common side-effect is headache. This should pass after a few days.

Type of medicineA nitrate
Used forAngina; heart failure
Also calledIsoket Retard®
Available asTablets, and longer-acting tablets (called modified-release tablets)

Isosorbide dinitrate is prescribed mainly to prevent angina pain from developing. Angina pain develops if part of your heart muscle does not get as much blood and oxygen as it needs. It is usually caused by narrowing of your coronary arteries due to a build-up of a fatty substance called atheroma. The narrowing makes it more difficult for blood to flow to your heart muscle.

Isosorbide dinitrate works in two ways. It relaxes blood vessels in your body (causing them to widen) and this reduces the strain on your heart, making it easier for your heart to pump blood around your body. It also relaxes and widens blood vessels in your heart (coronary arteries), which increases the flow of blood to your heart muscle.

Some isosorbide dinitrate tablets can also be used to provide quick relief of angina pain when it happens. They are also sometimes prescribed for people with heart failure (where the heart does not beat as efficiently as it should).

Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start isosorbide dinitrate it is important that your doctor knows:

  • If you are pregnant or breast-feeding.
  • If you have any problems with the way your liver works, or any problems with the way your kidneys work.
  • If you have low blood pressure.
  • If you have been told by a doctor you have low levels of iron in your blood (anaemia), or low levels of oxygen in your blood (hypoxaemia).
  • If you have an underactive thyroid.
  • If you have an eye condition called glaucoma.
  • If you have recently had a head injury or a heart attack.
  • If you have ever had an allergic reaction to a medicine.
  • If you are taking other medicines, including those available to buy without a prescription, herbal or complementary medicines. It is particularly important that you tell your doctor if you are using any medicines to help treat erectile dysfunction.
  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about nitrate medicines, and it will also provide you with a full list of side-effects which you could experience from taking isosorbide dinitrate.
  • Standard tablets (sometimes called immediate-release tablets) are taken three or four times a day, with the last dose usually being taken no later than 6 pm. Longer-acting tablets (called modified-release or 'Retard' tablets) are taken twice daily, the first dose in the morning and the second dose mid-afternoon. Your doctor will tell you which type of tablets you are being supplied with, and your dose will be printed on the label of the pack to remind you about how to take them. You can take isosorbide dinitrate tablets either before or after meals.
  • If you are taking modified-release tablets, you should swallow the tablet whole - do not chew, break or crush the tablet before you swallow. This is because the tablet is specially made to release the medicine in a controlled way.
  • Try to take the tablets at the same times of day each day, as this will help you to remember to take your doses regularly. If you forget to take a dose at your usual time, take it when you remember. However, if it is nearly time to take your next dose when you remember, then leave out the forgotten dose and take your next dose when it is due. Do not take two doses together to make up for a missed dose.
  • Modified-release isosorbide dinitrate tablets are not suitable to take to treat chest pain during an angina attack. Your doctor will prescribe you a short-acting nitrate for you to take if this happens. Glyceryl trinitrate (GTN) is commonly prescribed for this.
  • Try to keep your regular appointments with your doctor. This is so your doctor can check on your progress
  • The longer you take isosorbide dinitrate, the more your body can become used to it (called tolerance) and then it can have less of an effect. To avoid this, your doses may not be prescribed at equal intervals throughout the day. It is important that you follow the instructions your doctor gives you about when to take your doses.
  • It is best not to drink alcohol while you are on isosorbide dinitrate. Alcohol will increase the risk of you experiencing side-effects such as feeling dizzy and light-headed.
  • If you are having an operation or dental treatment, please remember to tell the person carrying out the treatment which medicines you are taking.
  • If you buy any medicines, please check with a pharmacist that they are suitable for you to take with isosorbide dinitrate.

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the most common ones associated with isosorbide dinitrate. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.

Common isosorbide dinitrate side-effectsWhat can I do if I experience this?
HeadacheAsk your doctor or pharmacist to recommend a suitable painkiller. This usually disappears after a few days
Feeling dizzy or tiredDo not drive or use tools or machines while affected
Feeling your heart is beating quickly, flushingIf either of these becomes troublesome, speak with your doctor

If you experience any other symptoms which you think may be due to the medicine, please speak with your doctor or pharmacist for further advice.

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.
Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Further reading & references

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Helen Allen
Current Version:
Peer Reviewer:
Prof Cathy Jackson
Document ID:
3855 (v25)
Last Checked:
Next Review:
The Information Standard - certified member

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