1. About isosorbide mononitrate and isosorbide dinitrate
Isosorbide mononitrate and dinitrate are types of heart medicine called nitrates. They are similar medicines that work in the same way, but the doses are different so you'll need to take the type that you're prescribed.
They are used to prevent angina symptoms (chest pain), they do not work to treat a current angina attack.
They are also given with other medicines to treat heart failure including left ventricular failure.
Isosorbide mononitrate and dinitrate comes as tablets, or capsules. Isosorbide dinitrate also comes as an injection or drip (infusion), which is given in hospital.
Both isosorbide mononitrate and dinitrate are only available on prescription.
2. Key facts
- Both isosorbide mononitrate and isosorbide dinitrate are broken down into nitrates in the body. Nitrates work by widening blood vessels (veins and arteries). This increases the blood supply to your heart, which gets more oxygen to your heart muscles. This helps your heart to work properly and reduces chest pain.
- The tablets and capsules usually start to work within 1 hour.
- The most common side effects are headaches and feeling dizzy, weak or tired.
- If you stop taking isosorbide mononitrate or isosorbide dinitrate, your symptoms may get worse.
- You'll usually take these medicines for a long time, possibly for the rest of your life.
3. Who can and cannot take isosorbide mononitrate and isosorbide dinitrate
Isosorbide mononitrate and dinitrate can be taken by most adults aged 18 years and above.
This medicine is not suitable for some people. Tell your doctor or pharmacist if you have:
- ever had an allergic reaction to isosorbide mononitrate or isosorbide dinitrate or any other medicine
- any other heart problems, including a recent heart attack
- any recent brain or head injuries or problems
- ever had a stroke
- underactive thyroid (hypothyroidism)
- low blood pressure (hypotension)
- anaemia
- glaucoma
4. How and when to take isosorbide mononitrate and isosorbide dinitrate
Take isosorbide mononitrate and dinitrate exactly as your doctor or pharmacist tells you to.
Isosorbide mononitrate comes as standard tablets and slow-release (modified release) tablets and capsules.
Isosorbide dinitrate comes as standard tablets and slow-release tablets.
Slow-release tablets and capsules release the medicine gradually into your body. This means you do not need to take them as often as standard tablets.
How to take tablets or capsules
Swallow the tablets or capsules whole with a drink of water. Do not chew or crush them.
You can take either tablets or capsules with or without food.
Your doctor may tell you to leave a gap of 4 to 12 hours a day (usually when you are sleeping) where you do not take the tablets or capsules. This is called a "nitrate low" period and is needed to make sure your medicine works properly.
If you take isosorbide mononitrate or dinitrate 2 or 3 times a day, your doctor or pharmacist will explain how to space out your doses. For example, if you are taking standard tablets twice a day, they may tell you to take 1 dose in the morning at 8am and the second dose in the afternoon at 2pm (leaving a gap of 6 hours between your first and second dose).
Dosage
How much isosorbide mononitrate or dinitrate you take depends on your symptoms, the brand of medicine and the type of tablets or capsules you are taking.
The usual dose to prevent angina
Isosorbide mononitrate standard tablets:
- 10mg, taken twice a day, up to a maximum dose of 120mg, split into smaller doses
Isosorbide mononitrate slow-release tablets or capsules:
- 25mg to 60mg, up to a maximum dose of 120mg, taken once a day
Isosorbide dinitrate standard tablets:
- 30mg to 120mg, split into smaller doses
Isosorbide dinitrate slow-release tablets:
- 40mg, taken once or twice a day, up to a maximum dose of 60mg to 80mg, taken 2 or 3 times a day
The usual dose to treat heart failure
Isosorbide mononitrate standard tablets:
- 10mg to 20mg, taken 2 to 3 times a day, or 40mg, taken twice a day, up to a maximum dose of 120mg daily, split into smaller doses
Isosorbide dinitrate immediate release tablets:
- 40mg to 160mg, taken daily, up to a maximum dose of 240mg a day, split into divided doses
What if I take too much?
Taking too much isosorbide mononitrate or dinitrate may cause your blood pressure to fall too low, making you feel sick, faint and dizzy. If this happens, sit or lie down and put your feet up.
Immediate action required: Call 999 now if:
you have taken too much isosorbide mononitrate or dinitrate and:
- your mouth (lips, tongue or gums), face or skin start to look blue or grey. If you have darker skin your gums or the skin around your eyes may turn blue or grey
Urgent advice: Contact 111 for advice if:
- you take too many isosorbide mononitrate or isosorbide dinitrate tablets or capsules, and you feel unwell
Go to 111.nhs.uk or call 111
If you need to go to A&E, do not drive yourself – get someone else to drive you or call an ambulance.
Take any leftover tablets or capsules, and the packet or leaflet with you.
5. Side effects
Like all medicines, isosorbide mononitrate and dinitrate can cause side effects, although not everybody gets them. Side effects often improve as your body gets used to the medicine.
Common side effects
Talk to your doctor or pharmacist if these side effects bother you or last more than a few days:
- headaches
- feeling dizzy or weak
- feeling tired or sleepy
- feeling sick (nausea)
- flushing
- swelling in lower legs, ankles or feet (oedema)
Serious side effects
Serious side effects after taking isosorbide mononitrate and dinitrate are rare.
Immediate action required: Call 999 or go to A&E now if:
- you are having breathing difficulties that are new or worse than usual
- you get weakness in your arm, or one side of your body or face, difficulty speaking, or loss of coordination – these could be signs of a stroke
- your mouth (lips, tongue or gums), face or skin start to look blue or grey. If you have darker skin your gums or the skin around your eyes may turn blue or grey – these are signs of low oxygen levels in your body
- your heart starts beating much faster or slower than usual
- you get chest pain that is different or worse than your usual angina pain
- you have fainted
- you get severe pain in your eye, headache, blurred vision or you suddenly go blind in one eye – these could be signs of acute angle closure glaucoma
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to isosorbide mononitrate and isosorbide dinitrate.
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
These are not all the side effects of isosorbide mononitrate and isosorbide dinitrate. For a full list, see the leaflet inside your medicines packet.
You can report any suspected side effect using the Yellow Card safety scheme.
6. How to cope with side effects of isosorbide mononitrate and isosorbide dinitrate
What to do about:
- headaches – make sure you rest and drink plenty of water. Paracetamol is safe to take with isosorbide mononitrate and dinitrate. Do not drink alcohol, as it could make your headaches worse. Headaches usually go away after a few days. Talk to your doctor if they last longer than a week or are severe.
- feeling dizzy weak, tired or sleepy – stop what you are doing and sit or lie down until you feel better. Do not drink alcohol, as it could make you feel worse. Do not drive, ride a bike or use tools or machinery until you feel better.
- feeling sick – avoid rich, greasy or spicy foods, as these could make you feel worse. Stick to small, simple snacks or meals if you're hungry. It might help to take isosorbide mononitrate and dinitrate after meals.
- flushing – try to cut down on coffee, tea and alcohol because they can make flushing worse. It might help to keep the room cool and use a fan. You could also spray your face with cool water or sip non-alcoholic cold or iced drinks.
- swelling in lower legs, ankles or feet – try to keep your feet up when sitting down. Raise the end of your bed. If does not improve after a week, see your doctor.
7. Pregnancy and breastfeeding
Isosorbide mononitrate and dinitrate and pregnancy
Isosorbide mononitrate and dinitrate can be taken in pregnancy. However, if you are pregnant or trying for a baby then you should be seen as soon as possible by a pregnancy specialist (obstetrician) and a heart specialist (cardiologist) so your heart and medicine can be reviewed.
Keep taking your medicine until you have had your review.
Isosorbide mononitrate and dinitrate and breastfeeding
There is no information about whether isosorbide mononitrate or dinitrate passes into breast milk, but the amounts are likely to be small.
Speak to your doctor or a pharmacist if you want to breastfeed while taking isosorbide mononitrate or dinitrate. If your doctor and health visitor say your baby is healthy, you may be able to take it while you're breastfeeding.
It's important that you keep taking your medicine to keep you well. Breastfeeding will also benefit both you and your baby.
If you notice that your baby is not feeding as well as usual, or seems unusually sleepy, or if you have any other concerns about your baby, talk to your health visitor, midwife or doctor.
Non-urgent advice: Tell your doctor if you're:
- trying to get pregnant
- pregnant
- breastfeeding
8. Cautions with other medicines
Some medicines can affect the way isosorbide mononitrate and dinitrate works.
If you take other medicines that lower blood pressure with isosorbide mononitrate and dinitrate, it can sometimes lower your blood pressure too much. This might make you feel dizzy or faint.
Tell your doctor if this happens to you. They may need to change your dose.
Check with a pharmacist or your doctor before starting isosorbide mononitrate or dinitrate if you're taking:
- medicines for erection problems including sildenafil, avanafil, tadalafil or vardenafil
- riociguat, used to treat pulmonary hypertension
- medicines for high blood pressure or heart problems
- medicines for depression or other mental health conditions
- medicines for migraine that contain ergotamine such as Migril
- sapropterin, a medicine for phenylketonuria (PKU)
Taking isosorbide mononitrate and dinitrate with painkillers
Paracetamol is safe to take with isosorbide mononitrate and dinitrate.
Do not take non-steroidal anti-inflammatory medicines (NSAIDs) regularly, such as ibuprofen, aspirin and naproxen (unless it's prescribed by your doctor). These may make your angina or heart failure worse.
Talk to your pharmacist if you need a painkiller stronger than paracetamol.
Important: Medicine safety
Tell your doctor or pharmacist if you're taking any other medicines, including herbal medicines, vitamins or supplements.
9. Common questions about isosorbide mononitrate and isosorbide dinitrate
How does isosorbide mononitrate and dinitrate work?
Isosorbide mononitrate and dinitrate belong to a group of medicines called nitrates. Nitrates are used to treat and prevent angina.
Angina is chest pain that happens when not enough blood gets to the muscles of the heart. It usually happens because your arteries have become hardened and narrowed.
Your heart muscles need oxygen in your blood to work. If your heart needs to work harder, during exercise for example, it needs increased blood flow to get more oxygen.
In angina, isosorbide mononitrate and dinitrate works by widening blood vessels (veins and arteries). This increases the blood supply to your heart, which gets more oxygen to your heart muscles and this reduces chest pain.
In heart failure, isosorbide mononitrate and dinitrate relaxes the blood vessels, making it easier for your heart to pump blood around your body.
How long does it take to work?
Isosorbide mononitrate and dinitrate usually starts to work within 1 hour. It will take a few days to prevent angina symptoms.
How long will I take it for?
Usually you will take isosorbide mononitrate and dinitrate for a long time, possibly for the rest of your life.
Some people may be able to stop taking it after certain types of heart surgery.
Can I take it for a long time?
Isosorbide mononitrate and dinitrate are both generally safe to take for a long time.
What will happen if I stop taking it?
Talk to your doctor if you want to stop taking isosorbide mononitrate or dinitrate.
If you have been taking it regularly and you stop taking it, your angina symptoms or heart failure may get worse.
If you are taking isosorbide mononitrate or dinitrate and are bothered by side effects, speak to your doctor. They may be able to change your dose or prescribe a different medicine instead.
Can I drink alcohol with it?
Drinking alcohol can increase the effects of isosorbide mononitrate and dinitrate. It can make your blood pressure too low and you may feel dizzy, lightheaded or sleepy.
If your heart failure is directly related to drinking alcohol, you may be advised to stop completely.
Is there any food or drink I need to avoid?
Apart from limiting alcohol, you can eat and drink normally while you are taking isosorbide mononitrate or dinitrate.
However, if you have angina you may have a higher risk of having a heart attack or stroke.
You can help reduce your risk of problems like these by:
Drinking alcohol can increase the effects of isosorbide mononitrate and dinitrate. It can make your blood pressure too low and you may feel dizzy, lightheaded or sleepy.
Are there other medicines for angina?
Medicines to treat angina attacks
If you have stable angina (the most common type), you'll be given medicine to take when you have an angina attack.
This is called glyceryl trinitrate, or GTN. It comes as a mouth spray or tablets that dissolve under your tongue.
Isosorbide mononitrate and dinitrate are not used to treat sudden angina attacks. They work by preventing attacks from happening.
Medicines to prevent angina attacks
If you have angina, to help avoid more attacks you may need to take at least 1 medicine every day for the rest of your life. Some people need to take 2 or more medicines.
Other medicines used to prevent angina attacks are:
- beta-blockers – to make the heart beat slower and with less force
- calcium channel blockers – to relax the arteries, increasing blood supply to the heart muscle
If you cannot take either of these medicines, you may be given another medicine such as ivabradine, nicorandil or ranolazine.
Your doctor will be the best person to decide what treatment is best for you.
Will I need to stop taking it before surgery or before tests?
Tell your doctor that you're taking isosorbide mononitrate or dinitrate if you're going to be put to sleep (using general anaesthesia), or you're having any kind of major operation.
Your doctor may advise you to stop taking isosorbide mononitrate or dinitrate before surgery. This is because it can lower your blood pressure too much when combined with some anaesthetics.
Will it affect my contraception?
Isosorbide mononitrate and dinitrate will not stop your contraception working, including emergency contraception.
However, if you have angina, oral contraceptives such as the combined pill are not recommended because they increase the risk of heart attack and stroke.
Talk to your doctor if you're taking a combined hormonal contraceptive.
Will it affect my fertility?
There is no clear evidence that isosorbide mononitrate or dinitrate affects fertility in men or women.
If you are trying to get pregnant, talk to your doctor.
Will it affect my sex life?
Isosorbide mononitrate or dinitrate is not likely to affect your sex life.
However, do not take medicines for erection problems if you are taking isosorbide mononitrate or dinitrate. These include:
- avanafil
- sildenafil (including Viagra)
- vardenafil
- tadalafil
Some people with angina worry that having sex will trigger an angina attack, but the risk of this happening is low. It is as safe as other forms of exercise with similar levels of effort.
Talk to your doctor if you are having problems with your sex life.
Do I need to avoid playing sports?
You do not need to avoid playing sports due to taking isosorbide mononitrate or dinitrate.
It's important to stay active if you have angina or heart failure.
It will help if you can:
- build up your activity level gradually and take regular breaks
- keep your GTN tablets or spray with you in case you need them
- use your tablets or spray before starting exercise, if you need to
Talk to your doctor if you're not sure it's safe for you to exercise.
Can I drive or ride a bike?
Isosorbide mononitrate and dinitrate can make some people feel dizzy, sleepy or faint.
If this happens to you, do not drive, ride a bike or use tools or operate machinery until you feel better.
How can lifestyle changes help the health of my heart?
Angina and heart failure is a warning sign that you are at risk of serious problems such as heart attacks and strokes.
To reduce your risk of problems like these, it may help to:
- eat a healthy balanced diet – aim to eat a diet that includes plenty of fruit and vegetables, wholegrains, fat-free or low-fat dairy products, and lean proteins. This should help you to stay healthy or lose weight, which reduces your risk of heart attacks and strokes. It's a good idea to cut down on salt too.
- cut down on alcohol – drinking too much alcohol is not good for the health of your heart. Try to keep to the recommended guidelines of no more than 14 units of alcohol each week. A standard glass of wine (175ml) is 2 units. A pint of lager or beer is usually 2 to 3 units of alcohol.
- quit smoking – smoking increases your heart rate and blood pressure.
- exercise – regular exercise keeps your heart and blood vessels in good condition. It does not need to be too energetic, walking every day will help.