Take isosorbide mononitrate or isosorbide 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.
Dosage and how to take isosorbide mononitrate or isosorbide dinitrate
How much isosorbide mononitrate or isosorbide dinitrate you take depends on your symptoms, the brand of medicine and the type of tablets or capsules you're taking.
Dose for angina
The usual dose to prevent angina is:
- isosorbide mononitrate standard tablets – 10mg, taken twice a day, up to a maximum dose of 120mg a day, 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 a day, 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
Dose for heart failure
The usual dose to treat heart failure is:
- 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 standard tablets – 40mg to 160mg a day, up to a maximum dose of 240mg a day, split into smaller doses
How to take it
Swallow the tablets or capsules whole with a drink of water. Do not chew or crush them.
You can take tablets or capsules with or without food.
Your doctor may tell you to leave a gap of 4 to 14 hours a day (usually when you're 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're 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).
How long to take it for
Usually you'll take isosorbide mononitrate or isosorbide 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.
Talk to your doctor if you want to stop taking it or you're bothered by side effects. They may be able to change your dose or prescribe a different medicine instead.
If you've been taking it regularly and you stop taking it, your angina symptoms or heart failure may get worse.
If you take too much
Taking too much isosorbide mononitrate or isosorbide dinitrate may make your blood pressure fall too low, making you feel sick, faint and dizzy. If this happens, sit or lie down and raise your legs.
Immediate action required: Call 999 now if:
You've taken more than your prescribed dose of isosorbide mononitrate or dinitrate and:
- your mouth (lips, tongue or gums), face or skin start to look blue or grey – if you have brown or black skin this may be easier to see on the palms of the hands, soles of the feet, lips, gums and inside the eyelids
- you have a seizure or fit
- you have severe breathing problems
Do not drive yourself to A&E.
Tell the person you speak to at 999 what medicine you've taken. They'll give you advice about what to do.
Urgent advice: Contact 111 for advice if:
- you take more than your prescribed dose of isosorbide mononitrate or isosorbide dinitrate, even if you do not have symptoms
Get help from 111 online or call 111
If you need to go to A&E, do not drive. Ask someone to drive you or call 999 and ask for an ambulance.
Bring the isosorbide mononitrate or isosorbide dinitrate packet or leaflet inside it, any remaining medicine, and any other medicines you take.