How and when to take isosorbide mononitrate and 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

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).