Isosorbide Mononitrate
1 medicine
Isosorbide mononitrate is a long-acting nitrate that prevents angina by relaxing blood vessels. It must never be combined with PDE5 inhibitors such as sildenafil or with riociguat, which can cause a dangerous drop in blood pressure.
Key facts
- Isosorbide mononitrate is a long-acting nitrate used to prevent angina attacks. It is the active substance the body produces when it breaks down isosorbide dinitrate, and it is taken once or twice daily on a fixed schedule.
- It is a prevention medicine, not a rescue treatment. It will not relieve an angina attack that has already started.
- Never take it with sildenafil, tadalafil, vardenafil, avanafil, or riociguat. Combining a nitrate with any of these drugs can drop your blood pressure to dangerous, sometimes fatal, levels.
- Seek urgent care for severe dizziness or fainting, chest pain that does not ease with rest, or a fast or irregular heartbeat.
What isosorbide mononitrate treats
Isosorbide mononitrate prevents angina, chest pain caused by reduced blood flow to the heart muscle, in people with coronary artery disease. Taken regularly, it reduces how often attacks happen. It does not treat an angina attack in progress, so a separate fast-acting nitrate is usually prescribed for that purpose.
How isosorbide mononitrate works
The body converts isosorbide mononitrate into nitric oxide, a signal molecule that relaxes smooth muscle in the walls of blood vessels. This widens veins and arteries, reducing the pressure the heart pumps against and improving blood flow to the heart muscle. Because it needs no further conversion by the liver, its effect is predictable and long-lasting.
Before you take it
- Do not take isosorbide mononitrate if you use a PDE5 inhibitor or riociguat, or if you have severe anaemia, very low blood pressure, or increased pressure inside the skull.
- Tell your prescriber about recent heart attack, aortic stenosis, hypertrophic cardiomyopathy, or glaucoma, since nitrates can affect these conditions.
- Alcohol adds to the blood-pressure-lowering effect and can worsen dizziness.
- Stand up slowly, especially when starting treatment or increasing the dose, since a sudden drop in blood pressure on standing is common.
Side effects
Common effects include headache (often most noticeable in the first days of treatment), flushing, dizziness, and a fast heartbeat.
Stop and seek urgent medical care for any of these:
- Fainting or severe lightheadedness.
- Chest pain that does not respond to rest.
- A fast or irregular heartbeat.
- Signs of a severe allergic reaction, such as facial swelling or difficulty breathing.
Safety essentials
- Never combine isosorbide mononitrate with sildenafil, tadalafil, vardenafil, avanafil, or riociguat. The combination can cause a severe, dangerous drop in blood pressure. If you take a nitrate and develop chest pain during sex, tell emergency staff you have taken it.
- Take doses with a built-in nitrate-free interval each day, usually overnight, as your prescriber directs. Continuous round-the-clock exposure lets the body build tolerance, so the medicine stops working as well.
- Do not stop long-term nitrate treatment abruptly. Stopping suddenly can trigger a rebound worsening of angina; any change in dose should be planned with your prescriber.
- Keep a fast-acting nitrate available for attacks in progress, since isosorbide mononitrate does not relieve pain that has already started.
This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.