Isosorbide mononitrate: long-acting nitrate for angina prevention

Isosorbide mononitrate is a vasodilator, meaning it relaxes vascular smooth muscle. The SmPC for Imdur describes it for the prophylactic management of angina pectoris. That means it is taken every day to reduce how often angina occurs, not to stop an attack that has started.

The patient leaflet is explicit that it is not for acute attacks. For those, a fast-acting GTN spray or tablet is used, as explained in the GTN guide in this series.

For the 60mg modified-release tablet, adults typically take one tablet once a day in the morning, with the possibility of increasing to 120mg daily. Treatment may be started at 30mg for 2 to 4 days to reduce the chance of headache. Other brands come as capsules or different strengths, so follow your own label.

Swallow the tablet whole with about half a glass of water and do not chew or crush it, because it is built to release slowly. Take it at the same time each morning.

The SmPC lists severe aortic stenosis, cardiac tamponade, mitral stenosis and severe anaemia as contraindications. It also states that patients treated with Imdur must not be given phosphodiesterase type 5 inhibitors.

Tell your prescriber about any heart valve disease, anaemia or other cardiac condition, and about every medicine you use.

Combining a nitrate with sildenafil and similar erectile dysfunction medicines is prohibited, because the two together can cause a dangerous drop in blood pressure, with a risk of fainting or heart attack, according to the SmPC.

This applies to the whole class of PDE5 inhibitors. If you are offered one by a pharmacist, an online service or a friend, tell them you take a nitrate.

Headache may occur when treatment starts but usually disappears after one to two weeks. Low blood pressure with dizziness and nausea occasionally develops but typically resolves during continued treatment. The leaflet notes that tolerance can develop with continuous use.

If a headache is severe or does not settle, ask a pharmacist or doctor rather than stopping the tablets, since the dosing plan may be adjustable. Report suspected side effects to the MHRA Yellow Card scheme.

The SmPC states that safety in pregnancy and lactation has not been established, so discuss this with your doctor if you may become pregnant. The leaflet also includes alcohol and driving warnings, so read the one that comes with your pack.

The leaflet describes it as a prescription-only medicine. Keep taking it as directed and do not stop it suddenly without speaking to your doctor.

A simple routine helps: place the tablet beside your toothbrush or breakfast things so that the morning dose is not forgotten, and keep a GTN spray or tablets in a pocket or bag as your separate plan for attacks. Remember that the nitrate you swallow each morning and the nitrate you use under the tongue are different products with different jobs.

At reviews, tell the nurse or doctor how often angina is still occurring, whether headaches have settled, and whether you have felt faint on standing. That information helps the prescriber decide whether the dose should stay where it is. If you are offered any new medicine, from a pharmacy or elsewhere, mention that you take a nitrate before accepting it.