Isosorbide Mononitrate

How it works

It is converted to nitric oxide, raising vascular smooth-muscle cyclic GMP to produce predominantly venous dilatation that reduces preload and myocardial oxygen demand.

Prescribing in practice

• A nitrate-free interval each day is needed to prevent tolerance, so dosing is timed to leave a low-nitrate period rather than spread evenly around the clock.
• Contraindicated with phosphodiesterase-5 inhibitors such as sildenafil because of the risk of severe hypotension.
• Use cautiously where preload reduction is harmful, such as hypotension, hypovolaemia or aortic and mitral stenosis, and do not stop abruptly after long-term use.

Monitoring

Monitor for postural hypotension, headache and adequacy of angina control, and ensure the nitrate-free interval is maintained.

Counselling the patient

• Headache is common at first and usually settles; take as prescribed to keep the daily low-nitrate gap.
• It prevents rather than relieves angina attacks, so keep a short-acting nitrate spray for acute symptoms.

Evidence & guidelines

A long-established antianginal supported by extensive clinical experience and reflected in NICE stable angina guidance.