Isosorbide mononitrate

How it works

It is converted to nitric oxide, which raises smooth-muscle cyclic GMP to produce venous and arterial dilatation, reducing cardiac preload and afterload and so lowering myocardial oxygen demand.

Prescribing in practice

• It is contraindicated with phosphodiesterase-5 inhibitors (such as sildenafil) because the combination can cause profound, potentially life-threatening hypotension.
• A daily nitrate-free interval is essential to prevent tolerance, so dosing should be asymmetric rather than evenly spaced around the clock.
• Headache and postural hypotension are common, especially on initiation and dose increases.

Monitoring

Monitor for symptomatic benefit and for hypotension, with blood pressure review particularly after initiation or dose change.

Counselling the patient

• Do not use erectile-dysfunction medicines such as sildenafil while taking nitrates.
• Headaches are common at first and usually ease with continued treatment; tell your doctor if they persist.
• Stand up slowly, as this medicine can make you feel dizzy or faint.

Evidence & guidelines

Long-acting nitrates are an established second-line antianginal option in NICE guidance for stable angina, used where beta-blockers or calcium-channel blockers are insufficient or unsuitable.