Glyceryl Trinitrate (Sublingual / IV)

How it works

It is converted to nitric oxide, causing venodilatation (reducing preload) and coronary vasodilatation, which lowers myocardial oxygen demand and relieves ischaemic pain.

Prescribing in practice

• Headache, flushing and hypotension are common.
• Tolerance develops with continuous exposure, so a nitrate-free interval is used for regular nitrate therapy.
• It is contraindicated with PDE5 inhibitors (e.g. sildenafil), which together cause profound hypotension.

Monitoring

Monitor blood pressure and symptom response, particularly with intravenous use.

Counselling the patient

• For an attack, sit down and use it; repeat as advised and call emergency services if pain persists after the advised doses/time.
• A brief headache is common.
• Never use it with erectile-dysfunction tablets such as sildenafil.

Evidence & guidelines

Standard for acute angina relief and used intravenously in acute cardiac care.