Glyceryl Trinitrate (GTN)

How it works

It is converted to nitric oxide, which raises vascular smooth muscle cyclic GMP and produces venous and arterial dilatation, reducing cardiac preload and afterload and improving coronary perfusion.

Prescribing in practice

• It is contraindicated with phosphodiesterase-5 inhibitors such as sildenafil and tadalafil, as the combination can cause profound, refractory hypotension.
• Avoid in haemodynamic states dependent on preload, such as significant aortic stenosis, hypertrophic obstructive cardiomyopathy and right ventricular infarction, where it may cause severe hypotension.
• Intravenous infusion requires close blood-pressure titration, and tolerance can develop with continuous use.

Monitoring

Monitor blood pressure and heart rate closely, with continuous monitoring during intravenous infusion.

Counselling the patient

• Sublingual GTN can cause a brief headache, flushing or light-headedness; sit down when using it.
• Never use this within a day of erectile-dysfunction tablets such as sildenafil.
• If chest pain persists despite repeated doses, call for emergency help.

Evidence & guidelines

Nitrates for acute coronary syndromes and acute pulmonary oedema are supported by NICE and ESC guidance.