Glyceryl Trinitrate (IV)

How it works

It is metabolised to nitric oxide, which raises vascular smooth-muscle cyclic GMP to cause venous (and at higher infusion rates arterial) dilatation, reducing preload, afterload and myocardial oxygen demand.

Prescribing in practice

• Infuse via a controlled pump with close blood-pressure monitoring because abrupt, profound hypotension can occur and the rate must be titrated to response.
• Contraindicated with phosphodiesterase-5 inhibitors such as sildenafil owing to the risk of severe hypotension, and avoid in marked hypotension or hypovolaemia.
• Continuous infusion leads to nitrate tolerance, and standard PVC giving sets adsorb the drug so non-absorbent infusion sets should be used.

Monitoring

Continuous blood pressure and heart rate monitoring is essential during titration, watching for hypotension, reflex tachycardia and headache.

Counselling the patient

• Headache and flushing are common as the medicine starts working.
• Tell staff promptly if you feel faint, dizzy or light-headed.

Evidence & guidelines

Long-established standard therapy for acute coronary and heart-failure presentations, supported by extensive clinical experience and UK guidelines.