Nitrates cause the relaxation of vascular smooth muscle resulting in:

  • Vasodilation
  • Peripheral pooling and reduced venous return
  • Reduced left ventricular end diastolic pressure (preload)
  • Reduced systemic vascular resistance (afterload)
  • Reduced myocardial energy and oxygen requirements
  • Relaxes spasm of coronary arteries

Also known as nitroglycerin

Pharmacology Review

  • Chest pain/discomfort of presumed cardiac origin not relieved by rest and reassurance with systolic BP > 90 mmHg where the heart rate is within 50-150 beats per minute.
  • Acute Cardiac Pulmonary Oedema with systolic BP >90 mmHg.
  • Autonomic Dysreflexia with systolic BP > 160 mmHg.
Critical Care
  • Control of hypertension (SBP ≥ 160mmHg) in patients with acute ICH/aortic dissection.
  • Hypersensitivity
  • Hypotension < 90 mmHg
  • Ventricular Tachycardia (VT)
  • Recent use of medications used for erectile dysfunction:
    • Sildenafil (Viagra®) or Vardenafil (Levitra®) or Avanafil (Spedra®) use in the previous 24 hours
    • Tadalafil (Cialis®) use in the previous 3 days
Critical Care
  • Acute CVA
  • Traumatic brain injury
  • Phosphodiesterase 5 inhibitor medication administration in past 24 hours
 Precautions / Notes
  • Nitrates are an early intervention and should not be delayed until on the stretcher or inside the ambulance
  • Administer to the patient in a seated or semi-recumbent position
  • Prime the bottle before using it for the first time by pressing the nozzle 5 times, spraying it into the air
  • Do not shake GTN bottle prior to administration
  • Assess BP before every dose
  • Severe hypotension is an uncommon side effect
  • Intoxication (effect are enhanced)
  • Phosphodiesterase 5 inhibitor medication administration in previous 4 days
COVID-19 / Febrile Respiratory Illness
  • Crews should allow the patient to administer their own GTN spray wherever possible
  • Allow patient to self-administer GTN spray under crew direction; stand clear and wait a minute before approaching the patient
  • If you have to use SJA supplied Glyceryl Trinitrate (GTN Spray), assess whether it can be reused and wipe with Clinell wipe after use. Discard the MDI in the sharps bin if the patient is very unwell or highly symptomatic of infectious respiratory condition.
  • Note: If administering St John supplied medication, crews are NOT to leave the remainder of the medication with the patient. This is a violation of the St John WA poisons licence and the Medicines and Poisons Act 2014.
  • No vehicle should be considered non-operational due to not having GTN available; if GTN is not available step up to the next level of pain relief.  

Infusion preparation

  • Mix 50mg of GTN up to 50ml in 5% Dextrose to make 1mg/mL to run through a syringe driver
 Weight-based Calculations
Cefazolin for fractures/prophylaxis
Presentation: /mL
Calculated dose:  in

Cardiac Chest Pain
  • 400 microg (1 spray) sublingually.
  • If pain persists after 5 minutes and BP maintained, consider further sprays of GTN at 5 minute intervals
  • Should the first 3 doses provide some relief but symptoms persist, continue with further doses at 5 minute intervals if no contraindications
Acute Cardiogenic Pulmonary Oedema
  • 400 microg (1 spray) sublingually
  • If BP maintained, consider further sprays of GTN at 5 minute intervals
  • Should the first 3 doses provide some relief but symptoms persist, continue with further doses at 5 minute intervals if no contraindications
Autonomic Dysreflexia
  • 400 microg (1 spray) sublingually.
  • Repeat doses at 5 minute intervals until symptoms resolve or systolic BP < 160mmHg.
Critical Care
ASMA approval required for all IV administration requests
Chest Pain / Acute Cardiogenic Pulmonary Oedema
  • Commence infusion at 1mg (1ml)/hr (or as instructed by ASMA)
  • Titrate infusion up or down at 0.5 – 1ml/hr increments every 15 minutes as tolerated by the patients BP (maintain SBP >90 mmHg) and to clinical effect (i.e. relief of pain / respiratory distress)
Control of hypertension (Autonomic Dysreflexia / ICH / Aortic Dissection)
  • Commence infusion at 1mg (1ml)/hr (or as instructed by ASMA)
  • Titrate infusion up or down at 0.5 – 1ml/hr increments every 15 minutes as tolerated by patient to maintain SBP <160mmHg
 Special Considerations

Note that when GTN infusion is used in conjunction with NIV for acute cardiogenic pulmonary oedema, the hypotensive effects are amplified. Titrate with caution and monitor BP regularly.

Side effects:

  • Hypotension (rare)
  • Tachycardia
  • Flushing
  • Headache
  • Dizziness
  • Spray bottle containing 200x atomised sprays
  • 50mg in 10mL for IV infusion
GTN Infusion
Current mode:
Extended Care:
Colour assist:


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Clinical Services

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Head of Clinical Services


Issue Date

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