Paramedic Student – Nee Naw Car

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Glyceryl Trinitrate

Details

Presentation:

0.3 mg tablet (Nitrostat)
50 mg patch (releases 0.4 mg/hr or 10 mg/24 hours)

Route:

Sublingual (S/L) – Place tablet under tongue and allow to dissolve. Patients may experience a mild tingling or burning sensation
Transdermal – Write date/time onto patch and apply to clean, dry, unbroken skin on chest or upper arm.

Onset of action:

1 – 3 minutes (S/L)
Up to 30 minutes (Transdermal)

Peak:

5 minutes (S/L)
2 hours (Transdermal)

Duration:

At least 25 minutes (S/L). Patch continually releases GTN until removed

Mode of action

Organic nitrate – relaxes vascular smooth muscle

Venodilaton promotes venous pooling and reduces venous return to the heart (reduces preload)

Arteriodilation reduces systemic vascular resistance and arterial pressure (reduces afterload)

Effects include:

  • Reduced myocardial O2 demand
  • Reduced systolic, diastolic and mean arterial blood pressure, whilst usually maintaining coronary perfusion pressure
  • Mild collateral coronary artery dilation may improve blood supply to ischaemic areas of myocardium
  • Mild tachycardia secondary to slight fall in BP
  • Preterm labour: uterine quiescence in pregnancy
  • Chest pain in acute coronary syndrome
  • Hypertension associated with acute coronary syndrome
  • Acute cardiogenic pulmonary oedema
  • Autonomic dysreflexia
  • Preterm labour (consult for GTN patch)
  • BP < 100 mmHg
  • HR > 150 bpm
  • HR < 50 bpm (except in autonomic dysreflexia)
  • Ventricular tachycardia
  • PDE5 inhibitors (current/recent use)
  • Riociguat (current use)
  • Use lower doses (ie. 300 mcg) in patients who are elderly (age > 60), have no previous exposure to GTN, or with recent MI, as they may be more susceptible to adverse effects
  • Right ventricular MI or inferior STEMI with systolic BP < 160 mmHg – use cautiously due to risk of severe hypotension from preload reduction
  • Preterm labour – concurrent use with other tocolytics
  • CV: hypotension, tachycardia, bradycardia (occasionally)
  • CNS: headache, dizziness, syncope
  • Other: skin flushing
Significant interactions
  • Phosphodiesterase 5 (PDE5) inhibitors including avanafil (Spedra), sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra). GTN increases the effects of PDE5 inhibitors resulting in profound hypotension. Do not administer GTN within:
    • 12 hours since the last dose of avanafil OR
    • 24 hours for sildenafil or vardenafil OR
    • 48 hours for tadalafil
  • Riociguat (Adempas) – used for pulmonary arterial hypertension. GTN increases the hypotensive effects of riociguat. Do not administer to patients currently taking this medication
Pregnancy
  • Considered safe to use
Breastfeeding
  • Monitoring required – use lowest effective dose and observe infant for adverse effects such as flushing or discomfort after breastfeeding
Notes
  • GTN is also known as nitroglycerin
  • GTN tablets should be stored in the original bottle, with the lid tightly closed after each use to prevent loss of potency.
  • Due to uncontrolled storage conditions inside an ambulance, unused GTN tablets should be discarded 6 months after first opening. Mark the expiry date on the bottle with a pen or permanent marker.
  • Do not administer the patient’s own GTN tablets or spray (Nitrolingual) unless unavoidable, as its storage may have been sub-optimal or it may be expired.
  • PDE5 inhibitors are used for multiple indications including sexual dysfunction, pulmonary arterial hypertension and benign prostatic hypertrophy. Both male and female patients should be asked about recent use prior to GTN administration
Infusion
  • None

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