Pharm 101: Glycerol trinitrate (GTN)

Class

Vasodilator


Pharmacodynamics
  • Causes release of NO in vascular smooth muscle, which increases cGMP causing smooth muscle relaxation and vasodilation
  • Affects arteries and veins, veins first / at lower concentrations
    • At lower doses, venodilation leads to decreased preload and stroke volume
    • At higher doses, arterial dilation leads to reduced blood pressure, which reduces CO and myocardial oxygen demand. Also causes dilation of coronary arteries
  • Decreases LV volume, therefore decreases LV wall tension and subsequent myocardial oxygen demand
  • Also decreases platelet aggregation (clinically insignificant)

Pharmacokinetics
  • Bioavailability 10-20%
  • Half life 2-8 mins
  • Liver metabolism to 1,2-dinitro derivative (significant vasodilator), excreted by kidney
  • Sublingual route, onset in 1-3 minutes, duration of action 15-30 mins
  • Tachyphlaxis occurs with continuous use due to a decrease in tissue sulfhydryl groups:
    • Smooth muscle develops tolerance to effects, especially with continuous IV infusion or long acting preparation
    • “Drug-free” interval of 8 hours between doses may reduce this

Clinical uses
  • Angina
  • Acute coronary syndrome
  • Hypertensive emergencies
  • APO
  • Aortic dissection (with beta-blockade)

Adverse effects
  • Headache
  • Postural hypotension
  • Tachycardia
  • Salt and water retention with longer acting nitrates

Precautions/contraindications
  • Hypotension
  • Inferior and posterior MI / RV infarct
  • Fixed cardiac output e.g. aortic stenosis, tamponade
  • Significant tachycardia or bradycardia

Further Reading

Pharm 101 700

Pharmacology 101

Top 200 drugs

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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