Glyceryl trinitrate (GTN)

Question 1

What is the MOA of GTN?

Answer 1

A vasodilator - acts on vascular smooth muscle - causing both arterial and venous dilation but mainly venous

Question 2

What are the clinical effects of GTN?

Answer 2

• Reduction in preload (venous return), this reduces ventricular filling and cardiac output and reduces oxygen demand on the heart
• Arterial dilation which reduces peripheral resistance (afterload), reducing force required by L ventricle to eject blood, reduces myocardial oxygen demand
• dilation of coronary arteries, this is less clinically significant

Question 3

What are the indications for GTN?

Answer 3

1. Myocardial ischemia
2. Cardiogenic pulmonary oedema
3. Hypertension associated with autonomic dysreflexia

Question 4

What are the contraindications for GTN?

Answer 4

• Systolic BP < 100 mm Hg
• HR < 40 bpm
• HR > 130 bpm in myocardial ischemia, STEMI or cardiac pulmonary oedema
• HR > 150 bpm if autonomic dysreflexia
• Ventricular tachycardia

Question 5

What are the cautions for GTN?

Answer 5

• STEMI esp STEMI involving the right ventricle (low cardiac output)
• Small, frail, physiologically unstable
• Poor perfusion (as it indicates reduced cardiac output)
• Dysrhythmia (as it can indicate reduced cardiac output)
• Erectile dysfunction drugs within last 24
• Known aortic or mitral stenosis (narrowing) - cardiac output may be reduced

Question 6

Should GTN be given to someone pregnant or breastfeeding?

Answer 6

Need for GTN in pregnant women unlikely but should be given if inducated

Question 7

What doseage of GTN should be given?

Answer 7

• Myocardial ischaemia: 0.4mg every 3-5 min increasing dosage to 10 minutes if caution
• Cardiogenic pulmonary oedema: 0.8mg every 3-5 min increasing dosage to 10 min if caution
• Autonomic dysreflexia: 0.4-0.8mg every 3-5 min
• Each ‘squirt’

Question 8

How should GTN be administered for a patient with a caution?

Answer 8

Patient should be lying flat
IV access is ideal - need to be ready to admin 0.9% NaCl IV if sig drop cardiac output or BP
Dosing increased to 10 minutes

Question 9

What are adverse effects of GTN?

Answer 9

Hypotension
Flushing
Headache
Tachycardia
Light-headedness

Question 10

What is the onset/duration time of GTN effect?

Answer 10

Onset 1-2 min

Duration 15-30 min

Question 11

What are common interactions

Answer 11

Effects may be increased with anti hypertensive medications:
Erectile dysfunction drugs (esp sildenafil) often act as anti

Question 12

What are the most common antihypertensive drugs

Answer 12

Beta blockers metoprolol, 
ace inhibitors ('prils). calciuim 
channel blockers ('pines) diuretics (furesimide, bendrofluorazide)