Glyceryl Trinitrate (GTN) CPG

Question 1

GTN - Presentation

Answer 1

0. 3mg tablet
1. 6mg tablets

Transdermal GTN Patch (50mg 0.4mg/hr release)

Question 2

GTN - Pharmacology

Answer 2

Principally a vascular smooth muscle relaxant

Actions:

• Venous dilatation promotes venous pooling and reduces venous return to the heart (reduces preload)
• Arterial dilatation reduces systemic vascular resistance and arterial pressure (reduces afterload)

The effects of the above are:

• Reduced myocardial O2 demand
• Reduced systolic, diastolic and mean arterial blood pressure, whilst usually maintaining coronary perfusion pressure
• Mild collateral coronial artery dilatation may improve blood supply to ischaemic areas of myocardium
• Mild tachycardia secondary to slight fall in blood pressure
• Preterm labour: Uterine quiescence in pregnancy

Question 3

GTN - Metabolism

Answer 3

By the liver

Question 4

GTN - Primary emergency indications

Answer 4

1. Chest pain with ACS
2. Acute LVF
3. Hypertension associated with ACS
4. Autonomic dysreflexia
5. Preterm labour (consult)

Question 5

GTN - Contraindications

Answer 5

1. Known hypersensitivity
2. Systolic blood pressure <110 mmHg tablet
3. Systolic blood pressure <90 mmHg patch
4. Sildenafil Citrate (Viagra) or Vardenafil (Levitra) administration in the last 24hr or Tadalafil (Cialis) administration in the previous 4 days (PDE5 inhibitors)
5. Heart rate > 150bpm
6. Bradycardia HR <50bpm (excluding autonomic dysreflexia)
7. VT
8. Inferior STEMI with systolic BP <160 mmHg
9. Right ventricular MI

Question 6

GTN - Precautions

Answer 6

1. No previous administration
2. Elderly Pt
3. Recent MI
4. Concurrent use with other tocolytics

Question 7

GTN - Route of administration

Answer 7

SL

Buccal

Transdermal

Infusion (interhospital transfer only)

Question 8

GTN - Side effects

Answer 8

Tachycardia

Hypotension

Headache

Skin flushing (uncommon)

Bradycardia (occasionally)

Question 9

GTN - Special notes (there are a shitload)

Answer 9

Storage:

• GTN is susceptible to heat and moisture. Make sure that tablets are stored in their original light resistant, tightly sealed bottles. The foil pack of the patches should be intact.
• Do not administer patient’s own tablets, as its storage may not have been in optimum condidtions or it may have expired.
• Patches should be discarded prior to use-by date.
• Since both men and women can be prescribed PDE5 inhibitors all patients should be asked if and when they last had the medication to determine if GTN is C/I.
• Tadalafil (Cialis) may also be prescribed to men for treatment of benign prostatic hypertrophy. This is a new indication for this medication and may lead to an increased number of patients under this treatment regimen.
• GTN by IV infusion may be required for an inter hospital transfer as per the treating doctor’s orders

Interhospital transfer:

The IV dose is to be prescribed and signed by the referring hospital medical officer. Infusions usually run in the range of 5 mcg/minute to 200 mcg/minute and increased 3-5 mcg/minute.

S/L effects:

Onset: 30sec - 2min

Peak: 5 - 10min

Duration: 15 - 30min

IV effects:

Onset: 30sec - 1min

Peak: 3 - 5min

Duration: 15 - 30min

Transdermal effect:

Onset: Up to 30min

Peak: 2hrs