GLYCERYL TRINITRATE

“GTN; NITROGLYCERINE”

1) Therapeutic drug action & mechanism(pharmacology)

• Relaxes all vascular smooth muscle, especially venous beds

[arterioles & precapillary sphincters are dilated less than other portions of the vascular tree]

• Higher dosages may be associated with arteriolar dilation

• Primary direct effect is a marked relaxation of large veins with increased venous capacitance and reduced ventricular preload

• Heart size & PVR are reduced in CCF

• May directly increase coronary blood flow

• Arteriolar dilatation reduces afterload, venous dilatation reduces preload [high PA, CVP & PAW pressures are reduced] thereby reducing MVO2; increased coronary blood flow increases O2 delivery to myocardium

2) Indications

• CCF associated with acute MI

• Severe unresponsive angina

• Control of BP perioperatively esp cardiovascular procedures

• Prolonged hypotension during anaesthesia to reduce surgical bleeding

• Effective in producing systemic vasodilation during rewarming on CPB

• Postoperative hypertension

• Used to offset vasoconstriction caused by adrenergic drugs

3) Effects on organs—side effects

• Relaxes all types of smooth muscle

• Relaxation of bronchi, GIT,

4) Toxic effects/ precautions with administration

• Hypotension is most common adverse effect

• Methaemoglobin

• Reflex tachycardia & increased contractility — increased myocardial work

• Reduced diastolic perfusion time due to tachycardia

5) Contraindications

• Tamponade

• Hypotension

6) Reversal, antagonism or antidote

• Excessive hypotension: stop infusion; elevate legs; a-adrenergic agonist

• Hypotension is most common adverse effect, when drug is discontinued, effect is rapidly reversed

7) Loading dose, maintenance dose, frequency & method of administration

• 50 mg/10 ml per ampoule added to 90 ml D5W

• Use non PVC tubing

• Can be given peripherally

8) Drug’s metabolism—Drug’s excretion—Half life (pharmacokinetics)

• Widely distributed in body

• Rapidly metabolised in liver

• Half-life 1-4 min

9) Important drug interactions

• May potentiate action of pancuronium

• Tricyclics may potentiate hypotensive effects