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13 Cards in this Set

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  • Back
Metered dose bottle delivering 0.4 mg doses.
Mechanism of action
GTN is a vasodilator. GTN dilates veins and arteries but the predominant effect is on veins. The exact mechanism of action is not clear but it appears that GTN results in the formation of nitric oxide, which is a vasodilator. GTN causes:

a)  Veinous dilation, which causes peripheral pooling of blood, reducing veinous return and preload. This reduces ventricular filling and cardiac output, which reduces myocardial work and myocardial oxygen demand. 

b)  Arterial dilation, reducing peripheral resistance and afterload. This reduces the force the left ventricle must overcome to eject blood into the systemic circulation, reducing myocardial oxygen demand. 

c)  A small amount of dilation of the coronary arteries. This increases the supply of blood to the myocardium.
The treatment of myocardial ischaemia or cardiogenic pulmonary oedema.
a)  Systolic BP less than 100 mmHg or

b)  HR less than 40/min or 

c)  HR greater than 150/min.
Relative contraindications:
a)  Right ventricular infarct or 

b)  Poor perfusion or 

c)  Dysrhythmia is present or 

d)  The patient has taken a drug for erectile dysfunction in the last 24 hours.
What are the doses of GTN we give?
0.4mg - 0.8mg metered dose.
When would you reduce the dose of GTN?
If the patient is small, elderly or hypotensive.
Onset of effect
1-2 minutes.
Duration of effect
The vasodilator effects of GTN are relatively short and usually last 10-30 minutes. However, in some patients the effect on blood pressure may be quite prolonged, lasting several hours (even in the absence of drugs for erectile dysfunction).
Common adverse effects
Hypotension, flushing, headache, tachycardia, light headedness.
What medications will increase the effects of GTN?
(a) The effects of GTN will be increased in patients taking beta blockers and other antihypertensives.

b)  There is a range of medicines (with multiple different names) used for erectile dysfunction and some of them (particularly sildenafil) are also used in the treatment of pulmonary hypertension. These medicines are long acting (12-24 hours) inhibitors of one of the subtypes of the enzyme phosphodiesterase. Inhibition of phosphodiesterase results in an enhanced effect of nitric oxide, which is a vasodilator. GTN may interact with such medicines, causing severe and prolonged hypotension if they have been taken within the last 24 hours. GTN is not contraindicated in this setting, but if used there must be a very strong indication and it must be used in 0.4 mg doses. If in doubt seek medical advice.
Spray under the tongue. If this cannot be achieved it is acceptable to spray onto the tongue or cheek.
GTN is indicated in cardiogenic pulmonary oedema. Would you use GTN for pulmonary oedema from other causes?