Nitrates

Question 1

What are common indications for nitrates?

Answer 1

• Acute angina
• ACS
• Prophylaxis for angina
• Pulmonary oedema

Question 2

What is the mechanism of action for nitrates?

Answer 2

NO increases smooth muscle cells relaxation. This results in venous and, to a lesser extent, arterial vasodilatation. Relaxation of the venous capacitance vessels reduces cardiac preload and left ventricular filling.

These effects reduce cardiac work and myocardial oxygen demand, relieving angina and cardiac failure. Nitrates can relieve coronary vasospasm and dilate collateral vessels, improving coronary perfusion. They also relax the systemic arteries, reducing peripheral resistance and afterload

Question 3

What mechanism of action is thought to contribute most to anti-anginal effects of nitrates?

Answer 3

Most of the anti-anginal effects are mediated by reduction of preload

Question 4

What are adverse effects of nitrates?

Answer 4

• Flushing
• Headaches
• Light-headedness
• Hypotension
• Tolerance

Question 5

When are nitrates contraindicated?

Answer 5

• Severe aortic stenosis
• Haemodynamic instability
• Hypotension

Question 6

What are important interactions to consider when using nitrates?

Answer 6

• Phosphodiesterase inhibitors
• Anti-hypertensives

Question 7

What dose of GTN would you prescribe someone in stable angina?

Answer 7

400-800 micrograms sublingually PRN

Question 8

What is the half-life of GTN?

Answer 8

<5 minutes

Question 9

How is GTN administered in ACS/acute heart failure?

Answer 9

Continuous IV infusion

Question 10

What dose of isosorbide mononitrate would you consider giving someone as prophylaxis for angina symptoms?

Answer 10

20 mg 2-3 times per day, then increase up to 120 mg daily in divided doses

Question 11

How often would you advise taking modified release ISMN tablets?

Answer 11

Once daily

Question 12

What dose of GTN is administered in an IV GTN infusion?

Answer 12

1 mg/ml

Question 13

What is important to do when prescribing a GTN infusion?

Answer 13

Provide instructions on how to increase the dose to relieve symptoms (e.g. ‘Increase GTN infusion rate by 0.5 mL/hr every 15–30 minutes until chest pain relieved’) while avoiding hypotension (e.g. ‘Keep systolic blood pressure >90 mmHg’)

Question 14

What dose interval should be used when using PRN GTN to treat angina symptoms?

Answer 14

5 minute intervals

Question 15

After how many doses of sublingual GTN should someone seek medical attention if chest pain does not resolve?

Answer 15

3 doses

Question 16

What approach can you adopt to avoid tolerance of nitrates developing?

Answer 16

Time doses to ensure there is a ‘nitrate-free period’ every day during a time of inactivity, usually overnight

For example, patients should be advised to take twice daily isosorbide mononitrate morning and mid-afternoon (rather than evening) to ensure >12 hours between pm and am doses