Glyceryl Trinitrate (GTN): A Drug Overview

This micro lecture is about the drug glyceryl trinitrate, GTN, which is used to treat acute coronary syndrome; which forms part of the blended learning materials available to all enrolled students.

In today’s micro lecture, we’re going to talk about the drug glyceryl trinitrate, GTN. GTN is a drug that we use to treat acute coronary syndrome. Let’s just remind ourselves what an acute coronary syndrome is.

An acute coronary syndrome is made up of three cardiac-related diseases, an ST-segment elevation myocardial infarction, a non–ST-segment elevation myocardial infarction, and unstable angina. Now, all of those conditions involve an occlusion of the coronary arteries. In other words, the arterial system that feeds oxygenated blood into the heart.

Now, when this happens, your patient is having what we know as a STEMI (ST-Elevation Myocardial Infarction), a non-STEMI, or unstable angina. Members of the public know this to be a heart attack. Now, it’s your job as the paramedic to recognise this quickly through your history taking and provide treatment through the use of aspirin, GTN, and some pain relief.

Now, glyceryl trinitrate is a venodilator. It dilates the coronary arteries and the circulation in the heart. Now, if this happens, what you’ll end up with is a resolution of the circulation going into the coronary arteries.

In other words, if you imagine that there’s been a blockage in the heart caused by atheroma, fatty plaque buildup in the coronary arteries, by dilating the vessel, making it bigger, you’re allowing the blood to circulate through the blockage. That’s the first thing that it does.

The second thing that it does is it reduces the amount of blood that goes back into the heart. That’s called preload. So it reduces the preload that goes back into the right atria, followed by the right ventricles, and eventually the left ventricle.

If the left ventricle has less blood to pump that will mean that the heart has actually got less work to do and therefore you will feel less pain. So it’s a really, really good drug. Now, you need to make sure that when you’re giving your patient GTN you go fully through the contraindications for GTN. Typical contraindications include head injury, stroke, low blood pressure, a heart rate below 50 or above 150 because it’s what we call a rate-dependent drug, like Viagra.

Now, there are always more side effects and more contraindications and different indications, depending on the guideline that you’re using and the ambulance service you’re working for. But the key contraindication you guys have to be mindful of, working as a paramedic … And if you guys ask any paramedic about this, they will always tell you that you’ve just got to watch out for the patient’s blood pressure.

Now, blood pressure has to be carefully considered for two reasons. Number one, if the blood pressure is already low, let’s say systolic of 100 or below, your patient is not going to really appreciate having DTM because it’s going to cause low blood pressure. A side effect of GTN is low blood pressure.

Another thing you have to be mindful of is if a patient’s already got high blood pressure we do not give GTN just because they’ve got high blood pressure. Now, that’s different if they’re having an acute coronary syndrome. If a patients having an acute coronary syndrome and they’ve got high blood pressure that’s fine. That’s great.

But if you see that the patient’s got high blood pressure, we don’t automatically go for the GTN and give it just because, oh, we’ve got this drug and we know it reduces the blood pressure. Because a patient who’s not having an ACS and they’ve got high blood pressure, the body is pushing the blood pressure up on purpose to try and help resolve that situation.

Okay, so that’s a brief session on glyceryl trinitrate. I hope you found it useful. My name’s Sam (from the Australian Paramedical College) and I look forward to talking to you next time. Thanks.

What is your career journey?

To discover how you can become a fully qualified Ambulance Paramedic or Basic/Advanced Life Support Medic, complete a personalised paramedical career development plan.