Principles of Pharmacology [Micro Lecture]

In today’s micro-lecture, Australian Paramedical College Hon. Snr. Lecturer Sam Willis discusses the principles of pharmacology which is one of the most important aspects of paramedic practice.

In today’s lecture we’re going to talk about The Principles Of Paramedic Pharmacology. Now, paramedic pharmacology is one of the most important aspects of paramedic practice, because the drugs that you guys will be giving as qualified paramedics are pretty powerful, and the patients rely on you to be able to administer them safely as well as monitor their effects, and that’s after you’ve made the initial assessments, and identify that the patient is indicated from in the first place.

Pharmacology is something that does form a big part of paramedic practice, but not only that. If you look at the literature, it’s an area of paramedic practice that has the largest error rates, and therefore is an area that requires some serious consideration to the factors when administering this to try, and help our patients. Now, the purpose of this session is to look at the key terms related to drug pharmacology, because when you give a drug you’ve got to have an understanding of how that drug is going to work on the body.

We’re gonna look at a number of key drug routes, because therefore you’ve gotta have an understanding of these so that you can make a decision as to which one is the quickest, or the best given the circumstance that you’re presented with, and we’re gonna talk about the safety checks as well, because safety is everything in paramedic practice. Let’s first start by looking at a couple of terms here, so pharmacology is the study of drugs. Pharma is the drug, and ology is the study of. Pharmacology, the study of drugs.

Now, when you guys are giving the drugs you’ve gotta think about all of these things here that we’ve just summarised, the best and most suitable route. Now, some drugs, you’ve got to understand that drugs act differently depending on the route that you give, they act quicker depending on the drugs that you give. Some are not suitable for some routes, and other routes are just not accessible. For example, if someone is significantly injured in their left arm, and their right arm you’re not gonna be able to cannulate that patient, so the route is really, really important to look at.

Bioavailability, drug half life, indications and contraindications, cautions and safety checks. Bioavailability really is about the amount of drug left to work on the body once the body has tried to destroy the drug. In other words let’s take an oral route. You take the drug, you crunch it, you’re starting to break it down with your teeth mechanically. Then the salivary glands inside your mouth start to break it down chemically. Eventually, it will go down into your stomach where your stomach will do this as well, and there’s also gastric juices there that will continue to break it down. Eventually that drug will move into the duodenum, and into the hepatic portal circulation. You can Google these terms at anytime.

Now, imagine that the drug has now gone into the bloodstream, and eventually, some of it has got onto the receptors that it’s supposed to be, you know where it’s supposed to be. Now, as well as going through all that system there’s also something called a plasma cell, so not all of that drug that gets into the blood will be available to do the job. Some of it is attached to the plasma cells, and rendered useless, because the plasma cell will take it away for excretion, but bioavailability, really it is about that very small amount of drug that we have allowed to get into our body, and it’s working on the cell. That’s bioavailability, and every drug has a bioavailability.

The drug half life is about the amount of drug your body is actually destroying, and, therefore, how long it takes your body to do that. For example, if adrenaline, for example, it’s got a half life of three to five minutes, that means that your body is breaking it down, and your liver is breaking it down. It’s broken half the drug down after three to five minutes. Therefore, you can know after three to five minutes, most of the drug has been destroyed.

Now, indications and contraindications. Indications are when you would give a drug, so let’s say you’ve got someone with asthma, indication for treating asthma is salbutamol, and indication for adrenaline, for example, one of the the indications for adrenaline, life threatening asthma and anaphylaxis. Now, there’s also a contrary indication, that means situations when you absolutely would not give a drug, so indication means when you would give the drug, and contraindication means when you absolutely would not give the drug.

Now, caution is something you also need to be mindful of. Just because something is not contraindicated, but it’s in a caution instead, it also means you gotta look at it, so if something says, “Caution, do not give this drug in pregnant women.” I’ll be cautious around it. You’ve gotta do your homework, you’ve gotta be able to stand up in a court of law, and say, “I read this, and these are the steps that I took to be able to make sure it was safe.” So, I might speak to the pregnant woman, and say, “Have you had this before? You might consider the clinical situation. Well, if I didn’t give this drug, the outcome would have been this.” A caution is still something you have to think about. Then there’s the safety checks. You’ve gotta go through the right processes before you give the drug.

Now, drug routes, intramuscular, intravenous, per orum, per rectum, subcutaneous, intraosseous, so they’re the ones that we’re going to talk about. Intramuscular just means into the muscle. Now, when you’re giving an intramuscular injection you have to try, and remember that once you’ve injected it into the muscle, you don’t have any control over what happens. For example, you don’t have any control over the rate, or how much, so for example, most intramuscular routes, I expect you only to give three to five milliliters, so they’re only very small doses. Once you’ve given that three to five millilitres, that’s it. The muscle will just absorb that drug, and you’ll start to see a response as appropriate.

Whereas in comparison to intravenous you can give a dose, then you can stop, and you can give another dose, and you can stop, and you can reassess. That’s what we call titrate to response. I’m gonna give this drug titrate to response. In other words I’m gonna give some, titrate, titrate, titrate. Oh, they’ve responded. I’m not gonna give anymore. You can actually do that. Per orum is another method for drug administration, it just means swallowing it. Now, the unfortunate thing about PO is that it’s a very slow drug route. It’s about 10 to 15 minutes. Intravenous has an absorption rate of about 30 seconds, because you’re going straight into the bloodstream. Intramuscular has anywhere from two to five minutes depending on the health of the muscles, and the circulation in the muscles, and the situation, and the type of drug, and how fast you give it, and the volume that you give it.

Per rectum is rectal, through the rectal, remembering that your anal cavity has got a high vascular concentrations, so lots of circulation, a highly effective route. Some ambulance services allow you to use it, and a good example is PR route for Benzodiazepines, so if someone’s having a convulsion, or the services just say, “We’re not gonna use that. Instead, you can use intra nasal.” Subcutaneous is underneath the fat, and that a clear example here is using insulin for hypoglycemic patients. However, most ambulance services do not allow paramedics to give it, because it’s a bit of a dangerous drug to give if you haven’t had any specific training.

And then, finally intraosseous, or into the bone is a route that you guys can give if you’re administering drugs that would have otherwise been used intravenously. For example, the rate of absorption for intraosseous infusion is equivalent to intravenous infusion. It’s a very good route. Now, historically, paramedics never used to have this in their scope of practice, then when ambulance services introduced it they used to only give it to patients who required, who were in cardiac arrest, or unconscious. Now, by today’s standards intensive care paramedics tend to be the ones who use this in conscious patients, because when you administer something through the IO route, it’s extremely painful for the patient, but it is a route that you’ve got available to you.

We’ve mentioned bioavailability, but you really do have to try, and understand what it means in terms of how important it is to drug administration. We’ve said that what it is, is the amount of drug available at the end when it’s been through the system, but just have a look at this. This really is a calculation, this really is, showed you the movement of drugs, so somebody eats it, it goes down through the pharynx, esophageus, into the stomach. It gets broken down by the diet … By the stomach itself through all the methods. Goes into the next stage of the system. It gets absorbed in the duodenum, and then, the rest of digestive digestive tract, and into the blood, so eventually it gets into the blood, and every drug that you give your patient will have a bioavailability calculation.

In other words, have a look at the bioavailability. For example, when you take paracetamol, it doesn’t have this number. It might say the bioavailability is 35%. That’s because by the time you’ve given it, and it’s broken it all down there’s only 35% left, so 35% of that tablet will work, whereas if you give paracetamol IV, it might say 99%, because the only thing that’s gonna interfere with that drug working when you give an IV route is the plasma cells, and there’s very little else to affect it, so do be mindful that bioavailability is very important particularly if you’re giving a drug, and you’re trying to consider how fast you need it to work, and how much you need it to work.

And, this is why, let’s say you’ve got the drug adrenaline. If you’re giving the IV you’ll give a lot smaller dosage than if you’re giving it IM, for example, because of the bioavailability, so this really is a term that you need to get your head around as a paramedic. Now, what we’ve said about half life is that half life is the amount of time it takes your liver to break down half the drug. Now, half life varies from person to person, because if you think about what’s happening, I’ve just told you all the different things that need to occur to break down the drug, so that means you have to have a healthy functioning liver, it means you have to have good circulation in the stomach, you’ve gotta have good production of acids, so all these things you have to have for your half life to be effective enough.

So, half life is the amount of time it takes for your body to break down half the drug, but it does vary from person to person as it says here. There are many different things that get in the way of a half life calculation, but as the paramedic if you know what drug is gonna be broken down in three minutes you can expect to see other signs and symptoms within five minutes. For example, if you are giving a patient adrenaline for anaphylaxis, anaphylaxis is a life threatening condition. If you know that it takes your body five minutes to two, well two to three, to five, depending on which [inaudible 00:11:30] route you go. Let’s say three to five minutes it takes to break down adrenaline. After five minutes, you’re gonna start to potentially see what’s called secondaries.

In other words, there’s no adrenaline left in the system therefore the symptoms could come back. Now, in my experience of using adrenaline intramuscularly for life threatening asthma, and for anaphylaxis, it’s worked really, really well, and then, hasn’t been any secondaries, but it doesn’t mean it won’t happen, because your body eliminates it after two to three minutes, or three to five minutes.

Now, indications, and contraindications is something we’ve just recently touched on, but what we said was that, they allow you to recognize when your ambulance service indicates you to use it. Now, I find this interesting, because let’s say you compare an ambulance service protocol between one state or another. What you’ll find is that one service will say, “Yes, you can give IM adrenaline for let’s say asthma.” Another one might say, “No, you can’t do that unless you’re an intensive care paramedic.” So, they’re always slightly different, but regardless, you have to follow your own clinical practice guidelines, and follow them even if you know that asthma, for example, is treated, life threatening asthma is treated with intramuscular adrenaline, but you’re not allowed to give it, then that means you’re not allowed to give it in your scope of practice. It’s just the way it is.

Now, there was a case last year whereby a paramedic crew went to a patient who had life threatening asthma, and they knew that they had to give adrenaline, but they weren’t allowed to give it, because it wasn’t, it was outside of their scope of practice. Now, they didn’t give it, and the patient died. It was very unfortunate, but they were staying within the guidelines that they were given. Now, of course, it went to court, and the ambulance service was sued, but the ambulance service protected their paramedics, because they had followed their protocols.

Now, if you go outside of your protocols, and it works, that’s great, but if you go outside, and it doesn’t work, and your patient’s harmed, then you’re in a lot of hot water, so not a lot of paramedics will risk their own career. It just gives you an idea of how your guidelines don’t always do what’s best for the patient, but if you wanna stay safe as a paramedic, then you’ve gotta follow them. Now, this is unfortunate that, that’s not always what’s in the patient’s best interests, and that’s what this term vicarious liability is. That means that if you followed your ambulance service guidelines, and it goes wrong they will cover you, because you’ve done everything that you should have done.

Okay, now cautions. Most drug guidelines will list cautions. Now, in my experience of working in ambulance services they all have it. Now, you’ve gotta be able to go through the cautions, and rule them out. A caution means to act carefully, so in other words, a bit like what I just said, one service might say you can give a drug for this condition, another doesn’t. Now, I’ll give you an example of how cultures have changed over the years. Historically, when you are giving aspirin for an acute coronary syndrome, a contraindication used to be if patients were actively on warfarin. Now, warfarin is a drug that sticks to plasma cells, and it floats around in the blood, and then, aspirin will come along, and knock the warfarin off the plasma cells, meaning that your patient is more likely to have a bleed, but over the years the thinking around it has changed.

If that patient’s having an acute coronary syndrome, therefore needs a dosage of aspirin, they’ve moved the warfarin over the years into a caution rather than a contraindication, because not giving the aspirin is much more detrimental than allowing a 300 milligram bolus of aspirin to interfere with the warfarin processes, so you still have to think about it. This is where your clinical decision making, and your critical thinking, and your communication, and team working comes into your safe clinical practice. Now, caution means you can administer a drug, however, you must have made consideration for all items listed in a caution, and, again, just make sure that you can rule them out before you give it, because you may be asked to defend yourself in a court of law later.

Now, your safety procedures really do come down to you as the individual, and I cannot emphasis enough that you go through some kind of process of safety checking. Just get yourselves on the internet, and have a look at the different cases that have been heard in courts about patients who have been harmed by paramedics making drug errors. You do not wanna be one of those patients, so paramedics that harm patients. Make sure you check it’s the right drug. You can do this by holding it to your patient, to your paramedic colleague, and saying, “What is this drug?” So, you wouldn’t say to them, “Is this drug adrenaline?” You would say, “What is this?” Get them to read it, because if there’s a drug right next to adrenaline, and it looks very similar to adrenaline, and you’ve pulled out the wrong drug, they’re more … Your crew mate is more likely to say, “Yeah, yeah, it’s adrenaline.” Because, it looks the same, and it could be the same, so get them to read it.

Make sure the container is not damaged, because therefore, the drug’s not contaminated. If it is, choose another drug and report that. Make sure it’s in date. Now, this is not unsafe from the viewpoint of contamination. However, it’s unsafe from the viewpoint that the drug will start to be less efficient if it becomes out of date. Check to make sure there’s no obvious discoloration, or that the packaging is not damaged, because, again, if there’s any type of damage to the drug, then it can be a problem for your patient. I’m reassessed that you are confident of the chosen route of administration, so go back through, and consider the bioavailability, go back through your guidelines to make sure that it’s in your scope of practice, and you’re not acting outside of them.

And then, finally make a check against your clinical practice guidelines. In other words, get your guideline out, and just double check the contraindications. Check the right dosage, and routes, and all those things. Do not try, and have any bravado about, “I’m a great paramedic because I know my drugs.” Those are the paramedics who make drug errors. It’s been proven by research. Just get into the drug areas, and have a look online. There’s plenty of it for you to look at. You need to be checking your guidelines for all of these things that we’re talking about, and get into the habit now whilst your in the training mode before you go out into clinical practice, and you harm yourself, harm someone, because you’re trying to prove how smart you are. Remember that once you’ve given the drug you cannot take it back.

Okay guys, so I hope you’ve enjoyed this session. What we’ve done in this session is we’ve looked at the key terms related to drug pharmacology, including bioavailability, half life indications, contraindications, cautions. We’ve looked at a range of drug routes including intraosseous, intramuscular, intravenous, per orum, per rectum. These are the key routes that your all gonna have available to you as a paramedic, and if you’re familiar with them now, then you’re gonna just find it so much easier to be able to treat a patient, and select a route when you get into your workshops as well as when you go to university, or go and work for an employer as well, because some of you may have never heard these terms before, and that’s fine as well.

And, of course, most importantly we’ve looked at the necessary safety checks that you must undertake before administering a drug, because really this is the most important part of paramedic practice. Making sure that you are safe, and keeping yourself safe, keeping your patients safe. I hope you’ve enjoyed this session guys. You can use the key terms from this lecture to go off, and do some more reading.

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