Pharmacokinetics- pharmacodynamics, pharmacogenetics with a nursing twist.
Hey, and welcome to nursing with Dr. Hobbick. And today I'm thinking about pharmacology. So today we're just going to hit the highlights for pharmacodynamics, pharmacokinetics and pharmacogenetics. So really, we need to if we're talking about pharmacology, we need to review medication names. Remember that there is a chemical name, which is, I don't even know these, right? This is the actual chemical structure, the composition, the molecular structure of a medicine, there's a generic name, which is actually the official name. So remember that all Ibuprofen is ibuprofen. But if it's under a trade name, or a brand name, it might be Motrin, or Advil, so it doesn't matter if it's Motrin, or Advil, it's still ibuprofen. And that's why the generic name is the official name. And if you're in nursing school, or preparing for the NCLEX, remember that all you're going to see is those official names. So make sure that you're learning your drugs that way. As far as classification, most of the time our medications or class based on their therapeutic effect on the symptoms they're going to relieve. Or the effect that they have on the body system. In other words, in anti infective is is against infection, right? And anti hypertensive is going to help with high blood pressure. Medications come in a lot of different forms. And this is going to affect how our pharmacokinetics work. So solids, liquids, topical medicines, things that we inject into people, that's called parenteral. So we think about pharmacokinetics. The phases are absorption, distribution, metabolism, and excretion. Absorption is where the medication goes from wherever it's administered into the bloodstream, right. So if it's taken by mouth, it's going to get disintegrated and dissolved. If it's given parentally, it's very fast, obviously, because if we give it like IV, it's going to go straight into the main, if you give it intramuscularly, there's a lot of blood flow there, that's going to help it absorb faster. So absorption can be affected by a couple of things, which we'll talk about in a minute. Distribution is how the medicine gets from the bloodstream to its point of action. So wherever it's going to actually work. Metabolism is the function of breaking it down or bio transformation. If you guessed liver, you guessed correctly, most of the time, this is going to happen in the liver. And then excretion of course is where it leaves the body. And it's typically the kidneys that are a main player and excretion. Not always. But typically. So let's talk about absorption for a second absorption happens via passive transport, active transport, or pinocytosis. If you don't remember those, make sure you look them up. The next thing that we need to think about is that absorption is is affected by the blood flow to the area where the medication is administered. If you administer with other medications or with food, they're going to affect how it is absorbed from the GI tract. And then once it absorbs into the GI tract, it's going to pass through the liver via the portal vein. And that's where we need to think about the first pass effect. These medications are given orally, they go into the blood into the portal vein via the intestinal lumen, and they go through the liver and are metabolized. That's the first pass effect. So part of the medication is going to be inactivated by the liver. And that means that whatever medication you take is not going to be 100% bioavailable. So medications like nitroglycerin or lidocaine. They're not given orally, down into the stomach. Because of this first, first pass effect, they have extensive first pass metabolism. And so most of the medication is actually inactivated. Now, because of these things, any changes in liver function or metabolism are going to affect medications. If the liver is not functioning well, then that first pass effect is not going to be as much as you expected. And so this patient can end up with extra medication in their bloodstream that we didn't expect. So the next one is distribution. This is really the movement of the medication from circulation to the body tissues, it can be affected by some of the same things that we saw in absorption, it's affected by the perfusion cardiac output. It's also affected by albumin. So medication binds to albumin particles, and the medication that's actually bound to the albumin then is not going to have an effect on the body tissues. So only the free medicine can affect the patient. What this means is if your patient for whatever reason, has a very low amount of albumin or protein in their bloodstream, they could again end up with a toxic level of medication available bioavailable in their blood. So we want to make sure that we're thinking about those things when we're thinking so medications next after distribution go through metabolism through the liver. This process is where the body changes the medication into a form to be excreted and We can think about half life now half life is it doesn't is not affected by the amount of medication given half life is the amount of time it takes the body to get rid of half of the amount of drugs. So doesn't matter how much drug you've given, it's going to be this much. So if the medication is a half life of six hours, and you give, say 40 milligrams, then in six hours, the patient will have 20 milligrams in their bloodstream. And in another six hours, they'll have 10 milligrams, and in another six hours, they'll have five so you can see how that works. So we want to reach a steady state with medications. That steady state is our therapeutic plateau. That's where we keep an even amount of medication in the patient's bloodstream, so that they will have the effect and not go down below the level of minimum effective concentration in the bloodstream. But we also don't want them to rise above the toxic levels. So we're looking for that steady, steady state and some medications it takes them some time to reach that steady state we think about SSRIs serotonin selective serotonin reuptake inhibitors, things like Zoloft, Sertraline is the generic name, those you know that they're taken, the patients are told that takes four to six weeks to really reach that steady state. So sometimes we'll do a loading dose. If you've ever taken a Z pack, you know, you take two tablets on the first day and then one tablet thereafter. That's a loading dose we also do a loading dose or a bolus of bolus means like a large amount at once. With heparin IV Heparin, you'll do a bolus and then you'll set it to whatever your ordered rate of flow and the the IV pump is. So after distribution and metabolism, then we have excretion. So this is where it leaves the body, usually the kidneys, but the liver can excrete medications through the bile, we have bowels that can eliminate lungs can eliminate some gaseous medications. So an X accouter exocrine glands like sweat glands, or mammary glands. So that's things that we need to think about. And that's why breastfeeding moms need to think about medications in their babies. So pharmacodynamics is the study of how drugs or the way drugs rather affects the body. So you've got your primary effect, this is what you want to happen. This is how you want the patient to be affected. secondary effects can be desirable or undesirable, secondary effect of Wellbutrin is that it helps people to or be appropriate, rather, helps people to stop smoking, right? That's not what it was designed for. But that's something that actually is pretty good at. And then we have this drug response relationship. So you have potency, maximal efficacy, and then the therapeutic index. So we want to keep the medication within the range of that therapeutic plateau. So to think about that, we need to think about onset, peak and duration. So onset is the time it takes for the medication to reach effective concentration or minimum effective concentration, the peak is the highest concentration in the bloodstream. So if we're giving something IV, if it's continuous, it's never going to have a peak, it just has a constant steady state IV is, is that way. But if it's something that's given IV intermittently say you just give it once every six hours, then the patient will have peaks and troughs. So if you think about a trough, like I used to have a farm, a trough is a big like bowl that you put water in for animals. So the trough, if you're thinking about the levels of blood and think about a graph, the peak is the top of the graph where we have the highest concentration of medicine and then it falls, and then it comes down. And hopefully it doesn't fall below that minimum effective concentration. So our steady state is to keep medications in between that toxic level at the high and the minimum effective concentration, we want it to stay in that therapeutic range. Duration is the length of time the medication exerts a therapeutic effect. So peak onset and duration are especially important to know when you're evaluating effects on your patients. So if your patient takes a medication, you need to know when it's going to reach that minimum effective concentration so that you can evaluate the patient. You want to know when the peak is going to be so that you can evaluate them for an undesirable or side effect. And then the therapeutic drug monitoring is something that we'll do with some medications not all were will monitor the peak and trough levels. So they go myosin comes to mind. It's something that we do peaks and troughs on the trough remember is the lowest concentration in the blood so this is right before the medication is due. So this would be something that you would want to draw 30 minutes before you hang that new Banco myosin peaks are similar. You're going to draw the peak while the patient right after the patient has finished getting their vancomycin level. So peaks and troughs help us get an idea That makes sure that the patient is within that therapeutic range and not going above toxic level or below minimum effective concentration. So when medications have an effect on the patient, it's really because they are binding to receptors to activate the receptor to produce a response or to inactivate the receptor. So there's four different families of receptors, something that you should review, I don't have time to really go through all that in this little podcast and try to keep it at a reasonable amount of time. So as far as effects on a patient, we do have, of course, the therapeutic effects, that's what you want the medication to do, you have side effects, which are secondary drug effects. These are things like morphemes can sometimes cause itching, and patients it's not an allergic reaction, it's a side effect, or ACE inhibitors like Lisinopril can cause a cough, drop, dry, cough, persistent dry cough, adverse reactions can be mild to severe. And so this can be something like anaphylaxis, or it could be just a rash that a patient gets pruritis or hives. These are usually undesirable, unintentional effects, adverse reactions. drug toxicity, of course, is the time when the medication exceeds the therapeutic range, which we don't want to happen. We do have interactions pharmacodynamic interactions between medications is something else the nurse needs to know. So they can have an additive. So you give one medication and another on top of that, and they add together, or they can have a synergistic where the sum of the two medications together is even better than they would have been on their own. It's like saying two plus two equals 10, where the additive effect is two plus two equals four antagonistic, meaning the medication is is working against each other. There can be interactions with nutrients with laboratory tests that we might do. And of course, there's photo sensitivity, that is something that's commonly caused by medications, these people need to make sure they wear sunscreen, and they're going to want sunglasses if they have that. pharmacogenetics is really just the study of how patients genomes affect drug response. This is an area that is getting a lot more attention nowadays. And it's helping us to individualize optimal drug treatment regimens. And help us find out, you know, some people, medications don't work for them. So we have people who, you know, maybe would benefit from a different medication to help them out. So that does bring us to some legal and ethical issues in medication administration. So as far as pharmacogenetics who has access to the genetic information, who owns it, the patient may want to refuse testing, or they may change their mind. So we need to think about those things. And of course, want to make sure that we are upholding to the ethical principle of justice, which is equal and fair treatment for everyone. So we think about all of these things, we can just kind of think about the nursing process, and medication administration or pharmacology and how we implement that. So for medications, we have to understand what the medication is going to do the mechanism of action, you need to know what effect you're looking for on purpose and the effects that might happen unintentionally, so your adverse side effects. So we need to do an assessment on the patient to make sure that they're appropriate to have the medication first. If your patient if you're getting ready to give them something to bring their blood pressure down, and their blood pressure's already low, then you probably don't want to do that, right. We need to identify any problems that they have this patient need medication, education, do they understand their medications? Of course, goal interventions would usually be our implement our implementation of administration. And then of course, we need to evaluate and when we're evaluating medications, we're evaluating for that therapeutic effect, and those adverse effects that could happen. So I hope you enjoyed this talk about pharmacokinetics, pharmacodynamics and pharmacogenetics. And I'll see you next time on nursing with Dr. Hobbick.