Welcome back to Nursing Pharmacology, everyone! I'm Julie, and I'm here with Eric and Ruby. Today, we're diving into how drugs actually work in the body—so, pharmacokinetics and pharmacodynamics. I know those words sound a bit intimidating, but I promise, they're not as scary as they seem.Yeah, and I think it's worth saying, if you caught our last episode, we talked a lot about where drugs come from and why it matters for patient safety. Today, we're building on that foundation—so, if you missed it, maybe go back and give it a listen. But for now, let's get into what happens after a drug enters the body.Right, so, pharmacokinetics is basically what the body does to the drug. Think of it as the journey the drug takes—how it moves, gets changed, and eventually leaves. And then pharmacodynamics is what the drug does to the body. That's the fun bit, like, how it actually makes you feel better or, you know, sometimes not so great.Exactly, Ruby. And when we talk about pharmacokinetics, there are four main phases: absorption, distribution, metabolism, and excretion. So, first, the drug has to get into the bloodstream—that's absorption. Then it travels around the body—distribution. After that, it's broken down—metabolism, mostly in the liver. And finally, it's eliminated—excretion, usually through the kidneys.And all of those steps can really impact how effective a drug is, right? Like, if something goes wrong with absorption, the drug might not even reach the bloodstream in the first place.Absolutely. I remember back in my cardiac ICU days, we had a patient who needed a fast-acting medication for arrhythmia. We had to think carefully about the route—IV versus oral—because the onset and duration are so different. If you don't understand how quickly a drug acts or how long it lasts, you can really impact patient outcomes. Timing is everything, especially in critical care.And that's why nurses need to know this stuff, right? It's not just about giving the pill and walking away. You gotta know what happens next.So, let's dig a bit deeper into absorption. There are a bunch of factors that affect how a drug gets into the bloodstream. Things like the route—so, is it IV, oral, inhaled, that sort of thing. But also, the rate of dissolution, surface area, blood flow, lipid solubility, and even pH can all play a role.Yeah, and honestly, the route makes a massive difference. Like, if you give something IV, it's straight into the bloodstream—boom, instant effect. But if it's oral, it has to survive the stomach acid, get absorbed in the intestines, and then, oh, the liver gets its hands on it first. That's the first-pass effect, and sometimes it chews up half the drug before it even gets to where it needs to go. It's like, "Surprise! You thought you were getting 40 milligrams, but nope, here's 10."That's a great point, Ruby. And it's why some drugs are given IV in emergencies—there's no time to wait for absorption. But even with IV, you have to think about distribution. Once the drug is in the blood, it doesn't just float around freely. Some of it binds to plasma proteins, and only the free drug is active. If two drugs compete for those binding sites, you can end up with more free drug than you expected, which can be dangerous.And then there's the blood-brain barrier, which is like the ultimate bouncer at a club. Only certain drugs can get through to the brain, and that's really important for things like treating infections or neurological conditions. The placental barrier works in a similar way, but it's not perfect—some drugs can still reach the fetus.Yeah, and I always think about how some drugs are like, "No worries, I'll just sneak through," and others are stuck outside. It's a bit like me trying to get into a fancy club in Melbourne—sometimes you just don't have the right shoes, you know?Ha! That's actually a pretty good analogy. And it's why we have to be so careful with drug choices in pregnancy or with patients who have brain injuries. The way drugs are distributed can really change their effects—and their risks.Alright, so after distribution, the next big step is metabolism. Most drugs are metabolized in the liver, thanks to the cytochrome p-450 system. This process makes drugs more water-soluble so they can be excreted. But here's where it gets tricky—some foods, like grapefruit, can mess with those liver enzymes and change how drugs are broken down. That's the so-called "grapefruit effect."And then, of course, excretion. The kidneys do most of the heavy lifting, but drugs can also leave the body through the skin, lungs, bowel, and even breast milk. If a patient has kidney problems, drugs can build up and cause toxicity, so we have to monitor that closely.And don't forget about half-life! That's how long it takes for half the drug to leave the body. So, if you're giving something like Isordil, which has a five-hour half-life, you have to think about how often to dose it. Lisinopril's got a twelve-hour half-life, so it's a different story. It's like, "How long till this is out of the system? How long till it kicks in?"Exactly. And that's where onset, peak, and duration come in. Onset is how quickly the drug starts working, peak is when it's at its strongest, and duration is how long it lasts. We use these concepts all the time in practice problems—like, if you give Isordil at noon, when will it reach steady state? When will it be out of the body?And let's not forget the therapeutic index. That's the ratio between the effective dose and the lethal dose. A high therapeutic index means the drug is relatively safe, but a low one means you have to be really careful. That's why we monitor peak and trough levels, especially for drugs with a narrow therapeutic index. It's all about keeping patients safe and making sure the drug is doing its job without causing harm.Yeah, and as nurses, we're the ones keeping an eye on all of that. It's not just about giving meds—it's about understanding how they work, how they're processed, and what could go wrong. It's a lot, but it's also what makes nursing so interesting, I reckon.Absolutely, Ruby. And that's a wrap for today! Next time, we'll dig even deeper into how drugs interact with receptors and what that means for patient care. Thanks for joining us, Eric and Ruby—and thanks to everyone listening. We'll see you in the next episode!Thanks, Julie. Always a pleasure. Take care, everyone, and don't forget to review those half-lives!Yeah, cheers, everyone! Go have a cuppa, and we'll catch you next time. Bye!

Episodes

How Drugs Work in the Body