Pharmacology is hard! So let’s practice some problems together!
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Today we’re going to be doing some interactive pharm practice. You will hear the problem and do your math and then we will check it together.
We are going to go over some basic tips for success and do some practice problems together. You will hear the problem, pause and do your math and meet me back to go over the math.
So here are some must know tips for you to really knock your math questions out! You may know some of these already but it doesn’t hurt to get a quick refresher. Make sure you read the question. See what it’s asking you. What’s the unit of measurement being used? What’s the order, including the dose and frequency of the medication? Do you need to convert measurements like from grams to milligrams or pounds to kilograms? Make sure you label everything so you don’t lose track of what you’re doing. If you had to convert a unit of measurement, make sure you keep using the converted unit so you don’t revert backwards. It’s super easy to get confused if you don’t. Also, and this is easily the most important step. Check your work! Make sure the answer is labeled and that you are actually answering the question. Some problems have multiple questions and I know I used to go back a lot and make sure I hit on everything. Did you round correctly, if at all? Is this what the question is asking? So even though going back to re-read the question can be time consuming, it’s definitely helpful in the long run and can save you some very valuable points.
Let’s take a quick look at the medication routes we’ll be working with. Oral medications we know are usually pill or liquid form. Pretty cut and dry there. Intramuscular injections is where things can get a little tricky, particularly when we’re talking about maximum doses to give in the syringe. So here are the 3 recommended sites. We have the deltoid, ventrogluteal and vastus lateralis. Simply put, your upper arm, midway between the hip and femur and the quads, in that order. We also have the dorsogluteal muscle, which is the buttocks, but it’s not an ideal spot because it sits so close to the sciatic nerve and the gluteal artery. The biggest thing you want to know is the maximum amount of medication you are allowed to give in each place. In the deltoid, we cannot inject more than 2ml of medication. In the ventrogluteal, do no exceed 2.5ml, and in the vastus lateralis, don’t exceed 5ml. If you must use the dorsogluteal muscle, the max is 4ml.
So enough of the technical stuff, let’s do some math! First we will work with basic formula. There are several different methods out there but basic formula is exactly as advertised: basic and straightforward. It’s simply Desired over Have times Vehicle (D/H x V) equals the amount to give. Desired is the ordered dose, Have is what you have on hand and Vehicle is how the drug comes so tablet, liquid or capsule. Most of what we do in this lesson is going to use this formula at some point.
Let’s take a look at an example. First off not every question is going to be worded this way, but it’s best this way for our purposes here. So remember the tips and tricks we reviewed at the beginning of this lesson. Take a look at what the question is asking. In this case, how many tabs are we giving each time. Now, take a look at the unit of measurement. They don’t match. The medication is ordered in grams and we have mg on hand. So the first thing you want to do is convert. An important thing about converting is that you always convert to what’s on hand. In this case, we will convert 0.5g to mg. Try it out. Your answer should be 500mg. Now that we have the right measurements, we can work. We are using basic formula here so it’s desired/have x vehicle. You can always break this down easier for yourself as well and put the numbers you are working with to the side to plug in when you’re ready. Go ahead and give this a try. So 500mg/250mg x 1 tab. Your answer should be 2, but don’t forget to go back to the question and make sure you answered it all. And label your answer! 2 tabs per dose.
Now we got the easy part out the way, let’s get a little more difficult. Calculations using body weight is a little different. We can still use basic formula, but not right away. So here’s an example. What you’ll notice here is the additional information. We now have a dose per kg in our order so we know to look for a weight somewhere, which is at the end of the problem. The child weighs 20 lbs. First thing’s first guys, we have to convert! Remember that 1kg = 2.2lbs so when you are given pounds and need to convert to kg, divide down. Try it. If you did the math correctly, you should have come up with 9kg. Now, we will use the body weight formula: dose x body weight x frequency. We are simply plugging the numbers in at this point: 20mg x 9kg x 1day= 180mg per day. But we aren’t done because we need to know how much to give in 3 divided doses. So let’s divide 180mg by 3. You should come up with 60mg per dose. Done right? Wrong. The question is asking how many mls the child will get per dose. So now we go a step further and use basic formula again: D/H x V. Our desired dose is 60mg per dose. What we have is 125mg per 5ml. Plug it in and try it out! You can multiply across and cancel out like units to make life easier for yourself. Your answer should be 2.4ml three times per day (TID).
IM calculations work pretty well with basic formula as well. I’ll let you work this problem out first and then we will walk through it. First you want to check your dosages and conversions. Both the order and what’s on hand are the same unit of measurement so there’s no need to convert. We can just jump right into the formula: D/H x V and plug in the numbers. So we have 60mg/80mg x 2ml. Multiply across and you get 120mg/ml/80mg. Cancel out like units and you’re left with 1.5ml.
Some quick key points to review. Remember to always read the question and be sure you understand what it’s asking for so you have your goal set. Basic formula can be used everywhere at some point. Understand what numbers you should be using. When you work with weight, the one thing you can count on is converting. This is the only time you can convert to what the order says so when remember, when you have weight in pounds, divide down! And last but not least, it never hurts anyone to take a quick look back and check your work!
We love you guys! Go out and be your best self today! And as always, Happy Nursing!