July 17, 2020 Updated: July 29, 2021 3 min read 2 Comments
Cathy Parkes BSN, RN, CWCN, PHN:
In this video series, I'm going to work through some dosing calculations. For those of you who can use a little extra help with that, I have nine problems that I'm going to work through. I have these problems posted on my website, LevelUpRN.com. You can print them out from my website and kind of work through them alongside me.
I also have the answer key. If you want to work through the problems independently and just check your answers, then you can just open the answer key and see how you did. I'm just going to take one problem at a time and I'll show you how I like to go through the problems.
The first problem I'm going to go over is how to calculate an oral dose. If your doctor prescribes like a tablet or a capsule, how do you calculate how many tablets or capsules your patient should get? In this particular problem, the order was for 0.4g of this medication, every 8 hours. What we have on hand are capsules with 200mg in each capsule. Let's work through this. What we need to give the patient is 0.4g. I can already see that because my capsules are in milligrams, I'm going to need to convert these grams to milligrams. I'm going to multiply. 1g is equal to 1000mg. At this point I can cross off this gram and this gram. One's on top, one's on bottom. I have milligrams. Now I need to figure out how many capsules my patient should get. I would multiply this. 200mg are in one capsule. my milligrams are going to cross off. then I would do my multiplication, which is 0.4, times a thousand, and then divide by 200. that would give me two capsules that I need to give my patient for the dose that is ordered. That's problem one.
Now I'm on Problem #2.We are going to calculate an oral dose again, but this time we have an order for a liquid medication. In this particular case, we have an order for 0.5g of a liquid medication to be administered every 12 hours. what we have available is this medication, in the following concentration. We will have 250mg within 5m of liquid. The question is, how many milliliters should we administer? Again, I'm going to start with what's ordered, which is 0.5g. you can see by what's available that I'm going to have to convert again to milligrams. I'm going to multiply 1000mg over 1g, and now I have milligrams, but I need to find out how many milliliters I need to give the patient. I'm going to multiply this times 250mg is in 5ml. I can cross off my milligrams, and if I multiply this out. I will get milliliters. in this case, I get 10ml. You can do this with your calculator. You would multiply 0.5 times 1000 times 5 divided by 250. that will give you 10ml. Again, I'm starting with the ordered dose and I'm just doing conversions to get to the unit of measure that is asked for in the problem. That is Problem 2.
We'll pick it up with Problem #3 next. The third type of problem I'm going to work through here is calculating an IV, IM, or a subcutaneous dose. In this particular example, the doctor has ordered 5,000 units of heparin to be given every 8 hours. What we have on hand are 10,000 units/ml. Per milliliter of liquid, there are 10,000 units of heparin, and we want to know, how many milliliters should we give with each dose? And then how many milliliters we're going to give over that 24 hour period. Let's first talk about what we're going to be giving per dose. Again, the order is for 5,000 units and what we have is 10,000 units in 1ml. Our units cross out here, we take 5,000 divided by 10,000 and we get 0.5ml. That's how much we're giving with each dose We're giving that every 8 hours. To calculate how many milliliters we're going to give over a 24 hour period, we're going to take that 0.5ml that we are giving per dose. We're giving that every 8 hours and we're going to multiply that times 24 hours. Our hours cross off. we're going to end up with, if you do the math here, 0.5 times 24, divided by 8 ends up being 1.5 milliliters total, that we're giving over a 24-hour period. That is Problem 3, we will move on to Problem 4 next.
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