Dosage Calculation: Reconstitution
by Cathy Parkes October 29, 2021 Updated: March 13, 2022 2 min read
Hi, I'm Cathy with Level Up RN. As promised, I am going to work through a reconstitution problem that was submitted by a viewer on YouTube. It is listed here on the screen.
So the order states that 125 milligrams of amoxicillin is ordered for administration every eight hours. And instructions for reconstitution state to add 74 milliliters of water to the contents of the bottle to yield 250 milligrams of amoxicillin per 1 teaspoon of suspension. How many milliliters will the nurse administer to this pediatric patient? So first of all, when you're given a reconstitution problem, they like to throw a lot of numbers at you.
And you may look at this and be like, "Ah, 125 milligrams, 74 milliliters, 250 milligrams, it's a lot." The bottom line, though, if they are asking you for the dose, the amount to give a patient, you only really care about the final concentration of the solution.
So we don't really care that 74 milliliters of water was added to make the concentration. The only numbers we really care about in this order are the fact that 125 milligrams are ordered, and the final concentration is 250 milligrams in 1 teaspoon of suspension.
So I'm going to work through this. I'm going to use dimensional analysis, which is my preference, because it's a little more straightforward and efficient and easier in my opinion. But you can absolutely use ratio and proportion or the formula method as well to solve this problem.
So we first write down what is ordered, which is 125 milligrams. That's usually where you start when it comes to dimensional analysis. Then we are going to multiply it times what is available. And the final concentration of our solution or suspension is 250 milligrams in 1 teaspoon, so 1 teaspoon over 250 milligrams. And you can see that our milligrams are going to cross off. We're going to be left with teaspoons.
But that's not what they're asking for in this problem, right? They are asking for how many milliliters will be administered. So that's where we need our conversion factor. And we know that 1 teaspoon equals 5 milliliters.
So we're going to multiply, again, times the conversion factor. 1 teaspoon equals 5 milliliters. And I want to make sure my milliliters are on top, when I'm multiplying times this conversion factor, because that's what I want to end up with, is milliliters. So you can see here that my teaspoons cross off, and I'm going to be left with milliliters, which is perfect.
So if I take 125 divided by 250, that 0.5, times 5 and I will end up with 2.5 milliliters. And if you look at the end of this question, it says, "If the answer is greater than 1, round to the 10th. If less than 1, round to the 100th." So we are over 1, and we are already rounded to the nearest 10th place there. So we're all set. So 2.5 milliliters will be administered to this patient. Hope that was helpful for you.
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