Math for Medication Administration
14 Calculating Medication Dosage
Lesson
Learning Outcomes
By the end of this chapter, learners will be able to:
- explain a method for solving medication dose problems, and
- correctly solve medication dose problems.
There are often multiple ways to solve problems involving math. In this workbook, the process of dimensional analysis is presented as one way to solve all types of medication related problems. You can continue to use this process when solving practice problems presented in this chapter. Using this form of problem solving can help you reduce errors if you struggle to remember formulas or figure out which formula to use as you can learn just one method to approach all the calculations.
Steps to Calculate Medication Amounts
- Read the information carefully. Avoid distractions when preparing medications so you can focus on the problem at hand. What information are you trying to calculate?
- Set up the formula. When beginning to calculate medication amounts it is helpful to always write down your work so you can check your work and so others can help you find errors if you have made a mistake.
- Calculate the answer by using a calculator or mental math.
- Check your work. Always double check your answer. Does it make sense? If you have determined you need to give 20 tablets for one dose this would be a red flag-an unlikely situation and indicates an error has probably been made. As a student, you should always have a supervising nurse check your math. After you graduate, there are specific high risk medications (like insulin) which must be double checked by another nurse. You may also decide that specific situations warrant asking someone to check, such as if you have been feeling tired or if there are distractions during your process of medication administration.
Sample Exercise 14.1: Determining the number of tablets required when the dose is more than the supply
How many tablets would you administer for the following medication order?
Order: prednisone 20 mg PO OD
Supply: prednisone 5 mg tablets
Answer:
4 tablets.
[latex]\text{x tablets}=\dfrac{\text{1 tablet}}{\text{5 mg}}\times{\text{20mg}}\\[/latex][latex]\text{x tablets}=\dfrac{\text{1 tablet}}{5\cancel{\text{ mg}}}\times{20\cancel{\text{ mg}}}\\[/latex][latex]\text{x tablets}=\dfrac{\text{20 tablet}}{5}\\[/latex][latex]\text{x tablets}=4[/latex]
Alternate Formula for Solving Medication Dose Problems
[latex]\dfrac{\text{Desired amount}}{\text{Amount in supply}}\times{\text{Volume of supply}}=\text{Quantity for dose}[/latex]
This may also be written as:
[latex]\dfrac{\text{Desired Amount}}{\text{Dose on hand}}\times{\text{Volume}}=\text{Dose}[/latex]
Or abbreviated as:
[latex]\dfrac{\text{D}}{\text{H}}\times{\text{V}}=\text{Dose}[/latex]
Regardless of the words or letters chosen to represent numbers in the formula, the numbers related to the medication problem are always in the same place.
Here is the same problem from the sample exercise above, us