Richard R. Espinosa, Austin Community College
Dosage Calculations
In the Conversions Module, the following guide was used to help set up the dimensional analysis problem. In this module, you will continue to use the guide as a model. Note, however, that the given quantity is also referred to as the doctor's order and a second variable has been added to the guide - dose on hand (DOH).
NOTE: If needed, review Conversions Module before proceeding.
The DOH, or stock supply, becomes the second variable in the problem. The DOH is the available dosage of medication that is on the shelf at the pharmacy or nursing station. DOH can be expressed as a common fraction. For example, if 1 tablet contains 350mg, it can be expressed as a fraction in the following ways:
Likewise, a fluid DOH can also be expressed as a common fraction. For example, if 1 mL contains 250mg, it can be expressed as a fraction in the following ways:
This is an example of DOH.
Equivalents and conversion factors are used in dosage calculations in order to cancel the unwanted units of measure that are no longer needed in the problem.
For example, the doctor ordered 500mg of medication but the DOH is 1 g tablets. You would need to use an equivalent to convert the doctor's orders to the same units as the DOH. In this case, the equivalent would be 1g = 1000mg.
Therefore:
500 mg
1
|
. | 1 g
1000mg
|
= 0.5 g |
Using an equivalent, you have converted the doctor's orders of 500mg to an equivalent of 0.5g.
A good rule to remember in order to prevent medication errors in solving dosage calculation problems is to ALWAYS use a zero before a decimal point. For example, in the problem just solved the answer should be given as 0.5g not .5g.
Continue for more examples in order to help you see and understand the concepts we have discussed.