Pills - Tablets & capsules

and other oral meds

Calculations involving tables and capsules are usually straight forward. We usually do these in our head without even thinking too much about them. Because we do have a good intuitive sense of doing this kind of problem, these make good practice thinking through using dimensional analysis technique ....

example one ...

The doc orders 0.25 mg synthroid PO daily.  Of course in the chart, it probably looks more like ...    .25    - yep - it's Greek to me too ...J

Pharmacy sends us 100 mcg scored tablets.  Remember our one and only formula - those are the 3 things we have to know to do any dose calculation. And we have them.

Ordered: 0.25mg

Available form : Tablets

Available dose : 100 mcg

We always start with what we want to know - that is, what are we actually going to give the patient? Tablets of course:

 

 

Our rule for using the factor-label method is to make our first factor something we know and write it so the unit corresponding to what we want to give, is in the same position :

 

 

Next we multiply it by the ordered dose.  If you have any question about how to write the ordered dose, that is, ordered dose / 1 or 1 / ordered dose, the rule is write it so the unit is opposite the corresponding unit of the available dose. Our available dose unit is a weight and it's on the bottom, so we write our ordered dose unit, also a weight, so its on the top. It doesn't matter that they aren't the same unit - they are the same class of unit, so we can treat them as being the same to setup the problem.

 

 

Now you notice in the above equation that our units of weight don't match.  Remember we can only cancel "identical" things: 2 numbers, 2 mg's, 2 mcg's and so forth.  If we attempted to cancel & calculate the above we get a very strange result :

 

 

 

Looking at the above "answer", you can see what we need to be able to finish.  We need a conversion factor that has both mg and mg in it since those are the units we need to get rid of in order to have only the unit of "what we want to know" (Tab) remaining.  Again, we write it so corresponding units are opposite. Our objective is to write our factors so EVERYTHING cancels out except what we want to know.

 

 

Now we can go through and cancel and then multiply all the numerators together and all the denominators together:

 

 

 

Since the only unit remaining is Tab, we can be sure we've done the problem correctly.

 

©1997-2006 Dale Sampson, RN