Determine the Cost of a Drug

You will probably see at least a couple retail price calculations on the exam. In a work situation, you will be inputting values into your pharmacy’s software to get a price. For exam purposes, know how to calculate these by hand.

If twenty tablets of Furosemide 40mg cost $3.40, how much would thirty tablets cost? Fifteen tablets?

There are two ways we can solve this problem. Both are relatively easy.

Method 1

The first method is simply breaking down our known information to find the cost per tablet. Since we know twenty tablets costs $3.40, divide the cost by the number of tablets:

$3.40 / 20 = $0.17 per tablet

Now that we have the cost per tablet, we can multiply $0.17 by the quantities in question:

$0.17 * 30 = $5.10 cost for thirty tablets

$0.17 * 15 = $2.55 cost for fifteen tablets

Method 2

In this method, we will set up the problem as a proportion that has an unknown. To be able to work it this way, you must be familiar with proportions and simple algebra.

The left side of the equation is what we have (both numerator and denominator is known.) The right side of the equation is what we want, but the denominator is unknown. We denote this as X.

After setting up the problems, cross multiply. This sets you up to solve the problems algebraically.

Example With Unit Conversion

Now let’s look at a slightly more complicated pharmacy retail math problem.

You are compounding a medication that requires 125mg of a certain powder. Your pharmacy purchases this powder in 5g bottles . The cost of one bottle is $30. What is the cost of 125mg of this powder?

Don’t be overwhelmed by the wordiness. Some of these problems are designed to trip you up with excess information. The first thing you might have noticed is unit conversion is necessary before we can solve the problem.

Let’s get our conversion set up. How many milligrams are equal to 1 gram?
This memorization is necessary. Be sure to know your common unit conversions. In this case, 1g is equal to 1,000mg so 5g equals 5,000mg.

Next, find the cost per milligram by dividing $30 by 5,000mg:

$30 / 5,000 = $0.006 per milligram

Taking the cost per milligram, we will multiply that by how many milligrams of powder we use for the compound:

$0.006 * 125 = $0.75 total cost of powder used in the compound