Pharmacy Technician Math

Get more confident in your pharmacy technician math skills with these great tips and explanations from an experienced pharm tech instructor.

by Michelle Goeking, BM, CPhT

A pharm tech in any area of  pharmacy practice will encounter some pharmaceutical calculations that will need to be performed.

The types of calculations will vary, but a solid understanding of algebra will help tremendously.

Though much of pharmacy technician math is based on simple arithmetic and  proportions, other more complex math using algebra and dimensional analysis will be needed to solve certain dosing calculations.

A Brief Lesson in Pharmacy Technician Math

The vast majority of pharmacy technician math calculations involve converting from one system of measurement to another. This can then be coupled with determining how long a drug supply will last or other dosing calculations. The metric system is a more precise measurement; therefore, a pharmacy technician must often be able to easily convert dosages from the household measuring system to the metric system. Many technician manuals and textbooks have tables with the most common conversions for reference.

For example, if the directions of a prescription state “give 1 teaspoonful by mouth three times daily for 10 days”, the technician will need to calculate the amount needed in milliliters.

By consulting the table (and eventually memorizing the most common conversions), you find that 1 teaspoon = 5 milliliters.

To determine days’ supply, one multiplies the dose in milliliters by the frequency and the number of days. So, 5 mL * 3 times per day * 10 days = 5 * 3 * 10 = 150 mL. By using conversions, the pharmacy technician can determine an accurate days’ supply.

This type of problem is typical for a retail pharmacy technician, but some of the content is definitely applicable to a technician working in a hospital.

Proportional Math

Proportions are commonly used to solve dosing problems of all sorts, and proportional math is one of the easiest ways to solve many of these pharmaceutical calculations. In both retail and hospital settings, the pharmacy technician may need to determine the volume of a drug needed for a patient.

What if a drug comes in a concentration of 250 mg/5 mL but the patient needs 600 mg? These types of problems can easily be solved using a proportion. In proportional math, one always puts the like units on the same side of the division bar to calculate.

To solve this problem, set it up similar to this: 250 mg / 5 mL = 600 mg / X. “Cross-multiply” and divide to solve for X to determine the number of milliliters the patient will need. The answer is 12 mL.

Math in Different Pharmacy Settings

A hospital or institutional pharmacy technician will also come across more advanced types of calculations involved with doses based on body weight or body surface area, percentage or ratio solutions, or drip rates.

Retail technicians may also need some basic business math skills besides those described above. Though the previous examples are commonly used, many other types of calculations are performed. Many excellent pharmacy calculations workbooks are available for study.

If one is interested in becoming a pharmacy technician but is a little rusty at math, a basic algebra review course or two at your local community college may also help. Though computers help streamline a lot of the calculations pharmacy technicians used to perform, these skills are still required and are necessary for the job and for national pharmacy technician certification.

Michelle Goeking (BM, CPhT) has been a practicing pharmacy technician for 16 years in both community and hospital settings. She has 5 years of experience creating and directing a pharmacy technician education program at a community college, as well as writing PTCE test items for various publishers. Michelle is currently enrolled in a doctor of pharmacy program at the University of Illinois at Chicago and is a practicing pharmacy intern.

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