Accurately performing pharmaceutical calculations is a critical component in
providing patient care in every pharmacy practice environment. Consequently,
pharmaceutical calculations are a vital part of any pharmacy curriculum.
Although most pharmaceutical calculations are not 'difficult,' it is a topic
that deserves attention because it requires flawless accuracy. Before students
are able to become optimally proficient at performing pharmaceutical
calculations and using them to contribute to optimal patient care, they must
understand approaches to pharmaceutical calculations that help minimize error
and maximize accuracy. The objectives of this introduction to pharmaceutical
calculations are:
1. Openly address common student perceptions so that these perceptions do not
hinder students' focus on pharmaceutical calculations.
2. Review the two main approaches to pharmaceutical calculations, proportion
and dimensional analysis, and describe advantages and shortcomings of each.
3. Provide recommendations for improving efficiency and accuracy while
avoiding errors and misinterpretations when completing pharmaceutical
calculations.
4. Describe methods for double-checking calculations.
Frequent Perceptions
Like any class, students come to a pharmaceutical calculations class with
perceptions and expectations. Some of these are accurate and some require
refinement or explanation. The following issues often come up when students
first come to the calculations course.
"I already know how to do this - it is just simple math."-Although some
pharmaceutical calculations require basic science knowledge, such as
interpreting a chemical formula to determine the number of equivalents per mole
or knowing that 1ml of water weighs 1g, a large part of performing
pharmaceutical calculations requires math skills learned prior to high school.
Students quickly recognize this fact and some may perceive that pharmaceutical
calculations should be easy. The fact of the matter is that pharmaceutical
calculations are NOT easy. No student in 8th grade was expected to be correct
100% of the time. The major difficulty in pharmaceutical calculations is not the
math, it is the fact that the margin for error is non-existent.
Some of the content of the remaining discussion will provide mathematical
reviews that will be quite basic to some students. This level of detail is
purposely provided so that all students fully understand these basic
mathematical concepts, as their future patients' doses, dosage forms, and lives
will depend on it.
"I can do this in my head."-As students and later as practitioners, there are
occasions when calculations are done without a paper and pen. Most students and
pharmacists do not need a paper and pen to determine that if 1 tsp contains 250
mg of amoxicillin, one half tsp will contain 125 mg. Students need to show their
work for even the simplest calculations, however. The obvious reason for this
(grading) is not the most important. Showing their work allows a student to
visualize the problem and slow down their thought process, making it less likely
for errors to occur. It also develops good habits for practice, when
documentation allows other practitioners to double-check work and easily see the
method of calculation used.
"It is boring - let's get to the exciting stuff."-Pharmaceutical calculations
are not glamorous. In fact, one could argue that they are somewhat mundane. This
can be particularly true early in a lecture series on pharmaceutical
calculations, when the topic focuses on understanding the basic concepts of
proportions and dimensional analysis (before diving into the slightly more
glamorous calculations themselves). The challenge lies in the fact that many
students (and instructors alike) would rather spend time discussing new and
innovative therapies for a condition than basic concepts in pharmaceutical
calculations, and consequently, it is tempting to rush through introductory
material. Calculations can be occasionally mundane, particularly the repetition
necessary to develop confidence as well as accuracy. Nevertheless, deliberate
and undivided attention to detail is required to clearly understand the basic
concepts that will serve as building blocks during later coursework. There can
be no misunderstanding of the basic concepts among students. Correct
calculations contribute just as much to patient outcomes as the newest methods
and guidelines for diagnosis, treatment, and prevention. Furthermore, errors in
calculations can make the otherwise best attempts at optimal patient care
catastrophic.
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