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Book excerpt: ‘Med Math Simplified’

Paramedic and nurse educator teaches principles of dimensional analysis for medication dose calculation


Editor’s note: Jamie Davis, the podmedic, is a nurse and paramedic educator. As the host of the MedicCast, a long-running EMS podcast, he has helped countless EMTs, paramedics, nurses, and allied health students with his tips, study tools, and ebooks, including his latest book, Med Math Simplified. The chapter excerpted below combines the concepts of dimensional analysis with a good old common sense approach to learning the math and formulas needed to safely and correctly arrive at drug doses for patients.

By Jamie Davis

Chapter 2: On Safety and Medications

Before we get started we should take a few moments to talk about safety and medication dosing. There are some important concepts we must review about how to safely note medications and doses. The correct notation of doses for medications is of utmost importance. For most of you this will be a review of basic medication safety but I urge you not to skip over it. This is a short but very important section of this book. Read through it and refresh your commitment to the “Five Rs of Medication Safety.”

What are the “Five Rs” or “Five Rights of Medication Safety” you ask? These are the things that you must ask yourself before giving any patient any medication. One of them is the reason for this book. It is simply “Right Dose.” But there are other, equally important rights for medication administration and safety that are just as important and go hand in hand with “Right Dose.” The Five Rights are:

  • Right Medication
  • Right Expiration Date
  • Right Patient
  • Right Route of Administration
  • Right Dose

Let’s look at each of the Five Rights in turn to make sure we understand all of them.

Right medication is the first and it seems kind of simple-minded to some. However the Institute for Safe Medication Practices has a list 9 pages long of commonly confused medications. These are medications that have names that are similar sounding when spoken aloud or similar looking when written out. If you want to see some of them for yourself visit the ISMP site for the complete list. You must compare the medication you are preparing to administer to the medication ordered and make sure it is the same.

Right expiration date is next up in the Five Rights and it, too seems simple. Often however, we don’t check expiration dates on medications we administer. We might assume that someone else has rotated the medication stocks to make sure that we use the oldest medication first and thus use meds before they expire. For infrequently used medications that sit in a drawer or on a shelf, however, that may not be the case. How do you know if you don’t check? It is a best practice to review the dates of any medication as a matter of routine so that you always catch out of date medications when they pop up.

Right patient is a very important step. In a hospital setting where you might be caring for many patients, it is easy to get your orders mixed up. You should verify that you have the right patient by checking their ID bracelet with their written orders to make sure you have the correct one. Even in a setting like home health care or in the back of an ambulance, checking some patient facts is important. While you may only have one patient at a time there are things about some medications that make it important to confirm they are the right patient for the drug at hand. Some drugs are not recommended for pregnant women for example. Some patients are allergic to some medications. Confirm they have no allergies to the medication at hand before you continue. Make sure they are the right patient for the drug.

Right route of administration is next and is equally important. How is the drug you are preparing to administer supposed to be introduced into the body? You must understand the differences between the various routes of administration. Some methods are more slowly absorbed than others. Your job is to know the correct routes of administration for the medications you are giving and know which of those routes is the most appropriate for a given situation.

Right Dose comes last and, as I have already said, that is the primary purpose of this book. We must be able to calculate the correct dose for each patient. There is more to dose than that, though. How you write that dose out for others to read back is also important. There are very specific rules surrounding how to write out medication doses correctly so that mistakes in dosing are avoided. When writing the doses out in your calculations, you must avoid writing the dose in such a way that someone else might make an error when reading it back or in the patient’s chart.

No Trailing Zeros - Look at the following dose for epinephrine 1:10,000 in cardiac arrest. Are you to administer 1.0 milligram (mg) or are you to administer 1 milligram (mg)? Which is correct? The second one is the correct answer. The first is too easy to mistake for 10 (ten) milligrams of epinephrine because the decimal point might be missed when reading it. The rule is no trailing zeros are to be used when writing a medication dose.

Use Leading Zeros - Similarly, look at the following dose for epinephrine 1:1,000 in cases of allergic reaction. Are you to administer 0.5 milligrams (mg) or are you to administer .5 milligrams (mg)? Which is correct? In this case the first answer is the correct one. Again, you might miss the decimal point in the second choice and administer 5 mg by mistake, a definite harmful mistake for the patient. The rule is to use a leading zero before the decimal point to draw attention to it and make sure that the correct dose is given.

Now that we’ve looked at some medication safety issues and reviewed the Five Rights, it is time to move on in the book. Next up we will look at some math basics to make sure we are all on the same page moving forward. In the next chapter, there will be some links to additional resources to do basic math review to make sure you are ready for the rest of the book.


Med Math Simplified: Dosing Math Tricks for Students, Nurses and Paramedics
MedicCast Productions; 1st edition
Copyright 2014 by Jamie Davis
Available on Amazon

About the Author

Jamie Davis, the Podmedic, is the host of the MedicCast and Nursing Show podcasts. As a paramedic and RN, he is passionate about educating health care professionals about emergency medicine and patient care. Check out all his programs at or connect with the Podmedic on Facebook or Twitter.

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