Intro to Math for Medications

Medication math involves simple algebra and competence in certain formulas and conversion rates that you will be required to know for the exam, which you need to make a 90%+ in order to pass (in our program at least). Here, I’m just going to go through the basic info you will need. KNOW THESE:

CONVERSIONS:

  • 1 teaspoon = 5 mL
  • 1 tablespoon = 15 mL
  • 1 ounce = 30 mL (therefore 1 ounce also = 2 tlbs or 6 tsps)
  • Roman numerals – V(5), X(10), XV(15)
  • 1 kg = 2.2 lbs
  • 1 grain (gr) = 60 mg; 65 mg for Tylenol
  • 1 L = 1000 mL
  • 1 mg = 1000 mcg
  • 1 gm = 1000 mg

ABBREVIATIONS:

  • AC = before meals
  • PC = after meals
  • PRN = as needed
  • q2h, q4h … = every 2 hours, every 4 hours
  • BID = twice daily
  • TID = 3x daily
  • QID = 4x daily
  • IVPB = intravenous piggy back
  • mcg = microgram VS mg = milligram
  • tabs = tablets

ADDITIONAL FYI:

  • Always LEAD with a ZERO. Never TRAIL with a ZERO.
    – 0.5 or 5 ✔ (correct)
    – .5 or 5.0 × (wrong)
  • Round to the nearest tenth when calculating for most medication problems, unless specified otherwise
  • Round to the nearest hundredth when calculating for drugs to be administered in a TB syringe (<1mL)
  • Round to nearest whole number for drops (gtt/min) & IV pumps (mL/hr)
  • For pills & tablets, make sure you answer is either a whole number or halves.
  • Insulin is only given in units.
  • Make sure all of your answers are label appropriately (tabs, mL/hr, mg, etc)

FORMULAS:

  • The easiest way, for me, to calculate simple drug dosages is through Ducks Have Quacks (Hurrrr??). You’ll learn the origin of that but it’s simply DESIRED/HAVE x QUANTITY = X (amount)
  • For an IV infusion when using a pump: amount to be given (mL)/time (hours)
  • For an IV infusion without a pump: amount (mL) x drip factor (gtt/mL)/T(hr) x 60 min

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Let’s try one out for fun. Basically your math exam will have a series of 20 questions, with a couple of pages of medicine labels on the back to refer to. Here’s an example of a test question:

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Here’s an example of the medicine label that you will read in order to get the information needed to solve this question:

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First thing you would do is LABEL. What are we looking for here? TABLETS! So label like so:

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Now, determine what formula you are going to use. We’re simply looking for “how many tablets per dose”. We can use the DHQ formula, but let’s double check. We have our D “desired” (375 mg), we have our H “have” (250 mg – from the drug label) & we have our Q “quantity” (1 mL – which is usually the case, unless otherwise specified). Now set up our equation & solve:

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Now double check your answer again. It’s in tablets so 1.5 is an acceptable number. Congratulations! You (most likely) just got first taste of medication math!

Again, this is just a small example of what to expect once you get closer to the math exam. You’ll learn more through practice. I highly encourage you to practice frequently. Take advantage of the opportunity!

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