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:
- 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
- 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
- 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)
- 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
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:
Here’s an example of the medicine label that you will read in order to get the information needed to solve this question:
First thing you would do is LABEL. What are we looking for here? TABLETS! So label like so:
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:
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!