1. Introduction to Medication Calculation
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Introduction to Medication Calculation
Student Success Immersion Program
University of Maryland, School of Nursing
Presentation created by Amanda Pfaff, RN, BSN

2. Objectives Introduce different forms of medication administration
Reading a drug label
Required conversion factors
Types of medication calculation
Rounding rules
Dimensional Analysis

3. Why is it important?
Medication administration is one of the chief responsibilities of a nurse
Nurses are often the “last line of defense”
Solid knowledge base helps prevent errors

4. Do Not Panic! This is an introduction
You are not expected to know this material at this time
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5. Different Types of Medication
Oral Medications
Supplied in a variety of forms
Tablets are the most common
If patient has difficulty swallowing some tablets can be broken, crushed, or capsules can be opened
Enteric coated and sustained/extended release should NEVER be crush
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6. Oral Medications cont. Oral medications may also come in liquid form
Elixirs and oral suspension
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7. Parenteral Medications
Parenteral: Outside the GI tract
Given when they can’t be given orally or when a rapid onset is desired
Absorbed directly in the bloodstream

8. Parenteral Routes Subcutaneous Injection: Beneath the skin, in fat
Intramuscular Injection (IM): in the muscle
Intradermal Injection: within the skin
Intravenously (IV): within the vein
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9. Parenteral Forms
Supplied as a liquid or as a powder that needs to be reconstituted
Ampules: single dose containers, need to be broken, made of glass
Vials: Glass or plastic container that is sealed with rubber stopper
Vials often contain more than 1 dose of the medication

10. Reconstitution
Some drugs are unstable in liquid form and must be in powder form until they are ready for use
Reconstituted: Dissolved with sterile diluents
Common Diluents: sterile water, sterile normal saline (NS), and 5% dextrose solution (D5W)
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11. Parenteral Forms
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12. IV Administration Gravity infusion Infusion pumps IV push (IVP)
IV Piggybacks (secondary infusions)- medications infused in addition to regular IV fluids, smaller amount
Demonstrate this using an actual IV pump borrowed from the lab
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13. IV Administration
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14. (via gravity or infusion pump)
IV Administration
IV drip
(via gravity or infusion pump)
Why do you need to round to a whole number?
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15. IV Administration IV Push
Why don’t you need to round to a whole number?
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16. Reading a Drug Label Brand name Expiration Generic name7
Brand name
Expiration
Generic name
Safety warnings
Dose
Form
Manufacturer
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17. Measurements Metric System is system of choice
All answers expressed as decimals NOT fractions
More accurate and simplistic

18. Measurement Conversions
1000 ml = 1 L
5 ml = 1 tsp
15 ml = 1 Tbsp
3 tsp = 1 Tbsp
30 ml = 1 oz
240 ml = 1 cup
8 oz = 1 cup
1000 mcg = 1 mg
1000 mg = 1 g
2.2 lb = 1 kg
At the time of your test it is expected that you will have these conversions memorized.

19. Common Metric Measures – Practice
Convert the following:
1 g = ____ mg
0.015 g = ____mg
750 mg = _____ g
0.5 L = ____ mL
g = _____ mg
1.2 g = _____ mg
0.008 g = ____ mg
Have the student go through the problems on their own and then work through the answers with them.

20. Common Metric Measures – Practice Answers
Convert the following:
1 g = 1000 mg
0.015 g = 15mg
750 mg = 0.75g
0.5 L = 500 mL
gm = 0.4 mg
1.2 g = 1200 mg
0.008 g = 8 mg
Have the student go through the problems on their own and then work through the answers with them.

21. Common Metric Measures – Practice
Convert 1.5 oz. into an equal volume of tablespoons (Tbsp.).
A patient weighs 154 lbs. What is this patient’s weight in kilograms?
The doctor instructed Bob to take 1 tablespoons of cough syrup every 12 hours. Bob only has teaspoons available to measure with. How many teaspoons should he take for each dose?
There are 2 bottles of milk of magnesia on the shelf at the pharmacy. One contains 10 oz. and the other has 300 mL. Which has the larger volume?

22. Common Metric Measures – Practice- Answers
3 Tbsp.
70 kg
3 tsp.
They are equal.

23. Units Some medications are measured in units
Common medications in units are: Heparin, Insulin, Epogen, Penicillin
Only insulin is measured and given in insulin syringes
Most other medications can be given in syringes marked in milliliters
Important to understand difference between units and other units of measure

24. Unit Syringes
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25. Pediatric Dosages
Children differ from adults because of their weight, height, metabolism of drugs, and immature body systems
Medications are calculated using the child or infant’s weight
Weight is always in kilograms
You will not be expected to do pediatric dosing in your first semester
Discuss that Adult practitioners round to the tenths, but Peds practitioners round to the hundreth

26. Daily Dose Ranges
Many drugs have “do not exceed” or “maximum doses” given in a range
The nurse and/or pharmacist must calculate the high and low end of the range to determine accuracy
Any dose outside the therapeutic range is unsafe whether it is to high or to low.
Example: Vancomycin is unsafe to the kidneys if too high but ineffective against infection if too low.

27. Rounding Basics
Round up to the next highest number if the digit to the right of the decimal is ≥ 5
The number stays the same if the digit to the right of the decimal is < 5

28. Rounding Rules Round all IV drip rates to a whole number
(by gravity or infusion pump)
Round all other answers to the nearest tenth
(includes IV push)
*If the question involves Kg, round Kg’s 1st, then continue problem with rounded weight. Round other calculations at the end of the problem.

29. Rounding examples 2.667 = 2.7 (rounded up)
2.444 = 2.4 (stays the same)
3.579 = 3.6 (rounded up)
= 1.2 (stays the same)

30. Rounding to the whole number
Same rules apply
Examples:
= 2 (rounded up)
= 2 (stays the same)
= 3 (stays the same)
= 5 (rounded up)

31. Dimensional Analysis A format for setting up problems
Advantage: Only need one equation to set up ANY problem
Similar to Algebra!

32. Dimensional Analysis
Place what you are solving for to the left of the equal sign
To the right of the equal sign set up your equation
First numerator is information you have about what you are solving for
First denominator is information you have that relates to the first numerator
Unit of measure for second numerator is the unit of measure for the first denominator

33. Example of Dimensional Analysis
The NP orders Augmentin 500mg PO daily. The drug arrives from pharmacy in 250mg tablets. How many tablets will you administer? Solving for tablets. 𝑋 𝑡𝑎𝑏𝑙𝑒𝑡𝑠 = 1 𝑡𝑎𝑏𝑙𝑒𝑡 250 𝑚𝑔 x 500 𝑚𝑔 1 𝑋 𝑡𝑎𝑏𝑙𝑒𝑡𝑠= 2 tablets

34. Example of Dimensional Analysis
The physician orders quinidine 0.6 g PO q 4 hr. Quinidine is supplied in 200 mg tablets.
(A) How many tablets will you give for one dose?
(B) How many tablets will you give in 24 hours?
Part A
𝑋 𝑡𝑎𝑏𝑙𝑒𝑡𝑠 = 1 𝑡𝑎𝑏𝑙𝑒𝑡 200 𝑚𝑔 x 1000 𝑚𝑔 1 𝑔 x 0.6 𝑔 1
𝑋 𝑡𝑎𝑏𝑙𝑒𝑡𝑠 = 3
Give 3 tablets for one dose
Part B
𝑋 𝑡𝑎𝑏𝑙𝑒𝑡𝑠 = 3 𝑡𝑎𝑏𝑙𝑒𝑡𝑠 4 ℎ𝑟 x 24 ℎ𝑟 1
You will give 18 tablets in 24 hrs

35. Infusion Pump Rates Always mL/hr 50 𝑚𝐿 30 𝑚𝑖𝑛 x 60 𝑚𝑖𝑛 1 ℎ𝑜𝑢𝑟
3000 𝑚𝐿 30 ℎ𝑜𝑢𝑟 = 100 𝑚𝐿 ℎ𝑜𝑢𝑟

36. Calculating Gravity Drip Rates
Always gtt/min
100 𝑚𝐿 1 ℎ𝑟 x 1 ℎ𝑟 60 𝑚𝑖𝑛 x 20 𝑔𝑡𝑡 1𝑚𝐿
100 𝑚𝐿 1 ℎ𝑟 x 1 ℎ𝑟 60 𝑚𝑖𝑛 x 20 𝑔𝑡𝑡 1𝑚𝐿
2000 𝑔𝑡𝑡 60 min = 33.3 𝑔𝑡𝑡 𝑚𝑖𝑛 = 33 𝑔𝑡𝑡 𝑚𝑖𝑛

37. Advice for Medication Calculation
Make sure you are answering what the question is ASKING
Evaluate your own learning style and do what works best for you
Choose a method which you can do consistently and accurately
When asked if a dose is safe, remember that going under AND going over a dose range is UNSAFE!
You have to round IV drips to the whole number, you can’t calibrate ½ of a drop! 
Remember: CONVERT, CALCULATE, AND MOST IMPORTANTLY…..CRITICALLY THINK (Does your answer make sense?)

38. Practice Makes Perfect
Medication calculation is a skill
Don’t get frustrated
Math with a purpose (Patient safety!)

39. Questions?
Lets practice!