Medications and Math
Bob Warner, MS, RN
Your Mission
if you choose to accept it
• Math Competency Scores needed
• NUR105
• NUR106
• NUR205
• NUR206
85% or better
90% or better
95% or better
100%
Mission Possible
Your Responsibility & Accountability
• Calculate with Confidence, 6th edition
• Chapters 1 – 22, 25….1st year
• Chapters 23 – 24…2nd year
• Accurate calculation of medication dosages is a
critical and necessary skill for nurses. Serious
harm can come to patients from math errors.
Medication Routes
include
Decimal Place Value
p. 29
• The first place to the right of the decimal is tenths.
• The second place to the right of the decimal is
hundredths.
• The third place to the right of the decimal is
thousandths.
• In the calculation of medication dosages it is
necessary to consider only three figures after the
decimal point (thousandths) (e.g., 0.375 mg).
Decimal Place Value
p. 29
• When there is no whole number before the
decimal point, it is important to place a zero in
front of it. This will emphasize its value and
prevent errors in interpretation.
.15…..NO
0.15….YES
• The source of many medication errors is
misplacement of a decimal point or incorrect
interpretation of a decimal value.
No Decimal Point
• When the amount is a whole number, do NOT
use a decimal point with trailing zeroes
15.0…..NO
15….YES
• The source of many medication errors is
misplacement of a decimal point or incorrect
interpretation of a decimal value.
Rounding Off
Decimals
p. 37
• Some syringes are
marked in tenths
and some, in
hundredths.
Rounding Off Decimals
p. 37
• To ensure accuracy, most calculation problems
require that you carry your division at least two decimal
places (hundredths place) and round off to the nearest
tenth.
Rounding Off Decimals
Guideline
Do Not Round until
the FINAL Answer step
Rounding Off Decimals
p. 37
• To express an answer to the nearest tenth,
carry the division to the hundredths place
(two places after the decimal). If the number
in the hundredths place is 5 or greater, add
one to the tenths place. If the number is less
than 5, drop the number to the right of the
desired decimal place.
Which is bigger?
And Rounding
• 2.001 2.01
• 0.13 0.31
• 45.9345
• 100.42
• 100.63
Equivalents
Metric
5 ml
15 ml
30 ml
1000 ml = 1 L
1 mg = 1000 mcg
1 gm = 1000 mg
1 kg = 1000 gm
Household
1 tsp
1 Tbs
1 oz
2.2 lbs
Calculating Intake & Output
p. 100
Abbreviations
p. 149 -158
• Need to memorize the most common
abbreviations
• P. 149 -150
• Be careful of the Do Not Use & Error-Prone
Lists
• p. 151, 156 - 158
Proportions
Chapter 14
Outer terms are the extremes, Inner terms
are the means. The product of the means
equals the product of the extremes
Step 1
5 : 25 :: 10 : 50
Step 2
5 x 50 = 25 x 10
Ratio-Proportion
Chapter 14
Step 1
_5_
25
=
_10_
50
Cross multiply
Step 2
5 x 50 = 25 x 10
Formula Method
Chapter 15
Desired
Have
x
Quantity
Dimensional Analysis
Chap. 16
http://www.youtube.com/watch?v=XKCZn5MLKvk&feature=player_em
bedded#!
http://www.youtube.com/watch?v=JreBcC2b0Mk
IV Flow Rate: mL/hour
p. 520
Amount of solution (mL)
Time in hours
= mL/hour
IV Tubing
IV Flow Rate: gtts/min
p. 523
Amount of solution (mL) x drop factor
= gtts/min
Time in minutes
Let’s Do Some Math Problems
Order: Lopressor 25 mg b.i.d.
Available: Lopressor 50 mg/tablet
Order: Coumadin 7.5 mg po daily
Available: Coumadin 5 mg/tablet
Order: Penicillin 750,000 units IV stat
Available: Penicillin 1,000,000 units/10 mL
Order: Kanamycin 300 mg IM
Directions on label: Add 2.7 mL sterile water = 1 g/3 mL
Order: Benadryl 30 mg po every 6 hours prn
Available: Benadryl 12.5 mg/5 mL
Order: Hydrochlorothiazide 0.05 g
Available: Hydrodiuril (Hydrochlorothiazide)
25 mg/tablet
Infuse 1 L normal saline (NS) in 8 hours.
How many mL/hr?
Infuse 1,000 mL NS in 8 hours. Drop factor is 20
gtt/mL.
How many gtts/min?