62 DOSAGE CALCULATIONS

DOSAGE
CALCULATIONS
Fundamentals of nursing pg
736-738
Medical Dosage Calculations
Olsen, et al



Objectives

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Goal
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Nursing students will demonstrate dosage
calculations competency by passing a required
dosage calculation test with a 90% or better.

Objectives
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Students will understand how to correctly
convert numbers between and within
apothecaries, household, and metric
measurement systems.

Students will demonstrate ability to accurately
calculate drug dosages


Dosage Calculation Test

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Must pass with a 90% or higher
Three attempts allowed to pass
You WILL NOT proceed in the program if
you do not pass the dosage calculation
exam
MUST complete remediation exercises
prior to second or third attempt
May use testing center issued calculator
for test (basic function calculator)


Testing in the Testing Center

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Must have CSI ID card or can’t get in
You must be checked in 1 hour prior to
testing center closing to receive test
Identify test as following:
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Class – NURP 106 (Fundamentals)
Instructor: Paula Hart
Test: Dosage Calculation Exam # (1, 2 or 3)


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Question- Why do we care about getting
100% on our dosage calculations test?
Answer- Because a human being could die
from a wrongly placed decimal point or an
accidental extra zero placed during a
dosage calculation…
It’s that important.
“3 babies died from the wrong dose of
heparin given. Dosage calculation errors
were made.”
Indianapolis Star/ Sept 19, 2006

What do you need to be successful?

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Review the content in this power point,
your text book, text book site, and Kaplan
site
Ask for help if you need it from your
instructors, math lab, internet sites
Use ALL available resources
PRACTICE, PRACTICE, PRACTICE


Ready to begin?


Math Review – Roman Numerals

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Read from left to right
A smaller numeral to the right of a larger
numeral is added to the larger numeral
A smaller numeral to the left of a larger
numeral is subtracted from the larger
numeral
Easily translated to Arabic numbers


Roman Numeral Practice

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XXX = _________
XIV = __________
iii = ____________
XXV = ___________
XIX = ____________
VI = _____________
XXIV =___________

Math Review cont

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You will need to review/refresh how to
multiply and divide whole numbers,
fractions and decimals, how to convert
minutes to hours, and any basic arithmetic
in your Medical Dosage Calculations book.


The Metric System

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The preferred system of measurement for
prescribing and administering meds.
Is a decimal system based on powers of 10
Base units are
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Grams- measures mass or weight, such as the
dose of a drug
Liters- measures the volume- such as the
amount of a drug or solution to administer

Metric System cont.

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The order of the six metric units from largest
to smallest can be remembered by:
King Henry Died of a Disease Called Mumps
(kilo-)(hecta-)(deka-)(base unit)(deci-)(centi-)
(milli-)
-gram
-liter
-meter

Value to base: k-1000, h-100, d-10, base-1, d-0.1, c0.01, m-0.001


Metric System cont
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Moving from one metric unit equivalent to
the next involves moving the decimal point
one place value to the left or right
depending on whether you are moving up
or down from the base.

If you are moving from a smaller to a larger
metric unit, such as mg to grams(gm) the
decimal moves to the left. (Left = Larger)
If your moving from larger to smaller, gm
to mg, then move the decimal to the right.


Metric System cont
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Examples- To state 1 mg in gm you would
move the decimal 3 place values to the
left. So, 1 mg= 0.001 gm.
To state 1 kg in gm you would move the
decimal point 3 places to the right. So, 1
kg=1000 gm.
Cubic centimeters (cc)=milliliters(ml)

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cc is no longer an acceptable abbreviation,
however you will see it used.

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Convert within a system to make it easier

to do calculations. Ex. 1000ml=1L


Apothecary and Household systems

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Common US systems of measurement but not
used worldwide.
Need to convert apothecary and household
units of measurement into the metric system.
Household conversions you need to memorize
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1tsp=5ml
1Tbsp=3tsp
1 ounce=30ml
16ounces=1lb
2.2lb=1kg


Apothecary and Household systems cont.

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Apothecary measurements
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gr xv is 15 grains
gr ii is 2 grains
gr 1/6 is 1/6th of a grain

Apothecary conversions you need to
memorize
gr i=60mg
 gr XV=1gm
You will be provided with charts to help you with
memorizing.
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Apothecary and Household systems cont.

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Examples
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2tsp=10ml (2tsp x 5ml=10ml)
8oz=240ml
100kg=220lb
gr ¾=45mg


Calculating Dosages
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Three ways:
Ratio & Proportion (solving for X)
 Dimensional Analysis (Preferred method)
 Formula
We will be teaching Dimensional Analysis in this
program.
You may choose the method you are most
comfortable with and use it consistently.



Calculating Dosages cont.

We all learn differently. It very important that you
identify the method that makes sense to you. If you
don’t know which method makes sense, try out
each method on the same set of practice problems
and see which way makes sense. Once you find a

method stick with it. Resist the temptation to
“formula hop.”
Whichever method you choose follow these 3 steps:
1.Convert
2. Think
3. Calculate
Always ask yourself does my answer make sense.
It is normal to feel nervous, so try to remember to
“KISS” (Keep It Simple Students)


Ratio and Proportion:
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Solve for X
Dose on hand
volume/tablet

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=

What the Dr. ordered
X

Example: The doctor orders 10 mg of a
drug and you have 5 mg tabs on hand. You
will give ____ tabs.
5mg = 10 mg
1 tab
X tab
5X = 10 x 1 = 5X = 10
X = 2 Tablets


Dimensional Analysis:

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Set up units of measurement so that they
cancel out, until you arrive at your correct
measurement
Always start with the dose ordered

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10mg

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1

X

1 Tab

=

5mg

10 Tab
5

=

2 Tablets


Formula:

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Do conversions first, and then plug it into
the equation to formulate the answer

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Dose ordered
Dose on hand
administer

Ie: 10 mg
5 mg

X

X

1 Tab

Amount
on hand

=

=

2 Tablets

Amount to


Conversion practice:

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1 gram = _________ mg
1 cc = ___________mL
1 oz = ___________ mL

1 cc = ____________ mL
3 t = _____________ T
1 T = ____________ mL
1 t = _____________ mL


Conversion practice:

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1 gram = ___________grains
60 mg = ____________ grains
1 kg = _____________ lbs
1 in = ______________ cm
120 mg = ____________ grains
0.5 gram = ____________ grains