Transcript Med-Math Dosage Calculation, Preparation, and Administration

Med-Math
NUR 152
Mesa Community College
3/27/2017
How To Solve Dosage Problems
• It’s OK to solve the
problem your way.
• Do not learn a new
math method if your
way works and you
get the correct
answer.
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Metric System
• Gram - the basic unit for weight
– Kilogram (kg)
– Milligram (mg)
– Microgram (mcg)
• Liter – the basic unit for volume
– Liter (L)
– Milliliter (mL)
• Meter – the basic unit for
length
– Centimeter (cm)
– Millimeter (mm)
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Dosage Measurement Systems
• Measures of Weight
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–
–
–
Gram: g
Milligram: mg
Microgram: mcg
g > mg
• 1 g = 1000 mg
• To multiply by 1000, move the decimal points three points to the
RIGHT
– mg < g
• 1000 mg = 1 g
• To divide by 1000, move the decimal point three places to the
LEFT
– mg > mcg
• 1 mg = 1000 mcg
• To multiply by 1000, move the decimal points three points to the
RIGHT
The Bad News!
• You will have to memorize the standard
equivalencies measurement.
– 1 g = 1000 mg
– 1 mg = 1000 mcg
– 1 grain = 60 (65 in some texts) mg
– 1 kg = 2.2 lbs
– 1 tbs = 15 mL
– 1 tsp = 5 mL
– 1 oz = 30 mL
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Metric Liquid Measures
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Liter = L
Milliliter – mL
1 teaspoon = 5 mL
1 tablespoon = 15 mL
1 ounce = 30 mL
1 pint = *approximately 500 mL
1 quart = *approximately 1 L = 1000 mL
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Decimals
• If a decimal fraction is not preceded by a
whole number, always place a zero in front
of it.
• Example:
– .25 is always 0.25
– Avoids interpretation errors
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Decimals
• Never follow a whole number by a decimal
point and a zero.
• Again, could result in a medication
misinterpretation.
• Example:
25.0
• Would be easy to read as 250.
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Apothecaries’ System
• Not as exact as metric system.
• Need to convert apothecary measures to
metric by using an equivalency table.
• Unit of measurement is written before the
number
• Example: six grains is gr 6 or gr vi
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Apothecary System
Use the clock to help you
remember gr and mg.
1 hr
60 min
60 mg = gr 1
¾ hr
60 min = 1 hr
¼ hr
45
min
15 min
15 mg = gr ¼
15 min = ¼ hr
30 mg = gr ½
30 min = ½ hr
½ hr
30 min
45 mg = gr ¾
45 min = ¾ hr
Apothecary Units of Measurement
• Grains - gr
• Drams -ʒ (3.887 grams)
• Ounce Symbol- ℥ (31.03 grams)
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Conversions R/T Weight
• Body weight is needed to calculate accurate
doses.
• Calculated in kilograms.
• 2.2 lbs = 1 kg
• To convert pounds to kilograms, divide by 2.2
and round to nearest tenth for adults,
hundredths for pediatrics.
• To convert kilograms to pounds, multiple by
2.2 and round to nearest tenth for adults,
hundredths for pediatrics.
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Converting Ounces to decimals
• 8 lbs. 9 oz. does not equal 8.9 pounds!
• Must convert the oz. to decimals to make
a proper equation
• 16 ounces in a pound
• 9 oz. = 0.5625
16 oz .
• 8 lbs + 9 oz. = 8.5625 lbs
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Rounding Rules
• Rounding is the last step of the problem.
For medication dosing, round to the
nearest tenth for adults and pediatrics
• Carry your division to at least two places
(hundredths place) and round off at the
end of the problem to the nearest tenth
for Adult and Pediatric dosages.
• Pediatric weight in kilograms is rounded
to the nearest one hundredth.
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Formula Method
• CALCULATING MEDICATIONS
Desire
Have
X Vehicle = Amount
Desire = Physician’s order
Have = Strength of drug in container
Vehicle= Form in which drug comes
Amount = How much to give to the client
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Abbreviate the Formula
DxV=A
H
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Example
• Order: 0.25 g
• Supply: 0.5 g per tablet
(D) 0.25 g x (V)1 tablet = ½ tab
(H) 0.5 g
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Example
• Order: Lasix 60 mg po every day
• Stock: Scored tablets labeled 40 mg
(D) 60 mg x (V) 1 tablet = 1 ½ tablets
(H) 40 mg
• Can you give this? YES.
• Give one full tablet and break the other
scored tablet in half.
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Conversions
• “Desired” and “Have” must be in the same
weight measure in order to do the
problem.
• Cannot be g and mg.
• You must CONVERT the “desired” weight
measure to the weight measure on the
drug label you “have”.
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Conversion Problem
• Order: 0.25 g
• Supply: 125 mg per tablet
• 1st step: Convert grams into mg
g > mg
0.25 g = 250 mg
(D) 250 mg x (V) 1 tablet = 2 tablets
(H) 125 mg
• YOU MUST LABEL THE ANSWER IN THE
FORM THE MED COMES IN!
• CIRCLE YOUR ANSWERS ON YOUR
TEST
Practice Problem
The order reads:
Zithromax oral suspension 400 mg po qd x 4 days
How would you set up this problem?
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• DxV=A
H
400 mg X 5 mL = A
200 mg
2 X 5 = 10 mL
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Let’s Practice
• Group work on Medication Problems
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