Transcript Medical Dosage Calculation

Medical Dosage Calculation
A Dimensional Analysis Approach
Tenth Edition
CHAPTER
6
Calculating Oral
Medication Doses
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Directory
• Classroom Response System Questions
• Lecture Note Presentation
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Classroom Response
System Questions
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #1
The order for Cardura is 6 mg po daily. The
following tablets are available: 1 mg, 2 mg, 4
mg and 8 mg. Which tablets would be the
best choice for this dose?
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #1 Choices
1.
2.
3.
4.
Six 1-mg tab
Three 2-mg tab
One 2-mg and one 4-mg tab
One 2-mg and four 1-mg tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #1 Response
1.
2.
3.
4.
Six 1-mg tab
Three 2-mg tab
One 2-mg and one 4-mg tab
One 2-mg and four 1-mg tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #2
A patient has been prescribed 5 mg of a
drug. Each tablet contains 0.005 g. How
many tablets equal the prescribed dose?
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #2 Choices
1.
2.
3.
4.
2 tab
1 tab
2 cap
3 tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #2 Response
1.
2.
3.
4.
2 tab
1 tab
2 cap
3 tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #3
Albuterol oral solution has been prescribed
for a patient experiencing an acute asthma
attack. The metered-spray device is labeled
90 mcg/actuation. If the patient administers
2 metered sprays, how many milligrams are
inhaled?
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #3 Choices
1.
2.
3.
4.
12.4 mg
8 mg
0.18 mg
0.8 mg
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #3 Response
1.
2.
3.
4.
12.4 mg
8 mg
0.18 mg
0.8 mg
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #4
The prescriber ordered 0.375 gram of a
drug. The label reads 250 mg per scored
tablet. How many tablets will you
administer?
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #4 Choices
1.
2.
3.
4.
1 ½ tab
1.3 cap
2 tab
1.005 tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #4 Response
1.
2.
3.
4.
1 ½ tab
1.3 cap
2 tab
1.005 tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #5
Your patient must receive 0.5 mg of digoxin
po stat. Tablets available contain 0.125 mg.
How many tablets will you administer to the
patient?
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #5 Choices
1.
2.
3.
4.
12.5 tab
1 tab
2 tab
4 tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Question #5 Response
1.
2.
3.
4.
12.5 tab
1 tab
2 tab
4 tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Lecture Note Presentation
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Learning Outcomes
1. Calculate simple (one-step)
problems for oral medications in
solid and liquid form.
2. Calculate complex (multi-step)
problems for oral medications in
solid and liquid form.
3. Calculate doses for medications
measured in milliequivalents.
4. Interpret drug labels in order to
calculate doses for oral
medication.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Learning Outcomes
5. Calculate doses based on body weight.
6. Calculate body surface area (BSA) using a
formula or a nomogram.
7. Calculate doses based on body surface area
(BSA).
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Simple (One-Step) Problems
• In the calculations you have done in
previous chapters, all the equivalents have
come from standard tables, for example, 1
t = 5 mL.
• In this section the equivalent used will
come from the strength of the drug that is
available, for example, 30 mg/mL.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.1
• The physician orders Lexapro (escitalopram oxalate) 10
mg po daily. Read the label below and determine the
number of milliliters you would administer.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.1 (continued)
• You want to change the 10 mg dose to
milliliters. Using the strength of the drug (5
mg per 5 mL) to form the unit fraction.
10 mg 5 mL

 ? mL
1
5 mg
10 mg 5 mL

 10 mL
1
5 mg
So, you would administer 10 mL.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.2
• Read the label below. How many tablets of this
narcotic analgesic will be needed for a dose
containing 10 mg of hydrocodone bitartrate and
1,000 milligrams of acetaminophen?
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example
6.2
Example
6.2 (continued)
• Vicodin is a combination drug composed of
hydrocodone bitartrate and acetaminophen.
Therefore, for computational purposes, you
need to only address the first listed drug
(hydrocodone bitartrate). Because the dose
requires 10 mg of hydrocodone bitartrate,
convert the 10 mg to the appropriate number of
tablets.
10 mg = ? tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.2 (continued)
• The strength of the drug is 5 mg (of
hydrocodone bitartrate) per tablet will be
used to form the unit fraction.
10 mg 1 tab

 ? tab
1
5 mg
2
10 mg 1 tab

 2 tab
1
5 mg
1
So, 2 tablets are needed for the dose.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.3
• The prescriber ordered potassium chloride 10
mEq po daily. The strength of the potassium
chloride solution is 20mEq/15 mL. Determine
how many milliliters of this electrolyte
supplement you should administer.
• You want to change 10 mEq to mL using the
strength of 20 mEq per 15 mL to form the unit
fraction.
10 mEq 15 mL

 ? mL
1
20 mEq
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example
6.3
Example
6.3 (continued)
10 mEq 15 mL

 ? mL
1
20 mEq
1
10 mEq 15 mL 15 mL


2
1
20 mEq
2
= 7.5 mL
So, you should administer 7.5 mL of potassium chloride
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Multi-Step Problems
• Given quantity
– 0.4 g
• Strength
– 1 tab = 100 mg
• Quantity you want to find
– ? tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.4
• Read the label below, and calculate the number
of tablets of Diflucan that contain 0.4 gram of
fluconazole.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.4 (continued)
• You want to change 0.4 g to tablets. The
strength of the tablets is 100 mg per tab.
0.4 g = ? mg = ? tab
0.4 g ? mg
? tab


1
? g
? mg
= ? tab
The unit fractions come from
1 g = 1,000 mg and 100 mg = 1 tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.4 (continued)
0.4 g 1,000 mg
1 tab


 ? tab
1
1g
100 mg
0.4 g 1,000 mg
1 tab


 4 tab
1
1g
100 mg
So, 4 tablets contain 0.4 gram of fluconazole.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Calculating Dosage by Body Weight
• Sometimes the amount of medication
prescribed depends on the patient’s body
weight. A patient who weighs more will
receive more of the drug, and a patient
who weighs less will receive less of the
drug.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.5
•
The physician orders Biaxin (clarithromycin) 7.5
milligrams per kilogram PO q12h. If the strength is 250
milligrams per 5 mL, how many mL of this antibiotic drug
should be administered to a patient who weighs 70
kilograms?
Body weight:
70 kg
Order:
7.5 mg/kg
Strength:
250 mg/5mL
Find:
? mL
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.5
• Multiply the size of the patient by the order
to determine how many milligrams of
Biaxin to give the patient.
70 kg 7.5 mg

 ? mg
1
1 kg
= 525 mg
So, the patient must receive 525 mg of Biaxin.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example
6.5
Example
6.5 (continued)
• Now convert the 525 mg of Biaxin to
milliliters. The strength of the solution is
250 mg/5 mL.
21
525 mg
5 mL

 ? mL
1
250 mg
525 mg
5 mL
21 mL


1
250 mg
2
= 10.5 mL
10
2
The patient should receive 10.5 mL of Biaxin by mouth
every 12 hours.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Calculating Dosage by
Body Surface Area
• Body surface area (BSA) is also used in
determining appropriate drug dosages.
This is particularly true of pediatric drugs
and drugs that are used for cancer
therapy.
• A patient’s BSA, which is measured in
square meters (m2), can be estimated by
using formulas or nomograms.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Calculating BSA Using Formulas
• Formula for metric units:
w
e
i
g
h
t
i
n
k
i
l
o
g
r
a
m
s

h
e
i
g
h
t
i
n
c
e
n
t
i
m
e
t
e
r
s
B
S
A

3
,
6
0
0
• Formula for household units:
w
e
i
g
h
t
i
n
p
o
u
n
d
s

h
e
i
g
h
t
i
n
i
n
c
h
e
s
B
S
A

3
,
1
3
1
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.6
• What is the BSA of a man who is 4 feet 10
inches tall and weighs 142 pounds?
• First, convert 4 feet 10 inches to 58
inches.
w
e
i
g
h
t
i
n
p
o
u
n
d
s

h
e
i
g
h
t
i
n
i
n
c
h
e
s
B
S
A

3
,
1
3
1
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.6 (continued)
1
4
2

5
8
B
S
A
3
,
1
3
1
2
.
6
3
0
5

1
.
6
2
m
2
Therefore, the BSA of this man is 1.62 m2
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Nomograms: BSA can also be approximated by using nomograms.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Nomograms
• When a straight line is drawn on the
nomogram from the patient’s height (left
column) to the patient’s weight (right
column), the line will cross the center
column at the approximate BSA of the
patient.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Nomograms
• In Example 6.6, using the calculation
formula, we calculated the BSA of the 4 ft
10 in patient to be 1.62 square meters. If
we use the nomogram to determine the
BSA, we get about 1.59 square meters.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Nomogram for Example 6.6
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.7
• A drug is ordered at 3.3 mg/m2 PO q12h
for three doses. How many scored 5-mg
tablets of this drug would you administer to
a patient with a BSA of 2.29 m2?
BSA:
Order:
Strength:
Find:
2.29 m2
3.3 mg/m2
1 tab = 5 mg
? tab
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.7 (continued)
• The patient’s BSA is 2.29 m2 and the order
is for 3.3 mg/m2. First, multiply the size of
the patient by the order to determine how
many milligrams of the drug to give the
patient.
2.29 m2 3.3 mg

 ? mg
2
1
m
≈ 7.56 mg
So, the patient must receive 7.56 mg of the drug.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Example 6.7 (continued)
• Finally, convert 7.56 mg to tablets
1 tab
7.56 mg 
5 mg
≈ 1.51 tab
This example could have been done in one line as follows:
2.29 m2 3.3 mg 1 tab


2
1
5 mg
m
So,
≈ 1.51 tab
scored tablets would be administered.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Chapter Summary
• It is crucial to ensure that every medication
administered is within the recommended
safe dose range.
• Some drugs, such as electrolytes, are
measured in milliequivalents (mEq).
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Chapter Summary
• Calculating doses by body weight
• Start calculations with the weight of the
patient.
• Multiply the size of the patient (kg) by the
order to obtain the dosage.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.
Chapter Summary
• Calculating doses by body surface area
• Body surface area (BSA) is measured in
square meters (m2 ).
• BSA is determined by using either a
formula or a nomogram.
• Start calculations with the BSA of the
patient.
Medical Dosage Calculations: A Dimensional Analysis Approach, Tenth Edition
June L. Olsen • Anthony P. Giangrasso • Dolores Shrimpton
Copyright ©2012, ©2008 by Pearson Education, Inc.
All rights reserved.