Download CHAPTER 14 Adult and Pediatric Dosages Based on Body Surface

CHAPTER 14 ADULT AND PEDIATRIC DOSAGES BASED ON BODY SURFACE AREA
125
CHAPTER 14
Adult and Pediatric Dosages Based on Body Surface Area
Objectives
The learner will:
1.
calculate BSA using formulas for weight and height.
2.
use BSA to calculate dosages.
3.
assess the accuracy of dosages prescribed on the basis of BSA.
Suggested Review Questions
1.
Why is body surface area (BSA) a factor considered by the prescriber when ordering
medication dosages?
2.
What are the nurse’s responsibilities when medications are prescribed based on BSA?
3.
What is the formula for calculating BSA?
Answers to Review Questions
1.
The BSA is the external surface of the body expressed in square meters (m2). It represents
a relationship between height and weight, and thus provides a more precise guide to the
maturity of body organs and metabolic rate, both important factors in the absorption,
distribution, metabolism, and excretion of drugs. Using the BSA to determine drug
dosages allows the prescriber to adapt doses to individual characteristics.
2.
Specific nursing responsibilities related to using BSA to determine drug dosages can vary
among health care institutions; however, the nurse always needs to be able to assess that
the medication dose prescribed is safe for the patient. Therefore, the nurse needs to know
how to calculate the BSA, how to calculate dosages based on BSA, and how to assess
prescriber orders based on BSA.
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126
3.
SECTION 5 DOSAGE CALCULATION FROM BODY WEIGHT AND BODY SURFACE AREA
The formula for calculating BSA using metric measures (kilogram and centimeter) is
BSA =
wt (kg) × ht (cm)
3600
The formula for calculating BSA using household measures (pounds and inches) is
BSA =
wt (lb) × ht (in)
3131
Remember that a calculator capable of computing a square root is needed; remember also
to express the final number, the BSA, to the nearest hundredth. The formulas are the same
for children and adults. However, if a nomogram is used to determine BSA, be sure to use
a pediatric nomogram when determining the BSA of children.
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CHAPTER 14 ADULT AND PEDIATRIC DOSAGES BASED ON BODY SURFACE AREA
127
Name ____________________________________________ Date ____________________
Chapter 14: Adult and Pediatric Dosages Based on Body Surface Area
Additional Practice Problems
Calculate the following BSAs using the appropriate formula. Calculate the BSA to the
nearest hundredth.
1.
An adolescent who weighs 142 lbs and is 4 feet 10 inches
__________________
2.
A child who weighs 13.6 kg and is 90 cm
__________________
3.
An adult who weighs 165 lbs and is 5 feet 8 inches
__________________
4.
A child who weighs 42 lbs and is 34 inches
__________________
5.
A child who weighs 11.3 kg and is 75 cm
__________________
6.
An adolescent who weighs 125 lbs and is 5 feet 2 inches
__________________
7.
A child who weighs 13.6 kg and is 62.5 cm
__________________
8.
An adult who weighs 200 lbs and is 6 feet 2 inches
__________________
9.
An adult who weighs 183 lbs and is 5 feet 10 inches tall
__________________
An adult who weighs 235 lbs and is 6 feet tall
__________________
10.
Calculate doses for the drugs indicated below based on the patient’s BSA. Calculate the
BSA to the nearest hundredth and medication dosages to the nearest tenth.
11.
A child is to receive dactinomycin 2.5 mg/m2 IVP daily for 5 days as treatment for
leukemia. The child weighs 48 lbs and is 4 feet 6 inches tall. Calculate the dose of
dactinomycin to be given each day.
12.
________________
A child is ordered an infusion of cytarabine 200 mg/m2 in 0.9% NaCl to infuse over 24
hours. If the child weighs 22.7 kg and is 120 cm, how many mg of cytarabine would you
add to the 9% NaCl?
________________
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128
13.
SECTION 5 DOSAGE CALCULATION FROM BODY WEIGHT AND BODY SURFACE AREA
An adult is ordered vinblastine 25 mg IVP weekly. The recommended dose is 3.7 to
18.5 mg/m2. The patient weighs 195 lbs and is 5 feet 11 inches tall. Is the ordered dose
within the recommended range?
14.
________________
A child is ordered didanosine 120 mg/m2 twice a day orally for 2 weeks. The child weighs
75 lbs and is 4 feet 3 inches tall. Didanosine is available in 25 mg, 50 mg, and 100 mg
tablets. What tablet combination would you use to administer the prescribed dose?
________________
15.
The physician ordered zidovudine 250 mg/m2 orally daily divided into 4 equal doses for a
5-year-old child who is HIV+. The child weighs 38 lbs and is 36 inches tall. The
recommended single dose of zidovudine is 100 mg/m2 to 180 mg/m2. Is the prescribed
dose within the recommended single dose range?
16.
________________
What is the single dose of phenytoin for a child who is 112 cm in length and weighs
25.3 kg if the recommended dose is 250 mg/m2 divided in 2 doses?
________________
Phenytoin is available as 125 mg/5mL. How much would you give for a single dose?
________________
17.
A child who is 60 inches and 75 lbs has prednisone ordered. The recommended daily dose
for immunosuppressive therapy is 6 to 30 mg/m2 in 2 divided doses. What is the daily dose
range for this child?
________________
If prednisone is available as 5 mg/5 mL syrup, what is a single dose for this child if
6 mg/m2 a day is ordered?
18.
________________
An adult who weighs 130 lbs and is 5 feet 6 inches needs methotrexate for leukemia. The
recommended dose is 3.3 mg/m2/day. What is the daily dose for this patient?
________________
Methotrexate is available as 2.5 mg/mL to be further diluted for IV infusion. How many
mL would be added to the IV infusion for this patient per dose?
________________
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CHAPTER 14 ADULT AND PEDIATRIC DOSAGES BASED ON BODY SURFACE AREA
19.
129
Ritalin® (methylphenidate) is ordered for a child who is 14.2 kg and 62 cm in length. The
recommendation is 10 mg/m2 each dose. How many mg does this child need for each dose?
________________
The Ritalin is supplied as 5 mg/tablet. How many tablets should this child receive with
each dose? (The tablet is scored.)
20.
________________
An adult who is 68.8 kg and 165 cm needs monthly IV doses of cyclophosphamide for
rheumatoid arthritis. The recommended monthly dose is 0.5 to 1 g/m2. What is the dose
range for this patient?
________________
If the lowest dose is ordered and cyclophosphamide for IV administration is available as
100 mg/5 mL, how many mL of medication would be added to IV fluid for infusion each
month?
________________
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130
SECTION 5 DOSAGE CALCULATION FROM BODY WEIGHT AND BODY SURFACE AREA
Solutions to Additional Practice Problems
Calculate the following BSAs using the appropriate formula. Calculate the BSA to the
nearest hundredth.
1.
4 feet 10 inches = 58 inches
BSA =
142 × 58
=
3131
8236
=
3131
2.630 = 1.621
Answer: rounded to nearest hundredth = 1.62 m2
2.
BSA =
13.6 × 90
=
3600
1224
=
3600
0.34 = 0.583
Answer: rounded to nearest hundredth = 0.58 m2
3.
5 feet 8 inches = 68 inches
BSA =
165 × 68
=
3131
11, 220
=
3131
3.583 = 1.893
Answer: rounded to nearest hundredth = 1.89 m2
4.
BSA =
42 × 34
=
3131
1428
=
3131
0.456 = 0.675
Answer: rounded to nearest hundredth = 0.68 m2
5.
BSA =
11.3 × 75
=
3600
847.5
=
3600
0.2354 = 0.485
Answer: rounded to nearest hundredth = 0.49 m2
6.
5 feet 2 inches = 62 inches
BSA =
125 × 62
=
3131
7750
=
3131
2.475 = 1.573
Answer: rounded to nearest hundredth = 1.57 m2
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CHAPTER 14 ADULT AND PEDIATRIC DOSAGES BASED ON BODY SURFACE AREA
7.
BSA =
13.6 × 62.5
=
3600
850
=
3600
131
0.236 = 0.485
Answer: rounded to nearest hundredth = 0.49 m2
8.
6 feet 2 inches = 74 inches
BSA =
200 × 74
=
3131
14800
=
3131
4.726 = 2.173
Answer: rounded to nearest hundredth = 2.17 m2
9.
5 feet 10 inches = 70 inches
BSA =
183 × 70
=
3131
12810
=
3131
4.091 = 2.022
Answer: rounded to nearest hundredth = 2.02 m2
10.
6 feet = 72 inches
BSA =
235 × 72
=
3131
16920
=
3131
5.404 = 2.324
Answer: rounded to nearest hundredth = 2.32 m2
Calculate doses for the drugs indicated below based on the patient’s BSA. Calculate the
BSA to the nearest hundredth and medication dosages to the nearest tenth.
11.
Calculate the BSA: 4 feet 6 inches = 54 inches
BSA =
48 × 54
=
3131
2592
=
3131
0.827 = 0.909 = rounded to
nearest hundredth = 0.91 m2
Calculate dose ordered:
2.5 mg × 0.91 m2 = 2.275 = rounded to nearest tenth = 2.3 mg
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132
12.
SECTION 5 DOSAGE CALCULATION FROM BODY WEIGHT AND BODY SURFACE AREA
Calculate the BSA:
BSA =
22.7 × 120
=
3600
2724
=
3600
0.756 = 0.869 = rounded to
nearest hundredth = 0.87 m2
Calculate dose ordered:
200 mg × 0.87 m2 = 174 mg
13.
Calculate the BSA: 5 feet 11 inches = 71 inches
BSA =
195 × 71
=
3131
13845
=
3131
4.421 = 2.102 = rounded to nearest hundredth; the
trailing zero is eliminated = 2.1 m2
Calculate dose range:
3.7 mg × 2.1 m2 = 7.77 mg = rounded to nearest tenth = 7.8 mg
18.5 mg × 2.1 m2 = 38.85 mg = rounded to nearest tenth = 38.9 mg
Compare ordered dose with recommended range. The ordered dose of 25 mg is within
recommended dosage range. The correct answer is Yes.
14.
Calculate the BSA: 4 feet 3 inches = 51 inches
BSA =
75 × 51
=
3131
3825
=
3131
1.221 = 1.104 = rounded to nearest hundredth; the
trailing zero is eliminated = 1.1 m2
Calculate ordered dose:
120 mg × 1.1 m2 = 132 mg to be given twice daily. One 100 mg tablet and one 25 mg
tablet would be the best tablet combination to give the amount of didanosine closest to the
amount ordered.
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CHAPTER 14 ADULT AND PEDIATRIC DOSAGES BASED ON BODY SURFACE AREA
15.
133
Calculate the BSA:
BSA =
38 × 36
=
3131
1368
=
3131
0.436 = 0.660 = the trailing zero is eliminated
= 0.66 m2
Calculate the ordered dose:
250 mg × 0.66 m2 = 165 mg daily divided in 4 equal doses = 41.25 or 41.3 mg per dose
(rounded to nearest tenth).
Calculate the dose range:
0.66 m2 × 100 mg/m2 = 66 mg lower single dose
0.66 m2 × 180 mg/m2 = 118.8 mg upper single dose
Compare the ordered single dose (41.3 mg) with the recommended single dose range
(66 to 118.8 mg). The ordered single dose is less than the lower dose of the recommended
single dose range. Therefore, the correct answer is No, the ordered dose is not within the
recommended single dose range.
16.
Calculate the BSA:
BSA =
25.3 × 112
=
3600
2833.6
=
3600
0.787 = 0.887 = rounded to nearest hundredth
= 0.89 m2
Calculate ordered single dose:
250 mg × 0.89 m2 = 222.5 mg ÷ 2 = 111.25 mg/dose (Do not round to nearest tenth until
determining the final volume of drug to be given.)
Determine amount of drug to give based on dose ordered. Use dimensional analysis.
mL
5 mL
111.25 mg
556.25
=
×
=
= 4.45 mL (rounded to nearest tenth) = 4.5 mL
mg
125 mg
1
125
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134
17.
SECTION 5 DOSAGE CALCULATION FROM BODY WEIGHT AND BODY SURFACE AREA
Calculate the BSA:
BSA =
75 × 60
=
3131
4500
=
3131
1.437 = 1.198 (rounded to nearest hundredth) = 1.2 m2
Determine dose range:
6 mg × 1.2 m2 = 7.2 mg/day
30 mg × 1.2 m2 = 36 mg/day
The dosage range is 7.2 to 36 mg/day.
Determine amount of drug to give based on dose ordered. Use dimensional analysis.
mL
5 mL
7.2 mg
36
=
×
=
= 7.2 mL/day ÷ 2 = 3.6 mL/dose
mg
5 mg
1
5
18.
Calculate the BSA: 5 feet 6 inches = 66 inches
BSA =
130 × 66
=
3131
8580
=
3131
2.74 = 1.655 (rounded to nearest hundredth)
= 1.66 m2
Determine daily dose based upon recommended dose:
3.3 mg × 1.66 m2 = 5.47 mg (Do not round to nearest tenth until determining the final
volume of drug to be given.)
Determine amount of drug to give based on dose ordered. Use dimensional analysis.
mL
1 mL
5.47 mg
5.47
=
×
=
= 2.188 (rounded to nearest tenth) = 2.2 mL.
mg
2.5 mg
1
2.5
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CHAPTER 14 ADULT AND PEDIATRIC DOSAGES BASED ON BODY SURFACE AREA
135
19. Calculate the BSA:
BSA =
14.2 × 62
=
3600
880.4
=
3600
0.244 = 0.494 (rounded to nearest hundredth)
= 0.49 m2
Determine the dose needed:
10 mg × 0.49 m2 = 4.9 mg needed for each dose
Determine amount of drug to give based on dose ordered.
Drug is supplied in 5 mg tablets. 4.9 mg is very close to 5 mg; therefore one tablet would
be given.
20.
Calculate the BSA:
BSA =
68.8 × 165
=
3600
11,352
=
3600
3.153 = 1.775 (rounded to nearest hundredth)
= 1.78 m2
Determine the dose range; transform g to mg:
0.5 g = 500 mg × 1.78 m2 = 890 mg
1 g = 1000 mg × 1.78 m2 = 1780 mg
The dosage range is 890 to 1780 mg.
Calculate the dose to be given. Use dimensional analysis.
mL
5 mL
890 mg
4450
=
×
=
= 44.5 mL
mg
100 mg
1
100
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