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Chapter 9: Calculations of Dosage
Dosages are another example of ratios:
25 mg
kg
This means the patient is to receive 25 mg
of the drug for every kg that he or she weighs
Chapter 9: Calculations of Dosage
Example Problem:
Abby has the flu and her parents want to
give her ibuprofen to reduce her fever
and help her feel better. Abby weighs
21 kg. She needs ibuprofen at a dose of
15 mg/kg. The ibuprofen comes as a
liquid and the bottle reads “160 mg
ibuprofen/5 mL”. How much of the liquid
does she get?
Chapter 9: Calculations of Dosage
Strategy 1 Proportion Method:
15 mg ibuprofen
?
=
kg weight
21 kg
? = 315 mg
This tells us how much ibuprofen she needs in
terms of mg, however, the drug comes as a
liquid and is administered by the mL. So, we
need one more step:
160 mg ibuprofen 315 mg
=
5 mL
?
? ≈ 9.8 mL
Chapter 9: Calculations of Dosage
Strategy 2 Unit Canceling Method:
21kg weight X
15 mg ibuprofen
5 mL
X
kg weight
160 mg ibuprofen
≈ 9.8 mL