Dosage Calculations-Formulas

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Dose divided by strength times quantity (ml or tablets)

Ratio and Proportion

1a. Supply over volume or amount
b. Volume or amount over X
2. Cross multiply
3. Divide the sides by X (value)
X = ?

Body Weight Dosing

mg X kg = patient dose (convert lbs to kg) 1kg = 2.2lbs
(divide total lbs. by 2.2kg to convert)
Example: 195/2.2 =88.6kg (be exact, round)
20mg X 88.6kg =1772mg (24 hour dose)
To figure # of doses in a day: Q12=2, Q8=3, Q6=4, Q4=6

Clark's Rule: means of calculating a child dose of medication from an adult dose on the basis of the child's weight in pounds.

child's weight in pounds divided by 150 (adult average weight)
times usual adult dose=child's dose (D/H X Q)
Example: 40/150 = 0.26 X UAD = Child's Dose

Young's Rule: means of calculating a child dose of medication on the basis of the child's age.

Age in Years divided by Age in Years plus 12 X Adult Dose = Child's Dose (example: 6/18= 0.33 X 500mg = 165mg)

Fried's Rule: means of calculating an infant dose of medication from an adult dose on the basis of the infant's age in months. (use with children up to one year)

Age in months divided by 150 (average adult weight) X Adult Dose = Child's Dose (example: 12/150 = 0.08 X 500mg = 40mg)

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