Practice problems · Weight-based dosing · 5 worked
Weight-based dosing practice problems (mg/kg)
A weight-based problem scales an order written per kilogram, such as 15 mg per kilogram, to the patient's weight, which is often given in pounds first. Using the weight in pounds as if it were kilograms makes the dose 2.2 times too large. These problems do not cover checking an order against a pediatric safe-dose range.
The rounding rule on this page
Every answer here is rounded once, at the end, under one stated rule: nearest tenth, half rounds up, except tablets and capsules, rates in milliliters per hour and drip rates in drops per minute, which go to the nearest whole number, half rounds up. Your program's rule may differ, and on an exam it is the one that counts.
Work each problem on paper first, then open its solution. Each one is one of the 20 problems in DoseReady's Weight-based dosing family, with the numbers the app drew for it.
No licensed clinician has reviewed the problem set. Where a problem and its source disagree, trust the source and what your program teaches.
Problem 1 of 5
A child weighs 88 lb. The order reads acetaminophen 15 mg per kilogram per dose by mouth every six hours as needed for fever. How many milligrams are given per dose?
Show the worked solution
Dimensional analysis
88 × 1 × 15 ÷ 2.2 ÷ 1 = 600
Ratio and proportion
Step 1
2.2 lb is to 1 kg as 88 lb is to x
88 × 1 ÷ 2.2 = 40
x = 40 kg
Step 2
1 kg is to 15 mg as 40 kg is to x
40 × 15 ÷ 1 = 600
x = 600 mg
Formula method
The formula method (D ÷ H × Q) does not fit this problem. The chain above is the working.
- The working comes to
- 600 mg
- The answer under the stated rule
- 600 mg
- Nearest tenth, half rounds up.
What each slip gives here
- Pounds used as kilograms1,320 mg
- Decimal point one place out6,000 mg or 60 mg
- Conversion factor inverted2,904 mg or 2.7 mg
- Conversion skipped40 mg
What this problem is built from
Problem 2 of 5
A child weighs 35.2 lb. The order reads potassium chloride oral solution 3 mEq per kilogram per day by mouth, divided into 4 equal doses. How many milliequivalents are given per dose?
Show the worked solution
Dimensional analysis
35.2 × 1 × 3 × 1 ÷ 2.2 ÷ 1 ÷ 4 = 12
Ratio and proportion
DoseReady does not yet set this problem out as a textbook proportion, with like units in the same places, so it is not shown here. The chain above is the working.
Formula method
The formula method (D ÷ H × Q) does not fit this problem. The chain above is the working.
- The working comes to
- 12 mEq
- The answer under the stated rule
- 12 mEq
- Nearest tenth, half rounds up.
What each slip gives here
- Pounds used as kilograms26.4 mEq
- Decimal point one place out120 mEq or 1.2 mEq
- Conversion factor inverted58.1 mEq or 1.3 mEq or 192 mEq
- Conversion skipped4 mEq or 48 mEq
What this problem is built from
Problem 3 of 5
A child weighs 44 lb. The order reads ondansetron 0.15 mg per kilogram intravenously once before chemotherapy. How many milligrams are given?
Show the worked solution
Dimensional analysis
44 × 1 × 0.15 ÷ 2.2 ÷ 1 = 3
Ratio and proportion
Step 1
2.2 lb is to 1 kg as 44 lb is to x
44 × 1 ÷ 2.2 = 20
x = 20 kg
Step 2
1 kg is to 0.15 mg as 20 kg is to x
20 × 0.15 ÷ 1 = 3
x = 3 mg
Formula method
The formula method (D ÷ H × Q) does not fit this problem. The chain above is the working.
- The working comes to
- 3 mg
- The answer under the stated rule
- 3 mg
- Nearest tenth, half rounds up.
What each slip gives here
- Pounds used as kilograms6.6 mg
- Decimal point one place out30 mg or 0.3 mg
- Conversion factor inverted14.5 mg or 133.3 mg
- Conversion skipped20 mg
Problem 4 of 5
An adult weighs 176 lb. The order reads enoxaparin 1.5 mg per kilogram subcutaneously once daily. How many milligrams are injected per dose?
Show the worked solution
Dimensional analysis
176 × 1 × 1.5 ÷ 2.2 ÷ 1 = 120
Ratio and proportion
Step 1
2.2 lb is to 1 kg as 176 lb is to x
176 × 1 ÷ 2.2 = 80
x = 80 kg
Step 2
1 kg is to 1.5 mg as 80 kg is to x
80 × 1.5 ÷ 1 = 120
x = 120 mg
Formula method
The formula method (D ÷ H × Q) does not fit this problem. The chain above is the working.
- The working comes to
- 120 mg
- The answer under the stated rule
- 120 mg
- Nearest tenth, half rounds up.
What each slip gives here
- Pounds used as kilograms264 mg
- Decimal point one place out1,200 mg or 12 mg
- Conversion factor inverted580.8 mg or 53.3 mg
- Conversion skipped80 mg
What this problem is built from
Problem 5 of 5
An adult weighs 70 kg. The order reads vancomycin 20 mg per kilogram per dose intravenously every twelve hours. How many milligrams are given per dose?
Show the worked solution
Dimensional analysis
70 × 20 ÷ 1 = 1,400
Ratio and proportion
1 kg is to 20 mg as 70 kg is to x
70 × 20 ÷ 1 = 1,400
x = 1,400 mg
Formula method
The formula method (D ÷ H × Q) does not fit this problem. The chain above is the working.
- The working comes to
- 1,400 mg
- The answer under the stated rule
- 1,400 mg
- Nearest tenth, half rounds up.
What each slip gives here
- Decimal point one place out14,000 mg or 140 mg
- Conversion factor inverted3.5 mg
- Conversion skipped70 mg
Practice under your own program's rules
In DoseReady you enter your program's passing score, notation and rounding rule once. Every answer is graded under that rounding rule, and each worked solution is written in your notation where the problem allows it.
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Exam practice, never for patient care.
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Other problem families
- Unit conversion practice problems for nursing students
- Tablet and capsule dosage calculation practice problems
- Oral liquid dosage calculation practice problems
- Injectable dosage calculation practice problems
- Reconstitution dosage calculation practice problems
- mL per hr IV rate practice problems
- IV drip rate practice problems (gtt/min)
- Infusion time practice problems