Calculate doses based on a patient's weight in mg/kg
Weight-Based Dosing
Many medications are prescribed by body weight — for example, "5 mg per kg." This means the dose depends on how much the patient weighs. Heavier patients get more; lighter patients get less.
Dose = Weight (kg) × Dose per kg (mg/kg)
Examples
Order: 10 mg/kg. Patient weighs 70 kg.
Dose = 70 kg × 10 mg/kg = 700 mg
Order: 5 mg/kg/day in 2 divided doses. Patient weighs 80 kg.
Daily dose: 80 × 5 = 400 mg/day
Per dose: 400 ÷ 2 = 200 mg every 12 hours
Converting Pounds to Kilograms
Weights are often given in pounds but dosing is in kg. Convert first: 1 kg = 2.2 pounds → Divide weight in lbs by 2.2 to get kg.
Order: 15 mg/kg. Patient weighs 154 lbs.
Convert: 154 ÷ 2.2 = 70 kg
Dose: 70 × 15 = 1,050 mg
💡 Pediatric dosing: Weight-based dosing is especially important for children. Always double-check by verifying the calculated dose falls within the safe range listed in the drug reference.
🎯 Practice Problems
1. Order: 8 mg/kg. Patient weighs 75 kg. What is the dose?
A) 83 mg
B) 150 mg
C) 600 mg
D) 9.4 mg
2. Order: 12 mg/kg. Patient weighs 176 lbs. What is the dose? (1 kg = 2.2 lbs)
A) 480 mg
B) 880 mg
C) 960 mg
D) 2,112 mg
3. Order: 20 mg/kg/day in 4 divided doses. Patient: 60 kg. How much per dose?
A) 80 mg
B) 120 mg
C) 300 mg
D) 1,200 mg
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🎯 Bonus Practice
1. A child weighs 22 lbs. Order: 10 mg/kg. What is the dose? (1 kg = 2.2 lbs)
A) 22 mg
B) 100 mg
C) 220 mg
D) 48.4 mg
2. Order: 5 mg/kg. Patient: 90 kg. Available: 150 mg tablets. How many tablets?
A) 2
B) 3
C) 4
D) 6
3. Order: 2 mg/kg/dose, given every 8 hours. Patient: 55 kg. What is the daily total?
A) 110 mg
B) 220 mg
C) 330 mg
D) 440 mg
4. Safe range: 10–15 mg/kg. Patient: 50 kg. Is a 600 mg dose safe?
A) Yes — within range
B) No — too low
C) No — too high
D) Can't determine
5. Order: 25 mg/kg. Patient weighs 198 lbs. Round to nearest 100 mg. What is the dose?