Two problem types pediatric exams lean on. Safe dose range asks you to work out the safe daily range from the child's weight and decide whether the order sits inside it. BSA dosing uses the Mosteller formula to find body surface area, then the dose per square metre.
Multiply the child's weight in kg by the low and high ends of the recommended range to get the safe daily range. Then multiply the ordered dose by the number of doses per day and compare. 20 kg, range 25–50 mg/kg/day: 500–1,000 mg/day. An order of 250 mg every 8 hours is 750 mg/day, so it is within range.
The comparison must be like with like. If the range is per day, compare the daily total. If the range is per dose, compare a single dose. Mixing the two is the most common way to call a safe order unsafe, or the reverse.
| Situation | Setup | Answer |
|---|---|---|
| 20 kg; 25–50 mg/kg/day; 250 mg q8h | 500–1,000 mg/day; 250 × 3 = 750 | Within range |
| 12 kg; 20–40 mg/kg/day; 200 mg q6h | 240–480 mg/day; 200 × 4 = 800 | Above range: hold and clarify |
| 33 lb; 10–20 mg/kg/day; 50 mg q12h | 15 kg → 150–300 mg/day; 50 × 2 = 100 | Below range: clarify |
An order outside the range is not given as written. The nurse holds it and contacts the prescriber to clarify. A dose below the range matters too: an underdosed antibiotic can fail to treat the infection.
| Situation | Setup | Answer |
|---|---|---|
| 120 cm, 24 kg; 30 mg/m² | √(120 × 24 ÷ 3,600) = √0.8 = 0.894 → 0.89 m²; 0.89 × 30 | 26.7 mg |
| 90 cm, 15.9 kg; 50 mg/m² | √(90 × 15.9 ÷ 3,600) = 0.63 m²; 0.63 × 50 | 31.5 mg |
| 47 in, 53 lb | √(47 × 53 ÷ 3,131) = √0.7956 = 0.892 | 0.89 m² |
BSA rounds to the hundredth. Some programs multiply the unrounded BSA by the dose instead, which can move the answer by a tenth (26.8 mg instead of 26.7 mg in the first example). The practice tool accepts both. BSA dosing is common for chemotherapy, where an independent double-check is standard practice.
Every safe range in this practice tool is stated in the question, as it would be on an exam. They are made-up numbers for practicing the math, not recommended doses for any drug, so none of the problems name a drug. In clinical practice, the range comes from a current pediatric drug reference, and many facilities build the check into their electronic order system.
Multiply the child's weight in kg by the low and the high mg/kg/day in the recommended range. That gives the safe daily range. Multiply the ordered dose by the doses per day and see whether the total falls inside it.
Hold the dose and contact the prescriber to clarify the order. Do not give it as written, and do not change the dose yourself.
BSA in square metres equals the square root of height in cm times weight in kg, divided by 3,600. In US units it is the square root of height in inches times weight in pounds, divided by 3,131.
Most programs round BSA to the hundredth and then multiply by the dose per m². Some carry the unrounded value through. The answers can differ by a tenth, so follow your program; the practice tool accepts either.