🧮 Med Calculations Cram
Pediatric weight-based dosing · highest-yield points
1The one conversion
Pounds ÷ 2.2 = kilograms
ALWAYS calculate in kilograms
Every weight-based dose starts here. Using a pound weight as kilograms more than doubles the dose — the most dangerous swap in pediatric math.
2Read the order first
mg/kg/dose = amount per single dose
mg/kg/day = total for the whole day
Per-dose order: multiply once, done. Daily order: total first, then divide by doses per day. Reading /day as /dose gives a full day's drug in every dose.
3The rounding rule
NEVER round the kg conversion
NEVER round a middle step
Round ONLY the final answer — nearest tenth
Carry every decimal through the whole problem. One rounding, at the very end, to one decimal place.
4Doses per day
Every 4 hours = 6 doses
Every 6 hours = 4 doses
Every 8 hours = 3 doses
Every 12 hours = 2 doses
24 ÷ hours between doses = doses per day. Every 8 hours is 3 doses — not 8. A wrong count makes a wrong dose.
5The five steps
1 · lb ÷ 2.2 = kg
2 · Read: /dose or /day?
3 · kg × rate = amount
4 · If /day: ÷ doses per day
5 · Round final to tenth — then safety-check
Same sequence on every problem. The math ends at Step 5; the verification does not.
6Course example — daily dose, divided
54 lb · 30 mg/kg/day · every 8 hours
Answer: 245.5 mg/dose
54 ÷ 2.2 = 24.545454… kg → × 30 = 736.363636… mg/day → ÷ 3 = 245.454545… → round last: 245.5 mg/dose.
7Single-dose example
39 lb · ibuprofen 10 mg/kg/dose
Answer: 177.3 mg/dose
39 ÷ 2.2 = 17.727272… kg → × 10 = 177.272727… → 177.3 mg/dose. Per-dose order = one multiplication, no dividing.
8Range check — the NOT safe example
48 lb · amoxicillin 300 mg every 8 hours
Ordered: 900 mg/day vs safe high end 872.7 → NOT SAFE
48 ÷ 2.2 = 21.818181… kg → safe range 20–40 mg/kg/day = 436.4–872.7 mg/day. Ordered 300 × 3 = 900 mg/day — over the top. Hold it and clarify with the prescriber.
9The ceiling check
Compare against the MAXIMUM allowable dose
Maximum is often the adult dose
Row 8's dose passed the adult maximum (500 mg/dose, 1,500 mg/day) and was still unsafe. The maximum is only a ceiling — the child's own weight-based range governs.
10Before it reaches the child
Independent double-check — second nurse, separately
Right concentration + formulation
Oral syringe — never a household spoon
Final sweep: units at each step · correct number of daily doses · dose inside the range and under the maximum. Then document, give, and monitor for effect and adverse effects.