Dosage Practice

Safe Dose Range Calculation: Is the Order Safe to Give?

Multiply the patient's weight in kilograms by the low end and the high end of the recommended range to get the safe window. Then compare the ordered dose, converted to the same basis (per dose or per day), against that window.

The Formula

low = min mg/kg × kg high = max mg/kg × kg safe if low ≤ ordered ≤ high

Per-day ranges are compared with the ordered dose multiplied by the number of doses a day.

How to work it out

  1. 1 Convert the weight to kilograms if needed.
  2. 2 Multiply by the low end of the range and by the high end. Those are the boundaries.
  3. 3 Put the order on the same footing. If the range is per day and the order is 150 mg every 6 hours, the order is 600 mg a day.
  4. 4 Compare. Inside the range: safe to give. Outside it: do not give, contact the prescriber.

Worked Examples

Example 1

Recommended: 20 to 40 mg/kg/day in divided doses. The child weighs 15 kg. Ordered: 150 mg every 6 hours. Is the order safe?

  1. Low: 20 × 15 = 300 mg/day. High: 40 × 15 = 600 mg/day.
  2. Ordered: 150 mg × 4 doses = 600 mg/day.
  3. 600 is within 300 to 600, so the order is safe.

Answer: Safe: 600 mg/day, at the top of the range

Example 2

Recommended: 5 to 7 mg/kg per dose. The patient weighs 22 kg. Ordered: 120 mg per dose. Is it safe?

  1. Low: 5 × 22 = 110 mg. High: 7 × 22 = 154 mg.
  2. 120 mg is between 110 and 154.

Answer: Safe: within 110 to 154 mg per dose

Try five free problems

One exact answer, rounded as asked, no partial credit. No sign-up needed.

Problem 1 of 3No sign-up needed

Recommended range: 25 to 50 mg/kg/day. The child weighs 12 kg. What is the maximum safe dose per day, in mg?

Round to the nearest whole number

mg

Common Mistakes

  • Comparing a per-dose order with a per-day range

    If the range is per day, multiply the single dose by how many are given a day before comparing.

  • Only checking the high end

    A dose below the minimum is also unsafe, because it may not work. Check both boundaries.

  • Rounding the boundaries

    Keep the boundaries exact. An order of 601 mg against a maximum of 600 mg is over, not close enough.

Questions Students Ask

What do I do if the order is outside the range?

Do not give it. Contact the prescriber, document the conversation, and follow your institution's policy. Exams expect the words 'hold and clarify'.

Where does the recommended range come from?

A drug reference. On exams it is given in the question. On the unit it is the formulary or a pharmacist.

Keep practicing in lesson 8: Safe Dose Range Checks

Fresh numbers every time. Ten correct answers finish the lesson. The practice round and the first five problems of lesson 1 are free.

Open lesson 8