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Dose Range & Maximum Dose Checks
Verify a supplied reference basis, calculate lower and upper limits, apply per-dose or daily maximums on the matching basis, and compare the prescribed dose without inventing limits.
MedMaths Learn pathway
Clinical Safety Checks
Use the maths as a safety check, not a reason to trust every number automatically.
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Dose Range & Maximum Dose Checks
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Reasonableness & Error Checking
Check the answer unit, inputs, scale and stated limits so an unexpected result triggers a recheck instead of blind acceptance.
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Lesson summaries
What each Clinical Safety Checks lesson teaches
A short recap of every lesson in this topic: the key idea, a worked example and the mistake students make most often. Open any lesson for the full step-by-step teaching and its four levels of practice.
Dose Range & Maximum Dose ChecksWhen a question supplies a dose range, checking an ordered dose against it is an arithmetic comparison: work out the range for the supplied weight, then see where the ordered dose falls. MedMaths does not decide what a range should be — the range always comes from the question.
When a question supplies a dose range, checking an ordered dose against it is an arithmetic comparison: work out the range for the supplied weight, then see where the ordered dose falls. MedMaths does not decide what a range should be — the range always comes from the question.
Formula
lower limit = lower dose per kg × weight · upper limit = upper dose per kg × weight
Worked example
A question supplies a range of 5–10 mg/kg per dose for a patient weighing 30 kg, and an ordered dose of 250 mg.
- 1Lower limit: 5 × 30 = 150 mg
- 2Upper limit: 10 × 30 = 300 mg
- 3250 mg falls between 150 mg and 300 mg.
The ordered dose sits inside the supplied range
Common mistake
Comparing the ordered dose against the per-kilogram figures directly. The range has to be scaled to the patient's supplied weight before any comparison means anything.
A range check compares two calculated numbers — it does not establish that a dose is clinically appropriate.
Reasonableness & Error CheckingBefore trusting an answer, estimate what it should be. Most calculation errors are wrong by a factor of ten, and an estimate catches those instantly — a volume that should be a little over one syringe should not come out as fifteen millilitres.
Before trusting an answer, estimate what it should be. Most calculation errors are wrong by a factor of ten, and an estimate catches those instantly — a volume that should be a little over one syringe should not come out as fifteen millilitres.
Worked example
480 mg is prescribed from a liquid labelled 250 mg in 5 mL, and a calculation produces 96 mL.
- 1Estimate: 480 mg is a little under twice 250 mg.
- 2So the volume should be a little under twice 5 mL — roughly 9 to 10 mL.
- 396 mL is about ten times too large, which points to a misplaced decimal.
- 4Recalculate: 480 ÷ 250 = 1.92; 1.92 × 5 = 9.6 mL.
9.6 mL — the estimate identified the error before the number was used
Common mistake
Trusting the calculator display. A calculator faithfully returns the answer to whatever was typed, including a typing error.
Estimate first, calculate second, and investigate any gap between the two.