Weight-based dosing: separate per dose from per day

Consider a fictional arithmetic exercise specifying 24 mg/kg/day in three equal doses for a 15.6 kg patient. The daily amount is 15.6 × 24 = 374.4 mg/day. Dividing by three gives 124.8 mg/dose. If a supplied hypothetical liquid contains 120 mg/5 mL, the volume is 5.2 mL per dose.

If the instruction instead said 24 mg/kg/dose, the amount would be 374.4 mg at each dose. That three-fold difference comes from interpreting the order, not from complicated multiplication. These values are invented for practice and are not dosing recommendations for any medicine or patient.

A question may explicitly give the weight to use, or ask you to determine an appropriate weight measure. Do not substitute an ideal or adjusted weight merely because you used it in a previous topic. If a drug-specific method is required, the relevant current clinical reference determines that method.

For this page's exercises, the stated kilogram weight is the calculation weight. If a problem gives pounds and supplies a conversion factor, apply that factor first and carry precision through the calculation. Do not combine pounds directly with an order expressed per kilogram.

A hypothetical infusion at 7 mcg/kg/min for a 68 kg patient supplies 476 mcg/min. Convert to 0.476 mg/min, then multiply by 60 to obtain 28.56 mg/hr. With a hypothetical concentration of 1.6 mg/mL, the rate is 17.85 mL/hr before any requested rounding.

A common error is to divide by 60 when moving from amount per minute to amount per hour. An hour includes sixty minutes of delivery, so the amount delivered in that hour is sixty times larger. Unit cancellation makes this direction clear.

A maximum dose, renal adjustment or route restriction can change what should be administered. Check those separately if the case asks for a clinical judgment. A calculated result is not automatically an acceptable regimen, and the examples here deliberately avoid prescribing a real drug.

Before entering a final answer, check the requested unit and time basis, verify the concentration and apply only the rounding rule specified. In your error log, distinguish a wrong weight from a per-day/per-dose error. Practise the weak step rather than repeating an entire case without knowing what went wrong.

Try it before reading the answer

Write your setup, units and check first. These are original practice exercises, not recalled exam items.

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