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Drugs Calculator: How to use Clark’s Rule (BASED ON BODY WEIGHT)

    Drugs Calculator: How to use Clark's Rule (BASED ON BODY WEIGHT)

    Clark's Rule

    (Based on Body Weight)

    Clark’s rule is an equation used to calculate pediatric medication dosage based on the known weight of a patient and a known adult dose of medication to be used. Clark’s rule equation is defined as the weight of the patient in pounds divided by the average standard weight of 150 pounds (68 kg) multiplied by the adult dose of a drug equals the pediatric medication dose.

    Example 1:

    If an adult dose of medications calls for 30mg and the child weighs 30 Ibs, what is the child dose?


    Child dose=30Ibs/150Ibs*30mg=6mg of medicine

    Example 2:

    Using Clark’s rule, what is the dose for a twelve yr old male who weighs 35kg, if the average adult dose is 500mg?


    1st convert kg to pounds; 1kg=2.2Ibs; 35kg=77Ibs

    Child dose=77Ibs/150Ibs*500mg=257mg of drug.


    • (Weight divided by 150 lbs.) x Adult Dose = Pediatric Dosage


    • (Weight divided by 68 kg) x Adult Dose = Pediatric Dosage

    General Tips:

    • Check that your answer makes sense clinically.
    • Triple check your work.
    • Have a colleague or pharmacist check your work.
    • Know general therapeutic drug doses for commonly administered medications.

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