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Drugs Calculator: How to Use Universal Formula

    Drugs Calculator: How to Use Universal Formula

    Universal Formula

    (Toney-Butler, 2021)

    In the universal formula (or “desired over have method”), the desired amount (D) is the dose  prescribed and the amount on hand (H) or the amount you “have” is the available dose or concentration. The quantity (Q) is the form and amount in which the drug is supplied (i.e. tablet, capsule, liquid). To calculate the dose, take the desired amount and divide it by the amount on hand, then multiply it by the quantity like this, D/H×Q=Dose. Here is the dose calculator based on this universal formula.

    For Example:

    Cephalexin 750 mg P.O. every 12 hours is ordered. The pharmacy stocks 250 mg tablets. How many tablets should be administered per dose?

    D=750, H=250, Q=1

    750/250×1 = 3Tablets

    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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