4.6: The Formula Method

The formula method is appropriate for use in most outpatient settings. If the medical assistant has any doubt about their calculations, they should seek assistance from a pharmacist or another staff member who is an eint with pharmacology math. Do not administer any drugs without being 100% certain that the calculation is correct.

The formula method is the dose ordered, divided by the dose available, multiplied by the dose form, which equals the dose to be given. The dose ordered and the dose available must be the same unit, so conversion may be necessary.

Dose Ordered X Dose Form = Dose to Give
Dose Available

DO X DF = DG
DA

Example:

The provider ordered 200mg of ABC drug to be given to the patient. The medical assistant finds ABC drug formulated in 100mg tablets.

Step 1: Determine if the ordered and available doses are in the same units. In this problem the DO and the DA are in mg, so no conversion is necessary.

Step 2: Determine the dose form. In this case, the DF is 1 tablet.

Step 3: Set up the formula.

Step 4: Calculate the dose to give (DG).

Answer: The dose to give (DG) is 2 tablets.

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