Drug-Calculation-Formulas-Common

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DRUG CALCULATION FORMULAS
Below are the most important calculation formulas that
you should know in preparing medications and drips.

Calculating Tablet Dosages

In calculating tablet dosages, the following formula is
useful:


DESIRED DOSAGE ÷ STOCK STRENGTH = NUMBER OF

TABLETS

The desired dosage is the ordered dosage of the
physician while the stock strength is the amount of drug
present in each tablet. Stock strength is also known as
stock dose.

Example:

• The physician orders 1,500 mg of calcium
carbonate for the patient. The drug is available in
250 mg tablets. How many tablets should be
given to the patient?

Desired dosage ÷ stock strength = number of tablets

, 2



1,500 mg ÷ 250 mg = 6 tablets

• The patient is ordered to have 2 g of potassium
chloride. The drug is available in 500 mg tablets.
How many tablets should be given?

Convert 2 g to mg = 2 x 1,000 = 2,000 mg
Desired dosage ÷ stock strength = number of tablets
2,000 mg ÷ 500 mg = 4 tablets



Calculating Mixtures and Solutions

The following formula is useful in calculating mixtures
and solutions:


DESIRED DOSAGE ÷ STOCK STRENGTH X STOCK VOLUME

= AMOUNT OF SOLUTION TO BE GIVEN

The desired dosage is the ordered dosage of the
physician. The stock strength is the amount of drug
present in the preparation while the stock volume is the
amount of the solution where the drug is diluted.
Example:

• The physician orders 375 mg of cefuroxime for the
patient. The drug is available in 750 mg vial. You