How to Do Medical Dosage Calculations

Health care workers learn how to do dosage calculations because most medications come in many different dosages, and pharmacies don't always have them all in stock. Calculating medical dosages involves using basic algebra to convert the dosage that appears on the medication order you want to fill to the dosage of the medication you have in stock. Researchers at the Department of Pharmacology at the Koirala Institute of Health Sciences determined, in a study they published in the "Nepal Medical College Journal," that health care workers need to improve their knowledge of correct dosage calculations to provide the best care to their patients.

Things You'll Need

• Calculator
• Paper
• Pencil

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Instructions

Finding Dosage Variables

• 1

  Determine the dosage the medication order or prescription calls for by looking for a number followed by a unit of measure, such as 500 mg or 100 mcg. Write this number down, and set it equal to D, which stands for desired dosage (example: D = 20 mg).

• 2

  Check how many tablets or capsules the medication order requires. Look on the order for a pound sign (#) followed by a number (example: #60). Set this number equal to Q, or quantity (example: Q = 60).

• 3

  Check what dosages of this medication your pharmacy has in stock by browsing the shelves or searching on the computer if your pharmacy maintains digital records. Write this number down and set it equal to S for stock dosage (example: S = 10 mg).

Calculating the Variables

• 4

  Set up the following math problem: (D x Q)/S = X, where X equals the number of pills or capsules that you must dispense to complete the order.

• 5

  Substitute the desired dosage (D), quantity (Q) and stock dosage (S) that you've previously written down for the variables D, Q and S (example: (20 x 60)/10 = X), which means that the prescription requires 60 tablets or capsules of 20 mg each.

• 6

  Solve for the part in parentheses using a calculator ,and rewrite the new problem below the previous one (example: 20 x 60 = 1,200, so the new equation becomes 1,200/10 = X).

• 7

  Solve the new division problem for X, the number of pills or capsules the medication order requires. (In the example, 1,200/10 = 120, so dispense 120 capsules at 10 mg each to fill an order that asks for 60 capsules at 20 mg each.)