0071483446.pdf

There are two methods nurses can use to calculate the desired dose. These are

the formula method or the ratio-proportion method. Either method will produce

same result. When applying either method, make sure that all the terms are in

the same units before calculating the desired dose. For example, the medication

order might be in grams and the dose on hand might be in milligrams. The nurse

will need to convert the grams to milligrams before calculating the desired dose

to give. Always convert to the unit of the “have” dose.

The formula method uses the following formula to determine the correct dose.

×V=A Quantity (Desired dose divided by dose you have

multiplied by vehicle of drug you have equals

the amount calculated to be given to the patient)

D =desired dose

H =dose you have

V=vehicle you have (tablets or liquids)

A=amount calculated to be given to the patient

Ratio and proportion method

H is the drug on hand (available)

V is the vehicle or drug form (tablet, capsule, liquid)

D is the desired dose (as prescribed)

x is the unknown amount to give, and

:: stands for “as” or “equal to.”

Multiply the means and the extremes. Solve for x; x is the divisor.

Example: Give 500 mg of ampicillin sodium by mouth when the dose on hand

is in capsules containing 250 mg.

500 mg divided by 250 mg multiplied by 1 capsule =2 capsules

Formula method:

Example: Give 375 mg of ampicillin when it is supplied as 250 mg/5mL.

375 mg divided by 250 mg multiplied by 5 mL = 7.5 mL

500

250 1

2

mg

mg

capsule

×=capsules

H: V:: D :x

Means

Extremes

D

H

(^118) CHAPTER 7 Dose Calculations