When calculating an oral dose, use the label information of the medication available on hand as the left hand side of the ratio. As usual, put units of measurement on the right side to match the left side and "plug in" the appropriate numbers from the ordered dosage. If the units of measurement do not match, you will have to convert first to get matching information.
Example problem #1: Ordered is Zyloprim 450 mg. You have available Zyloprim 300 mg tablets.
Set the ratio with the available medication as the left side and put units of measurement on the right to match the left.
300 mg = ____ mg
1 tab tab
Look back at order and plug in numbers into appropriate location and put the X in the vacant spot.
300 mg = 450 mg
1 tab X tab
Cross multiply and solve for X.
300 X = 450
300 X = 450
300 300
X = 1.5 or 1 1/2 tab
Example problem #2: You have a bottle of Tigan capsules of 250 mg each. Ordered is Tigan 0.5 g.
Set up the ratio using the medication on hand information.
250 mg = ____mg
1 cap cap
Note that the order is is grams, but you must have milligrams to plug in information on the right side of the ratio. Therefore, you have to convert. Remember to convert within the metric system, you move the decimal place to the left or right as needed. To convert from grams to milligrams, move decimal three places to the right. 0.5 g = 500 mg. You now have the information for the right side.
250 mg = 500 mg
1 cap X cap
250 X = 500
250 X = 500
250 250
X = 2 cap
In final answer, remember than only scored tablets can be divided into fractional doses---1/2 or 1/4 as scored. On a drug dosage test, if the problem does not say whether or not the tablet is scored and your answer is a fraction, leave the answer as calculated.
Tablets which are not scored, enteric coated tablets, and capsules cannot be broken. Answers can be in whole number only.