Section 2: Calculating the Number of Doses
If you know the total amount of drug available and you know the size of a single dose, you can calculate the number of doses that can be given from the drug available.
There are 20 g of drug A and each dose uses 4g. How many doses of drug A can be given?
If each dose is 4 g and there is a total of 20 g
then the number of doses possible is 20 / 4
ie 5 doses are possible
Total amount of drug = Size of Single Dose x Number of Doses
which rearranges to:
Total amount of drug A = Total Amount of Drug
Size of Single Dose
Number of Doses = 20 = 5
4
5 doses are possible.
There are 27g of a drug and each dose uses 300 mg of the drug. How many doses are possible?
Convert the mass of drug from grams to milligrams:
27g = 27000mg
If each dose is 300 m g and there is a total of 27000mg
then the number of doses possible is 27000 / 300
ie 90 doses are possible.
OR USING THE EQUATION:
Total amount of drug = Size of Single Dose x Number of Doses
which rearranges to:
Number of Doses = Total Amount of Drug
Size of Single Dose
Number of Doses = 27000 = 90
300
90 doses are possible.