Liquid Medicines and Injections
Completion requirements
This short tutorial will take you through the basic formula and rules for setting up drug calculations involving liquids medicines and injections. If you have understood the fundamental principles of the NHS1 formula, you should find this topic relatively straightforward.
If solving the problems without a calculator is difficult, then you should work through the resources in Topic 2 - Fractions, Decimals and Percentages.
1. General Numeracy Review
You must be secure with the following rules before beginning work on drug calculations:
- Fractions can be converted into whole or decimal numbers by dividing the top number (numerator) by the bottom number (denominator). For example, ¾ is equal to 3 ÷ 4 = 0.75
- A whole or decimal number can be converted to a fraction by dividing it by 1. For example, 3 can be represented by the fraction ³/1
- To multiply fractions, first multiply the top numbers (numerators) and write this number at the top of your new fraction. Then multiply the bottom numbers (denominators) and write this answer at the bottom of your new fraction. Then cancel down.
- When multiplying, you stay on the top of the line all the way across and then on the bottom line all the way across.
- If you are multiplying a fraction by a whole number, you need to put that whole number over 1 to create the correct fraction - e.g. a 5ml stock solution becomes 5/1. Multiplying both the numerator and the denominator by 5 would give you the wrong answer.