Calculations
This page is aimed at trainee pharmacists.☞ Why this subject matters...
There are many situations in which hospital pharmacists need to perform calculations, so you will have to be up to the required standard in order to practise. This page provides links to resources that may assist you and help you to achieve GPhC LO 32 Accurately perform calculations.
In addition, some questions in part 2 will require some calculation.
Feedback from the GPhC on which questions students find more difficult does vary from year to year. In the 2023 sittings, often trainees did not follow instructions in the exam question about rounding their answer and/or they failed to apply their knowledge to ensure the answer they gave was practical (e.g. when advising on a dose). In addition, some did not consider all of the information given to them in the questions relating to intravenous administration of medicines. You can read more here.
Registration exam
The registration assessment framework shows the common types of calculation that pharmacists might need to do in practice. It states that the registration exam is likely to include at least one calculation question involving each of the following in part 1:- doses and dose regimens
- dosage and unit conversions
- estimations of kidney function (see Renal tutorial)
- displacement volumes and values
- concentrations (e.g. expressed as w/v, % or 1 in x)
- dilutions
- molecular weight
- using provided formulae
- infusion rates
- pharmacokinetics (see Drug handling tutorial)
- health economics
- quantities to supply
In addition, some questions in part 2 will require some calculation.
Feedback from the GPhC on which questions students find more difficult does vary from year to year. In the 2023 sittings, often trainees did not follow instructions in the exam question about rounding their answer and/or they failed to apply their knowledge to ensure the answer they gave was practical (e.g. when advising on a dose). In addition, some did not consider all of the information given to them in the questions relating to intravenous administration of medicines. You can read more here.
The basics
Not everyone likes maths. But are you worried that you don’t really understand some of the basics? If so, then please take time to tackle this because pharmacists in hospital need to do calculations all the time. BBC Bitesize has a series of maths revision tools and worked examples aimed at GCSE students. This will help you with fundamental skills such as percentages, decimals, equations, and approximating.Calculations in the healthcare setting
CPPE has a package entitled Clinical Calculations for Pharmacy Professionals which covers all areas of practice. It includes calculations related to ideal body weight, creatinine clearance, dose and dose equivalence, strengths, displacement values and more. A further really helpful e-learning programme is Dispensary-based calculations for pharmacy technicians. The elearning for healthcare platform has several relevant modules including Calculating drug doses and Drug calculations in IV therapy. You will need to create an account but access is free.
The ResourcePharm website has a large collection of materials concerned with drug calculations in practice. You'll find example clinical problems involving calculations, worked examples, and maths tuition in a variety of healthcare settings. There’s a lot of material here ranging from basic to more specialist specialist from UK and international sources. Remember that practice may vary between countries and may not be representative of what happens in the NHS.
PharmaFactz is a US site that has example worked calculations including displacement values, concentrations, dilutions, and moles.
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