On a day-to-day basis, pharmacists are required to carry out checks and calculations on prescriptions and medicines information queries they may receive. These calculations can vary in complexity and often require reference materials. Undertaking and checking pharmaceutical calculations are critical for patient safety as they help reduce error risk and ensure that patients receive the correct dose.

However, given the busy nature of many dispensaries, a decrease in the requirement for extemporaneous dispensing, and at times, a lack of exposure to specialised dosages for paediatric patients, patients with renal impairment, or patients receiving palliative care, pharmacists may have fewer opportunities to maintain and refine their calculation skills, potentially leading to a decline in proficiency.

To address this, the IPU Professional Academy team in collaboration with Dr Paul McCague School of Pharmacy, Queen’s University Belfast developed the eLearning module ‘Pharmaceutical Calculations’ in 2021. This module, available to members on the IPU Professional Academy platform, aims to review common medicine-related calculations and provide opportunities to practice calculations across a broad range of scenarios.

This module consists of two eLearning presentations, a workbook of calculations, and answers to the workbook calculations questions. The eLearning module can be found on the IPU Professional Academy Website -> CPD for pharmacists -> eLearning Programme

This resource may be useful to pharmacists as a revision tool, or it could be used with APPEL students or pharmacy students helping them transition from theory to practice in the community pharmacy setting.

Key considerations when doing pharmaceutical calculations:

• Take your time;
• Write it down;
• Get a double check;
• Sense check your answer; and
• Maintain an error log.

Calculation questions will also be included in the IPU review medicines optimisation section from time to time.

Exemplar calculation question:

A baby is prescribed Oramorph 10mg/5mL at a dose of 80micrograms/kg qds. The baby weighs four kilograms. How many millilitres should be administered for each dose?

Answer:

80 micrograms / kg x 4kg = 320 micrograms = 0.32 milligrams

Concentration of formulation: 

10mg of drug in 5mL

0.32mg of drug in XmL

X = (0.32 x 5) / 10

X = 0.16 millilitres should be administered for each dose