Common Registration Assessment, Part 1

Medicine cost and switch calculations

The health economics part of the paper in three original questions: a cost per period, a comparison and a practice-wide saving.

Published 5 October 2026. Independent revision material, not GPhC questions, not for patient care.

A scientific calculator, a pen and a ruled notebook on a desk
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The Pharmaceutical Journal's concentrations, dilutions and health economics tutorial includes a practice-level example: a list size, a percentage on one medicine, a percentage clinically suitable to switch, and two prices. The answer is a saving over 30 days.

The method is always the same. Reduce the group first, convert each price to a cost for the same period, take the difference, then multiply.

The method

  1. Find the number of patients involved, one percentage at a time.
  2. Convert each pack price into a cost for the same period.
  3. Subtract to get the saving per patient.
  4. Multiply by the number of patients and state the period.

Three practice questions

Work each one on paper first, then open the answer. All drugs and patients are fictional.

Question 1

A practice has 12,000 patients. 2% take Drug M modified release once daily, and a review finds 25% of those are suitable to switch to immediate release twice daily. Modified release costs £90 per 60 tablets and immediate release costs £8 per 120 tablets. What is the saving over a 30-day supply if all suitable patients switch?

Show the answer

Answer: £2,460

Working: Patients on the drug: 12,000 × 0.02 = 240. Suitable: 240 × 0.25 = 60. Modified release for 30 days: 30 tablets at £90 ÷ 60 = £45. Immediate release: 60 tablets at £8 ÷ 120 = £4. Saving per patient = £41. 60 × £41 = £2,460.

Question 2

Drug N costs £14.50 for 28 tablets taken once daily. Drug P costs £6.30 for 56 tablets taken twice daily. What is the difference in cost for 30 days of treatment, to the nearest penny?

Show the answer

Answer: £8.79

Working: Drug N: 30 ÷ 28 × £14.50 = £15.54. Drug P: 60 tablets, 60 ÷ 56 × £6.30 = £6.75. Difference = £15.54 − £6.75 = £8.79. Always compare the same time period and the same number of days.

Question 3

A drug costs £2.40 for 28 tablets. How much does a 6-month supply (taking 26 weeks, one tablet daily) cost to the nearest penny?

Show the answer

Answer: £15.60

Working: 26 weeks × 7 = 182 tablets. £2.40 ÷ 28 = £0.0857 a tablet. 182 × £0.0857 = £15.60. Keep the unrounded price per tablet until the last step.

The journal's cost example

The tutorial's example switches some patients from once-daily modified-release quetiapine to twice-daily immediate release at a list size of 20,000, and asks for the 30-day saving. The numbers on this page are different. Prices here are invented and do not reflect current NHS prices.

Where marks are lost

  • Applying both percentages to the whole list instead of in sequence.
  • Comparing different time periods.
  • Forgetting the second daily dose changes the tablet count.

Frequently asked questions

Do I round the number of patients?

Only if the question says so. If the answer is not a whole number of patients, check the percentages.

Which price do I use?

The one in the question. Prices on the exam are given, so do not use real list prices.

Sources

The questions above are original and use fictional drugs. PreRegExamPrep is not affiliated with or endorsed by the General Pharmaceutical Council.

Practise until the method is automatic

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More calculation topics

See also the formula sheet, the eight sample questions and the approved calculator page.