Common Registration Assessment, Part 1

Ondansetron 4 mg and 8 mg tablets and five day courses for the GPhC assessment

Three original practice questions, with the working shown. Read the stated prescription or plan before calculating.

Published 2 November 2026. Independent revision material, not GPhC questions, not for patient care.

Glass of water beside pink tablets on a pink surface
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The manufacturer's UK product information lists ondansetron film-coated tablets in 4 mg and 8 mg strengths.

For nausea and vomiting caused by chemotherapy or radiotherapy, that product information recommends an 8 mg dose taken 1 to 2 hours before treatment, then 8 mg every 12 hours for up to 5 days.

The same information allows up to 24 mg as a single dose with dexamethasone before highly emetogenic chemotherapy, then 8 mg twice a day for up to 5 days afterwards.

Each question fixes the values needed for its arithmetic. Write the unit beside every step and distinguish a single dose from a daily total or course supply. All prescriptions and patients here are fictional; these are revision materials, not for patient care.

The method

  1. Identify the exact strength and frequency stated in the question.
  2. Double a twice daily dose to get the daily total before scaling up.
  3. Work out how many tablets make each stated dose from the given strength.
  4. Multiply the daily tablet count by the stated number of days, with at most 5 days in the stated course.
  5. Keep milligrams and tablets separate; convert only if the question asks.

Three practice questions

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

Question 1

A fictional patient takes ondansetron 8 mg twice a day for 5 days after chemotherapy. How many milligrams is the full course?

Show the answer

Answer: 80 mg

Working: 8 mg x 2 doses = 16 mg a day; 16 mg x 5 days = 80 mg.

Question 2

A fictional prescription reads ondansetron 8 mg twice a day for 5 days using 8 mg tablets. How many tablets should be supplied?

Show the answer

Answer: 10 tablets

Working: 1 tablet per dose x 2 doses = 2 tablets a day; 2 tablets x 5 days = 10 tablets.

Question 3

A fictional patient takes 8 mg twice a day for 5 days but only 4 mg tablets are available. How many tablets does the course need?

Show the answer

Answer: 20 tablets

Working: 8 mg / 4 mg = 2 tablets per dose; 2 tablets x 2 doses = 4 tablets a day; 4 tablets x 5 days = 20 tablets.

eMC SmPC: Ondansetron 4 mg film-coated tablets

https://www.medicines.org.uk/emc/product/5222/smpc

Where marks are lost

  • Reporting the single dose instead of the daily total for a twice daily schedule.
  • Extending the course beyond the stated number of days.
  • Treating arithmetic as evidence that a real prescription is clinically suitable.

Frequently asked questions

Are these official assessment questions?

No. They are original revision exercises, not official GPhC questions and not for patient care.

Can a dose-total calculation justify changing a real dose?

No. Follow the steps in the exercise. Real dose changes are gradual and need clinical checks.

How should I check the answer?

Check the requested unit, then work backwards from the quantity to the stated dose and duration.

Sources

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

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More calculation topics

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