Common Registration Assessment, Part 1

Carbimazole tablet strengths and titration doses for the GPhC assessment

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

Published 21 October 2026. Independent revision material, not GPhC questions, not for patient care.

A person reaching for a bottle of medicine
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The BNF lists carbimazole tablets in four strengths: 5 mg, 10 mg, 15 mg and 20 mg.

The BNF gives the usual adult starting dose for an overactive thyroid as 15 mg to 40 mg a day until the condition is controlled, usually after 4 to 8 weeks, then reduced gradually to 5 mg to 15 mg a day.

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

The method

  1. Identify the exact strength, dose and frequency supplied in the question.
  2. Calculate one dose first; divide prescribed mg by mg per tablet.
  3. Watch for a dose reduction part way through the plan.
  4. Scale to the stated duration only when a supply is requested.
  5. Check the tablet count is a whole number before reporting it.

Three practice questions

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

Question 1

A fictional prescription specifies carbimazole 15 mg once a day using 5 mg tablets for 28 days. How many tablets is the supply?

Show the answer

Answer: 84 tablets

Working: 15 ÷ 5 = 3 tablets a day. 3 × 28 = 84 tablets.

Question 2

A fictional plan starts carbimazole at 40 mg once a day using 20 mg tablets for 6 weeks. How many tablets is this first phase?

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Answer: 84 tablets

Working: 40 ÷ 20 = 2 tablets a day. 6 weeks is 6 × 7 = 42 days, so 2 × 42 = 84 tablets.

Question 3

After review, a fictional plan reduces carbimazole to 10 mg once a day using 5 mg tablets for 30 days. How many tablets is this phase?

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Answer: 60 tablets

Working: 10 ÷ 5 = 2 tablets a day. 2 × 30 = 60 tablets.

Exam approach

Titration questions split at the review point. Calculate each phase separately, then combine only if the question asks for a total.

Where marks are lost

  • Mixing up the four strengths when the strength is stated in the question.
  • Carrying the starting dose past the stated reduction.
  • Forgetting to convert weeks to days before multiplying.

Frequently asked questions

Are these official assessment questions?

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

Do I need to memorise the titration schedule?

The exercise supplies the doses. In the assessment, read any given product information exactly as written.

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.