Common Registration Assessment, Part 1

Thiamine tablet strengths and daily doses for the GPhC assessment

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

Published 29 October 2026. Independent revision material, not GPhC questions, not for patient care.

Vitamin capsules arranged with a slice of lemon
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The NHS lists thiamine as 50 mg and 100 mg tablets, and as a liquid containing 100 mg in 5 ml.

The NHS lists the usual adult dose for mild deficiency as 25 mg to 100 mg once a day, and for severe deficiency as 100 mg taken 2 or 3 times a day.

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 formulation, strength, dose and frequency supplied in the question.
  2. Convert a liquid strength of 100 mg/5 ml to 20 mg/ml if a dose-to-volume conversion is needed.
  3. Calculate one dose first; for tablets divide prescribed mg by mg per tablet.
  4. Scale to the stated frequency and duration only when a total quantity is requested.
  5. Apply whole-container or complete-day rounding only if the question specifies 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 thiamine 50 mg once a day for 28 days using 50 mg tablets. How many tablets cover the course, and how many mg in total?

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Answer: 28 tablets (1,400 mg)

Working: 1 tablet × 28 days = 28 tablets; 28 × 50 mg = 1,400 mg.

Question 2

A fictional plan for severe deficiency is thiamine 100 mg three times a day using 100 mg tablets. How many tablets and how many mg is that per day?

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Answer: 3 tablets (300 mg)

Working: 1 tablet × 3 doses = 3 tablets per day; 3 × 100 mg = 300 mg per day.

Question 3

A fictional prescription specifies thiamine 200 mg a day using the liquid containing 100 mg in 5 ml. What volume is needed per day?

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Answer: 10 ml

Working: 100 mg per 5 ml = 20 mg/ml; 200 mg ÷ 20 mg/ml = 10 ml per day.

NHS: How and when to take thiamine

https://www.nhs.uk/medicines/thiamine-vitamin-b1/how-and-when-to-take-thiamine/

Where marks are lost

  • Using a remembered strength or schedule instead of the stated product.
  • Reporting a daily total when the question asks for one dose or the course.
  • 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 quantity calculation justify a formulation switch?

No. Follow the formulation and prescription in the exercise. Real switches and dose changes 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.