Common Registration Assessment, Part 1

Chlorphenamine 4mg tablets and 24-hour maximums 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.

Person holding a bottle of allergy medicine
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The NHS lists chlorphenamine as 4 mg tablets; the usual dose for adults and children aged 12 years and over is 1 tablet every 4 to 6 hours, with no more than 6 tablets in 24 hours.

The NHS lists the usual dose for frail older adults as 1 tablet every 6 to 8 hours, with no more than 3 tablets in 24 hours.

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, dose interval and maximum supplied in the question.
  2. Convert a dose interval to doses per 24 hours by dividing 24 by the interval.
  3. Check any schedule against the stated 24-hour maximum before reporting a total.
  4. Multiply tablets by 4 mg when an answer is requested in mg.
  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 adult takes chlorphenamine 4 mg tablets at the stated maximum of 6 tablets in 24 hours. How many mg is that per day?

Show the answer

Answer: 24 mg

Working: 6 tablets × 4 mg = 24 mg per day.

Question 2

A fictional plan is 1 chlorphenamine 4 mg tablet every 6 hours. How many doses is that in 24 hours, and does it stay within the stated maximum?

Show the answer

Answer: 4 doses (within the maximum)

Working: 24 hours ÷ 6 hours = 4 doses; 4 doses is below the stated maximum of 6 tablets in 24 hours.

Question 3

A fictional frail older adult is limited to the stated maximum of 3 tablets in 24 hours. How many mg is that, and how many tablets would 5 days at this maximum use?

Show the answer

Answer: 12 mg per day (15 tablets)

Working: 3 tablets × 4 mg = 12 mg per day; 3 × 5 days = 15 tablets.

NHS: How and when to take chlorphenamine

https://www.nhs.uk/medicines/chlorphenamine-including-piriton/how-and-when-to-take-chlorphenamine/

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.

Practise until the method is automatic

Try 15 free questions with worked answers. No sign-up required.

Try 15 free questionsSee pricing

More calculation topics

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