Common Registration Assessment, Part 1

Clobetasol 0.05% cream amounts and weekly gram limits for the GPhC assessment

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

Published 1 November 2026. Independent revision material, not GPhC questions, not for patient care.

Woman applying cream to her hand
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The NHS describes clobetasol as a strong steroid used for skin conditions such as eczema and psoriasis.

The manufacturer's UK product information for Dermovate lists a 0.05% cream applied thinly once or twice a day, with a maximum of 50 g a week and courses of no more than 4 weeks.

A percentage weight in weight strength gives the milligrams of clobetasol in each gram of cream, which links pack size to the amount of active ingredient.

Each question fixes the values needed for its arithmetic. Write the unit beside every step and distinguish grams of cream from milligrams of clobetasol. All prescriptions and patients here are fictional; these are revision materials, not for patient care.

The method

  1. Identify the stated percentage strength and read it as grams per 100 g.
  2. Convert the percentage into milligrams per gram before scaling to a pack size.
  3. Multiply grams a week by the stated number of weeks for a course total.
  4. Round up to whole tubes only when the question asks for whole packs.
  5. Keep grams of cream and milligrams of clobetasol separate; label every step.

Three practice questions

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

Question 1

Clobetasol 0.05% cream contains 0.05 g of clobetasol in every 100 g of cream. How many milligrams of clobetasol are in a 50 g tube?

Show the answer

Answer: 25 mg

Working: 0.05 g in 100 g = 50 mg in 100 g = 0.5 mg in 1 g; 0.5 mg x 50 g = 25 mg.

Question 2

A fictional patient uses clobetasol cream at the stated maximum of 50 g a week for the stated maximum course of 4 weeks. How many grams is the full course, and how many whole 30 g tubes does it need?

Show the answer

Answer: 200 g; 7 whole tubes

Working: 50 g x 4 weeks = 200 g; 200 g / 30 g = 6.67, rounded up to 7 whole tubes.

Question 3

A fictional patient finishes a 30 g tube of clobetasol cream in 4 days. At that rate, how many grams a week is used, and by how much does it exceed the stated 50 g weekly maximum?

Show the answer

Answer: 52.5 g a week; 2.5 g over the maximum

Working: 30 g / 4 days = 7.5 g a day; 7.5 g x 7 days = 52.5 g; 52.5 g - 50 g = 2.5 g over.

NHS: Clobetasol

https://www.nhs.uk/medicines/clobetasol/

Where marks are lost

  • Reading 0.05% as 5 mg per gram instead of 0.5 mg per gram.
  • Rounding 6.67 tubes down to 6 when whole tubes are required for the full 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.

Why round up to whole tubes?

Part tubes are not supplied. When a course needs more than a whole number of packs, the next whole pack is supplied.

How should I check the answer?

Check the requested unit, then work backwards from the pack size to the stated strength 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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