Common Registration Assessment, Part 1

Clotrimazole pessary strengths and course nights for the GPhC assessment

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

Published 30 October 2026. Independent revision material, not GPhC questions, not for patient care.

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

The NHS lists the clotrimazole pessary doses for thrush as: a 100mg pessary used as 1 pessary every night for 6 nights in a row or 2 pessaries for 3 nights in a row; a 200mg pessary used as 1 pessary every night for 3 nights in a row; and a 500mg pessary used for 1 night only.

The NHS advises using pessaries at bedtime, not during a period, and to see a doctor if symptoms have not improved after 7 days.

The NHS warns that clotrimazole can damage the latex used in condoms and diaphragms, so contraception may not work as well as it should.

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 stated pessary strength and its course pattern before any multiplication.
  2. Multiply pessaries per night by nights to get the course quantity.
  3. Add days or nights only across the same course; do not mix strengths.
  4. For total-mg questions, multiply the pessary strength by the number of pessaries.
  5. Keep pessary count, nights and mg as separate units.

Three practice questions

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

Question 1

A fictional patient uses 100mg clotrimazole pessaries, 1 pessary every night for 6 nights. How many pessaries and how many mg is the course?

Show the answer

Answer: 6 pessaries; 600mg

Working: 1 pessary x 6 nights = 6 pessaries; 100mg x 6 = 600mg.

Question 2

A fictional prescription uses the 100mg pessary as 2 pessaries for 3 nights in a row. How many pessaries is that, and how does it compare with 1 pessary for 6 nights?

Show the answer

Answer: 6 pessaries; the same total

Working: 2 pessaries x 3 nights = 6 pessaries, the same as 1 pessary x 6 nights.

Question 3

A fictional patient uses a 200mg pessary every night for 3 nights. How many mg of clotrimazole is that in total?

Show the answer

Answer: 600mg

Working: 200mg x 3 nights = 600mg.

NHS: Clotrimazole

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

Where marks are lost

  • Applying the 6-night pattern to the 200mg or 500mg strength.
  • Counting nights instead of pessaries when 2 are used each night.
  • Treating arithmetic as evidence that a real course 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 matching totals mean courses are interchangeable?

No. Follow the strength and pattern in the exercise. Real product choice needs a pharmacist or prescriber.

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

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More calculation topics

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