Common Registration Assessment, Part 1

Bisacodyl tablet and suppository 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.

Hand holding a blister pack of white tablets
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The NHS lists the usual dose of bisacodyl tablets for adults and young people aged 12 years and over as 5 mg to 10 mg once a day at bedtime, starting with one 5 mg tablet and increasing to a maximum of two tablets (10 mg).

The NHS lists the suppository dose for adults and children aged 10 years and over as one 10 mg suppository once a day in the morning, and advises not to use bisacodyl every day for more than 5 days.

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. Calculate one dose first; for tablets divide prescribed mg by mg per tablet.
  3. Scale to the stated duration only when a total quantity is requested.
  4. Keep tablets and suppositories as separate counts; never combine them in one total.
  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 bisacodyl 10 mg at bedtime using 5 mg tablets for 5 days. How many tablets cover the course?

Show the answer

Answer: 10 tablets

Working: 10 mg ÷ 5 mg = 2 tablets per day; 2 × 5 days = 10 tablets.

Question 2

A fictional plan is one 10 mg bisacodyl suppository each morning for 3 days. How many suppositories and how many mg is that in total?

Show the answer

Answer: 3 suppositories (30 mg)

Working: 1 × 3 days = 3 suppositories; 3 × 10 mg = 30 mg.

Question 3

A fictional patient starts with one 5 mg bisacodyl tablet at bedtime and, after 2 nights, increases to the stated maximum of 10 mg at bedtime for a further 3 nights. How many 5 mg tablets are used in total?

Show the answer

Answer: 8 tablets

Working: 1 tablet × 2 nights = 2 tablets; then 10 mg ÷ 5 mg = 2 tablets per night; 2 × 3 nights = 6 tablets; 2 + 6 = 8 tablets.

NHS: How and when to take or use bisacodyl

https://www.nhs.uk/medicines/bisacodyl/how-and-when-to-take-or-use-bisacodyl/

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.