Common Registration Assessment, Part 1

Fybogel sachet doses and water volumes 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.

Bottle of supplements beside a glass of water
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The NHS lists the usual Fybogel dose for adults and children aged 12 years and over as 1 sachet of granules twice a day, mixed with at least 150 ml of cold water per dose.

For children aged 6 to 11 years, the NHS lists half to 1 level (5 ml) teaspoonful of granules twice a day, and advises adults to drink more than 2 litres of fluid each day while taking it.

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 age band, dose and frequency supplied in the question.
  2. Treat 1 sachet as one dose and count doses before scaling to days.
  3. Multiply the stated water volume per dose by the number of doses for a daily volume.
  4. Scale to the stated duration only when a total supply 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 plan is 1 sachet of Fybogel twice a day for 14 days. How many sachets are needed?

Show the answer

Answer: 28 sachets

Working: 1 sachet × 2 doses = 2 sachets per day; 2 × 14 days = 28 sachets.

Question 2

A fictional patient mixes each dose with the minimum 150 ml of cold water and takes 1 sachet twice a day. What is the smallest volume of water used for the doses each day?

Show the answer

Answer: 300 ml

Working: 150 ml × 2 doses = 300 ml per day.

Question 3

A fictional child aged 8 takes 1 level 5 ml teaspoonful of granules twice a day for 7 days. What total volume of granules is measured over the course?

Show the answer

Answer: 70 ml

Working: 5 ml × 2 doses = 10 ml per day; 10 × 7 days = 70 ml.

NHS: How and when to take Fybogel

https://www.nhs.uk/medicines/fybogel-ispaghula-husk/how-and-when-to-take-fybogel/

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.