Common Registration Assessment, Part 1

Cyanocobalamin tablet doses and daily micrograms 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.

Vitamins and capsules arranged in ceramic bowls
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The NHS describes cyanocobalamin as a man-made version of vitamin B12, used to treat or prevent low levels.

The manufacturer's UK product information lists 50 microgram tablets, with an adult dose of 50 to 150 micrograms a day.

The same product information gives oral maintenance for pernicious anaemia of at least 300 micrograms a day.

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 daily amount in micrograms and the tablet strength.
  2. Divide the daily amount by the tablet strength to count tablets per day.
  3. Calculate one day first, then scale to the stated number of days.
  4. Convert micrograms to milligrams only when the question asks: 1,000 micrograms = 1 mg.
  5. Keep micrograms, milligrams and tablet counts 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

A fictional patient takes cyanocobalamin 100 micrograms a day using 50 microgram tablets. How many tablets a day, and how many tablets is a 28-day supply?

Show the answer

Answer: 2 tablets a day; 56 tablets

Working: 100 micrograms / 50 micrograms = 2 tablets; 2 tablets x 28 days = 56 tablets.

Question 2

A fictional patient takes 150 micrograms a day for 7 days. What is the weekly total in micrograms and in milligrams?

Show the answer

Answer: 1,050 micrograms; 1.05 mg

Working: 150 micrograms x 7 days = 1,050 micrograms; 1,050 / 1,000 = 1.05 mg.

Question 3

A fictional patient with pernicious anaemia takes an oral maintenance dose of 300 micrograms a day using 50 microgram tablets. How many tablets is a 30-day supply?

Show the answer

Answer: 180 tablets

Working: 300 micrograms / 50 micrograms = 6 tablets a day; 6 tablets x 30 days = 180 tablets.

NHS: Cyanocobalamin

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

Where marks are lost

  • Mixing micrograms and milligrams in the same step without converting.
  • Forgetting that a maintenance amount stated per day still needs multiplying by the number of days.
  • 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 write micrograms in full?

Writing the unit in full avoids confusion with mg, which is a common source of calculation errors.

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.

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