Common Registration Assessment, Part 1

Primidone 250 mg tablets and stepwise evening titration for the GPhC assessment

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

Published 12 November 2026. Independent revision material, not GPhC questions, not for patient care.

White tablets scattered on a yellow background
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The manufacturer's UK product information for Primidone Aspire 250 mg tablets states that the usual starting dose in adults is 125 mg as a single dose in the evening.

The same information states that the daily dose is increased by 125 mg every 3 days until the patient is receiving 500 mg daily, and after that by 250 mg every 3 days until control is obtained, up to a maximum of 1.5 g daily.

The printed maintenance table gives 3 to 6 of the 250 mg tablets a day, that is 750 to 1,500 mg, in divided doses.

Each question fixes the values needed for its arithmetic. Write the unit beside every step and distinguish the single evening starting dose from a divided daily dose. All prescriptions and patients here are fictional; these are revision materials, not for patient care.

The method

  1. Halve the 250 mg tablet for the 125 mg starting dose.
  2. Count each 3-day step separately when working out when a target dose is reached.
  3. Use 125 mg steps up to 500 mg daily, then 250 mg steps above 500 mg.
  4. Divide the daily milligrams by 250 mg for the tablet count.
  5. Keep the 1.5 g maximum separate from the 750 to 1,500 mg maintenance range.

Three practice questions

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

Question 1

A fictional adult starts primidone at 125 mg as a single evening dose. Using 250 mg tablets, how much of a tablet is each starting dose?

Show the answer

Answer: Half a tablet

Working: 125 mg / 250 mg = 0.5, so each starting dose is half of one 250 mg tablet.

Question 2

A fictional adult starts primidone at 125 mg on day 1 and the daily dose rises by 125 mg every 3 days. On which day of treatment does the daily dose first reach 500 mg?

Show the answer

Answer: Day 10

Working: 500 mg - 125 mg = 375 mg to add; 375 / 125 = 3 increases; the increases fall on days 4, 7 and 10, so the dose first reaches 500 mg on day 10.

Question 3

A fictional adult takes a maintenance dose of 1,500 mg of primidone daily in 2 divided doses. Using 250 mg tablets, how many tablets is that per day and per dose?

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Answer: 6 tablets per day; 3 tablets per dose

Working: 1,500 mg / 250 mg = 6 tablets a day; 6 / 2 = 3 tablets per dose.

eMC SmPC: Primidone Aspire 250mg Tablets

https://www.medicines.org.uk/emc/product/14215/smpc

Where marks are lost

  • Adding 250 mg steps before the daily dose has reached 500 mg; the first steps are 125 mg.
  • Treating the 125 mg starting dose as a whole tablet instead of half of one 250 mg tablet.
  • Reading the 1.5 g maximum as the maintenance target rather than the ceiling.

Frequently asked questions

Are these official assessment questions?

No. They are original revision exercises, not official GPhC questions and not for patient care.

Does this calculation decide a real primidone dose?

No. Follow the stated prescription in the exercise. Real titration follows the prescriber and the product information for the named tablet.

How should I check the answer?

Halve the 250 mg tablet for 125 mg, count 3-day steps one by one, switch from 125 mg to 250 mg steps only after 500 mg daily, and divide milligrams by 250 for tablets.

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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More calculation topics

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