Common Registration Assessment, Part 1

Theophylline modified-release tablets and twelve hourly doses for the GPhC assessment

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

Published 4 November 2026. Independent revision material, not GPhC questions, not for patient care.

Pink tablets in stacked blister packs on a yellow surface
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 Uniphyllin prolonged-release tablets states that the usual adult maintenance dose is 200 mg every 12 hours, which may be titrated to 300 mg or 400 mg every 12 hours depending on response.

The same information states that the tablets must be swallowed whole and not broken, crushed or chewed, as this may lead to a rapid release of theophylline with the potential for toxicity.

It also states that plasma theophylline concentrations should ideally be maintained between 10 and 20 micrograms/ml.

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 a supply period. All prescriptions and patients here are fictional; these are revision materials, not for patient care.

The method

  1. Identify the stated twelve hourly dose in milligrams and the tablet strength supplied.
  2. Double the twelve hourly dose for the daily total, or divide it by the tablet strength for tablets per dose.
  3. Multiply the daily tablet count by the stated number of days for a supply quantity.
  4. Keep milligrams and tablets separate; convert only when the question asks.

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 theophylline 200 mg every 12 hours using 200 mg modified-release tablets. How many milligrams is the total daily dose?

Show the answer

Answer: 400 mg

Working: 200 mg x 2 doses each day = 400 mg each day.

Question 2

A fictional patient is titrated to theophylline 400 mg every 12 hours using 200 mg modified-release tablets. How many tablets are taken each day?

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Answer: 4 tablets

Working: 400 mg / 200 mg per tablet = 2 tablets per dose. 2 tablets x 2 doses = 4 tablets each day.

Question 3

A fictional prescription reads theophylline 300 mg every 12 hours using 300 mg modified-release tablets for 14 days. How many tablets should be supplied?

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Answer: 28 tablets

Working: One 300 mg tablet every 12 hours = 2 tablets each day. 2 tablets x 14 days = 28 tablets.

eMC SmPC: Uniphyllin 200 mg prolonged release tablets

https://www.medicines.org.uk/emc/product/100850/smpc

Where marks are lost

  • Treating a 12-hourly dose as a once-daily dose.
  • Using the plasma-concentration range as if it were the oral dose.
  • Counting one tablet without checking whether the stated tablet strength is 200 mg or 300 mg.

Frequently asked questions

Are these official assessment questions?

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

Why does the modified-release wording matter?

It identifies the formulation in the stated prescription. The questions use whole tablets and the exact stated strength.

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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More calculation topics

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