Common Registration Assessment, Part 1

Propylthiouracil tablet counts and titration to maintenance for the GPhC assessment

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

Published 9 November 2026. Independent revision material, not GPhC questions, not for patient care.

A hand holding two blister packs of tablets against a blue 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 propylthiouracil 50 mg tablets states that adults and the elderly initially take 300 to 600 mg daily, once daily or in divided doses, until the patient becomes euthyroid.

The same information states that when the condition is controlled, usually after 1 to 2 months, the dose is reduced to 50 to 150 mg daily and continued for 1 to 2 years.

It also states that in renal impairment the dose is reduced to 75% when the GFR is 10 to 50 ml/min and to 50% when the GFR is below 10 ml/min, and that propylthiouracil is not recommended for children under 6 years.

Each question fixes the values needed for its arithmetic. Write the unit beside every step and distinguish the initial phase from the maintenance phase. All prescriptions and patients here are fictional; these are revision materials, not for patient care.

The method

  1. Identify whether the stated plan is the initial phase or the maintenance phase.
  2. Divide the stated daily mg by the 50 mg tablet strength for the daily tablet count.
  3. Multiply the daily tablet count by the stated days for a supply quantity.
  4. Keep mg, tablet counts, weeks and days 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 adult starts propylthiouracil at 450 mg daily in divided doses, using 50 mg tablets. How many tablets are taken each day?

Show the answer

Answer: 9 tablets

Working: 450 mg / 50 mg per tablet = 9 tablets daily.

Question 2

A fictional adult takes propylthiouracil 300 mg daily during the initial phase, using 50 mg tablets. How many tablets are needed for 6 weeks?

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Answer: 252 tablets

Working: 300 mg / 50 mg = 6 tablets daily. 6 weeks = 42 days. 6 tablets x 42 days = 252 tablets.

Question 3

A fictional patient is controlled and reduced to the maintenance dose of propylthiouracil 100 mg daily, using 50 mg tablets. How many tablets are needed for 28 days?

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Answer: 56 tablets

Working: 100 mg / 50 mg = 2 tablets daily. 2 tablets x 28 days = 56 tablets.

eMC SmPC: Propylthiouracil 50mg Tablets

https://www.medicines.org.uk/emc/product/3123/smpc

Where marks are lost

  • Using the maintenance range of 50 to 150 mg daily for an initial-phase question that states 300 to 600 mg.
  • Miscounting the days; 6 weeks is 42 days.
  • Reporting tablets per day when the question asks for the whole course.

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 propylthiouracil dose?

No. Follow the stated prescription in the exercise. Real dosing follows thyroid response and is reduced once the patient is euthyroid.

How should I check the answer?

Divide the stated daily mg by 50 mg per tablet, then multiply by the stated number of days.

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.