Common Registration Assessment, Part 1

Fentanyl patch strengths and 3-day change intervals for the GPhC assessment

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

Published 30 October 2026. Independent revision material, not GPhC questions, not for patient care.

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The NHS lists fentanyl patches that release 12 micrograms to 100 micrograms of fentanyl every hour, and states that a patch is changed every 3 days, always removing the old one first.

The NHS advises not to use more than 1 patch at a time unless a doctor says so, and not to cut fentanyl patches.

The NHS lists the other forms for breakthrough pain: nasal spray containing 50 micrograms to 400 micrograms, tablets containing 100 micrograms to 800 micrograms, and lozenges containing 200 micrograms to 1,600 micrograms.

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 patch strength, wear time and change interval stated in the question.
  2. Convert days worn into hours by multiplying by 24 before applying a micrograms-per-hour rate.
  3. Calculate one patch first, then scale to the stated period.
  4. Divide the total days by the change interval to count patches; only round when the question says to.
  5. Keep micrograms and milligrams separate; convert only if 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 wears 1 patch releasing 25 micrograms per hour, changed every 3 days. How many patches are needed for 30 days?

Show the answer

Answer: 10 patches

Working: 30 days / 3 days per patch = 10 patches.

Question 2

A fictional patch releases 50 micrograms per hour. How many micrograms are released over the 3 days it is worn?

Show the answer

Answer: 3,600 micrograms

Working: 3 days x 24 hours = 72 hours; 50 micrograms x 72 hours = 3,600 micrograms.

Question 3

A fictional prescription supplies patches releasing 12 micrograms per hour for 90 days, with each patch changed every 3 days. How many patches is that?

Show the answer

Answer: 30 patches

Working: 90 days / 3 days per patch = 30 patches.

NHS: How and when to use fentanyl

https://www.nhs.uk/medicines/fentanyl/how-and-when-to-use-fentanyl/

Where marks are lost

  • Applying a micrograms-per-hour rate to days without converting to hours.
  • Reporting a daily total when the question asks for one patch or the whole 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 patch-count calculation justify changing a patch schedule?

No. Follow the schedule in the exercise. Real patch changes and dose adjustments 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.

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More calculation topics

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