Common Registration Assessment, Part 1
Phenoxymethylpenicillin age band doses and liquid strengths for the GPhC assessment
Three original practice questions, with the working shown. Read the stated prescription or plan before calculating.
Published 16 October 2026. Independent revision material, not GPhC questions, not for patient care.
The NHS lists phenoxymethylpenicillin as 250 mg and 500 mg tablets and two liquid strengths, 125 mg/5 mL and 250 mg/5 mL. The usual treatment dose for adults and children 12 years and over is 500 mg four times a day.
Younger children have age-band doses taken four times a day: 62.5 mg from 1 month to 11 months, 125 mg from 1 to 5 years and 250 mg from 6 to 11 years. A band is read from the supplied plan, not guessed from age alone.
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
- Identify the exact formulation, strength, dose and frequency supplied in the question.
- Convert an X mg/5 mL strength to mg/mL if a dose-to-volume conversion is needed.
- Calculate one dose first; for tablets or capsules divide prescribed mg by mg per unit.
- Scale to the stated frequency and duration only when a total quantity is requested.
- Apply whole-container or complete-day rounding only if the question specifies it.
Three practice questions
Work each one on paper first, then open the answer. All patients and prescriptions are fictional.
Question 1
A fictional 3-year-old is prescribed 125 mg four times a day, using the 125 mg/5 mL liquid. What volume is one dose, and what is the total daily volume?
Show the answer
Answer: 5 mL per dose, 20 mL per day
Working: 125 ÷ 125 × 5 = 5 mL per dose. 5 × 4 = 20 mL per day.
Question 2
A fictional 9-year-old is prescribed 250 mg four times a day for 7 days, using the 250 mg/5 mL liquid. What total volume is needed for the course?
Show the answer
Answer: 140 mL
Working: 250 ÷ 250 × 5 = 5 mL per dose. 5 × 4 × 7 = 140 mL.
Question 3
A fictional adult prescription specifies 500 mg four times a day for 10 days, using 500 mg tablets. How many tablets are needed?
Show the answer
Answer: 40 tablets
Working: 1 × 4 = 4 tablets per day. 4 × 10 = 40 tablets.
NHS: How and when to take phenoxymethylpenicillin
https://www.nhs.uk/medicines/phenoxymethylpenicillin/how-and-when-to-take-phenoxymethylpenicillin/
Where marks are lost
- Using a remembered strength or schedule instead of the stated product.
- Reporting a daily total when the question asks for one dose or the 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 quantity calculation justify a formulation switch?
No. Follow the formulation and prescription in the exercise. Real switches and dose changes 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.
Practise until the method is automatic
Try 15 free questions with worked answers. No sign-up required.
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See also the formula sheet, the eight sample questions and the approved calculator page.