Common Registration Assessment, Part 1
Co-amoxiclav tablet courses and liquid shelf life 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 describes a usual co-amoxiclav dose of 1 tablet, either 375 mg or 625 mg, taken 3 times a day, with doses at least 4 hours apart. A course usually lasts 5 to 14 days.
The pharmacy-made liquid is kept in the fridge and must not be stored or used for longer than 7 days from the date it was made up. Shelf-life arithmetic never extends that limit.
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 prescription specifies co-amoxiclav 625 mg, 1 tablet 3 times a day for 7 days. How many tablets are needed?
Show the answer
Answer: 21 tablets
Working: 1 × 3 = 3 tablets per day. 3 × 7 = 21 tablets.
Question 2
A fictional prescription specifies co-amoxiclav 625 mg, 1 tablet 3 times a day. What is the total daily amount, in mg and in g?
Show the answer
Answer: 1875 mg (1.875 g)
Working: 625 × 3 = 1875 mg. 1875 ÷ 1000 = 1.875 g.
Question 3
A pharmacy makes up a co-amoxiclav liquid on 6 April. The NHS limit is 7 days from the date it was made up. What is the last day it can be used?
Show the answer
Answer: 13 April
Working: 6 + 7 = 13, so 13 April is 7 days after 6 April. The liquid must not be used after that date.
NHS: How and when to take co-amoxiclav
https://www.nhs.uk/medicines/co-amoxiclav/how-and-when-to-take-co-amoxiclav/
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.