Common Registration Assessment, Part 1
Metronidazole tablet strengths and course quantities for the GPhC assessment
Three original practice questions, with the working shown. Read the stated prescription or plan before calculating.
Published 21 October 2026. Independent revision material, not GPhC questions, not for patient care.
The BNF lists metronidazole tablets in three strengths: 200 mg, 400 mg and 500 mg.
The BNF gives a usual adult dose for many anaerobic and skin infections as 400 mg every 8 hours, which is three times a day.
Each question fixes the values needed for its arithmetic. Write the unit beside every step and keep a single dose separate from a supply total. All prescriptions and patients here are fictional; these are revision materials, not for patient care.
The method
- Identify the exact strength, dose and frequency supplied in the question.
- Calculate one dose first; divide prescribed mg by mg per tablet.
- Apply the stated frequency: every 8 hours is three doses a day.
- Scale to the stated course length only when a supply is requested.
- Check the tablet count is a whole number before reporting 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 metronidazole 400 mg three times a day using 400 mg tablets for 7 days. How many tablets is the course?
Show the answer
Answer: 21 tablets
Working: 400 ÷ 400 = 1 tablet per dose. Three times a day is 3 tablets a day. 3 × 7 = 21 tablets.
Question 2
A fictional prescription specifies metronidazole 400 mg three times a day using 200 mg tablets for 5 days. How many tablets is the course?
Show the answer
Answer: 30 tablets
Working: 400 ÷ 200 = 2 tablets per dose. Three times a day is 6 tablets a day. 6 × 5 = 30 tablets.
Question 3
A fictional prescription specifies metronidazole 400 mg three times a day using 400 mg tablets for 14 days. How many tablets is the course?
Show the answer
Answer: 42 tablets
Working: 400 ÷ 400 = 1 tablet per dose. Three times a day is 3 tablets a day. 3 × 14 = 42 tablets.
Exam approach
Frequency conversions cause most errors here. Turn every 8 hours into three doses a day before multiplying by the course length.
Where marks are lost
- Counting one dose a day when the question says three times a day.
- Mixing up the 200 mg, 400 mg and 500 mg strengths when the strength is stated in the question.
- Reporting a daily total 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.
Do I need to memorise the strengths?
The exercise supplies them. In the assessment, read any given product information exactly as written.
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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