Common Registration Assessment, Part 1
Warfarin tablet strengths and daily doses 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 warfarin tablets in four strengths with distinct colours: 0.5 mg white, 1 mg brown, 3 mg blue and 5 mg pink. A daily dose may combine different colours. It also describes a liquid where 1 mL equals a 1 mg tablet.
The usual adult dose starts at 10 mg a day for the first 2 days, then settles between 3 mg and 9 mg a day. Doses change with blood test results, so only a prescribed dose belongs in a calculation.
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 warfarin 7 mg once daily. Tablets of 5 mg, 3 mg, 1 mg and 0.5 mg are available. What is the fewest number of tablets that makes one dose?
Show the answer
Answer: 3 tablets
Working: One 5 mg tablet plus two 1 mg tablets: 5 + 1 + 1 = 7 mg, using 3 tablets. A 3 mg tablet cannot reduce the count: 5 + 3 = 8 mg and 3 + 3 + 1 = 7 mg also needs 3 tablets.
Question 2
A fictional schedule specifies warfarin 10 mg once daily for the first 2 days, using 5 mg tablets. How many tablets are needed for those 2 days in total?
Show the answer
Answer: 4 tablets
Working: 10 ÷ 5 = 2 tablets per day. 2 × 2 = 4 tablets over 2 days.
Question 3
A fictional prescription specifies warfarin 4.5 mg once daily using the liquid, where 1 mL equals a 1 mg tablet. What volume is one dose?
Show the answer
Answer: 4.5 mL
Working: 1 mL equals 1 mg, so 4.5 ÷ 1 = 4.5 mL.
NHS: How and when to take warfarin
https://www.nhs.uk/medicines/warfarin/how-and-when-to-take-warfarin/
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.