Common Registration Assessment, Part 1
Digoxin microgram tablets 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 BNF lists digoxin tablets of 62.5 micrograms, 125 micrograms and 250 micrograms. The NHS describes a usual daily dose for adults and children over 10 years of 125 micrograms to 250 micrograms, after any initial dose.
Doses are usually lower for older people and for people with kidney disease. A total that falls inside a printed range is not evidence a dose suits any person.
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 digoxin 187.5 micrograms once daily, using 125 microgram and 62.5 microgram tablets. Which tablets make one dose, and how many is that?
Show the answer
Answer: One 125 microgram tablet and one 62.5 microgram tablet, 2 tablets in total
Working: 125 + 62.5 = 187.5 micrograms, so 2 tablets.
Question 2
A fictional prescription specifies digoxin 125 micrograms once daily for 7 days. What is the total weekly amount, in micrograms and in mg?
Show the answer
Answer: 875 micrograms (0.875 mg)
Working: 125 × 7 = 875 micrograms. 875 ÷ 1000 = 0.875 mg.
Question 3
A fictional prescription specifies digoxin 250 micrograms once daily, but only 62.5 microgram tablets are available. How many tablets make one dose?
Show the answer
Answer: 4 tablets
Working: 250 ÷ 62.5 = 4 tablets. The 250 microgram strength would need 1 tablet, so the label matters.
NHS: How and when to take digoxin
https://www.nhs.uk/medicines/digoxin/how-and-when-to-take-digoxin/
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.
More calculation topics
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See also the formula sheet, the eight sample questions and the approved calculator page.