Common Registration Assessment, Part 1
Desmopressin 0.1mg and 0.2mg tablets and divided daily doses for the GPhC assessment
Three original practice questions, with the working shown. Read the stated prescription or plan before calculating.
Published 7 November 2026. Independent revision material, not GPhC questions, not for patient care.
The manufacturer's UK product information for desmopressin 0.1 mg tablets, for the treatment of diabetes insipidus, states that the total daily dose normally lies in the range of 0.2 to 1.2 mg, and that a suitable starting dose in adults and children is 0.1 mg three times daily.
The same information states that the dose should then be adjusted according to the patient's response, and that for the majority of patients the maintenance dose is 0.1 mg to 0.2 mg three times daily.
Each 0.1 mg tablet contains 100 micrograms of desmopressin. The stated range of 0.2 to 1.2 mg is a total daily amount given in divided doses, so milligrams, micrograms and tablet counts all need separating.
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 a supply period. All prescriptions and patients here are fictional; these are revision materials, not for patient care.
The method
- Identify the stated single dose and the number of doses each day.
- Convert between milligrams and micrograms before dividing by the tablet strength.
- Multiply the daily tablet count by the stated number of days for a supply quantity.
- Keep milligrams, micrograms and tablets separate; convert only when the question asks.
Three practice questions
Work each one on paper first, then open the answer. All patients and prescriptions are fictional.
Question 1
A fictional patient takes desmopressin 0.2 mg three times daily. How many micrograms is this each day?
Show the answer
Answer: 600 micrograms
Working: 0.2 mg = 200 micrograms. 200 micrograms x 3 doses = 600 micrograms each day.
Question 2
A fictional patient starts desmopressin 0.1 mg three times daily using 0.1 mg tablets. How many tablets are needed for 28 days?
Show the answer
Answer: 84 tablets
Working: 0.1 mg / 0.1 mg per tablet = 1 tablet per dose. 1 tablet x 3 doses = 3 tablets each day. 3 tablets x 28 days = 84 tablets.
Question 3
A fictional patient takes the top of the stated daily range, 1.2 mg in divided doses, using 0.2 mg tablets. How many tablets is this each day?
Show the answer
Answer: 6 tablets
Working: 1.2 mg / 0.2 mg per tablet = 6 tablets each day.
eMC SmPC: DDAVP Tablets 0.1mg
https://www.medicines.org.uk/emc/product/1285/smpc
Where marks are lost
- Mixing milligrams and micrograms: 0.2 mg is 200 micrograms, not 200 milligrams and not 2 micrograms.
- Multiplying by the stated daily range instead of the actual dose in the prescription.
- Reporting a per-dose tablet count when the question asks for the whole course, or the other way round.
Frequently asked questions
Are these official assessment questions?
No. They are original revision exercises, not official GPhC questions and not for patient care.
Does this calculation decide a real desmopressin dose?
No. Follow the stated prescription in the exercise. Real dosing is adjusted to the patient's response within the stated daily range, and fluid intake is monitored.
How should I check the answer?
Check the requested unit first, converting milligrams to micrograms before counting tablets or days.
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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