Common Registration Assessment, Part 1

Timolol eye drop strengths and drops per day for the GPhC assessment

Three original practice questions, with the working shown. Read the stated prescription or plan before calculating.

Published 1 November 2026. Independent revision material, not GPhC questions, not for patient care.

Doctor applying eye drops for an elderly patient
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The NHS describes timolol eye drops as a beta blocker medicine used to lower pressure inside the eye.

The manufacturer's UK product information lists 0.25% and 0.5% drops, with a usual dose of one drop twice a day and the possibility of once daily maintenance.

Drop counts drive bottle supply: treating both eyes doubles the daily drop count, and a stated drops-per-ml figure converts a bottle size into days of use.

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

  1. Identify the stated strength, the number of treated eyes and the daily frequency.
  2. Multiply drops per dose by doses per day and by the number of eyes treated.
  3. Use the stated drops per ml to convert a bottle volume into a drop count.
  4. Divide the bottle's drop count by the daily drops to find how many days it lasts.
  5. Keep drops, millilitres and milligrams separate; convert only if 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 uses one drop of timolol twice a day in one eye. Taking a 5 ml bottle as 100 drops, how many days does one bottle last?

Show the answer

Answer: 50 days

Working: 1 drop x 2 doses = 2 drops a day; 100 drops / 2 drops = 50 days.

Question 2

A fictional patient uses one drop of timolol twice a day in both eyes. Taking a 5 ml bottle as 100 drops, how many days does one bottle last?

Show the answer

Answer: 25 days

Working: 1 drop x 2 doses x 2 eyes = 4 drops a day; 100 drops / 4 drops = 25 days.

Question 3

Timolol 0.5% eye drops contain 0.5 g in every 100 ml. How many milligrams of timolol are in a 5 ml bottle?

Show the answer

Answer: 25 mg

Working: 0.5 g in 100 ml = 500 mg in 100 ml = 5 mg in 1 ml; 5 mg x 5 ml = 25 mg.

NHS: Timolol eye drops

https://www.nhs.uk/medicines/timolol-eye-drops/

Where marks are lost

  • Forgetting to double the drop count when both eyes are treated.
  • Reading 0.5% as 5 mg per ml without writing out the conversion.
  • 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.

Why does the question state the drops per ml?

Drop size varies by bottle design. When a drops-per-ml figure is stated, use it exactly as given.

How should I check the answer?

Check the requested unit, then work backwards from the bottle size to the stated drops per day.

Sources

The questions above are original and use fictional patients and prescriptions. PreRegExamPrep is not affiliated with or endorsed by the General Pharmaceutical Council.

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