Common Registration Assessment, Part 1

Linezolid 600 mg twice-daily course supply for the GPhC assessment

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

Published 13 November 2026. Independent revision material, not GPhC questions, not for patient care.

Yellow tablets poured from a brown medicine bottle onto a surface
Photo from Pexels, used under the Pexels licence. It is a stock image and does not show the exercise.

The manufacturer's UK product information for linezolid 600 mg film-coated tablets gives 600 mg twice daily for adults.

The same information states that the duration of treatment depends on the pathogen, the site and severity of infection and the clinical response, and that the maximum treatment duration is 28 days.

It also states that linezolid has an oral bioavailability of approximately 100%, so no dose adjustment is needed when switching between intravenous and oral dosing.

Each question fixes the values needed for its arithmetic. Count tablets per 12-hourly dose and keep the 28-day maximum in view. All prescriptions and patients here are fictional; these are revision materials, not for patient care.

The method

  1. Start from 600 mg every 12 hours: one 600 mg tablet per dose.
  2. Multiply by two doses per day for daily totals.
  3. Multiply by the stated course length in days for the course supply.
  4. Check the course length against the printed 28-day maximum.

Three practice questions

Work each one on paper first, then open the answer. All patients and prescriptions are fictional.

Question 1

A fictional adult is prescribed linezolid 600 mg every 12 hours for 10 days. How many 600 mg tablets are needed for the whole course?

Show the answer

Answer: 20 tablets

Working: 600 mg every 12 hours is two doses a day, one tablet per dose. 2 x 10 = 20 tablets.

Question 2

A fictional adult is prescribed linezolid 600 mg every 12 hours for 14 days. How many tablets is that, and what is the total amount of linezolid in mg?

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Answer: 28 tablets; 16,800 mg in total

Working: 2 x 14 = 28 tablets. Each tablet is 600 mg, so 28 x 600 = 16,800 mg.

Question 3

A fictional patient switches from intravenous linezolid 600 mg every 12 hours to the tablets. What oral dose replaces it, and what is the longest course the product information allows?

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Answer: 600 mg orally every 12 hours; 28 days

Working: Because oral bioavailability is approximately 100%, the switch keeps the same 600 mg every 12 hours with no dose adjustment. The printed maximum treatment duration is 28 days.

eMC SmPC: Linezolid 600 mg Film-coated Tablets

https://www.medicines.org.uk/emc/product/2006/smpc

Where marks are lost

  • Treating the dose as once daily when it is every 12 hours.
  • Extending the course past the printed 28-day maximum.
  • Adding an unnecessary dose change when switching between intravenous and oral forms.

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 dose?

No. Follow the stated prescription in the exercise. Real dosing follows the prescriber and the product information for the named product.

How should I check the answer?

Count one 600 mg tablet per 12-hourly dose, double for the day, multiply by the stated days, and check against the 28-day maximum.

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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More calculation topics

See also the formula sheet, the eight sample questions and the approved calculator page.