Common Registration Assessment, Part 1

Teriparatide daily injection doses and pen supply for the GPhC assessment

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

Published 10 November 2026. Independent revision material, not GPhC questions, not for patient care.

A person checking a prepared syringe before a daily injection
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 Forsteo (teriparatide) states that the recommended dose is 20 micrograms administered once daily by subcutaneous injection in the thigh or abdomen, and that the maximum total duration of treatment is 24 months, which should not be repeated over a patient's lifetime.

The same information states that each pre-filled pen contains 28 doses of 20 micrograms, each dose delivered in 80 microlitres, and that Forsteo is available in pack sizes of 1 or 3 pens.

It also states that patients should receive supplemental calcium and vitamin D if dietary intake is inadequate, and that dosage adjustment based on age is not required in elderly patients.

Each question fixes the values needed for its arithmetic. Write the unit beside every step and distinguish doses from days of supply. All prescriptions and patients here are fictional; these are revision materials, not for patient care.

The method

  1. Read the stated number of doses per pen and the once-daily frequency.
  2. Multiply pens by 28 for the total doses, which equals the days of supply at one dose daily.
  3. Multiply the dose count by 20 micrograms for a total in micrograms.
  4. Keep doses, days, pens and micrograms 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 uses one Forsteo pen at the label dose of 20 micrograms once daily. How many days does one pen last?

Show the answer

Answer: 28 days

Working: Each pen contains 28 doses of 20 micrograms. At one dose daily, 28 doses = 28 days.

Question 2

A fictional patient is dispensed the 3-pen pack of Forsteo. How many doses is that in total, and how many weeks of once-daily treatment does it cover?

Show the answer

Answer: 84 doses; 12 weeks

Working: 3 pens x 28 doses = 84 doses. 84 days / 7 = 12 weeks.

Question 3

A fictional patient uses one Forsteo pen (28 doses of 20 micrograms). What total quantity of teriparatide in micrograms does the pen deliver over its use?

Show the answer

Answer: 560 micrograms

Working: 28 doses x 20 micrograms = 560 micrograms per pen.

eMC SmPC: Forsteo 20 micrograms/80 microlitres solution for injection in pre-filled pen

https://www.medicines.org.uk/emc/product/2215/smpc

Where marks are lost

  • Treating 28 doses as 28 weeks; one dose is used each day, so a pen lasts 28 days.
  • Multiplying pens by 20 micrograms for the pen total; 20 micrograms is one dose and a pen holds 28 doses, so 560 micrograms.
  • Counting 3 pens as 3 weeks of treatment; 3 pens hold 84 doses, which is 84 days or 12 weeks.

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 teriparatide course?

No. Follow the stated supply in the exercise. Real treatment is limited to a single 24-month course over a lifetime, under specialist care.

How should I check the answer?

Multiply pens by 28 doses first, then convert doses to days, weeks or micrograms as the question asks.

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.