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GPhC registration exam: Tackling health economics and quantities

What is the best method to approach pharmacoeconomic calculation questions?

In parts of the General Pharmaceutical Council registration exam about health economics, the most common types of pharmacoeconomic evaluation questions include cost minimisation, cost effectiveness, cost utility and cost benefit calculations. As with any other pharmaceutical calculations, the starting point is understanding the key concepts and formulas behind each calculation, then applying these to your given question.

After this, you need to practise a variety of questions with different styles and identify your errors. It gets better with more practise, but if you continue noticing errors, please check that you have understood all the key concepts.

Below are five worked examples. However, please feel free to use a method that works best for you and, as always, we are happy to hear your feedback.

For more worked example calculations, try our calculation questions, including extended matching calculation questions and dilution and compounding calculation questions.

Question 1: Quantities to supply

A 60-year-old man weighing 77kg is due to commence treatment with Drug X at the following dosing; initially 160mg, dose can alternatively be given as divided injections over 2 days, then 80mg after 2 weeks, then 40mg every 2 weeks for 4 weeks; maintenance 40mg every 2 weeks for 26 weeks. Drug X is available as 2 x 0.8mL pre-filled syringes containing 50mg/mL and costing £633.60 for a packet with 2 pre-filled syringes.

How many pre-filled syringes would you dispense to fulfil this prescription? Give your answer to the nearest whole number.

 

Click here for the comments, working out and answer

It is important to accurately follow the dosing information and duration because any misreading can make your calculation incorrect. Decide what information in the question you are going to use because sometimes not all information provided is relevant. In this case, you only need to note the doses, prefilled syringe sizes and strength, and the other information given is not required. Tabulating the dosing regimen, volume and number of syringes needed may make things much clearer. Now, proceed as follows:

Dose stated is: ‘initially 160mg, dose can alternatively be given as divided injections over 2 days, then 80mg after 2 weeks, then 40mg every 2 weeks for 4 weeks; maintenance 40mg every 2 weeks for 26 weeks’.

Calculate the volume that corresponds to each dose and the number of pre-filled syringes that corresponds to it as follows:

For 160mg, volume needed = 160mg/(50mg/ml) = 3.2mL;

Number of pre-filled syringes corresponding to 3.2mL = 3.2mL/ (0.8mL/syringe) = 4 syringes;

For 80mg, volume needed = 80mg/(50mg/mL) = 1.6mL;

Number of pre-filled syringes corresponding to 1.6mL = 1.6mL/ (0.8mL/syringe) = 2 syringes;

For 40mg, volume needed = 40mg/(50mg/mL) = 0.8mL;

Number of pre-filled syringes that correspond to 0.8mL = 0.8mL/ (0.8mL/syringe) = 1 syringe;

Start dose is 160mg = 4 pre-filled syringes;

After 2 weeks, it is 80mg = 2 pre-filled syringes;

After 2 weeks dose is 40mg every 2 weeks for 4 weeks = 2 pre-filled syringes

26 weeks at 1 pre-filled syringe every 2 weeks = 13 pre-filled syringes;

Total = 4 + 2 + 2 + 13 = 21 syringes.

Final answer = 21 syringes.

 

Question 2: Calculation of fees

Your pharmacy has started running a supervised consumption scheme for methadone and buprenorphine. The proposed fee structure is as follows; £52.68 per month per patient on 3 or more supervisions per week; £31.79 per month per patient on 2 or less supervisions per week; £0 for unsupervised patients. You have: 5 patients on daily supervised consumption Monday to Saturday; 5 patients on supervised consumption Monday, Wednesday and Friday; 5 patients on supervised consumption on Mondays only.

What fees in pounds (£) will the pharmacy receive each month? Give your answer to the nearest £1.

 

Click here for the comments, working out and answer

This is a straightforward question that requires you to accurately use the information provided. You could proceed as follows with your calculations:

10 patients on 3 or more supervisions = £52.68 x 10 = £526.80/month;

5 patients on 2 or less supervision per week = £31.79 x 5 = £158.95/month;

Total fees = £526.80 + £158.95 = £685.75 = £686 to the nearest pound/month.

Final answer = £686.

 

Question 3:

Anti-cancer Drug A costs £6,000/year and increases life expectancy by 6 years and the patient would expect a utility weight of health state of 0.6 for each year. A new anti-cancer Drug B costs £7,000/year and a patient would expect a life expectancy of 7 years and a utility weight of health state of 0.7 each year.

Calculate the incremental cost-effective ratio (ICER)/Quality Adjusted Life Years (QALY)? Give your answer to the nearest whole number.

Formula: Incremental cost-effective ratio (ICERs)/Quality Adjusted Life Years (QALY) = (cost of B - cost of A)/(QALY of B - QALY of A)

 

Click here for the comments, working out and answer

All the information you need including the formula is provided. Proceed as follows:

For Drug A;

QALY = 0.6 x 6 = 3.6;

Cost for 6 years = 6 x £6,000 = £36,000 

For Drug B;

QALY = 0.7 x 7 = 4.9;

Cost for 7 years = 7 x £7,000 = £49,000,

Incremental cost = £ 49,000 - £36,000 = £13,000;

Incremental QALYs = 4.9 - 3.6 = 1.3

ICER/QALY = (13,000)/(1.3) = £10,000/QALY.

Final answer:  £10,000/QALY.

 

Question 4:

You are the pharmacist prescriber at a gastroenterology department in a hospital. You are in the process of switching a 50-year-old man weighing 67kg from Drug A to Drug B. Drug A dosing: 1.5mg/kg daily; Drug A is available as 50mg tablets @ £34.39 for 50 tablets. Drug B dosing: initially 5mg/kg, then 5mg/kg to be taken at week 2 and 6 after initial dose, then maintenance 5mg/kg every 8 weeks for 26 weeks; Drug B is available as 120mg/1ml vial @ £755.32 per 1mL vial.

What is the difference in price in pounds (£) for switching treatment from Drug A to Drug B for a period of 6 weeks? Give your answer to the nearest £1.

 

Click here for the comments, working out and answer

You should break down your calculation into 2 parts, ie costs for Drug A and costs for Drug B. In doing so, you should decide what information is relevant. Pertinent information here includes: the patient’s weight (67kg), dosing for both drugs, duration, vial sizes, concentrations, strengths and costs. Now, proceed as follows:

Drug A costs calculation:

Drug A dosing = 1.5mg/kg x 67kg = 100.5mg/day = 100.5mg/(50mg/tablet) rounded to 2 tablets daily;

For 6 weeks you need 2 tabs/day x 7days/week x 6 weeks = 84 tablets;

Cost = £34.39/50 x 84 = £57.78;

Drug B costs calculation:

Drug B dose = initially 5 mg/kg, then 5 mg/kg, to be taken at week 2 and 6 after initial dose, then 5 mg/kg every 8 weeks for 26 weeks;

5mg/kg x 67kg = 335mg;

335mg/(120mg/1mL) = 2.79mL

2.79mL /(1mL/Vial) = 2.79 vials rounded to 3 x 1mL vials,

Therefore, you would need 3 vials to deliver the dose and discard any remainder.

For 6 weeks’ treatment, you would need: 

3 vials initially; 3 vials at week 2; 3 vials at week 6;

Total vials needed = 9;

Cost = 9 x £755.32 = £6,797.88;

Rise in cost = £6,797.88 - £57.7752 = £6,740.10 = £6,740 to the nearest £1.

Final answer = £6,740

 

Question 5:

A 60-year-old woman is currently taking dexamethasone orally, 12mg once daily and uses the 2mg strength tablets. She is due to be changed to oral prednisolone using the 5mg strength tablets. A packet of 28 x prednisolone 5mg tablets costs £0.97, and a packet of 50 x dexamethasone 2mg tablets costs £8.82.

Calculate the percent (%) savings in cost for switching from dexamethasone to prednisolone per daily dose. Give your answer to the nearest whole number.

Conversion: Prednisolone oral 5mg = Dexamethasone oral 750micrograms.

 

Click here for the comments, working out and answer

This question is testing – among other competencies – your knowledge of unit conversions (microgram to milligram), using proportions, working out equivalent steroid doses, calculating percentages (%) and knowledge of rounding rules. You should proceed as follows:

1.Conversion

Prednisolone oral 5mg = Dexamethasone oral 750micrograms (or 0.75mg);

X prednisolone = 12mg dexamethasone; Using proportions,

X/12 = 5/0.75;

X = 12x5/0.75 = 80mg prednisolone per dose.

Number of prednisolone tablets = 80mg/(5mg/tablets) = 16 tablets per dose.

Dexamethasone dose = 12mg/day,

Number of tablets per dose = 12mg/(2mg/tablet) = 6 tablets per dose.

2.Costs and savings

From above, you are effectively comparing the drop in cost as a (%) from using 6 dexamethasone tablets to using 16 prednisolone 5mg tablets.

Cost for 6 x dexamethasone 2mg tablets = (£8.82/50) x 6 = £1.0584;

Cost of 16 x 5mg tablets prednisolone = (£0.97/28) x 16 = £0.554285714,

Savings as a % = (£1.0584 - £0.554285714)/£1.0584 x 100% = 47.6% = 48% to the nearest whole number.

Final answer = 48%

 

As you have seen from the examples above, it is important to read the question fully in order to pick up all the important information you need to perform your calculations. We cannot emphasise enough the importance of knowing the conversion of units and an appreciation of rounding, as these were tested in all these questions. As highlighted earlier, get to know the underlying principles and concepts for each calculation topic by consulting relevant sources.

For a good introduction to the topic, please consult the relevant reference sources eg Essentials of Pharmacoeconomics Health Economics and Outcomes Research by Karen L. Rascati (author) Third edition (2020).

Authors:

Luso Kumwenda: MSc Community Pharmacy (Cardiff), B Pharm Hons (Zimbabwe), independent prescriber, MRPharms, mentor at UK Black Pharmacist Association and the Royal Pharmaceutical Society

Professor David R. Katerere: PhD Pharmaceutical Science (Strathclyde), Tshwane University of Technology, platform research chair – Pharmaceutical and Biotech Advancement and Development in Africa (PbADA)

Acknowledgements: The questions were kindly provided by: Focus Pre-Reg Revision

Disclaimer: The questions and explanations presented here are for educational purposes only and do not replace your training, knowledge and application of professional judgement as a pharmacist or pre-reg or prov-reg pharmacist. The views in this article are our own and do not represent the views of any organisations we are associated with.

This article was peer reviewed by Kate McComiskey, PhD MPSNI

 

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