3.3 An example of how QALYs are calculated.
| With treatment A | With treatment B |
|---|---|
| Estimated survival = 12 years | Estimated survival = 10 years |
| Estimated quality of life = 0.7 | Estimated quality of life = 0.5 |
| QALYs = 8.4 (12 × 0.7) | QALYs = 5 (10 × 0.5) |
| QALY gain from treatment QALYs (8.4 − 5) A over treatment B = 3.4 | |
If treatment A costs £10 000 more than treatment B, then the cost per QALY gained with treatment A is £2 941 (£10 000/3.4). If the cost per QALY is less than a stated threshold value, it would be considered a cost‐effective treatment.
Sensitivity analysis
As has been discussed, pharmacoeconomics is not an exact science and the assessment of cost‐effectiveness requires a number of assumptions and/or extrapolations to be made. A good analysis should test the effect of varying these assumptions across a range of likely possibilities, showing which assumptions are the main drivers of the ICER – this is known as sensitivity analysis.
In a simple analysis, this can be done by varying assumptions one at a time (univariate analysis). For example, if the estimated survival with treatment A is only 10 years (i.e. we take away the survival gain), then the QALY gain falls to 2 QALYs (10 × 0.7 = 7; 10 × 0.5 = 5, QALY gain = 7 − 5) – the ICER is now £5 000 (£10 000/2) which remains within usual cost‐effectiveness limits. The survival gain, which may be based on extrapolation from the clinical trial, is not essential for the drug to be considered cost‐effective. The utility values could be varied similarly.
In a more complex model involving multiple health states and more complex costs and benefits, it may be more appropriate to vary all the parameters at once across a range of likely values, giving a large number of possible ICERs reflecting different combinations of assumptions. This multivariate approach is often called probabilistic sensitivity analysis as it shows a range of possible ICERs with an estimate of the likelihood of the actual ICER being below any specified threshold value.
Pharmacoeconomics and decision‐making
Pharmacoeconomics and cost‐effectiveness assessment alone do not lead to decisions about which drug interventions a healthcare system should use. The economic assessment provides a structured, objective method to compare the costs and benefits of different possible interventions, but this may only be part of the decision‐making process. While an approach based purely on economic assessment might offer the greatest efficiency in a healthcare system, other factors, such as a desire to see equality of access to treatments or a desire to favour specific patients groups (e.g. children, or patients nearing the end of their life), may lead decision makers to adopt treatments with ICERs above the normal threshold (or reject treatments with ICERs below the normal threshold).
These difficult issues are ultimately matters of judgement rather than calculation, but the economic assessment at least provides useful background to the decision and reveals the extent to which efficiency is being sacrificed to the specific wishes of the healthcare system. While pharmacoeconomics clearly has its limitations, it offers the best available approach to underpinning the difficult decisions which scarcity and choice demand in increasingly cash‐limited healthcare systems worldwide.
REFERENCES
1 Drummond MF, Sculpher MJ, Claxton K, Torrance GW and Stoddart GL. Methods for the Economic Evaluation of Health Care Programmes, 4th Edn, 2015. Oxford University Press, Oxford
2 Gani R, Giovannoni G, Bates D, et al. Cost‐effectiveness analyses of natalizumab compared with other disease modifying therapies for people with highly active relapsing remitting multiple sclerosis. Pharmacoeconomics 2008; 26:616–627
3 Karnon J, Holmes MW, Williams R, et al. A cost utility analysis of clopidogrel in patients with ST elevation acute coronary syndrome. Int J Cardiol 2008; 140:315–322
4 Kendrick T, Chatwin J, Downick C, et al. Randomised controlled trial to determine the clinical effectiveness and cost‐effectiveness of selective serotonin reuptake inhibitors plus supportive care for mild to moderate depression and somatic symptoms in primary care. Health Technol Ass 2009; 13:22
5 Latimer N, Lord J, Grant R, et al. Cost‐effectiveness of COX 2 selective inhibitors and traditional NSAIDs alone or in combination with a proton pump inhibitor for people with osteoarthritis. BMJ 2009; 339:2538–42
6 Rogers G, Garside R, Mealing S, et al. Carmustine implants for the treatment of newly diagnosed high grade gliomas. Pharmacoeconomics 2008; 26:33–44
4 Practical prescribing
Most doctors will prescribe drugs on a daily basis. Approximately 640 million prescriptions are written in the UK annually, equivalent to 10 prescriptions per year for each member of the UK population. Although perceived as a routine and mundane component of the work of most clinicians, the process of good prescribing requires significant skill and care and should not be undertaken without due thought and consideration. Good prescribing involves the recommendation of the correct dose and formulation of an appropriate drug, accompanied by clear instruction regarding when, how and for how long it should be taken. A prescription should be written only when in possession of adequate clinical information about the patient and the symptoms, and ideally following solicitation of the patient's preferences and discussion of alternative treatment strategies. The need for thorough training in the skill of prescribing is highlighted by the high frequency with which drugs are prescribed at the wrong dose, through the wrong route or for the wrong condition. The likelihood of patient injury occurring as a result of a drug error has been estimated at approximately 3% per inpatient stay, an error rate that would not be tolerated by major airlines handling passengers' baggage, and surely not acceptable in modern hospitals given the potential severity of the consequences. This chapter reviews the components of good prescribing practice and discusses the pitfalls inherent in the process.
Good prescribing: questions to ask yourself before prescribing a drug
Is drug treatment really necessary?
It is obvious that while appropriate drug therapy can be of great benefit, inappropriate therapy is not harmless. On all occasions, there should be a positive reason for prescribing a drug. Drug treatment should never become a routine. In hospital, it is still not uncommon to find ‘routine’ prescriptions for hypnotics, analgesics and purgatives without any consideration of individual need. Many patients may expect a consultation to result automatically in the prescription of a medicine, the provision of unnecessary antibiotic therapy for a viral illness being a common example. These situations are clearly undesirable and represent bad prescribing practice.
Which drug should I choose?
When drug treatment is indicated, it is mandatory that the most appropriate agent is given in the correct dose and in a regimen that results in optimum treatment with minimum adverse effects. Selection of the best drug requires consideration of factors that relate not only to the range of drugs available, but also to both the patient and the condition being treated. Age and disease may influence kinetics and dynamics to a significant degree and should be reflected in the choice of agent. Choosing the
