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Objective To evaluate the cost utility of interferon beta-1b in secondary progressive multiple sclerosis.
Design Population based cost utility model (healthcare perspective). Data on use of health services were obtained from case records and routine morbidity data and utility values from a EuroQol survey. Local and published costs were used. Effectiveness was modelled using data on relative risk reductions from a randomised trial of interferon beta-1b.
Setting Tayside region, 1993-5.
Subjects 132 ambulatory people with secondary progressive multiple sclerosis.
Main outcome measures Cost per quality adjusted life year (QALY) gained. Rate of relapse and proportion becoming wheelchair dependent over three years.
Results The number needed to treat for 30 months to delay time to wheelchair dependence in one person by nine months was 18 (95% confidence interval 5 to 26). For every 18 people treated for 30 months, six relapses would be prevented, gaining 0.397 discounted QALYs. The cost per QALY gained was 1 024 667 [pounds sterling] (276 466 [pounds sterling] to 1 485 499 [pounds sterling]). If treatment was restricted to patients attending neurology services, the number needed to treat was 14 (cost per QALY gained 833 514 [pounds sterling] (161 358 [pounds sterling] to [infinity])). The cost per QALY gained was not sensitive to changes in cost which took account of a societal perspective.
Conclusions The cost per QALY gained from interferon beta is high because of the high drug cost and modest clinical effect. Resources could be used more efficiently elsewhere.
Interferon beta is the first treatment to alter the natural course of relapsing-remitting multiple sclerosis.[1-3] In a recent trial involving 718 people the drug was also shown to modify the secondary progressive form of the disease, reducing relapse rates over a 30 month follow up. Furthermore, the proportion of interferon beta-1b recipients who became wheelchair dependent was reduced by 32%, and this benefit lasted for nine months. A lack of effect on progression of disability was mooted as a reason for not making interferon beta-1b (which costs over 9600 [pounds sterling] a year for each patient) more widely available to patients with relapsing-remitting multiple sclerosis in the United Kingdom. The disease course is different in secondary progressive multiple sclerosis, so evidence from trials in relapsing-remitting multiple sclerosis cannot be extrapolated to patients with secondary progressive disease.
The results of the recent trial in secondary progressive multiple sclerosis will increase demand for interferon beta-1b, placing further pressure on limited budgets. As resources are limited, spending on treatments such as interferon beta means foregoing benefits from other forms of care--this is known as the opportunity cost. To allow comparison of the relative merits of alternative options we conducted a cost utility analysis of treatment with interferon beta-1b in secondary progressive multiple sclerosis based on the benefits shown in the recent trial (box).
We compared the effect of treating a cohort of people with secondary progressive multiple sclerosis with interferon beta for 30 months against existing best practice without interferon beta. Ideally, we would have used effectiveness data derived from a meta-analysis of clinical trials, but only one completed trial exists with data in the public domain. Therefore, our model represents a best case scenario based on current knowledge (box). We estimated the costs and benefits of a programme of treatment in sufficient people to postpone wheelchair dependence in one person. Although we took a health service perspective, we allowed for a societal perspective through use of sensitivity analysis.
We aimed to identify all patients with multiple sclerosis in Tayside in order to have a representative cohort. Residents of Tayside region (population 395 600) with multiple sclerosis were identified from four sources (neurology department records, visual evoked response requests, Scottish morbidity records, and a survey of the region's general practitioners). Diagnosis was confirmed from hospital or primary care case records. Capture-recapture methods indicate that our point estimate of prevalence on 1 September 1996 was 94% complete. Using accepted definitions, we identified people with secondary progressive disease on the basis of the most recent information in their case records.
Patients who had diagnosed secondary progressive disease on 1 January 1993 formed the cohort for this study (population cohort). To explore the effect of limiting prescription to ambulatory patients with more active disease, a subset of the population cohort who were either admitted to the neurology unit or referred to neurology outpatient clinics at Tayside hospitals during January 1993 to June 1993 were identified (neurology subset). In Tayside, people with secondary progressive multiple sclerosis are not routinely followed up but are referred to the outpatient clinic for specialist management of new problems such as relapses or other chronic symptoms. All of the cohort was followed up until 31 December 1995.
Relapse rates and wheelchair dependence
We used the same definitions of relapse as the clinical trial. Admissions for treatment of a relapse and the year in which patients became wheelchair dependent were identified from hospital case records. …