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Raeburn B Forbes a Department of Neurology, Ninewells Hospital and
Medical School, Dundee DD1 9SY, b Argyll and Clyde Health
Board, Paisley PA2 7BN, c Scottish Health Purchasing Information Centre, Aberdeen AB15 6RE
Correspondence to: R B Forbes, Department of Neurology, Royal
Victoria Hospital, Belfast BT12 6BA
raeburn.forbes{at}royalhospitals.n-i-nhs.uk
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Abstract |
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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 (£276 466 to
£1 485 499). If treatment was restricted to patients attending
neurology services, the number needed to treat was 14 (cost per QALY
gained £833 514 (£161 358 to
)). 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.
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Key messages
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Introduction |
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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.4 Furthermore, the proportion of interferon beta-1b recipients who became wheelchair dependent was reduced by 32%, and this benefit lasted for nine months.4 A lack of effect on progression of disability was mooted as a reason for not making interferon beta-1b (which costs over £9600 a year for each patient) more widely available to patients with relapsing-remitting multiple sclerosis in the United Kingdom.5 The disease course is different in secondary progressive multiple sclerosis,6 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
sclerosis4 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.7 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).4
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What is cost utility analysis?
The main benefit of a healthcare intervention should be greater
"health." A potential measure of "health" is the quality
adjusted life year (QALY). To calculate a QALY, the duration of health
state (in years) is multiplied by a factor representing the quality
("utility") of that health state. The quality (or utility) value
for economic evaluation is usually derived from a health index. In
health indices, health is rated along an interval scale, where 1 equals
perfect health and 0 represents dead. It is also possible to rate
health states with a negative value Values for the cost per QALY gained across a range of different
interventions can be used to inform resource allocation decisions.
There are arguments for limiting access to interventions which have a
very high cost per QALY, as there may be alternative uses for those
funds which are more efficient |
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Methods |
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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.
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Formula for calculating cost per QALY gained by treatment with
interferon beta-1b in secondary progressive multiple sclerosis
Cost per QALY gained=net cost of treatment/number of QALYs gained where Net cost of treatment=total cost of treatment Total cost of treatment=number needed to treat (NNT)×30 months×unit cost of interferon beta-1b NNT=Number needed to treat to delay time to wheelchair dependence by nine months |
Study population
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.8 Capture-recapture methods
indicate that our point estimate of prevalence on 1 September 1996 was
94% complete.9 Using accepted definitions,6
we identified people with secondary progressive disease on the basis of
the most recent information in their case records.
Relapse rates and wheelchair dependence
We used the same definitions of relapse as the clinical
trial.4 Admissions for treatment of a relapse and the year
in which patients became wheelchair dependent were identified from
hospital case records. Ideally, we would have calculated the proportion
who became wheelchair dependent within 30 months (the same follow up as
the trial4), but the case records lacked detail. Thus the
number needed to treat to delay time to wheelchair dependence could be
an underestimate.
Costs saved by delaying time to wheelchair dependence and
prevention of relapses
We estimated the costs saved by delaying time to wheelchair
dependence by nine months using data from a cost analysis based on
information from 672 members of the Multiple Sclerosis Society of Great
Britain and Northern Ireland (table 1).14 Other estimates
of the cost of multiple sclerosis to the United Kingdom did not have
sufficient detail for our model.
15 16
We identified
resources used during hospital treated relapses in Tayside and valued
them using cost data from local NHS trust finance directorates (Robert
Hudson, personal communication). We distinguished between fixed and
non-fixed costs when costing relapses, but this was not possible for
wheelchair dependence as the study14 lacked that
information. We assumed that each community treated relapse required 20 minutes' consultation with a general practitioner17 and
that untreated relapses did not incur health service costs (although
general practitioner costs may have been incurred). The cost of
corticosteroids was taken from the 1995 British National
Formulary.18 All costs were adjusted to a 1995 price
base using the hospital and community health services price index
(Department of Health, London).
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Calculation of quality adjusted life years
To determine current health we conducted a postal survey of people
with multiple sclerosis in Tayside in Spring 1998 (three years after
the end of follow up) after obtaining permission from general
practitioners. This survey created a baseline from which to estimate
the effect of interferon beta. Respondents indicated their current
level of ambulation on a postal ambulation scale (based on the scale of
McAlpine and Compston19) and completed the EuroQol (EQ-5D)
health related quality of life instrument.20 Responses
from people with secondary progressive multiple sclerosis were
selected. We obtained values for EQ-5D health states from published
social tariffs using mean valuations based on 10 year trade off
values.21 The EQ-5D was chosen as it is simple to complete
and has been extensively tested in UK populations. In an unpublished
survey of 67 Tayside residents we had previously established that that
increasing postal ambulation scale scores accurately identified people
with increasing severity of multiple sclerosis and that appropriate
changes in utility values were occurring.
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Cost utility ratios
Assuming a 32% relative reduction in the proportion of people who
become wheelchair dependent during follow up, we calculated the number
needed to treat22 for 30 months to postpone wheelchair
dependence by nine months for one person; 95% confidence intervals for
the numbers needed to treat were calculated from the 95% confidence
limits for the absolute risk reduction and expressed as number needed
to treat (harm) to number needed to treat (benefit).23 In
our cost utility model, interferon beta-1b cost £800 per patient per
month.18 Other costs associated with interferon beta
treatment were not included as we had no reliable estimate from our
local practice. Using trial data we estimated that 12% of hospital
relapses would be prevented, that corticosteroid use would decrease by
21%, and that 31% of untreated relapses would be
prevented.4 Treatment costs in the second and third years
were discounted at a rate of 6% (UK treasury rate). Upper and lower
limits of the cost utility ratios were estimated using the 95%
confidence intervals of the number needed to treat.
Sensitivity and threshold analyses
A sensitivity analysis explored the effect of (a)
increasing the cost of each additional nine months of wheelchair dependence (taking account of a societal perspective), (b)
changes in the unit cost of interferon beta-1b, (c) changes
in the number of, and discount rate applied to, QALYs gained, or
(d) assuming that the relative reduction in hospital
admission and corticosteroid use was 31% (not 12% or 21%). Assuming
that an acceptable threshold of cost utility would be £10 000 per
QALY gained,24 we determined the changes required to model
variables to breach this threshold. We also performed threshold
analyses at £20 000, £30 000, and £50 000 per QALY gained.
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Results |
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We identified 756 people with multiple sclerosis in Tayside during 1993-5. Of these, 178 had secondary progressive disease, 46 of whom were already wheelchair dependent. There were 132 people in the population cohort, and 17 people in the neurology subset.
Wheelchair dependence
Twenty four (18%) of the population cohort became wheelchair
dependent within 36 months of follow up. We estimated that the number
needed to treat with interferon beta-1b for 30 months to postpone
wheelchair dependence by nine months was 18 (95% confidence interval 5 to 26). Four (24%) of the neurology subset became wheelchair
dependent. The number needed to treat to postpone wheelchair dependence
by nine months in the neurology subset was 14 (number needed to treat
(harm) 9 to
to number needed to treat (benefit) 3).
Relapse rates
We identified 32 admissions for treatment of a relapse in the 36 month follow up period, giving a rate of 0.08 (95% confidence interval
0.06 to 0.11) per patient-year. A total of 56 discrete corticosteroid
episodes were identified in 21 people. Three people had concomitant
bronchodilators prescribed, so their steroids were assumed to be for
asthma. One oral steroid prescription preceded an admission to hospital
for relapse by 15 days; all other episodes of community and hospital
treated relapses were mutually exclusive. The rate of community treated relapses was 0.15 (0.11 to 0.18) per patient-year. In the 30 months to
the end of December 1995, the neurology subset experienced seven
hospital admissions for relapse and four community corticosteroid prescriptions and therefore an estimated 11 untreated relapses.
Quality adjusted life years gained
We sent a postal survey to 569 people with multiple sclerosis, of
whom 402 (71%) returned valid responses. Of these 402, 84 had
secondary progressive disease. Using these 84 responses and a discount
rate of 6% for benefits, treatment of 18 members of the population
cohort and 14 members of the neurology subset for 30 months would
result in a gain of 0.397 and 0.357 QALYs respectively.
Cost utility ratios
Table 3 shows the main values used to calculate the cost utility
ratios. The net cost per QALY gained from interferon beta-1b in
secondary progressive multiple sclerosis was £1 024 393 (95%
confidence interval £276 191 to £1 484 824). For the neurology
subset, the cost per QALY gained was £883 209 (£179 209 to
).
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Sensitivity and threshold analyses
A 190% increase in the cost of each additional nine months of
wheelchair dependence from £2840 to £5153 (which takes account of a
societal perspective) reduced the cost per QALY gained by only 0.2%. A
25% increase in the number of QALYs gained in secondary progressive
multiple sclerosis (to 0.496 discounted QALYs) reduced the cost per
QALY gained in the population cohort by 20% (to £819 514). If the
unit cost of interferon beta-1b was reduced by half to £4800 per
patient a year, the cost per QALY gained fell by 49.4% to £506 407.
If we assumed that 31% of hospital admissions and community treated
relapses were prevented (in the trial 31% of all relapses were
prevented, but only 12% of hospital admissions and 21% of steroid use
was prevented4) the cost per QALY gained was £832 399
(£221 831 to £1 208 133) in the population cohort and £628 797
(£122 079 to
) in the neurology subset. None of the proposed
thresholds could be breached without extreme changes to the model's
variables (table 4).
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Discussion |
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The recent trial showing benefit from interferon beta in secondary progressive multiple sclerosis4 has led to a call for the treatment to be made available immediately to all patients with that form of the disease.25 The Multiple Sclerosis Society of Great Britain and Northern Ireland issued minimum standards of care for people with multiple sclerosis26 and is planning a national campaign to raise the profile of the disease in the United Kingdom.27 Despite the need for improvements in the care of people with multiple sclerosis, our analysis shows that treatment with interferon beta-1b has a significant opportunity cost and resources could probable be used better elsewhere.
Robustness of cost utility model
Studies that take a health service perspective are often
criticised for ignoring social costs of disease. This is particularly
relevant to multiple sclerosis, as healthcare expenditure is typically
15% to 20% of the total cost of the disease.
14 15 28
However, our cost utility ratio was unaffected by changes in the cost
of care, and arguments that interferon beta-1b might have an acceptable
cost utility ratio if social costs were considered29 now
seem implausible. Other countries have estimated similar costs for nine
additional months of severe disability (Belgium: 9200 ecu (£6345)
health and social service perspective30; United States
$2911 (£1712) healthcare perspective31; and Canada
$11 427 (£4395) societal perspective28). This model
should be valid outside the United Kingdom unless the cost of an
additional nine months of wheelchair dependence and six relapses
exceeds £400 000.
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Comparisons with other healthcare interventions
Treatment of secondary progressive multiple sclerosis with
interferon beta-1b is one of the least efficient interventions for
improving health in a population. We identified 104 citations on
Medline using the terms "cost" and "quality adjusted life year"
from 1995 to October 1998. The median cost per QALY from the 128 cost
utility ratios cited was £15 625 (interquartile range £9167 to
£74 969) and only one other study exceeded £1 million per QALY
gained.33 Although comparisons of the cost per QALY gained
may conceal important methodological differences,34
Richards was probably correct to conclude that most competing demands
for healthcare funds are likely to produce greater health gains than interferon beta for multiple sclerosis.5
Alternative uses for funds for interferon beta-1b
Our cost utility ratios are of a similar size to estimates in
studies of relapsing-remitting multiple sclerosis
£328 000 to
£809 000 per QALY in Britain35 and $300 000 in
Canada.36 Although targeting treatment at patients with
more active disease seemed more efficient than treating all patients
with secondary progressive disease, the opportunity cost was still substantial.
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Acknowledgments |
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We thank the medicines monitoring unit (MEMO) of the University of Dundee; R Hudson, D Carson, M Foster, and L Dick of the Scottish Health Purchasing Information Centre costing unit; Shirley Macdonald; and Andrew Owen.
Contributors: RBF and RJS had the idea for the study. RBF, AL, NW and RJS contributed to study design. RBF was responsible for data collection, performed the analysis of results, and wrote the first draft of the manuscript. AL, NW, and RJS all edited and approved the final version of the manuscript. RBF and RJS are guarantors of the study.
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Footnotes |
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Funding: None.
Competing interests: RBF and RJS were investigating and evaluating neurologists for a clinical trial of Antegren in multiple sclerosis, sponsored by Athena Neurosciences. RBF has received funding to attend a conference from Serono. RJS has received grants from Serono, Schering Healthcare, and Biogen to fund attendance at conferences.
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(Accepted 24 August 1999)
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