A systematic review and economic model of the effectiveness and ...

The review of the economic evidence from the
literature and the manufacturers’ submissions
highlighted a number of potential limitations in
existing studies assessing the cost-effectiveness of
MPH, DEX and ATX in children and adolescents
diagnosed with ADHD, including HKD. In
particular, the review highlighted limitations in
estimating treatment effectiveness and associated
utility values. In an attempt to overcome these
limitations, a new economic model was developed
for this report. The scope of this review is to
identify the most cost-effective treatment strategy
for children and adolescents with ADHD, once
one has assessed there to be a need for medical
management. The scope specifically excludes the
choice between medical management and nondrug
interventions, for example MPH compared
with BT without concurrent medication.
Methods
A new model was developed to assess the costeffectiveness
of IR-MPH (3–4 hour action), ER-
MPH (8 and 12 hour action), DEX and ATX for
the treatment of ADHD and HKD in children and
adolescents. The model assesses the use of these
drugs alone and in combination with a
behavioural therapy element (combination
therapy). The model is probabilistic, meaning that
relevant input parameters are entered as
probabilistic distributions rather than point
estimates in order to represent the uncertainty
around each point estimate. 146 The following
sections of the report outline the structure of the
model, the key assumptions made and the data
sources used to populate the model.
Overview
The model has been developed to estimate costs
from the perspective of the UK NHS and Personal
Social Services (PSS), and health outcomes in
terms of QALYs. The model was developed in
Excel and the evidence synthesis used to calculate
clinical effectiveness parameters was conducted in
WinBUGS. 147 The model considers a hypothetical
cohort of children aged 6 years. For the base case
analysis, a 1-year time horizon was selected. As
noted in the review of the literature and the
manufacturers’ submissions, this time span
Chapter 6
Economic model
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Health Technology Assessment 2006; Vol. 10: No. 23
excludes the long-term outcomes associated with
ADHD. It is known that patients can remain on
treatment for more than 1 year, but there is a lack
of data about the mechanism that determines the
length of treatment. In particular, there is a lack of
data for discriminating between treatments in
terms of length of treatment for responders.
Similarly, there is a lack of data regarding the
relative effect of the alternative treatments on
other long-term outcomes, including long-term
adverse events and cost offsets. These issues will
be discussed further in following sections of the
report.
In a secondary analysis, we explore a limited
extrapolation of the model beyond 1 year using an
estimate of the age-dependent decline of
symptoms with ADHD. 148
Treatment strategies
The model considers alternative sequences of
treatments. Patients who withdraw or fail on each
treatment are assumed to move to the next in line,
until they reach no treatment at the end of the
sequence. It is assumed that medication is received
as part of a comprehensive treatment plan that
includes visits to child psychiatrists and
paediatricians. The model separately assesses
three formulations of MPH, and it is assumed that
individuals who withdraw from one formulation
would not be offered one of the alternative
formulations, as they contain the same active
ingredient.
Clearly, treatment sequences could be composed
of strategies featuring one, two or three active
treatments. Conducting such an analysis allows us
to estimate the incremental cost-effectiveness of
adding a second or third active treatment option.
Such an analysis was conducted (see Appendix 8),
and the results show that strategies with three
active treatments are cost-effective. Subsequently,
the results presented for the base case analysis and
the sensitivity analyses concern only those
treatment strategies featuring three active
treatments. The benefit of omitting these extra
strategies from the base case analysis and other
sensitivity analyses is to simplify greatly the
presentation of results (19 strategies instead of 38,
without considering combination therapy). The
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