E-drug: Use of the DDD for comparison of consumption (cont)
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This is a contribution to the ongoing discussion on the suitability of the
DDD in such different areas as drug consumption statistics and pricing and
reimbursement.
I represent the WHO Collaborating Centre for Drug Statistics Methodology in
Oslo, which is actually assigning all official ATC codes and DDDs. We want
to point out some of the main principles one has to be aware of when
planning to use the DDDs for some purposes.
The basic definition of the DDD is: The DDD is the assumed average
maintenance dose per day for a drug used for its main indication in adults.
It should be emphasized that the defined daily dose is a unit of
measurement and does not necessarily reflect the recommended or Prescribed
Daily Dose. Doses for individual patients and patient groups will often
differ from the DDD and will necessarily have to be based on individual
characteristics (e.g. age and weight) and pharmacokinetic considerations.
Drug consumption data presented in DDDs only give a rough estimate of
consumption and not an exact picture of actual use. DDDs provide a fixed
unit of measurement independent of price and formulation enabling the
researcher to assess trends in drug consumption and to perform comparisons
between population groups.
In our publication Guidelines for ATC classification and DDD assignment
(August 1998) it is emphasised that basing reimbursement, therapeutic
reference pricing and other pricing decisions on ATC/DDD classifications is
a misuse of the system.
Defined Daily Doses are not designed necessarily to reflect therapeutically
equivalent doses. This is because:
- Therapeutically equivalent doses are very difficult to establish
and particularly to the precision required when making pricing decisions.
- Even when based on market research data, the doses used in actual
practice may not necessarily reflect therapeutically equivalent doses (and
most of the time will not do so). Prescribed daily doses do not
necessarily include an effect consideration.
- Average daily doses may and do change over time, but there is a
reluctance to alter the DDDs unless the dose movements are large or there
is some particular reason such as a change in the main indication.For all
these reasons the DDD assignments are not suitable for comparing drugs for
reimbursement and pricing purposes. They are designed solely to maintain a
stable system of drug consumption measurement, which can be used to follow
trends in utilization of drugs within and across therapeutic groups.
Basing reimbursement decisions indiscriminately on certain ATC groups is
not recommended, since the indications for use of drugs often differ widely
between countries, and the ATC code is decided according to what is
considered to be the main international use.
It is also important to be aware of the fact that ATC codes and DDDs are
closely connected and to use DDDs without taking the ATC classification
into consideration can give you quite confusing results in your statistics.
More information about the publications published by the WHO Centre in Oslo
(Guidelines and ATC/DDD index) can be obtained from the centre.
Irene Litleskare
WHO Collaborating Centre for Drug Statistics Methodology
P.O. Box 100 Veitvet
n-0518 Oslo, Norway
tel +47 22 16 98 11
fax+47 22 16 98 18
e-mail: Irene.litleskare@nmd.no
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