Guidelines for ATC classification and DDD assignment - WHOCC

achieved. The harmonisation process was initiated in order to minimise the
confusion of having two very similar classification systems.
It should be emphasised that there are many differences between the EphMRA
classification and the ATC classification. This means that data prepared using the
ATC classification cannot be directly compared with data prepared using the
EphMRA system. The abbreviation ATC is unfortunately also used for the
EphMRA classification, which can cause confusion.
The EphMRA classification system is used worldwide by IMS (Intercontinental
Medical Statistics) in producing marketing research statistics for the pharmaceutical
industry.
III. DDD (DEFINED DAILY DOSE)
A. Definition and general considerations
The basic definition of the unit is:
The DDD is the assumed average maintenance dose per day for a drug used for its
main indication in adults.
A DDD will only be assigned for drugs that already have an ATC code.
It should be emphasised that the defined daily dose is a unit of measurement and
does not necessarily reflect the recommended or Prescribed Daily Dose (see page
31). 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.
For the optimal use of drugs, it is important to recognise that genetic polymorphism
due to ethnic differences can result in variations in pharmacokinetics of drugs.
However, only one single DDD is assigned per ATC code and route of
administration. The DDD should reflect global dosage irrespective of genetic
variations.
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, currencies, package size and strength enabling
the researcher to assess trends in drug consumption and to perform comparisons
between population groups.
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