Postal address:
WHO Collaborating Centre for Drug Statistics Methodology
Norwegian Institute of Public Health
P.O.Box 4404 Nydalen
0403 Oslo

Visiting/delivery address:
Marcus Thranes gate 6
0473 Oslo

Tel:  +47 21 07 81 60

Application for DDD alterations

Principles for DDD reviewing and alterations
As the dosages used may change over time, it will always be necessary to make some alterations. The International Working Group for Drug Statistics Methodology may review a DDD whenever the Group finds it appropriate.

Changes of DDDs should be kept to a minimum and avoided as far as possible.  Too many alterations will always be disadvantageous for long-term studies on drug utilization.  Before alterations are made, difficulties arising for the users are weighed against the benefits achieved by the alteration.

  • The same principles used to assign new DDDs also apply when DDDs are reviewed.
  • Changes are generally not made unless they are at least in the order of 50 %.  This rule is not used for the three year revision of DDDs, where smaller alterations are allowed.  Further, minor alterations are allowed for important drugs, which are frequently used (e.g. the DDD for cimetidine was changed from 1.0 g to 0.8 g).

DDD review after three years (to the top)
All newly assigned DDDs are reviewed during the third year after inclusion in the ATC Index with DDDs.  The DDDs are reviewed at the first semi-annual meeting of the International Working Group for Drug Statistics Methodology.  The following are considered:

  • Recommended dosages as listed in drug catalogues in different countries and/or published in peer reviewed scientific journals or major international textbooks
  • Data on prescribed daily doses (PDDs) from a range of countries.  Figures showing the prescribed daily dose (PDD) are important when reviewing an assigned DDD.  Usually more data concerning PDDs are available after a three years period than at the time of marketing
  • Established main indication and therapy profile of the preparation (i.e. has the main indication changed?)
  • Existing DDDs in the ATC group.
  • Written objections to the DDD which have been received.

When reviewing combination products, changes in the DDDs for the different active ingredients are an important consideration.

Further reviews of DDDs (to the top)
After the first three years period, the DDD normally remains unchanged for at least five years unless the WHO Working Group decides to make a total revision of all DDDs assigned in an ATC group. Proposed DDD changes from users of the system, based on new information will always be considered, but only after the three years revision has been performed.

Data requirements (to the top)
When requesting changes of DDDs, the data requirements are similar to the data required for new DDDs.  An important basis for the ATC/DDD system is to maintain a stable database for drug consumption studies.  Because of this, there need to be compelling reasons to change DDDs. Conclusive arguments might be: 

  • a change in the main indication so that the average dose used has been altered. 
  • a large change (in the order of 50 %) in the average dose used. This would need to be supported by detailed market research data in a range of countries including developing countries.  However, for the three year revision a smaller change can be accepted.

Minor changes in DDD for reimbursement, pricing or marketing purposes will not be considered.

Procedure (to the top)
A change in DDDs should be proposed and explained in writing, and addressed to the WHO Collaborating Centre for Drug Statistics Methodology.  Any user may in principle propose changes in DDDs.

All proposals for changes will be discussed by the WHO International Working Group for Drug Statistics Methodology.

The steps in the evaluation procedure for changes to DDDs are the same as the procedures for ATC alterations.

Deadlines for applications (to the top)
Deadlines for applications

Last updated: 2009-11-18