DDD Application

New DDD

Procedures

New DDDs are assigned on request from the users.  Requests for new DDDs should be addressed to the WHO Collaborating Centre for Drug Statistics Methodology (Application form). Electronic applications are preferred and applications are free of charge. Any user may in principle propose a new DDD (e.g. health authorities, manufacturers, researchers and others). However, as with ATC code assignment, it is the manufacturer who will usually have the best access to the required information for new drugs.

A DDD will only be assigned for substances which have received an ATC code, or where the ATC code can be assigned in connection with the DDD. DDDs are not assigned before marketing is approved in at least one country. 

All new DDDs are discussed and approved by the WHO International Working Group for Drug Statistics Methodology.

The steps in the approval procedure for new DDDs are very similar to the procedure for new ATC codes: 

• The ATC/DDD Centre will confirm receipt of the request for a new DDD and give information to those requesting the DDD (the applicant) about the time schedule for discussion at the following Working Group meeting.
• After approval of the minutes of the Working Group meeting, the decision from the meeting concerning the DDD is distributed from the ATC/DDD Centre to the applicant.   
• The new DDDs are published on this website (New ATC/DDD and alterations) and in the next issue of the WHO publication: WHO Drug Information. A deadline is then allowed for interested parties to comment or object to the new DDD. 
• If objections, justified on submitted evidence, are received, the DDD will be discussed again at the following meeting of the Working Group. If the decision is kept, then the decision is considered final after this meeting.  If a new decision is taken by the Working Group, notification of this new DDD is published at our website and in the next issue of the publication WHO Drug Information. A deadline is then allowed for any interested part to comment or object to the decision. 
• If no objections are received, the new DDD is considered final, and included in the next issue of the ATC classification index.  A list of final DDDs is also published semi-annually at this website (New ATC/DDD and alterations) and in the WHO Drug Information.

Data requirements

The following information is required when requesting a new DDD:

• Dose ranges and dosing instructions for each indication in the product information approved by one or more major regulatory authorities
• Proposal for a DDD justified by the submitted information.
• Status concerning marketing authorisation.
• Doses used in clinical trials to support marketing if available.
• Market research data on doses used in practice in various countries if such data are available.
• Where the drug is to fit into an existing ATC classification, comparative dosing information should be provided if available.  It is difficult to define therapeutically equivalent doses with the degree of precision often asked for, and the DDDs within therapeutic groups do not necessarily represent therapeutically equivalent doses.

DDD alterations

Principles for DDD reviewing and alterations

DDDs sometimes need to be reviewed because dosages may change over time, e.g. due to the introduction of new main indications or new research. The International Working Group for Drug Statistics Methodology may review a DDD whenever the Group finds it appropriate.

A major aim of the WHO Collaborating Centre for Drug Statistics Methodology and Working Group is to maintain stable ATC codes and DDDs over time. This allows trends in drug utilization to be studied without the complication of frequent changes.  Changes in DDDs are to be kept to a minimum and avoided as far as possible, as too many alterations are 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 sometimes accepted for important drugs, which are frequently used.

DDD review after three years

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 if available. Figures showing the prescribed daily dose (PDD) can be useful if available 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 input from users to the DDD.

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

Further reviews of DDDs

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

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 system for drug consumption studies.  Because of this, there need to be compelling reasons to change DDDs. Arguments for DDD changes might be:

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

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

Procedure

Any user may in principle propose changes in DDDs. There is no application form for DDD changes. Proposal for changes should be sent to the WHO Collaborating Centre for Drug Statistics Methodology.  All proposals 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.