[e-drug] The use of stems in International Nonproprietary Names (6)

["Irene Litleskare" <whocc@fhi.no>]

E-DRUG: The use of stems in International Nonproprietary Names (6) 
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Dear All,

The WHO Collaborating Centre for Drug Statistics Methodology is responsible for the 
development and maintenance of the ATC/DDD system. We want to comment to 
the ongoing discussion on the use of the ATC/DDD system for classification of the 
INN stems. From our point of view it is not necessarily an advantage to use the 
ATC/DDD system as a classification system in the 'Selection of International 
Nonproprietary Names (INN) for pharmaceutical substances' book. The INN stem is 
based on an assumed mechanism of action or on chemistry. The ATC code would of 
course be in accordance with the INN stems in some ATC groups. On the other 
hand, similarities in mechanism of action or in chemistry could result in substances 
used in totally different indications and therefore also belonging to totally different 
ATC groups.

Many INN stems are decided for groups of substances that have never reached the 
market. These stems need a pharmacological classification but there are no logical 
ATC groups where they belong. Many ATC groups also contain substances with 
different INN stems and the level of detailing in the pharmacological or chemical 
description of the INNs can not be obtained by using the ATC classification. 

Since many substances are withdrawn from clinical development before they reach 
the market, they will never receive an ATC code. The ATC/DDD system is primarily 
intended as a tool in drug utilization statistics, and the Centre therefore tries to avoid 
assignment of ATC codes for substances that will never receive a marketing 
authorisation. The Centre also want to have information about possible indications 
and mechanisms of action as close to the point of approval of a marketing 
authorisation as possible, to assure that we have a good basis for the assignment of 
an ATC code for the substance. 

To conclude, using the ATC/DDD system as a sort of pharmacologic/chemical 
description of the INN stems could be confusing and in some cases also misleading. 
The ATC classification has not been developed to be used for this specific purpose 
but to contribute with a useful but more 'rough' grouping of medicines which reflects 
the actual drug market. The INNs for single substances that are classified in the 
ATC system are however cross linked in the INN database in the WHO Headquarters. 
If a substance has an ATC code, the code can be obtained by searching on specific 
INNs in the INN database (http://mednet.who.int). 

We hope this clarifies the view of the WHO Collaborating Centre concerning the use 
of the ATC/DDD system in connection with the INN stems. We intend to continue the 
good collaboration with the INN programme regarding updating of the ATC codes for 
INNs that have reached the market place. 

Yours sincerely 

Irene Litleskare

WHO Collaborating Centre for Drug Statistics Methodology
P.O. Box 4404 Nydalen
N-0404Oslo
Norway
Tel: +47 23 40 81 60/+47 23 40 81 36
Fax: +47 23408146
e-mail: whocc@fhi.no
Website: whocc.no