Guidelines for ATC classification and DDD assignment - WHOCC

Two examples of this are as follows:
- Sex hormones in certain dosage forms or strengths are only used in the treatment
of cancer and are thus classified under L02 - Endocrine therapy. Remaining
dosage forms/strengths are classified under G03 - Sex hormones and modulators
of the genital system.
- Clonidine is available in two different strengths. One strength, which is used
mainly in the treatment of hypertension, is classified under C02 -
Antihypertensives. Another strength mainly used in the treatment of migraine is
classified under N02C - Antimigraine preparations.
Different pharmaceutical forms for topical and systemic use are also given separate
ATC codes.
Example:
Prednisolone in single ingredient products is given several ATC codes due to
different therapeutic use and different local application formulations.
A07EA01 Intestinal antiinflammatory agents (enemas and foams)
C05AA04 Antihemorrhoidals for topical use (suppositories)
D07AA03 Dermatological preparations (creams, ointments and lotions)
H02AB06 Corticosteroids for systemic use (tablets, injections)
R01AD02 Nasal decongestants (nasal sprays/drops)
S01BA04 Ophthalmologicals (eye drops)
S02BA03 Otologicals (ear drops)
A medicinal product may be used for two or more equally important indications,
and the main therapeutic use of a drug may differ from one country to another.
This will often give several classification alternatives. Such drugs are usually only
given one code, the main indication being decided on the basis of the available
literature. Problems are discussed in the WHO International Working Group for
Drug Statistics Methodology where the final classification is decided. Crossreferences
will be given in the guidelines to indicate the various uses of such drugs.
The ATC system is not strictly a therapeutic classification system. At all ATC
levels, ATC codes can be assigned according to the pharmacology of the product.
Subdivision on the mechanism of action will, however, often be rather broad, since
a too detailed classification according to mode of action often will result in having
one substance per subgroup which as far as possible is avoided (e.g.
antidepressants). Some ATC groups are subdivided in both chemical and
pharmacological groups (e.g. ATC group J05A - Direct acting antivirals).
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