Guidelines for ATC classification and DDD assignment ... - WHOCC

For all combination products where the DDD assigned deviates from the principlesgiven above, a list of DDDs are available from the Centre (published on the websitewww.whocc.no).3. Other factorsa) Fixed dose groupsFor some groups of products, it has been considered most appropriate to estimatethe average use for products within a group instead of establishing accurate dosesfor every product, e.g. cough mixtures in ATC group R05 and multivitamins inATC group A11. For the multivitamins the composition of various products maydiffer, but the average recommended dose is usually the same. Such DDDs arecalled "fixed dose".In some ATC groups, it has been decided to use fixed DDDs for all combinationproducts given in e.g. number of tablets regardless of strength. These rules areclearly stated in the chapters in the respective ATC levels in this publication (e.g.ATC group A02AD, A02BD and A02BX).For eye drops used in glaucoma therapy (S01E), a fixed dose regardless of strengthhas been established in the different subgroups. This is based on the assumptionthat, per dosage given, only one drop is applied in each eye, regardless of strength.When fixed doses are assigned, these will be further described in the guidelines forthe different ATC groups.b) Depot formulationsDepot formulations (e.g. sustained release formulations) are usually assigned thesame DDDs as the ordinary dosage forms. Exceptions to this main rule aredescribed in the guidelines for the different ATC groups.c) Intermittent dosingIn certain therapeutic groups, e.g. hormones, many of the products are administeredintermittently. In such cases, the dose administered is divided by the number ofdays in the treatment period to obtain the average daily dose. This means thatmedicament free periods in between courses are included in the treatment period.This applies to e.g. depot antipsychotics (N05A) and contraceptive pills (G03A),which are given intermittently.26