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

Use of the ATC/DDD system allows standardisation of drug groupings and a stabledrug utilization metric to enable comparisons of drug use between countries,regions, and other health care settings, and to examine trends in drug use over timeand in different settings.Drug consumption figures should preferably be presented as numbers ofDDDs/1000 inhabitants/day or, when in-hospital drug use is considered, asDDDs per 100 bed days. Sales or prescription data presented inDDD/1000 inhabitants/day may provide a rough estimate of the proportion of thepopulation within a defined area treated daily with certain drugs. For example, thefigure 10 DDDs/1000 inhabitants/day indicates that 1% of the population onaverage gets a certain treatment daily. This is only true if the prescribed dosecorresponds to the DDD.For antiinfectives (or other drugs normally used in short periods) it is oftenconsidered most appropriate to present the figures as numbers of DDDs perinhabitant per year, which will give an estimate of the number of days for whicheach inhabitant is, on average, treated annually.For example, 5 DDDs/inhabitant/year indicates that the consumption is equivalentto the treatment of every inhabitant with a 5 days course during a certain year.Alternatively, if the standard treatment period is known, the total number of DDDscan be calculated as the number of treatment courses, and the number of treatmentcourses can then be related to the total population.For some drug groups where DDDs have not been established, alternative ways ofpresenting data are recommended. For example, consumption of dermatologicalpreparations can be presented in grams of ointment, cream etc, and antineoplasticagents in ATC group L01 can be presented in grams of active ingredient.When there is a known discrepancy between the prescribed daily dose (PDD) andthe DDD, it is important to take this into account when interpreting drugconsumption figures. Caution should also be taken in situations where therecommended dosage differs from one indication to another (e.g. antipsychotics), insevere versus mild disease (e.g. antibiotics) and where PDDs may differ from onepopulation to another (e.g., according to sex, age, ethnicity or geographic location).Finally, it should be taken into considerations that some prescribed medications arenot dispensed, and the patient does not always take all the medications, which aredispensed. Specially designed studies are required to measure actual drug intake atthe patient level.34