Appropriate international measures for outpatient antibiotic prescribing and consumption: recommendations from a national data comparison of different measures.

Objectives: Many European countries have engaged in awareness campaigns to decrease outpatient antibiotic use and several measures have been proposed, e.g. the number of defined daily doses (DDDs) or packages per 1000 inhabitants per day, producing conflicting findings. Therefore, we set out to explore what measure is most appropriate.
Methods: Outpatient data on each dispensed and reimbursed medicinal package in Belgium between 2002 and 2009 were aggregated at the level of the active substance in accordance with the Anatomical Therapeutic Chemical classification and expressed as the numbers of DDDs (WHO, version 2010), packages, treatments and insured individuals per 1000 inhabitants, insured individuals and patient contacts, per day, and in July-June years. Using these measures, time trends of outpatient antibiotic use were compared and explored in detail.
Results: Expressed per 1000 inhabitants per day, outpatient antibiotic use increased between 2002-03 and 2008-09 in DDDs, whereas in packages, treatments and insured individuals it decreased. The same was true for use expressed per 1000 insured individuals or when allowing for the decreasing number of patient contacts. Increasing numbers of DDDs per package (more items per package and higher doses per unit for amoxicillin and co-amoxiclav) explain these discrepancies.
Conclusions: The number of packages is a more appropriate measure than the number of DDDs when assessing outpatient antibiotic use over time and the impact of awareness campaigns in countries dispensing 'complete packages'. We recommended the use of different complementary measures or caution when interpreting trends based only on DDDs.