Comparison of dose standard units for drug utilisation studies

Objective. As employment of different dose standards would be impractical and confusing, the aim of this article is to compare the defined daily dose (DDD) with some more recently proposed standards, namely, the minimum marketed dose (MMD), the equipotential dose (ED), the average daily dose (ADD), and the non-standard prescribed daily dose (PDD). Methods. Literature review, critical comparative analysis. Results. The DDD, defined by an independent scientific committee assisting the WHO Collaborating Centre for Drugs Statistics Methodology, has been employed in a large number of national and international comparative studies at the population level, usually as number of DDDs per 1000 inhabitants per day. However, the DDD can also be used at the individual level. The PDD, not being a standard unit, can be appropriately used in a second step to explain differences detected by the DDD methodology. Conclusions. A globally accepted dose standard unit is important in drug utilisation studies, particularly if different investigations are to be compared. None of the alternatives seemed to offer any advantage over the DDD. Hence there is reason to advocate use of the DDD as the sole standard dose unit in all pharmacoepidemiologic studies.