Using defined daily doses to study the use of antibacterials in UK hospitals

Increasing resistance to antibacterials is a major public health problem. Antibacterial use is considered to be the main selective pressure driving this resistance, and the rate at which resistance develops has been shown to be associated with drug consumption. It has been suggested that reductions in the development of resistance will only result from significant changes in antibacterial use. Despite the majority of antibacterial courses being prescribed in primary care, the prevalence of both antibacterial use and antibacterial resistance is higher in secondary care. Surveillance of hospital use of antibacterials is therefore particularly important. There are several ways in which antibacterial consumption can be assessed. In UK secondary care, expenditure is routinely used. However changes in pricing structure and the availability of generic medicines make it difficult to compare different organisations and different periods. Consumption can also be expressed in terms of numbers of packs dispensed, but this also has limitations as pack sizes vary both within and between institutions.The ideal way of monitoring consumption would be based on individual prescription data, but this will not be practical in UK hospitals until the widespread availability of electronic prescribing with appropriate reporting facilities. In the meantime, point prevalence studies have been used to study antibacterial use. This method gives detailed information about prescribing but only at one point in time. Outside the UK, the calculation of defined daily doses (DDDs) is widely used.The DDD is the assumed average maintenance dose per day for a drug when used for its main indication in adults with normal organ function. DDDs for most drugs have been defined by the World Health Organization. Inpatient usage is usually expressed per 100 occupied bed days (OBD) to take into account variation in workload; however, this does not take into account case mix. Use of this internationally accepted standard enables the use of antibacterial agents with different doses to be compared, aggregation of data to assess usage of different antibacterial classes, and comparisons between centres. For example, the European Surveillance of Antibiotic Consumption (ESAC) project group has explored the use of this approach to measure OBJECTIVE — To explore the feasibility of using defined daily doses (DDDs) to measure antibacterial consumption in a UK hospital and identify the methodological issues encountered.