An approach for the estimation of drug prescribing using the defined daily dose methodology and drug dispensation data - Theoretical considerations and practical applications

Objective: To test the hypothesis that comparison of defined daily dose (DDD) and drug user data may help to estimate drug exposure in a defined population and provide information about drug prescribing patterns. Methods and results: First, comparison of DDD figures with the number of apparent drug users (ADU, i.e., individuals for whom at least one prescription of the drug had been dispensed during a given time period) is demonstrated to correspond to the product of the prescribed daily dose (PDD) and the proportion of days in which the drug had been taken (days of treatment/days in a time period, D). The resulting equation (DDD/day)/ADU in a time period = PDD x D is then applied to the analysis of different sets of drug dispensation data. Examples show that this approach may be helpful to monitor drug prescribing patterns over time. Moreover, in definite situations, it may provide reliable estimates of either PDD or D. Conclusions: Comparison of DDD and drug user data is suggested to be a cost-effective strategy to monitor drug prescribing patterns from an epidemiological perspective, which may be useful to researchers involved in drug utilisation studies as well as to health authorities for monitoring and regulatory purposes.