[Relation between defined daily doses (DDD) and prescribed daily doses: a 3-month analysis of outpatient data from a statutory health insurance company].

AIM Defined daily doses (DDD) are used to analyse drug utilisation. For frequently prescribed drug groups, we studied to what extent the DDD correspond to the average prescribed daily doses (PDD). METHODS We analysed all drugs prescribed for more than three months to insured of a large health insurance fund in Mecklenburg-Vorpommern, one federal state in Germany. PDD for plain ACE inhibitors, selective beta-antagonists and some antidiabetics (sulfonylurea compounds) were calculated and compared with their DDD. RESULTS During the study period, about 38 500 patients received continuous prescriptions of each ACE inhibitors or selective beta-antagonists, and about 9 000 of sulfonylurea compounds. PDD differed from DDD in varying degrees. For ACE inhibitors, PDD ranged between 1.5 DDD (for captopril) and 3.5 (for ramipril). The PDD for beta antagonists were on average 0.9 DDD, similar for bisoprolol (0.8 DDD) and metoprolol (0.9 DDD). As for oral antidiabetics, doctors prescribed 1.0 DDD glibenclamid per day and patient and 2.0 DDD glimepirid. Depending on differences between DDD and PDD, real daily costs for drug therapy differed from the theoretical costs per DDD, for example in the case of ramipril they were 0.24 euros compared to 0.07 euros. CONCLUSION The PDD were much higher than the DDD for several frequently prescribed drugs. Consequently, the daily drug costs exceeded the drug costs based on DDD. Evaluations of drug costs on the basis for DDD require careful interpretation. Moreover, the number of DDD alone is not a valid measurement for the appropriateness of drug therapy and can only give a rough estimate of the number of patients treated, at least for the drug groups in this study.