gms | German Medical Science

Background: To determine persistence and compliance with pharmacy claims data, the prescribed daily dosage (PDD) should be known. Because it is not compulsory for physicians in Germany to note this information on the prescription, other ways of calculation like the DDD of the WHO [1] or the dosing information according to the SPC can be used. The aim of this investigation was to test the influence of estimating the prescribed daily dosage with the DDD or with information from the SPC in patients being treated with beta blockers.

Materials and methods: We utilized the DAPI database (Verein Deutsches Arzneiprüfungsinstitut e.V. , Eschborn), which comprises anonymous claims data of prescribed medicinal products dispensed at community pharmacies in Germany at the expense of the statutory health insurance funds.

Patients were included if they received at least one prescription for a beta blocker in monotherapy between January and June 2005. In order to observe only newly treated patients, no prescriptions of beta blockers were allowed in the 12 months prior to the first prescription in 2005. In the following 6 months (January to December 2005), patients had to receive at least one further prescription (defined as index prescription) for the same drug.

For analyses of persistence and compliance within 24 months from the index date, two different methods were applied: the occurrence of treatment gaps in dispensed drugs as well as the medication possession ratio (MPR).

The average amount of units (e.g. one tablet) to be taken per day was assessed according to the SPC. Based on this, the measurement variables MPR_SPC and Gaps_SPC (duration until the first occurrence of a gap) were determined.

In addition, the DDD according to the definition of the WHO in 2010 was used. The corresponding measurement variables were denominated as Gaps_DDD and MPR_DDD.

Results: In total, 98,828 patients initiated therapy with at least two prescriptions for a beta blocker in 2005.

Results of the calculation based on the DDD differed from those based on information from the SPC: Median duration until the first occurrence of a gap was 75 days according to the DDD, whereas 227 days passed until the first gap appeared calculated with the information from the SPC. The proportion of non-persistent patients (at least one treatment gap in the observation period) was higher with Gaps_DDD than with Gaps_SPC accordingly (95.4% vs. 77.6%).

Furthermore, MPR values differed considerably (median MPR_DDD: 0.342, median MPR_SPC: 0.684). The proportion of non-compliant patients (defined as having MPR values <0.8) according to MPR_DDD was much higher compared to the MPR_SPC (87.7% vs. 55.2%).

Conclusions: The DDD for beta blockers compared to the dosing frequency according to the SPC is relatively high. This may lead to an underestimation of the MPR and the duration until the occurrence of a first gap in treatment with the DDD method – especially in patients receiving beta blockers in preparations with (tablet) strengths lower than the DDD. Therefore, the DDD seems to be of limited suitability for the determination of the number of the PDD relative to the information from the SPC.