Abstract

Background: Today it is well recognized that it is not possible to fully determine the safety of a medicin-al product prior to marketing authorization. Even though there are strict requirements that need to be met before a drug can be introduced to the market, new safety risks may come to light at any time point throughout the life of a drug. Therefore, there is a need for safety monitoring of marketed drugs. In Denmark the Danish Health and Medicines Authority (DHMA) monitors the safety of marketed drugs by means of different methods and sources. Not all of these are equally widely used by the DHMA and they would like to expand the use of some of the sources in order to enhance the safety monitoring of drugs. One of these sources is the Register of Medicinal Product Statistics (RMPS). The RMPS is a register which is owned and managed by the DHMA. The register is the only register of its kind, containing data on redeemed prescriptions of an entire population over many years and thereby holds unique opportunities in regard to investigating how and to what extent a drug is used in Denmark. It is possible that such an investigation can contribute to safety monitoring.

Aim: The aim of this study was to investigate whether and how methods for investigating the utilization of a drug by using dispensing data available in the RMPS can contribute to safety monitoring at the DHMA in the future. To investigate this, the utilization of the antidepressants Cymbalta and Xeristar was investigated as an example.

Materials and methods: This was a register-based retrospective study. The study population consisted of Danish residents who redeemed at least one prescription of Cymbalta/Xeristar from1st of January 2005 to 31st of December 2010. Several aspects of the drug utilization were investigated. These were: size and composition of the user population in regard to age and gender distribution, switch between drugs, average amount of redeemed drug in Defined Daily Doses (DDDs), and concomitant use with contraindicated drugs. By comparing the results to the recommended use of the drugs, the extent of off-label use was investigated.

Results: In this study it was found that users of Cymbalta/Xeristar in Denmark were of both genders and in all age groups. Furthermore, it was found that the average amount of redeemed drug in DDDs per user increased over the study period. It was also detected that some users switched to another antidepressant and that some were in concomitant treatment with contraindicated drugs.

Conclusion: By means of the applied methods it was possible to investigate the utilization of Cymbalta/Xeristar and based on this detect alarming tendencies in the drug utilization which constituted potential safety issues for the users. It was discussed that an investigation using the methods demonstrated in this study could also be performed for other drugs when adjusted to the drug in question. In regard to this, it should be considered that the applied methods have both strengths and limitations and are more applicable for some drugs than others. Overall it was suggested that the methods applied in this study using dispensing data available in the RMPS offer an additional approach with widespread applicability for safety monitoring at the DHMA.