Adherence to tamoxifen therapy after conversion to a discount pharmaceutical in breast cancer patients in Germany

Background: The aim of this study is to investigate the risk of discontinuing therapy in breast cancer patients treated with tamoxifen both with and without conversion to a discount pharmaceutical (tamoxifen) and to analyse the negative consequences of rebate contracts on the compliance of breast cancer patients among gynaecologist and general practitioner practices in Germany. Methods: This retrospective analysis was performed using the IMS Disease Analyzer® database. Women with a diagnosis of breast cancer and a first time prescription of tamoxifen from January 2008 to December 2011 were selected. The principle outcome measure was the incidence of hormone treatment discontinuation rates within three years after the index date. Treatment discontinuation of tamoxifen was defined as 90 days without this or an alternative hormonal therapy (aromatase inhibitors) during that time. Results: In total, 3,620 patients were included in the persistence analysis. 1,712 (47.3%) patients were converted to a discount product. Within three years of follow up, the discontinuation rates increased to 51.5% for switched patients and 46.3% for patients that were not switched (p < 0.01). Hazard ratios of the three-year risk of tamoxifen therapy discontinuation were adjusted for age, sex, gynaecologist care, patient and physician's residency, and baseline comorbidities (osteoporosis, diabetes, depression and thrombosis, and side effects). These analyses revealed a significantly increased risk of treatment discontinuation for patients who were switched to a discount pharmaceutical compared to patients without conversion to a discount pharmaceutical (HR: 1.27, CI: 1.05 – 1.53, p = 0.014). Conclusions: This analysis highlights an association between the initiation of rebate contracts and a negative impact on the compliance of breast cancer patients on an adjuvant hormonal treatment. The impact of rebate contracts on the health of patients and health care costs should be evaluated in further therapeutic fields through additional research projects.