Patterns of medication use following breast cancer diagnosis: an Australian population-based study

PURPOSE: This study aimed to examine patterns of medication use and polypharmacy following breast cancer diagnosis. METHODS: This retrospective cohort study used breast cancer data from the South Australian Cancer Registry linked with medication dispensing records, death registry, and inpatient hospital records. Women diagnosed with invasive breast cancer between July 2012 and March 2014 were followed for 5 years from diagnosis. All medications were defined using the Anatomical Therapeutic Chemical classification, and patterns of use were analysed in one-yearly intervals. The changes in the use of medications and polypharmacy (≥ 5 concomitant medications versus not) from Year-2 to Year-5 of breast cancer diagnosis were examined using generalised estimating equations models with binary logistic distribution. RESULTS: The study included 2005 women (mean age = 61.1 years). The use of endocrine therapy for breast cancer decreased over time (odds ratio (OR) 0.88; 95%CI = 0.86-0.90). In contrast, the likelihood of being dispensed specific cardiovascular medicines increased with each successive time period including agents acting on renin-angiotensin system (OR 1.03; 95%CI = 1.01-1.05), lipid-modifying agents (OR 1.06; 95%CI = 1.03-1.08), beta-blockers (OR 1.08; 95%CI = 1.04-1.11), and cardiac therapy (OR 1.12; 95%CI = 1.06-1.18). There was an increased likelihood of polypharmacy over time (OR 1.08; 95%CI = 1.04-1.11) with the prevalence ranging from 25% (Year 2) to 29% (Year 5). Several characteristics were associated with polypharmacy including older age, a lower socioeconomic status, and a higher burden of comorbidities. CONCLUSION: The use of several medication classes increased over time suggesting development of new comorbidities and higher likelihood of polypharmacy. Medication management in breast cancer survivors offers potential to identify those with complex needs of polypharmacy and comorbidity.