Age-related differences in the prevalence of potential drug-drug interactions in ambulatory dyslipidaemic patients treated with statins

Background and objective: Elderly patients may be at higher risk of drug-drug interactions (DDIs) because of polypharmacy. This study evaluated age-specific differences in the prevalence of clinically relevant potential DDIs (pDDIs) in ambulatory dyslipidaemic patients treated with an HMG-CoA reductase inhibitor (statin). We hypothesised that elderly patients are at higher risk for pDDIs because of the presence of more drugs and drugs with a higher potential for DDIs in this age group. Methods: A total of 2742 dyslipidaemic ambulatory patients treated with a statin were included in this cross-sectional study. Drug treatment was screened for clinically relevant pDDIs using an electronic drug interaction program (DRUG-REAX (R) System). Results: The study sample consisted of 483 (17.6%) patients aged! 54 years, 732 (26.7%) aged 55-64 years, 924 (33.7%) aged 65-74 years and 603 (22.0%) patients aged >= 75 years. Patients >= 75 years had significantly more pharmacologically active substances prescribed than patients aged <= 54 years (mean 5.8 vs 3.8, respectively; p < 0.001). Cardiovascular diseases such as coronary heart disease, heart failure or arrhythmias were also significantly more prevalent in patients aged >= 75 years than in younger patients. The overall prevalence of pDDIs increased significantly from 7.9% in those aged <= 54 years to 18.4% in patients aged >= 75 years (p < 0.001). The frequency of both pDDIs associated with statins and non-statin pDDIs increased with age. Risk factors for pDDIs in patients aged >= 75 years were arrhythmias, heart failure and the number of pharmacologically active substances prescribed. The more frequent prescription of cardiovascular drugs with a high potential for pDDIs (e.g. amiodarone and digoxin) in patients aged >= 75 years was mainly responsible for the observed increases in statin and non-statin pDDIs in this age group. Conclusions: Compared with younger patients, elderly dyslipidaemic patients are at a higher risk for clinically relevant pDDIs, mainly because of a higher number of drugs prescribed. In addition, patients aged >= 75 years were prescribed more drugs with a high potential for DDIs, especially drugs used for the treatment of arrhythmias and heart failure. The risk for adverse reactions associated with pDDIs may often be reduced by dose adjustment, close monitoring or selection of an alternative drug.