Prevalence and Factors Associated with Potential Drug-Drug Interactions in Older Community-Dwelling Adults: A Prospective Cohort Study

Background: Older patients are at increased risk of drug-drug interactions (DDIs) due to polypharmacy. Cardiovascular and central nervous system (CNS) drugs are commonly implicated in serious DDIs. Objectives: This study aimed to determine the prevalence and factors associated with potential ‘severe’ cardiovascular and CNS DDIs among older (≥ 70 years) community-dwellers. Methods: This was a prospective cohort study using linked data from a national pharmacy claims database and waves 1 and 2 of The Irish LongituDinal study on Ageing (TILDA). ‘Severe’ cardiovascular and CNS DDIs were identified using the British National Formulary 77 and Stockley’s Drug Interactions. The prevalence of ‘severe’ DDIs (any DDI vs. none) was calculated. Logistic regression was used to examine the association between sociodemographic, functional ability, and medication-related factors and the risk of DDI exposure between waves 1 and 2. Results: A total of 1466 patients were included [mean age (standard deviation) = 78 (5.5) years; female n = 795, 54.2%]. In total, 332 community-dwellers aged ≥ 70 years [22.65%, 95% confidence interval (CI) 20.58–24.86] were potentially exposed to at least one ‘severe’ cardiovascular or CNS DDI, with more than half (54.82%) of this cohort dispensed the same DDI for a prolonged time (≥ 3 consecutive claims). Aspirin-warfarin was the most frequently dispensed (co-prescribed) DDI (n = 34, 10.24%, 95% CI 7.39–14.00), followed by atorvastatin-clarithromycin (n = 19, 5.72%, 95% CI 3.64–8.81). Polypharmacy [≥ 10 vs. < 5 drugs, odds ratio (OR) 13.40, 95% CI 8.22–21.85] and depression (depressed vs. not, OR 2.12, 95% CI 1.34–3.34) were significantly associated with these DDIs, after multivariable adjustment. Conclusion: ‘Severe’ cardiovascular and CNS DDIs are prevalent in older community-dwellers in Ireland, and those with polypharmacy and depression are at a significantly increased risk.