237 Drug–drug interactions and the risk of adverse drug reaction hospital admissions in the older population: a prospective cohort study

Abstract Background Drg–Drg Interactions (DDIs) can lead to medication-related harm; the older population is at greatest risk. We estimate DDI prevalence and the average causal effect of DDI exposure on adverse drug reaction (ADR)-related hospital admission in an older (≥65 years) population admitted acutely to hospital in Ireland. We also examine the effect of DDI exposure on health-related quality of life (HRQoL) and Length of Stay (LoS) in hospital. Methods Prospectively collected (2016–17) data from the Adverse Drg Reactions in an Ageing PopulaTion cohort were used (N = 798). Medication (current/recently-discontinued/over-the-counter) and objective clinical data (e.g. renal function) were available. DDIs (which may result in a life-threatening event/permanent detrimental effect) were identified using the BNF and Stockley’s. Causal inference models were developed using directed acyclic graphs. HRQoL was measured using the EQ-5D-5L. Multivariable logistic regression was performed using SAS (v9.4). Results N = 782 patients using ≥2drugs were included, mean age = 80.9(±7.5); 52.2% female; 92.2% polypharmacy (≥5drugs); 45.1% had an ADR-related hospital admission. N = 316 (40.4% [95% Confidence Interval (CI):37.0–43.9]) patients with at least one DDI at hospital admission. After controlling for confounding, the average causal effect of DDI exposure on ADR-related hospital admission was Odds Ratio (OR) = 1.2 [95% CI: 0.9–1.6]. This risk was significantly increased for patients exposed to DDIs which increase bleeding risk (OR: 2.0 [1.3–3.1]); for aspirin-warfarin (OR: 2.8 [1.4–5.7]) and esomeprazole-escitalopram (OR: 3.2 [1.1–10.3] DDIs. Patients with a DDI had a lower HRQoL (mean EQ-5D: 0.49 [±0.39]) compared to those with none (mean EQ-5D: 0.58 [±0.41], p = 0.08). Patients with an ADR-related hospitalisation and DDI had a significantly greater LoS in hospital (8 [Interquartile Range:5–17] days) compared to those with no DDI (6[Interquartile Range: 3–13] days, p = 0.02). Conclusion DDIs are prevalent among older adults on acute admission to hospital, and increase the risk of ADR-related hospitalisation, significantly for patients with DDIs that increase bleeding risk. Patients with a DDI had lower HRQoL, and prolonged LOS in hospital.