Retrospective multi-centre cohort study of polypharmacy, the Drug Burden Index and associations with outcomes in older surgical inpatients

Background Comprehensive medication utilisation and its association with outcomes are not well described in older surgical inpatients. Objectives Investigate medication utilisation and the associations of the number of medications and exposure to anticholinergic and sedative medications measured using the Drug Burden Index (DBI exposure) with outcomes in older surgical inpatients. Methods A multi-centre retrospective cohort study of surgical patients ≥65 years at five Australian hospitals admitted for ≥48 hours, from 4 January 2022 to 3 January 2023. The number of regular medications was counted on admission and discharge. DBI exposure throughout admission was calculated using the area under the curve for DBI/days of admission (AUC DBI/days). Multilevel regression was conducted for outcomes on/during admission [falls, adverse drug events (ADEs), delirium, pressure ulcers, Hospital Frailty Risk Score (HFRS), length of stay (LOS)]. Results The 13 815 participants (51.1% male) had a median (IQR) age of 77 (71–84) years. The median number of medications was 5 (2–9) on admission and 9 (6–13) on discharge. The median AUC DBI/days was 0.13 (0–0.5). The number of admission medications was associated with delirium [adjusted odds ratio (aOR) 1.02, 95% CI: 1.01–1.04], ADEs (aOR 1.03, 95% CI: 1.01–1.04), pressure ulcers (aOR 1.04, 95% CI:1.02–1.06), HFRS [adjusted rate ratio (aRR) 1.01, 95% CI:1.001–1.02] and increased LOS (aRR 1.011, 95% CI: 1.008–1.014). The AUC DBI/days was associated with falls (aOR 1.29, 95% CI: 1.18–1.41), delirium (aOR 1.63, 95% CI:1.46–1.82), ADEs (aOR 1.26, 95% CI: 1.11–1.43), pressure ulcers (OR 1.60, 95% CI: 1.38–1.86), HFRS (aRR 1.27, 95% CI:1.17–1.37) and increased LOS (aRR 1.36, 95% CI:1.32–1.40). Conclusion Polypharmacy is common amongst older surgical inpatients, and the number of medications increased from admission to discharge. Increased DBI exposure was associated with adverse outcomes.