Polypharmacy and emergency readmission to hospital after critical illness: a population-level cohort study

Background: Polypharmacy is becoming increasingly prevalent and is closely linked to drug interactions. The impact of polypharmacy has not been previously quantified in survivors of critical illness who have reduced resilience to stressors. The study aimed to identify factors associated with pre-admission polypharmacy and ascertain whether polypharmacy is an independent risk factor for emergency readmission to hospital following discharge from a critical illness. Methods: Population wide cohort study which consisted of patients admitted to all Scottish general intensive care units (ICU) between 1st January 2011 and 31st December 2013, whom survived their ICU stay. Patients were stratified by presence of pre-admission polypharmacy, defined as being prescribed 5 or more regular medications. The primary outcome was emergency hospital readmission within 1-year of discharge from index hospital stay. Results: Of 23,844 ICU patients, 29.9% were identified with polypharmacy (n=7,138). Factors associated with polypharmacy included female sex, increasing age and social deprivation. Emergency 1-year hospital readmission was significantly higher in the polypharmacy cohort (51.8% vs 35.8%,P<0.001). After confounder adjustment, patients with polypharmacy had a 22% higher hazard of emergency 1-year readmission (adjusted hazard ratio[adjHR] 1.22, 95% confidence interval[CI] 1.16-1.28,P<0.001). On a linear scale of polypharmacy each additional prescription conferred a 3% increase in hazard of emergency readmission by 1-year (adjHR 1.03, 95%CI 1.02-1.03,P<0.001). Conclusions: This national cohort study of ICU survivors demonstrates that pre-admission polypharmacy is an independent risk factor for emergency readmission. In an ever-growing epidemic of polypharmacy, this risk factor may represent a substantial burden in the at-risk post-intensive care population.