Clinical Characteristics and Prognostic Factors among Hospitalized Patients with Substance Use Disorders: Findings from a Retrospective Cohort Study of a Canadian Inpatient Addiction Medicine Service.

Introduction: Inpatient addiction medicine services (AMS) were developed in response to the growing needs of hospitalized individuals with substance use disorders (SUDs). AMS aim to enable timely initiation of pharmacologic treatment, build hospital capacity to support patients who use substances, and facilitate transition to community services. As an emerging service being adopted in hospitals across North America, the model of care, populations served, substance use trends, and clinical trajectory has not been widely described. This work aims to characterize patients accessing care through the AMS, establishing predictors for clinical trajectories in hospital including patient-initiated discharge (PID) and hospital re-admission.Methods: Using a retrospective cohort design, we describe all patients seen by the AMS between 2018 and 2022 across four hospitals in Hamilton, Ontario. Patients seen by AMS were hospitalized and qualified for a SUD based on DSM-V criteria. The study used descriptive statistics to describe the cohort, where appropriate adjusted timeto-event survival models were constructed to identify predictors for hospital re-admission.Results: Patients seen by the AMS (n = 695) frequently lacked access to primary care (47.0 %) and less than half (44.3 %) were receiving community addiction services on admission. The majority met criteria for opioid use disorder (OUD), with injecting being the primary consumption route (54.8 %). Patients exhibited high acuity, with 34.2 % requiring critical care measures. Provision of OAT substantially increased to 77.9 % of patients (29 % on admission). PID occurred in 17.8 % of patients and was significantly associated with an admitting diagnosis of suicidal ideation, infection, heart failure, and distinct substance use profiles including methamphetamine, fentanyl, and heroin use (p < 0.05). PID conferred a 66 % increased risk for re-admission (Hazard-Ratio: 1.66; 95 % CI: 1.08, 2.54; p = 0.02).Conclusion: Patients served by AMS primarily include individuals with OUD presenting with the associated medical complications and substantial deficits in the social determinants of health (e.g., high housing insecurity, poverty, and disability). PID occurs among 1 in 5 people and is associated with higher rates of re-admission. By identifying individuals at higher risk of adverse outcomes, these results provide an opportunity to improve outcomes in this high-risk, high-vulnerability population.