Injectable-Only Overlapping Buprenorphine Starting Protocol in a Low-Threshold Setting.

Importance: Initiating buprenorphine for opioid use disorder (OUD) in outpatient settings has become more difficult for individuals using fentanyl. Novel buprenorphine starting strategies are needed, especially for people experiencing homelessness. Objective: To evaluate the short-term outcomes of the implementation of an injectable-only overlapping buprenorphine starting protocol in a low-threshold clinic and field-based setting serving individuals with OUD and active fentanyl use. Design, Setting, and Participants: This retrospective observational cohort study was based on electronic health record data from September 2024 to January 2025 of an urban low-threshold voluntary OUD treatment program embedded in a drop-in center that offered care in the clinic and at various outreach sites, including shelters, supportive housing buildings, and encampments. Patients with moderate to severe OUD using fentanyl were included if they chose to have initial medications ordered for the injectable-only overlapping buprenorphine starting protocol between September 1 and November 30, 2024. Follow-up data were collected through January 15, 2025. Exclusion criteria were consumption of sublingual buprenorphine in the week prior, current methadone use, or lack of active fentanyl use. Exposure: The injectable-only overlapping buprenorphine starting protocol, which does not require the cessation of fentanyl use before or during the process, includes the following steps: day 1 involves a weekly 8-mg injection without preceding sublingual buprenorphine, day 2 involves a weekly 16-mg injection, and day 3 involves a monthly 128-mg or 300-mg injection. Main Outcomes and Measures: The outcomes and cascade of care were rates of protocol initiation (receipt of the initial 8-mg buprenorphine injection), completion (eventual receipt of all 3 long-acting buprenorphine injections), and 2-month retention (receipt of a second monthly buprenorphine injection within 45 days of the first). Results: Ninety-five individuals met the inclusion criteria. These patients had a median (IQR) age of 39 (23-69) years and included 52 men (55%), 75 (79%) of whom were experiencing homelessness or living in permanent supportive housing. Of the 95 patients included, 85 (90%) initiated the protocol, 71 (75%) eventually completed the protocol, and 61 (64%) received a second monthly long-acting buprenorphine injection. Conclusions and Relevance: This retrospective cohort study found that a novel injectable-only overlapping buprenorphine starting protocol had a relatively high rate of completion and 2-month retention in a low-threshold setting for individuals with OUD who used fentanyl, most of whom were experiencing homelessness. These findings suggest that this protocol is a promising potential pathway for patients to start buprenorphine in the outpatient setting.