Supplementary Material for: Intravenous Misuse of Methadone, Buprenorphine and Buprenorphine-Naloxone in Patients Under Opioid Maintenance Treatment: A Cross-Sectional Multicentre Study

Background: The act of intravenous misuse is common in patients under opioid maintenance treatment (OMT), but information on associated factors is still limited. Objectives: To explore factors associated with (a) intravenous OMT misuse, (b) repeated misuse, (c) emergency room (ER) admission, (d) misuse of different OMT types and (e) concurrent benzodiazepine misuse. Methods: We recruited 3,620 patients in 27 addiction units in Italy and collected data on the self-reported rate of intravenous injection of methadone (MET), buprenorphine (BUP), BUP-naloxone (NLX), OMT dosage and type, experience of and reason for misuse, concurrent intravenous benzodiazepine misuse, pattern of ­misuse in relation to admission to the addiction unit and ER ­admissions because of misuse. According to inclusion/exclusion criteria, 2,585 patients were included. Results: Intravenous misuse of OMT substances was found in 28% of patients with no difference between OMT types and was associated with gender, age, type of previous opioid abuse and intravenous benzodiazepine misuse. Repeated OMT misuse was reported by 20% (i.e., 71% of misusers) of patients and was associated with positive OMT misuse experience and intravenous benzodiazepine misuse. Admission to the ER because of misuse complications was reported by 34% of patients, this outcome being associated with gender, employment, type of previous opioid abuse and intravenous benzodiazepine misuse. OMT dosage was lower than the recommended maintenance dosage. Conclusions: We offered new information on factors associated with intravenous OMT misuse, repeated misuse and ER admission in Italian patients under OMT. Our data indicate that BUP-NLX misuse is not different from that of BUP or MET. Choosing the more expensive BUP-NLX over MET will likely not lead to the expected reduction of the risk of injection misuse of the OMT. Instead of prescribing new and expensive OMT formulations, addiction unit physicians and medical personnel should better focus on patient’s features that are associated with a higher likelihood of misuse. Care should be paid to concurrent benzodiazepine and OMT misuse.