title: Initiation into prescription opioid injection and associated trends in heroin use among people who use illicit drugs.
abstract: Prescription opioid (PO) injection among people who use illicit drugs (PWUD) is an ongoing concern, yet little is known about drug use trajectories associated with initiating PO injection, including potential associations with heroin use. This study aimed to identify predictors of PO injection initiation among PWUD, and examine trends in heroin use before and after initiating PO injection.
  
  
  
  Data were merged from three cohorts of PWUD recruited between September 2005 and November 2015. Predictors of PO injection initiation were identified using extended Cox regression models. Trends in heroin use pre- and post-initiation were examined with McNemar's test and compared to matched controls with linear growth curve models.
  
  
  
  Among 1580 participants, 247 initiated PO injection yielding an incidence density of 3.9 (95% Confidence Interval [CI]: 3.4-4.4) per 100 person-years. In a multivariable analysis, independent predictors of PO injection initiation included heroin injection (Adjusted Hazard Ratio [AHR]=4.39, 95% CI: 3.24-5.95) and non-injection PO use (AHR=1.99, 95% CI: 1.25-3.17). In a sub-analysis, compared to matched controls, PO injection corresponded with elevated heroin use post-initiation (p≤0.05).
  
  
  
  In this study, heroin use and non-injection PO use strongly predicted PO injection initiation. Those who initiated PO injecting had elevated heroin use patterns post-initiation compared to controls. These findings suggest that transitioning to PO injection does not appear to be a substitute for heroin use among PWUD. These findings highlight the importance of addressing PO injection in harm reduction and treatment settings.
authors: British Columbia Centre for Excellence in HIV/AIDS, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, BC, V6Z 1Y6, Canada; School of Population and Public Health, University of British Columbia, 2206 East Mall, Vancouver, BC, V6T 1Z3, Canada.
authors: Stephanie
authors: S
authors: Lake
authors: British Columbia Centre for Excellence in HIV/AIDS, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, BC, V6Z 1Y6, Canada; Department of Medicine, University of British Columbia, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, BC, V6Z 1Y6, Canada.
authors: M-J
authors: MJ
authors: Milloy
authors: British Columbia Centre for Excellence in HIV/AIDS, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, BC, V6Z 1Y6, Canada.
authors: Huiru
authors: H
authors: Dong
authors: British Columbia Centre for Excellence in HIV/AIDS, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, BC, V6Z 1Y6, Canada; Department of Medicine, University of British Columbia, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, BC, V6Z 1Y6, Canada.
authors: Kanna
authors: K
authors: Hayashi
authors: British Columbia Centre for Excellence in HIV/AIDS, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, BC, V6Z 1Y6, Canada; Department of Medicine, University of British Columbia, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, BC, V6Z 1Y6, Canada.
authors: Evan
authors: E
authors: Wood
authors: British Columbia Centre for Excellence in HIV/AIDS, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, BC, V6Z 1Y6, Canada; Department of Medicine, University of British Columbia, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, BC, V6Z 1Y6, Canada.
authors: Thomas
authors: T
authors: Kerr
authors: British Columbia Centre for Excellence in HIV/AIDS, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, BC, V6Z 1Y6, Canada; School of Public Policy, Simon Fraser University, Suite 3271-515 West Hastings Street, Vancouver, BC, V6B 5K3, Canada. Electronic address: uhri-kd@cfenet.ubc.ca.
authors: Kora
authors: K
authors: DeBeck
mesh_terms: D000328:Adult; D000701:Analgesics, Opioid / Q000008:administration & dosage*; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D003932:Heroin / Q000008:administration & dosage*; D006801:Humans; D013287:Illicit Drugs / Q000009:adverse effects; D007267:Injections; D008297:Male; D009293:Opioid-Related Disorders / Q000175:diagnosis / Q000453:epidemiology*; D063487:Prescription Drug Misuse / Q000009:adverse effects; D011446:Prospective Studies; D015819:Substance Abuse, Intravenous / Q000175:diagnosis / Q000453:epidemiology*; D011795:Surveys and Questionnaires; D055815:Young Adult
chemical_list: D000701:Analgesics, Opioid; D013287:Illicit Drugs; D003932:Heroin
keywords: Heroin; Initiation; Injection drug use; Prescription opioids