Opioid agonist therapy (OAT) in people who inject drugs was found to be associated with an increased likelihood of treatment initiation for concomitant hepatitis C virus (HCV) infection, according to the findings of a large Canadian retrospective longitudinal cohort study published in Clinical Infectious Diseases. Although injection drug users have a disproportionately high rate of HCV compared with the general population in Canada, their rate of HCV treatment initiation remains lower than the general population, the authors wrote.
The multicenter team of investigators accessed the British Columbia Hepatitis Testers Cohort (BC-HTC) for data on injection drug users and included people diagnosed with chronic HCV infection. The main outcome was HCV treatment initiation, which the investigators assessed using PharmaNet HCV treatment dispensing data. Initiation of treatment for HCV was defined as at least 1 episode of medication being dispensed, regardless of treatment completion.
The investigators evaluated OAT status using PharmaNet OAT dispensing data and created a time-varying variable for current OAT; an anchored variable for recent, past, or never OAT; and a cascade of retention for OAT ranging from less than 3 months to more than 24 months.
All data were available from January 1996 through June 2019. However, to account for the significant effect that direct-acting antivirals (DAAs) had on HCV treatment, the investigators restricted their time-to-event analysis to the beginning of the DAA era, which was October 27, 2013, in Canada (when the first DAA-containing regimen was approved for treatment of chronic HCV infection), in order to measure the impact of OAT on HCV treatment initiation.
There were 19,108 individuals who inject drugs identified as having chronic HCV infection between January 1992 and June 30, 2019. There were 13,803 patients during the DAA era, 10% of whom had HIV/AIDS and 48% of whom reported harmful alcohol use. Among recent and past users of injection drugs from the DAA era, 52% and 69% had a history of opioid use, respectively, and 56% and 59% had a history of stimulant use, respectively.
In the entire cohort, 39% never received OAT compared with 33% of patients from the DAA era. Most of the patients overall (60%) and from the DAA era (68%) never started treatment for HCV.
In the OAT retention cascade, 5770 patients were on OAT as of June 2019, with 47% having started HCV treatment at any time up until that point. As the length of time on OAT increased, the proportion of patients receiving HCV treatment increased. Among patients who were retained on OAT for more than 24 months, 58% had started HCV treatment compared with 22% of people who inject drugs who were not on OAT by the end of the study period.
Both univariate and multivariate analyses of patients from the DAA era showed a significant association between current OAT and HCV treatment initiation (hazard ratio [HR], 1.50; 95% CI, 1.41-1.59; adjusted HR, 1.50; 95% CI, 1.40-1.61). OAT was significantly associated with HCV treatment initiation in the overall cohort, as well. Starting 1 year after HCV diagnosis for patients in both the DAA era and the overall cohort, those currently on OAT had a higher probability of initiating HCV treatment.
The study authors noted that stimulant and opioid use were likely under-reported, and the study had the inherent limitation of using administrative data instead of self-reported drug use data.
In conclusion, the investigators wrote that their findings “provide further rationale to increase integration of HCV treatment with substance use services, in an effort to intensify HCV treatment initiation.”
Disclosure: Multiple study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.
Bartlett SR, Wong S, Yu A, et al. The impact of current opioid agonist therapy on hepatitis C virus treatment initiation among people who use drugs from in the DAA era: a population-based study. Clin Infect Dis. Published online June 14, 2021. doi:10.1093/cid/ciab546