BACKGROUND: This study investigated treatment adherence among people with recent injecting drug use in a study of sofosbuvir/velpatasvir therapy for HCV infection. METHODS: SIMPLIFY is an international open-label, single-arm multicentre study that recruited participants with recent injecting drug use (previous six months) and chronic HCV genotype (G) 1-6 infection between March and October 2016 in seven countries (19 sites). Participants received sofosbuvir/velpatasvir once-daily for 12 weeks administered in a one-week electronic blister pack (records the time and date of each dose) for 12 weeks. We evaluated non-adherence (<90% adherent) as measured by electronic blister-pack assessed using logistic regression and generalised estimating equations (continuous) with detailed analyses of dosing dynamics. RESULTS: Among 103 participants, 97% (n = 100) completed treatment. Median adherence to therapy was 94%. Overall, 32% (n = 33) were considered non-adherent (<90% adherence). Adherence significantly decreased over the course of therapy. Recent stimulant injecting (cocaine and/or amphetamines) at treatment initiation and during treatment was independently associated with non-adherence. Inconsistent dose timing (standard deviation of daily dose timing of >/=240 min) was also independently associated with non-adherence to therapy. Factors associated with inconsistent dose timing included lower levels of education and recent stimulant injecting. SVR was similar among adherent and non-adherent populations (94% vs. 94%, P = 0.944). CONCLUSION: This study demonstrated high adherence to once-daily sofosbuvir/velpatasvir therapy among a population of people with recent injecting drug use. Recent stimulant injecting prior to and during DAA therapy and inconsistent dose-timing during treatment was associated with non-adherence. However, there was no impact of non-adherence on response to therapy, suggesting that adherence is not a significant barrier to successful DAA therapy in people with recent injecting drug use.
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