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Injection Drug Users and Adherence to Hepatitis C Treatment


Adherence to hepatitis C treatment was high regardless of injection drug use, a recent Australian study found. Interferon ineffectiveness was primarily driven by discontinuing therapy early rather than skipping doses.

Hepatitis C treatment is most effective for people who have recently been infected with hepatitis C virus (HCV). Sustained virological response (SVR) rates are as high as 88% among recently infected individuals treated with pegylated interferon monotherapy for 12-24 weeks, and as high as 74% among HIV positive people recently coinfected with HCV who are treated with pegylated interferon plus ribavirin.

The Australian Trial in Acute Hepatitis C (ATAHC) study found that SVR rates were higher among HCV monoinfected participants who adhered to therapy than among those who did not achieve good adherence (63% vs 29%, respectively). The study also found that SVR rates were similar among participants who did and did not inject drugs during treatment (59% vs. 53%), and rates were not related to frequency of injection.

Many healthcare providers are reluctant to treat current and recovering injection drug users (IDUs) despite data showing that treatment response rates among IDUs are comparable to those among non-IDUs. Although there is widespread concern that IDUs may not be able to stay on treatment, little is known about adherence to hepatitis C treatment in these populations.

In a study described in the July 2011 Journal of Hepatology, Jason Grebely and colleagues measured adherence at various times during acute hepatitis C treatment to better understand its role in treatment success, how it affects people with recently acquired HCV infection, and differences or similarities in adherence between IDUs and non-IDUs.

All participants were recruited between June 2004 and November 2007 from a network of hospitals in Australia. Participants were eligible if they received their first anti-HCV antibody test result within the past 6 months and had either:

  • Acute clinical HCV infection, defined as symptomatic seroconversion illness characterized by ALT levels greater than 10 times the upper limit of normal at least 1 year before the initial antibody test;
  • Asymptomatic HCV infection with seroconversion defined as having a negative anti-HCV antibody test in the 2 years before the positive result.

Of the 109 participants, 74 (68%) had HCV monoinfection and 35 (32%) were HCV/HIV coinfected. The median age was 35 years and 79 patients (74%) were men; 55% of participants had HCV genotype 1, while the remaining 45% had genotypes 2, 3, or their results were missing. Neither heavy alcohol use nor active drug use were exclusion criteria, and 82 participants (75%) had a history of current or previous injection drug use.

Participants with HCV monoinfection were treated with weekly pegylated interferonmonotherapy for 24 weeks, while those with HIV/HCV coinfection were treated with pegylated interferonplus ribavirin (1000-1200 mg for those with genotype 1 and 800 mg for those with genotypes 2 or 3), also for 24 weeks. Participants were seen at baseline, every 2 weeks through week 8 of treatment, and then every 4 weeks.  Participants completed a questionnaire every 12 weeks, providing information about injection drug use, social functioning, and psychological parameters.

Adherence to pegylated interferon was defined as taking 80% of scheduled doses for 80% of the treatment period (80/80). Ribavirin adherence was not measured because only 32% of participants were coinfected and prescribed ribavirin. Treatment response was based on intention-to-treat, including all participants who received even a single injection of pegylated interferon. The primary endpoint was the proportion of study participants who achieved SVR, or undetectable HCV RNA at 48 weeks (24 weeks after the end of treatment).


  • Among all study participants, the pegylated interferon 80/80 adherence rate was 82%.
  • 15 participants (14%) missed 1 or more pegylated interferon dose, translating to an on-treatment adherence rate of 99%.
  • Participants who had ever injected drugs and those who had never done so had similar adherence:
    • pegylated interferon 80/80 adherence: 81% vs 85%, respectively;
    • mean number of weeks on treatment: 20% vs 21%;
    • proportion who completed 24 weeks of treatment: 68% vs 74%;
    • proportion with 1 or more missed pegylated interferon doses: 13% vs 15%.
  • Likewise, participants who had used and those who had not used injection drugs 30 days before beginning HCV treatment also had similar pegylated interferon 80/80 adherence, mean number of weeks on treatment, proportion who completed the 24 weeks of treatment, and proportion with 1 or more missed doses.
  • Among participants who injected drugs while on treatment, pegylated interferon 80/80 adherence, mean number of weeks on treatment, completion of 24 weeks, and missing 1 or more doses were again comparable to those who did not inject drugs during treatment.
  • Compared to the 25% of participants who did not report a history of injection drug use, participants with drug injection experience were on average younger, more likely to be women, less likely to have education beyond high school, less likely to have stable housing, and less likely to have part-time or full-time work.
  • Pegylated interferon 80/80 adherence was more likely among people with privately owned accommodations and those with HIV coinfection, but less likely for those with no education beyond high school.
  • In the overall study population, the only factor associated with pegylated interferon 80/80 adherence was education beyond high school.
  • Among participants not lost to follow-up, pegylated interferon 80/80 adherence and treatment completion were similar among people with depression during treatment, injection during in the 30 days prior to beginning treatment, alcohol consumption during treatment, and a maximum social functioning score during treatment.
  • The mean number of weeks on treatment was 20, broken down as follows:
    • 0-4 weeks: 10%;
    • 5-19 weeks: 14%;
    • 20-23 weeks: 6%;
    • All 24 weeks: 70%.
  • Reasons for discontinuing treatment included physician-directed early termination, patients’ unwillingness to continue therapy, virological non-response (6 participants stopped at week 12 due to a lack of early virological response), loss to follow-up, side effects, death, and people who tested HCV RNA positive at screening but negative at the start of treatment (spontaneous clearance or test error).
  • Discontinuations due to side effects were primarily a result of mental health problems -- depression, insomnia, mood swings, and fatigue.
  • Of the 13 participants unwilling to continue treatment or lost to follow-up, 10 had a history of injection drug use, but only 3 of the 10 had injected in the 30 days before beginning treatment.
  • Of the 11 participants who discontinued treatment prior to 4 weeks, 4 were unwilling to continue or lost to follow-up, 3 had side effects, 1 died, and 3 tested HCV RNA positive at screening but negative at the start of treatment.
  • Comparing HCV monoinfected and HIV/HCV coinfected groups, coinfected participants had a somewhat higher pegylated interferon adherence rate (91% vs 77%) and greater mean number of weeks on treatment (22% vs 20%), but these were not statistically significant.
  • The proportion of people in each group that missed at least 1 pegylated interferon dose was comparable.
  • The likelihood of achieving an SVR was considerably higher among participants with pegylated interferon 80/80 adherence compared to those without.
  • However, there was no difference in SVR between people who did and did not miss doses while on treatment.
  • Participants who completed the full 24 weeks of treatment were significantly more likely to achieve SVR (76%) than those who discontinued therapy between 0-4 weeks (9%), 5-19 weeks (33%), or 20-23 weeks (43%).

“This study demonstrates a high adherence to pegylated interferon among HCV and HCV/HIV injecting drug users...receiving treatment for recent HCV infection,” the researchers wrote. “These data suggest that recent [injection drug use] does not influence subsequent adherence to HCV therapy.”

They continued, “[T]he majority of sub-optimal pegylated interferon exposure in this study was due to early discontinuation of treatment as opposed to missed doses during therapy.”

Injection drug use, whether recent or current, did not independently predict non-adherence, although socioeconomic factors including lack of education and stable housing were independent predictors of non-adherence.

The authors noted some limitations of their study:

  • Adherence was measured by nurse assessment, possibly causing under-reporting of missed doses and overestimating adherence;
  • Self-report, which is subject to recall bias and the desire to please researchers, is also likely to overestimate adherence;
  • The HIV/HCV coinfected group could not be fully assessed because it was too small (32% of study participants) and varied from the monoinfected group across a wide range of social and demographic demographics.
  • The overall small size of the study.

This study “does raise the question of whether comprehension of the rationale for treatment and treatment side effects may play a part in maximizing adherence, and suggests that further focus needs to be given to pre-treatment education and preparation,” Grebely and colleagues recommended.

The researchers concluded, “These data suggest that adherence is not compromised among IDUs, supporting guidelines that active IDUs should not be excluded from HCV therapy and the decision to initiate HCV treatment in active IDUs should be made case by case...Strategies to enhance adherence will be important, particularly given the potential for drug resistance with the roll-out of directly acting antivirals.”

Investigator affiliations:National Centre in HIV Epidemiology and Clinical Research, University of New South Wales (UNSW), Sydney, Australia; HIV/Immunology/Infectious Diseases Clinical Services Unit, St. Vincent’s Hospital, Sydney, Australia; Centre for Population Health, Burnet Institute, Melbourne, Australia; Infectious Diseases Unit, The Alfred Hospital, Melbourne, Australia; Department of Medicine, Royal Adelaide Hospital, Adelaide, Australia; Kirketon Road Centre, Sydney, Australia; Inflammation and Infection Research Centre, School of Medical Sciences, UNSW, Sydney, Australia



J Grebely, G Matthews, M Hellard, et al (ATAHC Study Group). Adherence to treatment for recently acquired hepatitis C virus (HCV) infection among injecting drug users. Journal of Hepatology 55(1):76-85 (abstract). July 2011.

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