Opioid substitution treatment increases chances that people who inject drugs will have good adherence to HIV therapy

Opioid substitution treatment (OST) increases the chances of people who inject drugs achieving good adherence to highly active antiretroviral therapy (HAART) by 68%, Canadian investigators report in the online edition of AIDS.

Researchers monitored 1852 people living with HIV, who were injecting drugs and who were eligible for HIV treatment, for an average of 5.5 years. They wanted to see if there was a causal relationship between OST and adherence to HIV treatment – at least 95% adherence assessed by pharmacy refill. After controlling for potential confounders, OST increased the odds of HIV treatment adherence by two-thirds, a finding that remained robust in a sensitivity analyses.

“This study demonstrates the substantial benefits of OST in linking HIV-positive opioid-dependent individuals into HAART in a universal healthcare setting with freely available HAART,” comment the authors. “There is a priority to expand access to OST particularly within HIV-positive populations, to optimize HIV treatment uptake and adherence and its subsequent individual and population health and economic benefits.”

People who inject drugs are globally marginalised and have high rates of HIV infection. They are also one of the groups least likely to benefit from HIV treatment and have poor rates of treatment uptake and adherence.

In most developed countries, OST with methadone or buprenorphine is indicated for the treatment of people who inject drugs who are opioid-dependent. OST may have benefits for people living with HIV who inject drugs in terms of adherence to HIV treatment. It is possible that OST increases the likelihood of adherence because of the stability to provides to users. OST is also likely to provide linkage to healthcare services, therefore allowing people to access HIV treatment and adherence support.

Investigators in British Columbia, Canada, wanted to determine the causal effect of OST exposure on adherence to HIV treatment among people living with HIV who inject drugs.

They linked records regarding OST use and HIV treatment adherence for 1852 people who inject drugs who became eligible for HIV treatment between 1996 and 2010. Adherence to HIV treatment was defined as at least 95% pharmacy refill per calendar month. OST exposure was defined as at least 95% days of OST dispensed per calendar month.

A third of people included in the study were women and the median age was 35 years. A fifth of individuals were on OST when they started or became eligible for HIV treatment; 39% of individuals had accessed OST in the past. By the end of follow-up, 50% of the study population has accessed OST.

Patients spent over half (56%) the time they were receiving OST on HIV treatment. If out of OST, patients were receiving HIV treatment for only 36% of the time.

Overall, OST doubled the chances of good adherence to HIV treatment (AOR = 1.96; 95% CI, 1.72-2.24). The benefits of OST remained highly significant when the investigators took into account potential confounders (AOR = 1.68; 95% CI, 1.48-1.92).

“This study has demonstrated a 68% increase in the odds of HAART medication refill due to OST exposure,” comment the authors.

The positive effects of OST remained apparent in sensitivity analyses that changed definitions of OST exposure (requirement to be on minimum effect dose; requirement to be on stable maintenance dose) or HIV treatment adherence thresholds.

The authors believe their findings have important implications for the provision of health care and OST to people living with HIV who inject drugs.

“The benefits in HAART medication refill adherence caused by exposure to OST lead directly to improved disease progression profiles, as well as reductions in infectivity through viral suppression,” the investigators write. “These secondary benefits of OST should be incorporated directly into simulation models developed to determine the long-term cost-effectiveness of competing OST modalities and population-level OST uptake.”