Low-threshold methadone maintenance reduces HIV risk for people who inject drugs

Receiving methadone maintenance therapy through primary care physicians or community pharmacies significantly reduced the risk of HIV infection for people who inject drugs in Vancouver, findings of a cohort study published this week in Lancet HIV show.

Methadone maintenance therapy is a form of opioid substitution therapy. Its provision in drug treatment programmes has been shown to reduce the risk of HIV infection in people who inject drugs in several cities in the United States, but access to methadone remains restricted both in the United States and in many other countries.

One barrier to obtaining methadone lies in the restrictions placed on access and prescribing. Services with a high threshold to access – such as only prescribing methadone within a drug detoxification programme, with regular tests to check on heroin use – limit access to methadone to those drug users who are able to undertake such a programme.

Harm reduction approaches to injecting drug use have emphasised the importance of lowering the threshold for access to methadone, in order to enable drug users to avoid drug injecting. `Low-threshold` methadone provision can include prescribing through primary care physicians (as in France and British Columbia), walk-in methadone clinics (as in Hong Kong) and mobile harm reduction services (Amsterdam).

In Canada methadone has been available for prescription since 1996. In the province of British Columbia primary care physicians prescribe methadone, which is dispensed as daily or weekly doses at community pharmacies.

To assess the impact of low-threshold methadone prescribing on the risk of HIV acquisition among people who inject drugs in the Vancouver area, researchers at the British Columbia Centre for Excellence in HIV/AIDS and the University of British Columbia examined data from the Vancouver Injection Drug Users Study. This cohort study recruited people who inject drugs in 1996 in the Greater Vancouver area.

The study assessed the risk of HIV infection according to methadone use in 1639 people who were HIV-negative at baseline and who returned for at least one follow-up visit at which they were tested for HIV. The study sample were older than people who did not return for HIV testing, and less likely to have reported unprotected sex. Approximately two-thirds were men (67%). At baseline 20% of the study sample had received methadone in the previous six months.  

Participants were followed for a median of 75.5 months, during which time 138 acquired HIV infection, an incidence of 1.21 per 100 person-years. After four years of follow up the cumulative incidence of HIV in those who had received methadone at baseline was 2.3%, compared to 8.9% in those not receiving methadone. People receiving methadone at baseline were less likely to inject heroin daily, to borrow a used syringe or to engage in unprotected sex.

Methadone maintenance was associated with a 36% reduced risk of acquiring HIV during the follow-up period after controlling for patterns of drug use including syringe borrowing and cocaine injecting, and demographic or situational factors including ethnicity, age, incarceration and sex work (adjusted relative hazard 0.64, 95% confidence interval 0.41-0.98).

In an accompanying editorial comment, Zunyou Wu of the Chinese Center for Disease Control and Prevention and Roget Detels of the University of California Los Angeles School of Public Health note that “drug use is an illness for which methadone is an essential medicine.” They noted the low coverage of methadone in the cohort, which was recruited on the street rather than in clinic settings, and the importance of more intensive efforts to reach people who inject drugs in order to limit HIV transmission.