Methadone reduces the risk of HIV transmission in people who inject drugs (PWID), as reported by an international team of researchers in a paper published October 5 in the online edition of theBritish Medical Journal. This team included Dr. Julie Bruneau from the CHUM Research Centre (CRCHUM) and the Department of Family Medicine at the University of Montreal.

"There is good evidence to suggest that opiate substitution therapies (OST) reduce drug-related mortality, morbidity and some of the injection risk behaviors among PWID. However, to date there has been no quantitative estimate of the effect of OST in relation to HIV transmission. This new study provides solid evidence demonstrating the link between these treatments and a reduced risk of HIV transmission," notes Dr. Bruneau, one of the six investigators who worked with Dr. Matthew Hickman, the study's principal investigator and Professor in Public Health and Epidemiology at the University of Bristol (UK).

"These results are important given that increases in HIV incidence have been reported among PWID in a number of countries in recent years, where opiate substitution therapies are illegal or severely restricted," adds Dr. Bruneau. 

Injection drug use is a major risk factor for the transmission of HIV and AIDS. It is estimated that around 5-10% of HIV infections worldwide are due to injection drug use. Methadone and buprenorphine are the main forms of drug prescribed for addicts and are frequently prescribed as opiate substitution therapies.

The results of this study are the fruit of an international collaborative effort. Authors from the US, Canada, Italy and Australia carried out a review and pooled analysis (known as a meta-analysis) of several published and unpublished studies from multiple countries (including the USA, Canada, the UK, the Netherlands, Austria, Italy, Thailand, Puerto Rico and China) to determine the association between OST and HIV transmission among PWID. The nine selected studies looked predominantly at males between 26 and 39 years old and totalled 819 incidents of HIV infection with 23,608 person-years of follow-up.

After analysing these studies, authors found that OST was associated with a 54% reduction in risk of HIV infection among PWID. There were differences between the studies, including different background rates of HIV infection, making it impossible to calculate an "absolute risk reduction" for HIV infection that would translate to all settings. And not all studies reported adjustments to the intervention to take account of other factors that might influence the association between OST and HIV infection. But the impact of OST on HIV was strong and consistent in further analyses in the paper. There was weak evidence to suggest that longer duration of OST exposure may be associated with greater benefit.

For Dr. Bruneau, the results of this study favour the promotion of opiate substitution therapies: "These therapies can reduce HIV transmission among PWID not only in countries in which there is a high incidence of this disease, but also in Quebec where there has been an increase in the use of illicit opiates intravenously, particularly among youths, and where access to OST is problematic."