October 5, 2012

Methadone Cuts HIV Risk

By Michael Smith, North American Correspondent, MedPage Today

Published: October 04, 2012

Reviewed by Dori F. Zaleznik, MD; Associate Clinical Professor of Medicine, Harvard Medical School, Boston

Injection drug users on opiate substitution treatment with methadone cut their risk of HIV infection by more than half, researchers reported.

In a systematic review and meta-analysis, people on methadone treatment had a 54% reduction in the risk of HIV compared with the usual incidence of the infection seen among injection drug users, according to Georgie MacArthur, BSc, of the University of Bristol in Bristol, England, and colleagues.

The finding "supports calls for the global increase of harm reduction interventions" aimed at injection drug users, MacArthur and colleagues argued online in BMJ.

The estimated prevalence of HIV is about 40% among the world's roughly 16 million injection drug users, the researchers noted, and injection drug use has driven several recent HIV outbreaks in Europe.

A standard approach to treating addiction is opiate substitution with methadone or buprenorphine (Subutex) but there has been no quantitative estimate of the effect of substitution therapy on HIV transmission.

To help fill the gap, MacArthur and colleagues conducted a systematic review, looking for data on how opioid substitution affected HIV incidence.

All told, they found 12 published studies with data on the effect of substitution treatment on HIV transmission, and they obtained unpublished data from three other studies.

All of the 15 studies looked at methadone substitution, they reported.

For a meta-analysis, data from nine studies – from the U.S., Canada, the U.K., The Netherlands, Austria, Italy, Thailand, Puerto Rico, and China -- could be pooled, they found, including 819 new HIV infections over 23,608 person years of follow-up.

The analysis showed "strong evidence" of a benefit: the rate ratio was 0.46, with a 95% confidence interval from 0.32 to 0.67, which was significant at P<0.001.

MacArthur and colleagues cautioned, however, that there was heterogeneity between studies that "could not be explained by geographical region, site of recruitment, or the provision of incentives."

Not all of the studies adjusted for confounding factors, but analysis of a subset of six that did still suggested that methadone substitution was associated with a 40% reduction in HIV risk.

The researchers cautioned that all of the included studies were observational and subject to both selection and attrition bias.

"The extent to which the studies were representative of all people who inject drugs and are receiving opiate substitution treatment is unclear," they noted.

Despite such limitations, however, the findings are "strong quantitative evidence of an association between opiate substitution treatment and reduced risk of HIV transmission among people who inject drugs," they concluded.

The study is a bookend to an earlier systematic review that found that substitution treatment reduced activities associated with a high risk of HIV transmission, according to Linda Gowing, PhD, of the University of Adelaide in Adelaide, Australia.

Taken together, the two studies "provide strong evidence" that the treatment – at least with methadone -- cuts both high-risk behavior and the risk of acquiring HIV, Gowing argued in an accompanying editorial.

She cautioned that the benefits of substitution therapy are likely to be lost when treatment stops -- especially if the treatment is not voluntary -- or when patients relapse and resume injecting drugs.

Policymakers, she argued, should aim at "maximizing the proportion of injecting drug users in the treatment program and promoting their retention" in care.

The study had support from the Centre for the Development and Evaluation of Complex Interventions for Public Health Improvement, the British Heart Foundation, Cancer Research UK, the Economic and Social Research Council, the Medical Research Council, the Welsh Assembly Government and the Wellcome Trust.

The journal said MacArthur did not report any conflicts.

The journal said Gowing did not report any conflicts.

Primary source: BMJ
Source reference:
MacArthur GJ, et al "Opiate substitution treatment and HIV transmission in people who inject drugs: systematic review and meta-analysis" BMJ 2012; 345: e5945.

Additional source: BMJ
Source reference:
Gowing LR "The role of opioid substitution treatment in reducing HIV transmission" BMJ 2012; 345: e6425.

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