Opiate substitution treatment associated with reduced risk of HIV transmission among injection drug users

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Key findings:

  1. This meta-analysis found a 54% reduction in risk of HIV infection associated with opiate substitution treatment among injection drug users.
  2. HIV incidence was reported to be higher in methadone detoxification treatment when compared to placebo or methadone maintenance therapy.

Primer: HIV prevention and disease control are priorities in public health. Rates of HIV infection amongst injection drug users are alarmingly high due to the efficiency of transmission through sharing of injecting equipment. Opiate substitution treatment aims to reduce risk of transmission by prescribing a drug with similar effects as the drug of use but with reduced associated risk. Currently, the most common form of substitution therapy is methadone syrup taken orally. Burphrenine has recently become more widely used in the form of an oral tablet. Alternatives to substitution therapy include detoxification or residential rehabilitation. Substitution treatment has been associated with reductions in behaviors that carry a high-risk of HIV transmission and could potentially improve adherence to antiretroviral therapy in patients already diagnosed with HIV. An earlier systematic review found that treatment is consistently associated with reduced illicit opioid use, injection drug use, sharing of injecting equipment, and multiple sex partners, but this review could not quantify the risk reduction due to methodological limitations.

Background reading:

  1. Gowing LR. The role of opioid substitution treatment in reducing HIV transmission. BMJ 2012;345:e6425.
  2. Gowing L, Farrell MF, Bornemann R, et al. Oral substitution treatment of injecting opioid users for prevention of HIV infection. Cochrane Database of Systematic Reviews 2011, Issue 8. Art. No.:CD004145. DOI:10.1002/14651858.CD004145.pub4.

This [systematic review] study: This systematic review and meta-analysis sought to determine the effect of opiate substitution therapy on HIV transmission among injection drug users. The review included data from 15 observational studies, of which 12 were published and 3 were unpublished. Methadone maintenance treatment was generally associated with lower risk of HIV infection. Data from 9 studies which could be appropriately pooled in a meta-analysis quantified this effect as a 54% reduction in risk of HIV infection (rate ratio 0.46, 95% CI 0.32-0.67; P<0.001) with significant heterogeneity between studies. Univariable meta-regression analysis found no evidence that the effectiveness of methadone maintenance treatment varied by geographical region, site of recruitment, or provision of incentives to participants. As a secondary objective, the review identified four studies comparing methadone detoxification treatment with either no treatment or with methadone maintenance treatment and HIV incidence was reported to be higher in those undergoing detoxification.

In sum: This study provides the first quantitative estimate of the association between opiate substitution therapy and HIV incidence. These results strengthen and support findings of a previous review by identifying additional relevant studies. This was achieved by including studies that were not yet published and studies where effects of opiate substitution treatment were reported with secondary analyses and therefore may not have had relevant terms in the title or abstract. The study had a number of limitations. A key limitation is that results were based on data from observational studies, which are prone to bias; a randomized controlled trial, however, is no longer ethical given the large beneficial effect observed with opiate substitution treatment. Results may overestimate or underestimate true effects if, for example, more motivated individuals tend to enter treatment or infrequent/lower-risk injection drug users were not included. The control of confounders was inconsistent between studies and the effect of co-interventions, such as supervised injection facilities, is unclear. The generalisability of the results is also limited since studies on treatments other than methadone maintenance did not meet eligibility criteria. Further investigation is necessary to determine the safety and effectiveness of non-methadone substitution treatments. Greater attention should also be directed at reducing risk of HIV transmission through sexual behavior.

 Click to read in BMJ

Written by [AdC] and [AC]

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