Interactions between methadone and medications used to treat HIV infection: A review

Background: It is critical for providers caring for HIV-positive methadone recipients to have accurate information on pharmacologic interactions between methadone and antiretroviral therapy. If providers do not have these data, symptoms of narcotic withdrawal or excess due to medication interactions may be mismanaged, and antiretroviral regimens may be suboptimal in efficacy or associated with increased side effects and toxicities. This review was undertaken to clarify what is known about interactions between pharmacotherapies of opiate dependence and HIV-related medications, to suggest clinically useful approaches to these issues, and to outline areas which need further study. Methods: A search for relevant published papers and abstracts presented at scientific meetings was conducted using electronic databases. These documents were obtained and reviewed, and additional publications referenced in them were also reviewed. Results: Pharmacokinetic interactions between methadone and zidovudine, didanosine, stavudine, abacavir, nevirapine, efavirenz and nelfinavir have been documented. The mechanisms, clinical implications and management of these interactions are reviewed. Conclusions: Interactions between methadone and some HIV-related medications are known to occur, yet their characteristics cannot reliably be predicted based on current understanding of metabolic enzyme induction and inhibition, or through in vitro studies. Only carefully designed and conducted pharmacologic studies involving human subjects can help us define the nature of the interactions between methadone (and other pharmacotherapies for opiate dependence) and specific HIV-related medications. Clinicians must be aware of known interactions and be alert to the possibility that interactions which are still undocumented may be present among their patients.