Dolutegravir (DTG, GSK1349572) is an integrase inhibitor that is currently in Phase 3 clinical development for the treatment of HIV infection. As HIV-infected subjects may also be receiving methadone for opioid dependence, an evaluation of the potential interaction between DTG and methadone is warranted. The primary objective of this study is to determine whether concomitant administration of DTG can affect the pharmacokinetics (PK) of methadone. As a secondary endpoint, the PK of DTG will be compared to historical data. This study will be open-label with subjects receiving DTG and stable doses of methadone. The study will be conducted at one center in Canada in adult male and female subjects.