Study (ING112961) is a Phase IIb, multicentre, open-label, single arm, two cohorts, pilot study to assess the antiviral activity of GSK1349572 containing regimen in HIV-1 infected ART-experienced adults with raltegravir (RAL) resistance. The study will include approximately 50 ART-experienced subjects with either current or past virologic failure to RAL. All subjects must harbour isolates with RAL resistance mutations at Screening. Subjects should also have documented genotypic and/or phenotypic resistance to at least one compound from each of three or more of the approved classes of ART (including integrase inhibitors [INIs]). Subjects with current RAL virologic failure will substitute RAL with GSK1349572 50mg once daily and continue the remaining components of their failing regimen through Day 10. Subjects with historical RAL virologic failure will add GSK1349572 50mg once daily to their failing regimen through Day 10. On Day 11 all subjects will continue GSK1349572 and optimize their background therapy. Antiviral activity, safety and tolerability of GSK1349572 will be evaluated at Day 11 and over time through at least Week 24.