GSK1349572 has shown to be effective against viruses in a short-term monotherapy study in adults with no previous exposure to integrase inhibitors. The purpose of this study is to determine whether GSK1349572 is effective in the treatment of HIV-infected patients who no longer respond to treatment with the approved integrase inhibitor raltegravir and carry viruses with resistance to this drug. The safety and efficacy of GSK1349572 50mg once daily in combination with the background HIV drugs previously administered (unless discontinuation of a particular drug is required) will be assessed over 10 days (functional monotherapy phase), followed by the evaluation of the safety and efficacy of GSK1349572 given with a new optimised background regimen from Day 11 through at least Week 24.