In Part A, approximately 12 subjects will receive GSK1349572 50mg every 24 hours (q24h) for 5 days (Treatment A). Subjects will then be administered GSK1349572 50mg q24h in combination with FPV/RTV 700/100 mg every 12 hours (q12h) (Treatment B) for 10 days. There will be no washout between treatments. In Part B 15 subjects will receive a single 50 mg dose (2 x 25mg tablet) in 3 different tablet variants of the same formulation, differing only in particle sizes of GSK1349572, under fasted conditions in a three-way crossover design. Safety evaluations and serial PK samples will be collected during each treatment period. A follow-up visit will occur 7-14 days after the last dose of study drug.