GSK1349572 is an integrase inhibitor being developed for the treatment of human immunodeficiency virus (HIV)-1 infection by GlaxoSmithKline (GSK) on behalf of Shionogi-ViiV HealthcareLLC. In HIV-infected patients where combination antiretroviral therapy is the standard of care, it is likely that it will be dosed with boosted protease inhibitors (PIs) including fosamprenavir/ritonavir (FPV/RTV or FPV/r). As FPV and RTV are modulators (induction as well as inhibition) of Uridine diphosphate glucuronosyltransferase (UGT) and Cytochrome P450 (CYP)3A which are the primary and secondary metabolic pathways of GKS1349572, it is likely that FPV/RTV will affect the pharmacokinetics (PK) of GSK1349572, therefore a drug interaction study is warranted and will be evaluated in Part A of this study. Part B will evaluate the effect of particle size of tablet variants on the PK of GSK1349572.