In this study, approximately 16 subjects will receive raltegravir 400mg twice daily for 5 days (Treatment A) followed by a washout period. In Period 2, subjects will receive GSK2248761 200mg once daily for 5 days (Treatment B). There will be no wash out between Period 2 and 3. Subjects will then be administered raltegravir 400mg twice daily in combination with GSK2248761 200mg once daily (Treatment C) for 5 days. Subjects will be housed in the unit for the duration of the study. 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.