Evaluating the Effect of CHanging EnfuvirtidE to Raltegravir in HIV Infected Subjects

This is a single-arm, open-label, non-randomized pilot study in human immunodeficiency virus type 1 (HIV-1) positive patients who have an undetectable viral load on their current enfuvirtide containing medication regimen. The treatment regimen will consist of replacing enfuvirtide with MK-0518 400 mg twice a day given as part of the patient's HIV medication regimen. The study regimen will be administered for 24 weeks, with patients given the option of continuing on the study medication past that time if they wish to. Patients serve as their own control as they have viral control (HIV ribonucleic acid (RNA) below limits of quantification) for at least 6 months with enfuvirtide prior to switch to raltegravir.