Inclusion Criteria:

• Subjects on Raltegravir-containing regimen with confirmed virological failure (VL >500c/mL for > 3 months).
• Patients treated with a raltegravir-containing regimen for at least for 24 weeks.
• CD4 cell count > 50 cell/mm3.
• Adherence >90%, measured by short -self report questionnaire during the 3 months preceding the study entry.
• No reasonable additional therapeutic options

Exclusion Criteria:

• History or suspicion of alcohol or drug use which in the investigator's opinion would likely compromise subjects' safety and/or study procedures.
• A positive urine drug test for amphetamines, cocaine and opioids at two consecutive screenings (a positive drug test at study screening will be repeated at baseline).
• Life expectancy less than 6 months.

• Subject has any currently active AIDS defining illness (Category C conditions according to the CDC Classification System for HIV Infection 1993) with the following 2 exceptions:

  1. Stable cutaneous Kaposi's Sarcoma that is unlikely to require any form of systemic therapy during the study period.
  2. Wasting syndrome due to HIV infection if, in the investigator's opinion, it is not actively progressive.
• Any active clinically significant disease (e.g. TB, cardiac dysfunction) or findings during screening of medical history or physical examination that in the investigator's opinion, would compromise the outcome of the study.
• Pregnant or breast-feeding female.
• Renal impairment: serum creatinine > 2 x ULN.
• Chronic Hepatitis B or C with ALT or AST > 3 x ULN.
• Acute Hepatitis A, B or C. Acute Hepatitis A, B or C.
• Any grade 3 or 4 toxicity according to the enhanced ACTG grading severity list, except for grade 3 or 4 asymptomatic triglyceride/cholesterol elevations, isolated grade 3 increased in GGT, grade 3 increases in glucose, asymptomatic grade 3 increases in amylase with no elevation of lipase.
• Currently significant diarrhea, gastric stasis or constipation that in the investigator's opinion could influence drug absorption or bioavailability.
• Subjects with clinical or laboratory evidence of significantly decreased hepatic function or decompensation, irrespective of liver enzyme levels (INR > 1.3 or albumin < 30g/l or bilirubin > 2.5 x ULN).