Safety and Effectiveness of Lopinavir/Ritonavir in Individuals Who Have Failed Prior HIV Therapy

Inclusion Criteria for Step 1 Participants: * HIV infected * Continuous treatment with a three-drug, NNRTI-containing regimen for at least 6 months prior to study entry * Viral load of 1,000 copies/ml or greater and less or equal to 200,000 copies/ml obtained within 30 days of study entry * Negative pregnancy test within 48 hours of study entry * Willing to use acceptable forms of contraception for the duration of the study * Laboratory values obtained within 30 days of study entry: * Hemoglobin greater or equal to 8.0 g/dL * Platelet count greater or equal to 50,000/mm3 * Estimated Creatinine Clearance greater or equal to 60 mL/min x ULN * AST (SGOT), ALT (SGPT) and alkaline phosphatase \< 3 x ULN * Total bilirubin less or equal to 2.5 x ULN * Ability and willingness of participant or legal guardian/representative to give informed consent Inclusion Criteria for Step 2 Participants: * Virologic failure on LPV/r monotherapy defined as viral load of 400 copies/ml or greater after 24 consecutive weeks on LPV/r monotherapy OR virologic failure after initial viral suppression on LPV/r monotherapy * Estimated creatinine clearance of 60 ml/min or greater * Negative pregnancy test within 48 hours of entry into Step 2 * Willing to use acceptable forms of contraception for the duration of the study Exclusion Criteria for All Participants: * Breastfeeding * Known allergy or sensitivity to study drugs * Active drug or alcohol use or dependence that, in the opinion of the investigator, would interfere with study adherence to study requirements * History of chronic hepatitis B infection Exclusion Criteria for Step I Participants: * Prior use of any protease inhibitor treatment * Acute therapy for any serious medical condition within 14 days of study entry. For ongoing or chronic therapy, the participant must be on the treatment regimen for at least 14 days, and clinically stable prior to entry. If a potential participant has TB and has received treatment for more than 2 weeks, the TB treatment would have to be modified to include a rifabutin-containing regimen. TB compatible syndromes will also be carefully evaluated prior to entry. Exclusion Criteria for Step 2 Participants: \- Active opportunistic infection, including tuberculosis (TB)