The purpose of this study is to test 2 different dosing regimens of GW433908/ritonavir (RTV) versus lopinavir (LPV)/RTV when each is given with 2 active reverse transcriptase inhibitors (RTIs), in patients who have taken anti-HIV drugs without success.

Patients will receive 2 dosing regimens of GW433908/RTV or LPV/RTV, in combination with 2 active RTIs, after failing their first or second protease inhibitor-containing regimen. Patients are required to be on therapy at time of screening and must remain on this therapy until Day 1.

Inclusion Criteria

Patients may be eligible for this study if they:

• Have a viral load of 1,000 or more copies/ml.
• Have taken protease inhibitors (PIs).
• Have taken PI drugs for at least 12 straight weeks and have had virologic failure on the PIs.
• Are now taking antiretroviral therapy.
• Are male or female and are at least 13 years old (or 18 if local requirement) and can provide consent from parent or guardian if under 18.
• Are females unable to have children or, if are able to have children, are not pregnant and agree to use approved birth control.

Exclusion Criteria

Patients will not be eligible for this study if they:

• Have taken APV or LPV for more than 1 week.
• Have taken tenofovir disoproxil fumarate (TDF) or adefovir.
• Have taken more than 2 PIs.
• Are unable to take 2 active RTIs, as specified by the study.
• Have an active CDC Category C disease.
• Have certain abnormal laboratory tests.
• Are pregnant or breast-feeding.
• Have a serious health problem (e.g., diabetes, heart problems, hepatitis) that might risk the safety of the patient.
• Have a history of significant kidney or bone disease.
• Are not able to take drugs by mouth and cannot absorb them.
• Have had pancreatitis or hepatitis within the previous 6 months.
• Have a drug allergy or other allergy which might cause a problem during the study.
• Have had radiation or chemotherapy within 28 days of taking the study drug, or expect to need these during the study.
• Have taken drugs that affect the immune system (corticosteroids, interleukins, interferons) or drugs with anti-HIV activity (hydroxyurea or foscarnet) within 28 days prior to taking the study drug.
• Have had any HIV vaccine within 3 months before taking the study drug.
• Have taken certain other drugs within 28 days prior to taking the study drug, or expect to need them during the study.
• Use alcohol or illicit drugs in a way that the doctor feels would interfere with the study.
• Are not able to take the study drugs.
• Have inadequate kidney function.