Men's and women's bodies may process anti-HIV drugs differently. The purpose of this study is to determine the differences in blood levels of soft gel capsules and tablets of lopinavir/ritonavir (LPV/r) in HIV infected men and women.

It is estimated that 50% of people living with HIV/AIDS worldwide are women. HIV infected women face different psychosocial issues than men, and their bodies may react differently to HIV treatment. However, most of the data on the safety and efficacy of antiretrovirals (ARVs) used in the treatment of HIV infection are from studies conducted primarily in men. LPV/r in tablet form was approved by the FDA in October 2005. This study will determine the differences in pharmacokinetics (PK) in men and women taking a soft gel capsule and a tablet formulation of LPV/r.

No ARVs will be provided by this study. In Step 1, participants will receive soft gel capsules of LPV/r. All Step 1 participants will be asked to join Step 2 of the study upon completion of Step 1. In Step 2, participants will receive tablets of LPV/r. During the study, participants in both Step 1 and 2 will take a treatment regimen of LPV/r twice daily and one or more of the following: a nucleoside reverse transcriptase inhibitor (NRTI), tenofovir disoproxil fumarate, or enfuvirtide. Medical and medication history, blood collection, and clinical assessments will occur at study screening for both Steps 1 and 2. Participants in both steps will be asked to complete a medication diary from study entry to the day of the PK visit. The PK visit will occur within 30 days of study screening; blood collection for PK analysis will also occur at this visit.

Note: Step 1 enrollment ended as of 06/28/06.

Inclusion Criteria

• HIV infected
• Have taken twice-daily LPV/r (soft gel formulation for Step 1 participants and tablet formulation for Step 2 participants) for at least 14 days immediately prior to step screening and are willing to continue taking LPV/r until the PK visit of that step
• Have taken LPV/r in combination with at least one of the following for at least 14 days immediately prior to study step screening: zidovudine, lamivudine, emtricitabine, stavudine, abacavir sulfate, didanosine, zalcitabine, tenofovir disoproxil fumarate, enfuvirtide, AND are willing to continue taking them until the PK visit of that step
• Body weight of more than 50 kg (110 lbs) for Step 1 participants only

Exclusion Criteria:

• Non-nucleoside reverse transcriptase inhibitor or dual protease inhibitor regimen within 30 days prior to study entry
• Require certain medications
• Current drug or alcohol abuse that, in the investigator's opinion, may interfere with the study
• Serious illness requiring systemic treatment or hospitalization within 30 days of study screening
• Acute AIDS-related opportunistic infection within 90 days of study entry