This study is a 48-week study designed to evaluate the safety and efficacy of a fixed-dose combination tablet administered once-a-day versus the individual tablets administered twice-a-day within 3-drug combination regimens in ART (antiretroviral)-experienced HIV-1 infected patients.

• Drug: abacavir/lamivudine
• Drug: abacavir
• Drug: lamivudine

Inclusion Criteria:

• Currently receiving an initial antiretroviral therapy (ART) regimen composed of the drug abacavir (ABC) 300mg twice a day, plus the drug 3TC (lamivudine) 150mg twice a day in combination with either a protease inhibitor or non-nucleoside reductase inhibitor (NNRTI) for at least 24 weeks.
• NOTE: Subjects who have required a change in initial protease inhibitor (PI) or NNRTI therapy due to intolerance (not treatment failure) are eligible. Subject must be on a stable regimen of the second PI or NNRTI therapy for at least 6 months before enrollment in this study.
• Plasma HIV-1 RNA less than 400 copies/mL for at least 3 months immediately preceding the screening visit, and at screening.
• CD4+ cell count of at least 50 cells/mm3 at screening.
• Written informed consent to participate in the study before participation.
• Male or female (Females of child-bearing potential must have a negative serum pregnancy test at screening and agree to an acceptable method of contraception.)

Exclusion Criteria:

• History of a CDC Clinical Category C event requiring treatment (not including cutaneous Kaposi's sarcoma) within 45 days of the screening visit. Treatment for the acute event must have been completed at least 30 days before screening.
• Subject is enrolled in one or more investigational drug studies which may impact HIV RNA suppression.
• Subject is unable to complete the 48-week dosing period, evaluations and assessments.
• Subject is pregnant or breastfeeding.
• History of clinically relevant inflammation of the pancreas or hepatitis within 6 months prior to screening.
• Subject suffers from a serious medical condition, such as diabetes or heart problem.
• Pre-existing mental, physical, or substance abuse disorder.
• History of inflammatory bowel disease or malignancy, intestinal ischemia, malabsorption, or other gastrointestinal dysfunction.
• Abnormal laboratory results within 28 days before the first dose of study medication.
• Required treatment with radiation therapy or cytotoxic chemotherapeutic agents within 28 days before screening, or will need these during the study.
• Subject requires treatment with immunomodulating drugs such as systemic corticosteroids, interleukins, vaccines, or interferons within 28 days prior to screening, or subject has received an HIV-1 immunotherapeutic vaccine within 90 days prior to screening.
• Asthmatic subjects using inhaled corticosteroids are eligible for enrollment.
• Subject requires treatment with foscarnet, hydroxyurea or other agents with documented activity against HIV-1 in vitro within 28 days of screening.
• Subject has a history of allergy to any of the study drugs.