Children are placed into 1 of 4 treatment groups based on age: Group 1, 3 months to 24 months; Group 2, 25 months to 6 years; Group 3, 7 years to 12 years; Group 4, 13 years to 17 years. They receive baseline evaluations. Antiretroviral-naive patients receive emtricitabine plus stavudine plus lopinavir/ritonavir. Antiretroviral-experienced patients replace lamivudine with emtricitabine. Patients return to the clinic for follow-up visits at Weeks 2 and 4 and then every 4 weeks until Week 48. Safety is evaluated using adverse events, which are reviewed at every clinic visit. Clinical laboratory data and full-profile pharmacokinetics of emtricitabine are evaluated at some visits. After the Week 48 study evaluations are completed, individual patients may continue to receive study medication (as provided by the sponsor) until commercially available, if certain criteria are met.

Inclusion Criteria

Children may be eligible for this study if they:

• Are at least 3 months old and no older than 17 years of age. This is the age the child needs to be at the time they begin the study.
• Are HIV positive.
• Weigh more than 5.5 pounds. A newborn child must have reached at least 38 weeks of gestation.
• Have or have not taken anti-HIV drugs. Those that have not must have a viral load between 5,000 and 500,000 copies/ml at screening. Those that have must have been taking anti-HIV drugs, including lamivudine, for at least 3 months and have a viral load of no more than 400 copies/ml at screening.
• Have a CD4 count of more than 200 cells/mm3.
• Have written consent from parent or guardian.
• Are willing to use effective birth control during the study and for 1 month after the last dose of emtricitabine, if sexually active.

Exclusion Criteria

Children will not be eligible for this study if they:

• Are pregnant or breast-feeding.
• Cannot follow the visit or dosing schedule or are not available for 1 year.
• Have taken experimental drugs or vaccines (except for emivirine and experimental forms of approved drugs) within 30 days of study start.
• Have nerve damage in their arms or legs.
• Have trouble eating or taking drugs.
• Have serious diarrhea within 30 days before study entry.
• Have had any serious illness within 30 days of study screening. Any treatment must have been finished 14 days before study entry.
• Have had an AIDS-related (opportunistic) disease within 12 months of screening.
• Are being treated for tuberculosis.
• Have had pancreatitis.
• Require certain drugs.