The purpose of this study is to measure blood levels of abacavir in children and adolescents over a period of time following a single dose so that a dosage for adolescents can be determined.

Little is known about how abacavir is cleared by the body in adolescents. It has been shown that young children require a higher abacavir dose based on weight than adults. Older children, or adolescents, may not require as high a dose. This study may provide information as to whether the children's dose or the adult dose is better for HIV-infected adolescents.

Pharmacokinetic differences between children and adults have resulted in recommended doses of abacavir based on weight that are higher for children than for adults. There are insufficient data to determine whether the pediatric or adult dose is more appropriate for HIV-infected adolescent patients. This study measures pharmacokinetic data for abacavir in the adolescent population so that an appropriate dosage can be determined.

Patients are evenly enrolled into 2 groups based on Tanner Stage. Group I patients are Tanner Stage 1 or 2 (pre-pubertal). Group II patients are Tanner Stage 3, 4, or 5 (pubertal). Each patient receives a single oral dose of abacavir given as the commercially available oral solution. Pharmacokinetic blood samples are collected before dosing and at 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4, 6, and 8 hours post dose for abacavir concentrations.

Inclusion Criteria

Patients may be eligible for this study if they:

• Are 9 to 18 years of age.
• Are HIV-positive.
• Have a CD4 cell count above 200 cells/microL.
• Have a viral load (level of HIV in the blood) under 100,000 copies/ml.
• Have not changed their anti-HIV drugs for the 4 weeks before study entry.
• Are able to swallow study medications.
• Both males and females, agree to use a barrier method of birth control for 3 days after taking the abacavir dose for this study. (This study has been changed. In the earlier version, no birth control was needed.)
• Can be followed at a participating Pediatric AIDS Clinical Trials Unit (PACTU) for the entire study.
• Provide written consent of a parent or guardian, if under 18 years of age.

Exclusion Criteria

Patients will not be eligible for this study if they:

• Have liver or kidney problems, as shown by screening tests.
• Have medical or surgical problems that affect movement or absorption in the stomach or gut.
• Have an opportunistic (AIDS-related) or serious bacterial infection requiring medicine at the time of enrollment.
• Have any diseases (other than HIV infection) or other findings that, in the investigator's opinion, might make it harmful for the patient to be on the study.
• Have a history of chronic alcohol use.
• Fall outside of a certain weight range for their age.
• Are pregnant or breast-feeding.
• Are receiving or have received abacavir.
• Are receiving nonnucleoside reverse transcriptase inhibitors, including efavirenz, delavirdine, or nevirapine; hydroxyurea; mycophenylate; rifampin, rifabutin, anticonvulsants, or other drugs that affect the liver; or chemotherapy for active cancer.
• Have received interferons, interleukins, HIV or other vaccines, or experimental therapy within 30 days before entering the study.