There are no data on efficacy, safety and pharmacokinetics of ATV/r-based HAART in HIV-infected Asian children. Therefore, the investigators aim to evaluate the pharmacokinetics, efficacy and safety of ATV/r-based HAART in Thai HIV-infected children.

Non-nucleoside reverse transcriptase inhibitor (NNRTI)-based HAART have been commonly prescribed as the first-line HAART for HIV-infected children in resource-limited settings. Protease inhibitor (PI)-based HAART are the recommended second-line regimen after failing NNRTI-based HAART. The most commonly used PI in Thailand is lopinavir/ritonavir (LPV/r). However, the metabolic complications of lopinavir/ritonaive (LPV/r) such as hyperlipidemia and lipodyrtrophy are common and a concern for HIV-infected children as it may contribute to the development of cardiovascular disease in the longer term. There are data on efficacy, safety and pharmacokinetics of ATV/r-based HAART in HIV-infected adults but none in children. Furthermore, many studies in both adults and children have shown that different ethnicities can result in different pharmacokinetic response to antiretroviral drugs. As a result of this, this study investigated the efficacy, safety and pharmacokinetics of ATV/r-based HAART in HIV-infected Asian children.

Inclusion Criteria:

1. HIV-infected children
2. Age from 6- 18 years old
3. Body weight ≥ 25 kg at screening visit
4. ARV history, the children can be categorized in one of these 2 groups
5. ALT <200 IU/L at screening visit
6. Total bilirubin < 3 mg/dL at the screening visit
7. Can swallow capsule
8. Written informed consent from caregivers and assent (from children aged 7-17 years who know their HIV status)

Exclusion Criteria:

1. Active opportunistic infection
2. Relevant history or current condition, illness that might interfere with atazanavir/ritonavir absorption, distribution, metabolism or excretion.
3. Use of concomitant medication that may interfere with the pharmacokinetics of ATV/r (i.e. efavirenz, indinavir, proton pump inhibitor, antacids, cisapride, clarithromycin, rifampin etc.)
4. Pregnancy or lactating at screening visit
5. Liver diseases e.g. hepatitis B carrier, chronic hepatitis, cirrhosis
6. Inability to understand the nature and extent of the study and the procedures required.