PENTA15: Pharmacokinetic Study of Once Versus Twice Daily Abacavir in HIV-1 Infected Children Aged 3 to <36 Months

Inclusion Criteria: * Infants and children with confirmed presence of HIV-1 infection * Infants and children aged 3 to \<36 months * Parents/guardians able and willing to give written, informed consent * Currently on combination ART including Abacavir (ABC) oral solution with or without Lamivudine (3TC) oral solution, for at least 12 weeks and expected to stay on this regimen for at least a further 12 weeks. * HIV-1 RNA viral load either; * suppressed HIV-1 RNA viral load (i.e. \<400 copies/ml) * non-suppressed, but low, HIV-1 RNA viral load (i.e. 400-20 000 copies/ml). The non-suppressed children should have had a stable or decreasing HIV-1 RNA viral load prior to study entry and should be considered to be still gaining benefit from the current regimen * Stable or rising CD4+ cell percent prior to study entry and should not be expected to fall within the next 12 weeks. Exclusion Criteria: * Intercurrent illness * Receiving concomitant therapy except prophylactic antibiotics * Abnormal renal or liver function (grade 3 or above)