Pharmacokinetics of Lopinavir/Ritonavir Superboosting in Infants and Young Children Co-infected With HIV and TB

Inclusion Criteria: * Documentation of a confirmed diagnosis of HIV-1 infection following SA clinical guidelines * Weight \>3kg ≤15 kg at enrolment * \> 42 weeks gestational age * On LPV/r-based therapy or about to start a LPV/r-based antiretroviral combination therapy with 2 NRTIs \[ABC+3TC or AZT+3TC or d4T+3TC\] * Clinical diagnosis of TB requiring RIF-based therapy * Parent or legal guardian able and willing to provide written informed consent and able to attend study visits. Exclusion Criteria: * For neonates, less than 42 weeks gestation and 14 days old * Concomitant/chronic treatment with potent enzyme-inducing/inhibiting drugs other than those in the study treatments . See Appendix E (minor inducers/inhibitors and drugs used as part of management of the condition are allowed eg. Steroids) * Anticipation at the start that anti-TB treatment duration will be longer than 9 months * Any other condition/finding that, in the investigator's opinion, would compromise the child's participation in this study eg. alanine transferase (ALT) more than 10 times upper limit of normal (ULN), or chronic renal, hepatic or gastrointestinal disease such as malabsorption. * Children with known malignancies and contraindications to taking LPV/r * Treatment with experimental drugs for any indication within 30 days prior to study entry; participation in another study may be approved by the study team.