Pharmacokinetics and safety of rifabutin in young hiv-infected children receiving rifabutin and lopinavir/ritonavir

Objectives: Co-treatment of HIV and TB in young children is complicated by limited treatment options and complex drug-drug interactions. Rifabutin is an alternative to rifampicin for adults receiving a ritonavir-boosted PI. We aimed to evaluate the short-term safety and pharmacokinetics of rifabutin when given with lopinavir/ritonavir in children. Patients and methods: We conducted an open-label study of rifabutin dosed at 5 mg/kg three times a week in HIV-infected children ≤5 years of age receiving lopinavir/ritonavir. Intensive steady-state pharmacokinetic sampling was conducted after six doses. The Division of AIDS 2004, clarification 2009, table for grading severity of adverse events was used to classify drug toxicities. The study was registered with Clinical Trials.gov, number NCT01259219. Results: Six children completed the study prior to closure by institutional review boards. The median (range) AUC0-48 of rifabutin was 6.91 (3.52-8.67) μg·h/mL, the median (range) Cmax of rifabutin was 0.39 (0.19-0.46) μg/mL, the median (range) AUC0-48 of 25-O-desacetyl rifabutin was 5.73 (2.85-9.13) μg·h/mL and the median (range) Cmax of 25-O-desacetyl rifabutin was 0.17 (0.08-0.32) μg/mL. The neutrophil count declined in all children; two children experienced grade 4 neutropenia, which resolved rapidly without complications. There was strong correlation between AUC0-48 measures and neutrophil counts. Conclusions: Rifabutin dosed at 5 mg/kg three times per week resulted in lower AUC0-48, AUC0-24 and Cmax values for rifabutin and 25-O-desacetyl rifabutin compared with adults receiving 150 mg of rifabutin daily, the current recommended dose. We observed high rates of severe transient neutropenia, possibly due to immaturity of CYP3A4 in young children. It remains unclear whether a safe and effective rifabutin dose exists for treatment of TB in children receiving lopinavir/ritonavir.