Objectives: An efavirenz-based antiretroviral therapy (ART) regimen is preferred for children more than 3 years of age with tuberculosis. However, rifampin, a key component of antituberculosis therapy, induces CYP2B6. An increased dose of efavirenz is recommended in adults weighing more than 50 kg who require rifampin, but there is scant information in children being treated for tuberculosis.
Design: Plasma efavirenz concentrations were compared in 40 children during concomitant treatment for tuberculosis and HIV-1, after stopping rifampicin, and in a control group of children without tuberculosis. Associations with antituberculosis treatment, metabolizer genotype (based on CYP2B6 516G→T, 983T→C, and 15582C→T), weight, and time after dose were evaluated.
Results: Compared to children with extensive metabolizer genotypes, efavirenz concentrations were increased 1.42-fold (95% confidence interval, CI 0.94–2.15) and 2.85-fold (95% CI 1.80–4.52) in children with intermediate and slow metabolizer genotypes, respectively. Concomitant antituberculosis treatment increased efavirenz concentrations 1.49-fold (95% CI 1.10–2.01) in children with slow metabolizer genotypes, but did not affect efavirenz concentrations in extensive or intermediate metabolizer genotypes. After adjustment for dose/kg, each kilogram of weight was associated with a 2.8% (95% CI 0.9–4.7) decrease in efavirenz concentrations. Despite higher milligram per kilogram doses, a higher proportion of children in the lowest weight band (10–13.9 kg) had efavirenz concentrations less than 1.0 mg/l than larger children.
Conclusion: Antituberculosis treatment was not associated with reduced efavirenz concentrations in children, which does not support increased efavirenz doses. Children with slow metabolizer genotype have increased efavirenz concentrations during antituberculosis treatment, likely due to isoniazid inhibiting enzymes involved in accessory metabolic pathways for efavirenz.
aDivision of Clinical Pharmacology in the Department of Medicine
bInstitute of Infectious Disease and Molecular Medicine
cCenter for Infectious Disease Epidemiology and Research
dSchool of Child and Adolescent Health, University of Cape Town
ePaediatric Infectious Diseases Unit, Red Cross War Memorial Children's Hospital, Cape Town
fHarriet Shezi Children's Clinic, Wits Reproductive Health and HIV Institute, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
gInfectious Diseases Institute, Makerere University, Kampala, Uganda
hUniversity of Dublin School of Medicine, Trinity College, Dublin, Ireland
iDepartments of Medicine, Pharmacology, Pathology, Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
Correspondence to H.M. McIlleron, K-45 Old Main Building, Groote Schuur Hospital, Observatory 7925, Cape Town, South Africa. E-mail: firstname.lastname@example.org
Received 6 December, 2012
Revised 1 March, 2013
Accepted 4 March, 2013