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Influence of CYP2B6 516G>T polymorphism and interoccasion variability (IOV) on the population pharmacokinetics of efavirenz in HIV-infected South African children

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Abstract

Objective

To investigate the influence of CYP2B6 516G>T polymorphism, as a covariate, and of interoccasion variability (IOV) on the oral clearance (CL/F) of efavirenz (EFV) in treatment-naïve black South African children over a period of 24 months post-antiretroviral therapy (ART) initiation.

Methods

HIV-infected black children (n = 60, aged 3–16 years), with no prior exposure to ART, eligible to commence ART and attending an outpatient clinic were enrolled into this study. Blood samples were taken at mid-dose interval at 1, 3, 6, 12, 18 and 24 months post-ART initiation. EFV plasma samples were determined with an adapted and validated LC/MS/MS method. Genotyping of the CYP2B6 G516T single nucleotide polymorphism (SNP) was performed using polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP). NONMEM was used for the population pharmacokinetic modelling.

Results

EFV concentrations below 1 μg/mL accounted for 18% (116/649), EFV concentrations >4 μg/mL accounted for 29.5% (192/649) and concentrations within the therapeutic range (1–4 μg/mL) represented 52.5% (341/649) of all the samples determined. The covariates age, weight and CYP2B6 G516Tgenotype were included in the final model with population estimates for CL/F determined as 2.46, 4.60 and 7.33 L/h for the T/T, G/T and G/G genotype groups respectively.

Conclusions

The inclusion of both age and weight to predict accurate EFV CL values for the respective genotype groups within this paediatric population was required, whereas the addition of gender and body surface area did not improve the predictions. The importance of introducing IOV in a PK model for a longitudinal study with sparsely collected data was again highlighted by this investigation.

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Acknowledgements

M. Viljoen received a Thuthuka research grant [North-West University and the National Research Foundation (NRF)] and a self-initiative grant from the Medical Research Council (MRC). T.M. Meyers is a Fogarty fellow supported by grants 5U2RTW007370 and 5U2RTW007373. The authors would like to thank the research staff of the Harriet Shezi Children’s Clinic. We are grateful to all study participants and their caregivers who have contributed to this study.

Conflict of interest

No competing financial interests exist.

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Authors and Affiliations

  1. Unit for Drug Research and Development, Division of Pharmacology, School of Pharmacy, North-West University, Potchefstroom, South Africa

    M. Viljoen & M. Rheeders

  2. Division of Pharmacokinetics and Drug Therapy, Department of Pharmaceutical Biosciences, Faculty of Pharmacy, Uppsala University, Uppsala, Sweden

    M. O. Karlsson

  3. Harriet Shezi Children’s Clinic, Chris Hani Baragwanath Hospital, Department of Paediatrics, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa

    T. M. Meyers & H. Gous

  4. Wits Institute for Sexual Reproductive Health HIV & Related Diseases, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa

    H. Gous

  5. Division of Human Genetics, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa

    C. Dandara

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  1. M. Viljoen
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Viljoen, M., Karlsson, M.O., Meyers, T.M. et al. Influence of CYP2B6 516G>T polymorphism and interoccasion variability (IOV) on the population pharmacokinetics of efavirenz in HIV-infected South African children. Eur J Clin Pharmacol 68, 339–347 (2012). https://doi.org/10.1007/s00228-011-1148-7

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