Efavirenz therapy in children living with HIV : the role of pharmacogenetics for plasma level variation and treatment results

Background: Efavirenz (EFV) is used in HIV antiretroviral therapy (ART) and metabolized by CYP2B6, with great interindividual variability in plasma levels, due to pharmacogenetic variation. This impacts both viral efficacy and toxicity and has led to adjusted dosing for adults. Adult studies suggest that EFV hydroxy metabolites contribute to CNS toxicity, but pediatric data are lacking. Optimized EFV dosing in children remains challenging, especially as HIV drug resistance (HIVDR) is increasing.

Aims: To investigate the impact of pharmacogenetic variations on the plasma levels of EFV and its metabolites in children in Uganda and Sweden, and to explore how these concentrations correlate with viral outcomes, adverse effects, and HIVDR.

Methods: Study I was performed in a multi-ethnic cohort, Sweden. Retrospectively collected EFV plasma levels from 36 children <18 years with ongoing/previous EFV-therapy, were investigated for associations to single nucleotide polymorphisms (SNP) in EFV-metabolizing enzymes. Studies II-IV were prospective, observational and performed in 99 Ugandan ART- naïve children, aged 3-12 years. Plasma levels of EFV, phase I and phase II metabolites including a newly identified metabolite (EFAdeg) were quantified with LC-HRMS/MS (liquid chromatography high resolution with-tandem-mass-spectrometry) at 2, 6, 12 and 24 weeks after ART start and examined for association to SNPs, CNS toxicity and viral outcomes. Pretreatment HIVDR (PDR) was assessed.

Results: In study I, a multivariate mixed-effects restricted maximum likelihood regression model, (REML) identified genotypes CYP2B6*6 T/T, CYP2B6*11 G/G and CYP2A6*9 A/C, as independent predictors of EFV plasma concentrations, explaining 75% of interindividual variation. In study II-IV, CYP2B6 metabolizer phenotype (based on composite CYP2B6 c.516C>T/c.983T>C) and CYP2B6*11 G/G, predicted EFV plasma levels, with a REML model explaining 70% of EFV variation. No autoinduction was seen. Subtherapeutic EFV levels were linked to VL> 40 cop/ml and newly acquired HIVDR. The PDR prevalence was 20% and predicted poor virological outcomes. CNS symptoms were linked to supratherapeutic EFV levels, but not EFV metabolites. EFV metabolites, quantified for the first time in children, had a distinct distribution according to CYP2B6 metabolizer phenotype.

Conclusions: CYP2B6 and CYP2A6 genotypes were identified as key predictors of EFV plasma concentrations in Ugandan and Swedish children and explained a significant proportion of interindividual variability. Autoinduction was not seen. Subtherapeutic EFV levels were linked to poor viral outcomes, while supratherapeutic levels were linked to CNS toxicity. EFV metabolite profiles differed by CYP2B6 phenotype and had no correlation to CNS symptoms. These findings highlight the need for genotype-informed EFV dosing in children to optimize efficacy and minimize adverse effects.

List of scientific papers

I. Soeria-Atmadja S, Österberg E, Gustafsson LL, Dahl ML, Eriksen J, Rubin J, Naver L. Genetic variants in CYP2B6 and CYP2A6 explain interindividual variation in efavirenz plasma concentrations of HIV-infected children with diverse ethnic origin. PLoS One. 2017;12(9). https://doi.org/10.1371/journal.pone.0181316

II. Sandra Soeria-Atmadja, Pauline Amuge, Sarah Nanzigu, Dickson Bbuye, Jaran Eriksen Johanna Rubin, Adeodata Kekitiinwa, Celestino Obua, Marja-Liisa Dahl, Madeleine Pettersson Bergstrand, Anton Pohanka, Lars L Gustafsson, Lars Naver. Sub- and supratherapeutic efavirenz plasma concentrations with risk for HIV-therapy failure are mainly genetically explained in Ugandan children: the prospective GENEFA cohort study. British Journal of Clinical Pharmacology. [Accepted]

III. Sandra Soeria-Atmadja, Madeleine Pettersson Bergstrand, Pauline Amuge, Sarah Nanzigu, Dickson Bbuye, Johanna Rubin, Adeodata Kekitiinwa, Celestino Obua, Marja-Liisa Dahl, Anton Pohanka, Lars L Gustafsson, Lars Naver, Jaran Eriksen. Plasma concentration profiles of efavirenz and its metabolites in Ugandan children during 6 months of follow-up show association between plasma concentrations and CNS toxicity, but no signs of autoinduction. [Manuscript]

IV. Soeria-Atmadja S, Amuge P, Nanzigu S, Bbuye D, Rubin J, Eriksen J, Kekitiinwa A, Obua C, Gustafsson LL, Naver L. Pretreatment HIV drug resistance predicts accumulation of new mutations in ART-naïve Ugandan children. Acta Paediatr. 2020;109(12):2706-2716. https://doi.org/10.1111/apa.15320