CYP2B6 genotype-directed dosing is required for optimal efavirenz exposure in children 3-36 months with HIV infection.

OBJECTIVES

To determine safety-specific, efficacy-specific and genotypic-specific dose requirements of efavirenz (EFV) in children aged 3 to less than 36 months with HIV infection.

DESIGN

IMPAACT P1070 was a 24-week prospective cohort trial of EFV (as open capsules) and two nucleoside reverse transcriptase inhibitors in children with HIV infection 3 to less than 36 months without tuberculosis (Cohort 1).

METHODS

CYP2B6 G516T genotype was determined, and intensive pharmacokinetics was performed at week 2. EFV dose was adjusted if outside the target area under the curve (AUC) 35-180 μg*h/ml. Pharmacokinetic and CYP2B6 G516T genotype data were used to model EFV exposures based on Food and Drug Administration (FDA)-approved doses.

RESULTS

Forty-seven participants, median age 19 months, initiated the study regimen with 24 weeks median follow-up; 38 516GG/GT and 9 516TT genotypes. Initially, median EFV AUC was higher in 516TT vs. 516GG/GT (median 490 vs. 107 μg*h/ml; P = 0.0001) with all 516TT above AUC target. Following an amendment that reduced the 516TT EFV dose by 75%, pharmacokinetic modeling predicted that 83% of participants met the AUC target (31/38 516GG/GT, 8/9 516TT). In contrast, modeling using P1070 data predicted that FDA-approved doses would produce subtherapeutic AUCs in almost one-third of participants with 516GG/GT and excessive AUCs in more than 50% with 516TT genotypes.

CONCLUSION

CYP2B6 G516T genotype strongly influences EFV exposures in this age group. Genotype-directed dosing yields therapeutic EFV concentrations and appears to outperform other dosing approaches.