Journal Article

Pharmacogenetics of Plasma Efavirenz Exposure after Treatment Discontinuation: An Adult AIDS Clinical Trials Group Study

Heather J. Ribaudo, David W. Haas, Camlin Tierney, Richard B. Kim, Grant R. Wilkinson, Roy M. Gulick, David B. Clifford, Catia Marzolini, Courtney V. Fletcher, Karen T. Tashima, Daniel R. Kuritzkes and Edward P. Acosta

in Clinical Infectious Diseases

Published on behalf of Infectious Diseases Society of America

Volume 42, issue 3, pages 401-407
Published in print February 2006 | ISSN: 1058-4838
Published online February 2006 | e-ISSN: 1537-6591 | DOI: http://dx.doi.org/10.1086/499364
Pharmacogenetics of Plasma Efavirenz Exposure after Treatment Discontinuation: An Adult AIDS Clinical Trials Group Study

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Background. Efavirenz has a long plasma half-life and a low genetic barrier to resistance. Simultaneously stopping treatment with all agents in efavirenz-containing regimens may result in functional efavirenz monotherapy that selects for drug-resistant human immunodeficiency virus type 1. Lower plasma efavirenz clearance is associated with a cytochrome P450 2B6 gene (CYP2B6) polymorphism (516G→T) that is more frequent among African American individuals than among European American individuals.

Methods. We characterized relationships between this polymorphism and predicted plasma efavirenz concentration-time profiles after discontinuation of therapy with use of data obtained from subjects receiving therapy. Pharmacokinetic parameters were estimated using population-based methods. Concentrations after discontinuation of therapy were predicted from subject-specific estimates.

Results. Median estimated efavirenz half-lives were 23, 27, and 48 h for patients with CYP2B6 position 516 GG (78 patients), GT (60), and TT (14) genotypes, respectively (P < .001). After therapy was stopped, plasma efavirenz concentrations in patients with GG, GT, and TT genotypes were predicted to exceed 46.7 ng/mL (the estimated protein-adjusted 95% inhibitory concentration for wild-type virus) for a median of 5.8 days (interquartile range [IQR], 4.4–8.3 days), 7.0 days (IQR, 5.0–8.0 days), and 14 days (IQR, 11.1–21.2 days), respectively (P < .001). Plasma efavirenz levels were predicted to exceed 46.7 ng/mL for >21 days in 5% of subjects with GG genotype, 5% of subjects with GT genotype, and 29% of subjects with TT genotype.

Conclusions. The CYP2B6 position 516 TT genotype or a prolonged measured elimination half-life may predict increased risk of developing drug resistance among patients who discontinue efavirenz-containing regimens. This has implications for strategies to safely discontinue antiretroviral regimens while avoiding the emergence of drug resistance.

Journal Article.  4957 words.  Illustrated.

Subjects: Infectious Diseases ; Immunology ; Public Health and Epidemiology ; Microbiology

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