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      Dependence of Efavirenz- and Rifampicin-Isoniazid–Based Antituberculosis Treatment Drug-Drug Interaction on CYP2B6 and NAT2 Genetic Polymorphisms: ANRS 12154 Study in Cambodia

      Author(s): 1 , 2 , 3 , 4 , 5 , 6 , 6 , 5 , 3 , 2 , 3 , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , the CAMELIA (ANRS 1295-CIPRA KH001) Study Group
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      Journal: The Journal of Infectious Diseases
      Publisher: Oxford University Press (OUP)

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          Abstract

          We investigated the population pharmacokinetics and pharmacogenetics of efavirenz in 307 patients coinfected with human immunodeficiency virus and tuberculosis and included in the Cambodian Early vs Late Initiation of Antiretrovirals trial (CAMELIA) in Cambodia. Efavirenz (600 mg/d) and stavudine plus lamivudine were administered in addition to standard antituberculosis treatment, including rifampicin and isoniazid. Blood samples were obtained a mean of 14 hours after efavirenz intake at weeks 2 and 6 after initiation of efavirenz and weeks 22 (efavirenz plus antituberculosis drugs) and 50 (efavirenz alone) after initiation of antituberculosis treatment. Ten patients participated in an extensive pharmacokinetic study after week 50. CYP2B6 G516T and C485-18T polymorphisms were the most significant covariates, with weight showing a significant minor effect. Change in efavirenz apparent clearance in patients taking both efavirenz and antituberculosis treatment was highly dependent on NAT2 polymorphism, as a possible surrogate of isoniazid exposure. Patients carrying the CYP2B6 516 TT genotype and slow-acetylation NAT2 phenotype had the lowest efavirenz apparent clearance. These data suggest that the inducing effect of rifampicin is counterbalanced by a concentration-dependant inhibitory effect of isoniazid on efavirenz clearance.

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          The cytochrome P450 2B6 (CYP2B6) is the main catalyst of efavirenz primary and secondary metabolism: implication for HIV/AIDS therapy and utility of efavirenz as a substrate marker of CYP2B6 catalytic activity.

          Julia Gorski, Philip Ward, D Flockhart … (2003)
          We used human liver microsomes (HLMs) and recombinant cytochromes P450 (P450s) to identify the routes of efavirenz metabolism and the P450s involved. In HLMs, efavirenz undergoes primary oxidative hydroxylation to 8-hydroxyefavirenz (major) and 7-hydroxyefavirenz (minor) and secondary metabolism to 8,14-dihydroxyefavirenz. The formation of 8-hydroxyefavirenz in two HLMs showed sigmoidal kinetics (average apparent Km, 20.2 micro M; Vmax, 140 pmol/min/mg protein; and Hill coefficient, 1.5), whereas that of 7-hydroxyefavirenz formation was characterized by hyperbolic kinetics (Km, 40.1 micro M and Vmax, 20.5 pmol/min/mg protein). In a panel of 10 P450s, CYP2B6 formed 8-hydroxyefavirenz and 8,14-dihydroxyefavirenz from efavirenz (10 micro M) at the highest rate. The Km value for the formation of 8-hydroxyefavirenz in CYP2B6 derived from hyperbolic Eq. 12.4 micro M) was close to that obtained in HLMs (Km, 20.2 micro M). None of the P450s tested showed activity toward 7-hydroxylation of efavirenz. When 8-hydroxyefavirenz (2.5 micro M) was used as a substrate, 8,14-dihydroxyefavirenz was formed by CYP2B6 at the highest rate, and its kinetics showed substrate inhibition (Ksi, approximately 94 micro M in HLMs and approximately 234 micro M in CYP2B6). In a panel of 11 HLMs, 8-hydroxyefavirenz and 8,14-dihydroxyefavirenz formation rates from efavirenz (10 micro M) correlated significantly with the activity of CYP2B6 and CYP3A. N,N',N"-Triethylenethiophosphoramide (thioTEPA; 50 micro M) inhibited the formation rates of 8-hydroxyefavirenz and 8,14-dihydroxyefavirenz from efavirenz (10 micro M) by > or = 60% in HLMs) and CYP2B6, with Ki values < 4 micro M. In conclusion, CYP2B6 is the principal catalyst of efavirenz sequential hydroxylation. Efavirenz systemic exposure is likely to be subject to interindividual variability in CYP2B6 activity and to drug interactions involving this isoform. Efavirenz may be a valuable phenotyping tool to study the role of CYP2B6 in human drug metabolism.
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            Pharmacogenetics of efavirenz and central nervous system side effects: an Adult AIDS Clinical Trials Group study.

            Andrew Gulick, Camlin Tierney, Heather J Ribaudo … (2004)
            Efavirenz is an effective antiretroviral agent, but central nervous system side effects occur commonly, and population (racial) differences in pharmacokinetics and response have been reported. Efavirenz is metabolized by cytochrome P4502B6 (CYP2B6). We investigated whether polymorphisms in CYP2B6, CYP3A4, CYP3A5, and MDR1 were associated with efavirenz central nervous system side effects and pharmacokinetics. Twenty-four week cohort from a randomized study. Adult AIDS Clinical Trials Group study A5097s examined relationships between central nervous system side effects and efavirenz plasma concentration-time profiles in HIV-infected subjects. Efavirenz plasma pharmacokinetics were estimated by a population-based method. Central nervous system symptoms were assessed by questionnaires and neuropsychological testing. Study subjects included 89 (57%) European-Americans, 50 (32%) African-Americans, and 15 (10%) Hispanics. The CYP2B6 T/T genotype at position 516 (GlnHis) was more common in African-Americans (20%) than in European-Americans (3%), and was associated with greater efavirenz plasma exposure (P < 0.0001). The median efavirenz [area-under-the-curve] (0-24 h) according to G/G, G/T, and T/T genotype was 44 (n = 78), 60 (n = 60), and 130 (n = 14) mug.h/ml, respectively (P < 0.0001). The CYP2B6 G516T genotype was also associated with central nervous system symptoms at week 1 (P = 0.036). Analysis of DNA from other subjects confirmed population differences in frequency of the G516T variant. No associations were apparent with the other polymorphisms studied. A CYP2B6 allelic variant that is more common in African-Americans than in Europeans-Americans was associated with significantly greater efavirenz plasma exposure during HIV therapy. Inter-individual differences in metabolism may, in part, explain susceptibility to efavirenz central nervous system side effects.
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              Earlier versus later start of antiretroviral therapy in HIV-infected adults with tuberculosis.

              François-Xavier Blanc, Thim Sok, Didier Laureillard … (2011)
              Tuberculosis remains an important cause of death among patients infected with the human immunodeficiency virus (HIV). Robust data are lacking with regard to the timing for the initiation of antiretroviral therapy (ART) in relation to the start of antituberculosis therapy. We tested the hypothesis that the timing of ART initiation would significantly affect mortality among adults not previously exposed to antiretroviral drugs who had newly diagnosed tuberculosis and CD4+ T-cell counts of 200 per cubic millimeter or lower. After beginning the standard, 6-month treatment for tuberculosis, patients were randomly assigned to either earlier treatment (2 weeks after beginning tuberculosis treatment) or later treatment (8 weeks after) with stavudine, lamivudine, and efavirenz. The primary end point was survival. A total of 661 patients were enrolled and were followed for a median of 25 months. The median CD4+ T-cell count was 25 per cubic millimeter, and the median viral load was 5.64 log(10) copies per milliliter. The risk of death was significantly reduced in the group that received ART earlier, with 59 deaths among 332 patients (18%), as compared with 90 deaths among 329 patients (27%) in the later-ART group (hazard ratio, 0.62; 95% confidence interval [CI]; 0.44 to 0.86; P=0.006). The risk of tuberculosis-associated immune reconstitution inflammatory syndrome was significantly increased in the earlier-ART group (hazard ratio, 2.51; 95% CI, 1.78 to 3.59; P<0.001). Irrespective of the study group, the median gain in the CD4+ T-cell count was 114 per cubic millimeter, and the viral load was undetectable at week 50 in 96.5% of the patients. Initiating ART 2 weeks after the start of tuberculosis treatment significantly improved survival among HIV-infected adults with CD4+ T-cell counts of 200 per cubic millimeter or lower. (Funded by the French National Agency for Research on AIDS and Viral Hepatitis and the National Institutes of Health; CAMELIA ClinicalTrials.gov number, NCT01300481.).
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                Author and article information

                Journal
                Title: The Journal of Infectious Diseases
                Publisher: Oxford University Press (OUP)
                ISSN (Electronic): 1537-6613
                ISSN (Print): 0022-1899
                Publication date Created: February 1 2014
                Publication date Created: February 01 2014
                Publication date Created: August 29 2013
                Publication date Other: February 1 2014
                Publication date (Print): February 01 2014
                Publication date (Electronic): August 29 2013
                Volume: 209
                Issue: 3
                Pages: 399-408
                Affiliations
                [1 ] Genetics Institute, University College London, United Kingdom
                [2 ] UMR738 INSERM, University Paris Diderot, Paris
                [3 ] Assistance Publique-Hôpitaux de Paris, Bicêtre Paris-Sud University Hospital, Le Kremlin Bicêtre
                [4 ] University Paris-Sud, EA4123, Chatenay-Malabry, France
                [5 ] University of Health Sciences
                [6 ] Institut Pasteur du Cambodge, Phnom Penh, Cambodia
                Article
                DOI: 10.1093/infdis/jit466
                PubMed ID: 23990572
                SO-VID: 52b1b5b8-dcf1-4e72-9498-f1c109efdb38
                Copyright © © 2013
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