title: Efavirenz plasma concentrations and cytochrome 2B6 polymorphisms.
abstract: BACKGROUND
  Interpatient variability in efavirenz concentrations may be due to CYP2B6 genetic polymorphisms. Efavirenz concentration and pharmacogenomic data are scarce in Latino patients.
  
  
  OBJECTIVE
  To evaluate the difference in trough and midpoint efavirenz plasma concentrations between HIV-positive Latino and white patients. In addition, this study evaluated the association between efavirenz concentrations and CYP2B6 polymorphisms in Latino and white HIV-positive subjects.
  
  
  METHODS
  This pilot study included 10 Latinos and 10 whites. Two efavirenz blood concentrations were determined: a trough and a midpoint. CYP2B6 genetic polymorphisms were analyzed at the 516 (G to T) and 785 (A to G) codons. The Mann-Whitney test was used to determine whether efavirenz concentrations varied with ethnicity. The Kruskal-Wallis test was used to determine whether efavirenz concentrations varied with CYP2B6 genetic polymorphisms. Efavirenz concentrations were expressed as medians (minimum, maximum).
  
  
  RESULTS
  Midpoint concentrations were 1.58 μg/mL (1.36, 6.02) and 3.14 μg/mL (1.74, 7.72) for whites and Latinos, respectively (p < 0.05). Trough concentrations did not vary as a function of ethnicity. Ten percent of Latinos and whites tested positive for homozygous variants of CYP2B6-516 and CYP2B6-785. One white subject tested positive for the homozygous variant of CYP2B6-1459. Trough concentrations for 516TT, 516GT, and 516GG (wild type) were 5.13 μg/mL (4.13, 6.12), 2.13 μg/mL (1.33, 3.37), and 1.44 μg/mL (0.59, 2.92), respectively (p < 0.05). Trough concentrations for 785GG, 785AG, and 785AA (wild type) were 5.12 μg/mL (4.13, 6.12), 1.98 μg/mL (1.33, 3.37), and 1.27 μg/mL (0.59, 2.92), respectively (p < 0.05). None of the patients took concomitant medications that impacted CYP2B6 metabolism.
  
  
  CONCLUSIONS
  Trough efavirenz concentrations were significantly higher in patients with the 785 (A to G) and 516 (G to T) variants. Midpoint efavirenz concentrations in Latinos were significantly higher than those of whites.
authors.affiliation: Pharmacy Department, Santa Clara Valley Medical Center, San Jose, CA, USA.
authors.forename: Tristan
authors.initials: T
authors.lastname: Lindfelt
authors.forename: John
authors.initials: J
authors.lastname: O'Brien
authors.forename: Jessica C
authors.initials: JC
authors.lastname: Song
authors.forename: Rajul
authors.initials: R
authors.lastname: Patel
authors.forename: Dean L
authors.initials: DL
authors.lastname: Winslow
mesh_terms: D000328:Adult; D000480:Alkynes; D019380:Anti-HIV Agents / Q000097:blood* / Q000627:therapeutic use; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D048588:Benzoxazines / Q000097:blood* / Q000627:therapeutic use; D003521:Cyclopropanes; D065702:Cytochrome P-450 CYP2B6; D005260:Female; D015658:HIV Infections / Q000097:blood / Q000188:drug therapy / Q000235:genetics; D054303:HIV Reverse Transcriptase / Q000037:antagonists & inhibitors; D006630:Hispanic or Latino; D006801:Humans; D008297:Male; D008875:Middle Aged; D010089:Oxidoreductases, N-Demethylating / Q000235:genetics*; D010865:Pilot Projects; D011110:Polymorphism, Genetic; D011446:Prospective Studies; D018894:Reverse Transcriptase Inhibitors / Q000097:blood* / Q000627:therapeutic use; D044465:White People
chemical_list: D000480:Alkynes; D019380:Anti-HIV Agents; D048588:Benzoxazines; D003521:Cyclopropanes; D018894:Reverse Transcriptase Inhibitors; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; D065702:Cytochrome P-450 CYP2B6; D010089:Oxidoreductases, N-Demethylating; D054303:HIV Reverse Transcriptase; C098320:efavirenz