Efavirenz Plasma Concentrations and Cytochrome 2B6 Polymorphisms

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 mu g/mL (1.36, 6.02) and 3.14 mu g/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 5167 516GT, and 516GG (wild type) were 5.13 mu g/mL (4.13, 6.12), 2.13 mu g/mL (1.33, 3.37), and 1.44 mu g/mL (0.59, 2.92), respectively (p < 0.05). Trough concentrations for 785GG, 785AG, and 785AA (wild type) were 5.12 mu g/mL (4.13, 6.12), 1.98 mu g/mL (1.33, 3.37), and 1.27 mu g/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.