Increased efavirenz concentrations were associated with CYP2A6 -48 TG in all subjects ( P = 3.810 ( -4 ) ) and in Black subjects ( P = 0.027 ) and White subjects ( P = 0.0011 ) analysed separately ; and with UGT2B7 735 G/G homozygosity in all subjects ( P = 0.006 ) and in Black subjects ( P = 0.046 ) and White subjects ( P = 0.062 ) analysed separately .