effect of different co-variables, (for example, age, weight, gender, during of antiretroviral therapy and genetic polymorphisms of CYP2B6, and the ABCB1 transporter) on the pharmacokinetics of efavirenz. Their study stated that the genetic polymorphism of CYP2B6 could clarify around 27% of the variations in clearance of efavirenz (Cabrera et al., 2009). This outcome agrees with results of another study done in 2009 in which it has been reported that genetic varieties of CYP2B6 added to 31% of inter-individual variability in mean clearance of efavirenz (Arab-Alameddine et al., 2009).

It has been proposed that CYP2B6 might be in charge of metabolizing nevirapine into its 3- and 8-hydroxy metabolites (Erickson et al., 1999). Also Chou et al (2010) proposed that clearance of nevirapine can likewise be affected by genetic polymorphisms of CYP2B6 516 G>T. In spite of the fact that CYP2B6 had a slighter effect with nevirapine than with efavirenz, clearance of nevirapine was significantly decreased in HIV Cambodian patients, mutation 2.95 L/h for subjects with a genotype homozygous for the wild-sort allele versus 1.86 L/h for subjects homozygous for the CYP2B6 516T. Besides, Mahungu et al (2009a) demonstrated that the CYP2B6 516 G>T variation was a noteworthy predictor of nevirapine trough plasma concentrations. The other SNP, 983 T>C polymorphism has just been found in Hispanic and African populaces (Klein et al., 2005; Mehlotra et al., 2007). More results from another study demonstrated that heterozygosity for the CYP2B6 983 T>C was fundamentally connected with higher plasma concentrations of nevirapine in dark patients (Wyen et al., 2008). Another study affirms the significant effect of CYP2B6 983 T>C SNP, so patients heterozygous for this allele having a 40% reduction in oral clearance rates (Schipani et al., 2011).

5.4 CYP2C19
The CYP2C subfamily enzymes represent about 20% of all hepatic P450s (Imaoka et al., 1996). Also, CYP2Cs have a few genetic polymorphisms that affect drug responses. Of the four members from this subfamily, CYP2C19 has a clinical interest for HIV drugs.