portrayed for the CYP2B6, also more than 100 SNPs have been described. Among various variants, the CYP2B6*6 haplotype (785 A > G, 516 G >T) give rise to reduction in the catalytic activity and a huge decrease in the expression of the protein. The frequency of the mutant allele, CYP2B6*6, varies among various ethnic groups: 25% in white persons, 15 to 40% in Asians, and more than half in black African and Africans Americans (Lang et al., 2001; Mehlotra et al., 2006). The CYP2B6*16 (785 A > G; 983 T > C) or the CYP2B6*18 (983 T > C) variations that are generally common in black populations, result in a decrease in the expression of the relating protein without influencing its intrinsic catalytic activities (Wang et al., 2006).

Efavirenz is mostly metabolized by CYP2B6 into 8-hydroxy efavirenz and less so throughout accessory pathways including CYP3A4/5, CYP2A6, and UGT2B7 (Ward et al., 2003; Desta et al., 2007). Additionally, efavirenz can induce its own metabolism as a self-inducer of CYP2B6 (Zhu et al., 2009). This self-induction might be specific for certain tissues that would also propose specific induction mechanism (Lee et al., 2006). In that capacity, the fractional metabolic clearance of efavirenz would be in charge of around 90% of its systemic clearance (Wardetal.,2003). Administration orally of adailydose of 600 mg of efavirenz is connected with wide inter-individual differences in plasma concentrations (Csajka et al., 2003).

Numerous studies have reported a relationship between genetic polymorphisms of CYP2B6 and the pharmacokinetics of efavirenz (Carr et al., 2010). Tsuchiya et al (2004) stated an increase in efavirenz plasma concentrations in CYP2B6*6/*6 people. An additional study demonstrated a relationship between the CYP2B6 516 G > T variation and A) increased intra-cellular concentrations of the medication in PBMCs (peripheral blood mononuclear cells), B) an increase in the area under the curve for efavirenz, and C) a higher toxicity risk in the CNS, central nervous system, of individuals homozygous for the allelic variation (Rotgeretal., 2005a). in 2006, Wang et al. demonstrated that the concentrations of efavirenz steady-state were higher in Africans that were carriers of the CYP2B6*16 allelic variation than in different patients (Wang et al., 2006).

Another study done by Cabrera et al (2009) built up a population pharmacokinetics mo