Figure 2: EFV plasma levels and polymorphisms in the CYP2B6 gene. The change 516G>T ([Gln172His]) in CYP2B6 results in a lower enzyme activity of CYP2B6 which leads to a greater EFV plasma levels. EFV plasma levels above 4μg/mL are associated to higher incidence of central nervous system toxicity. The graphic shows mean EFV plasma levels according to CYP2B6-516 genotype. EFV: Efavirenz; GG: common genotype; GT: heterozygote genotype; TT: homozygote polymorphic genotype; CNS: central nervous system.