Data on genetic polymorphisms associated with response to anti-HIVdrugs has accumulated over the years. Information
on how polymorphisms influence drug metabolism and transport to target sites is important in guiding dosage or selection of
appropriate alternative therapies. This study determined the frequency of MDR1 C3435T and CYP2B6 G516T polymorphisms
associated with the transport and metabolism of efavirenz and nevirapine, in a population of South African HIV infected patients.
In addition, association of polymorphisms with immunologic and virologic factors was investigated. A 207bp of MDR1 exon
26 and a 161bp of CYP2B6 exon 4 were obtained from patients by polymerase chain reaction. Analysis of population-based
sequences of MDR1 revealed a frequency of 89% and 11% of C and T alleles respectively (n = 197; X2 = 0.974; p = 0.324).
Restriction fragment length polymorphism (RFLP) analysis of the CYP2B6 gene revealed a prevalence of 9.5% of GG, 78.4%
of GT and 12.1% of TT genotype (n = 199; X2 = 65.204; p = 0.00). There was no significant difference between immune
recovery and decline in viral load (n = 53), with genotype after repeated calculations of analysis of variance (ANOVA).