Effects of genetic variability on rifampicin and isoniazid pharmacokinetics in South African patients with recurrent tuberculosis.

Aim: We report the prevalence and effect of genetic variability on pharmacokinetic parameters of isoniazid and rifampicin. Materials & methods: Genotypes for SLCO1B1, NAT2, PXR, ABCB1and UGT1A genes were determined using a TaqMan((R)) Genotyping OpenArray (TM). Nonlinear mixed-effects models were used to describe drug pharmacokinetics. Results: Among 172 patients, 18, 43 and 34% were classified as rapid, intermediate and slow NAT2 acetylators, respectively. Of the 58 patients contributing drug concentrations, rapid and intermediate acetylators had 2.3- and 1.6-times faster isoniazid clearance than slow acetylators. No association was observed between rifampicin pharmacokinetics and SLCO1B1, ABCB1, UGT1Aor PXR genotypes. Conclusion: Clinical relevance of the effects of genetic variation on isoniazid concentrations and low first-line tuberculosis drug exposures observed require further investigation.