Pages 7

Cytochromes P450, mainly CYP1A2 and CYP2C19, are involved in the transformation of lefl unomide to A77 1726. The analysis of SNPs in CYP1A2 and CYP2C19 genes showed that genetic variability in leflunomide-metabolizing enzymes influences leflunomide metabolite concentrations and so the treatment response. This result is in line with the fi ndings that A77 1726 serum concentration predicts response to treatment in patients with RA (van Roon EN 2005).