Leflunomide is a
disease-modifying antirheumatic drug used for the treatment of
rheumatoid arthritis (RA).
Cytochromes P450, mainly
CYP1A2 and
CYP2C19, may be involved in the transformation of
leflunomide to
leflunomide metabolite (
A77 1726, 2-cyano-3-hydroxy-N-[4-(trifluoromethyl)phenyl]-2-
butenamide). The aim of this study was to investigate whether genetic polymorphisms in
CYP1A2 and
CYP2C19 influence
leflunomide pharmacokinetics, treatment response, and the occurrence of
adverse drug reactions (ADRs). The study included 67 patients with RA and 4 patients with
polyarthritis resembling RA and
psoriasis treated with
leflunomide.
A77 1726 steady-state plasma concentrations were determined by validated high-performance liquid chromatography with UV detection. A population pharmacokinetic model was developed to estimate the oral clearance (CL/F) and volume of distribution (V/F). A genotyping approach was used to determine C-163A, C-729T, and T-739G in the
CYP1A2 gene as well as single nucleotide polymorphisms that characterize
CYP2C19*2, *3, *4, and *17 alleles. A large interindividual variability in trough
A77 1726 steady-state plasma concentrations was observed (from 1.9 to 156.9 mg/l).
A77 1726 CL/F was 71% higher in carriers of the
CYP2C19*2 allele compared with noncarriers. The
A77 1726 average steady-state plasma concentration was associated with the treatment response. Patients with a greater decrease in
C-reactive protein (CRP) had higher average steady-state plasma
A77 1726 concentrations: 49.7 +/- 39.0 mg/l in patients with DeltaCRP of more than 8.5 mg/l compared with 24.8 +/- 13.7 mg/l in patients with DeltaCRP of <or=8.5 mg/l (p = 0.015). No association of
A77 1726 steady-state plasma concentrations with the occurrence of ADRs was observed. Our results suggest that genetic variability in
leflunomide-metabolizing
enzymes influences
leflunomide metabolite concentrations that are associated with the treatment response but not with
leflunomide-induced toxicity.