Leflunomide is a commonly used disease modifying drug in the treatment of Rheumatoid Arthritis (RA). Its effects are mediated via inhibition of dihydroorotate dehydrogenase (DHODH) by its active metabolite teriflunomide, and the pharmacokinetics of teriflunomide are highly variable. We examined the association between DHODH haplotype and plasma teriflunomide concentration with response to leflunomide in patients with RA where leflunomide was added to existing disease modifying drugs after failure to achieve an adequate response with conventional ‘triple therapy’.
Patients with RA who were taking, or were about to initiate leflunomide were included. Participant characteristics including DHODH haplotype were determined. Up to five plasma samples were collected after leflunomide was initiated for assays of total and free teriflunomide concentration. Disease activity was determined via the 28‐joint disease activity score (DAS28). The association between DAS28 and patient covariates was determined by linear mixed effect modelling.
A total of 67 patients were included in the study. The DAS28 after initiation of leflunomide was associated with baseline DAS28 (β=0.70, p<0.001) and was higher in those who carried DHODH Haplotype 2 (β=0.56, p=0.01) and did not carry the shared epitope (β=0.56, p=0.013). As total and free plasma teriflunomide concentration increased, DAS28 was significantly lower (p<0.001 and p=0.001 respectively). When considering threshold concentrations, teriflunomide concentrations above 16 mg/L were associated with a DAS28 that was 0.33 lower, and when free teriflunomide concentration was above 35 µg/L, DAS28 was 0.32 lower.
Teriflunomide concentration and carriage of DHODH Haplotype 2 are associated with response to leflunomide in patients with RA, and a total plasma teriflunomide concentration of at least 16 mg/L is needed to maximise the likelihood of response.
- Dihydroorotate Dehydrogenase
- rheumatoid arthritis
- therapeutic drug monitoring
- precision medicine