Prediction of the therapeutic response to methotrexate at 24 weeks by methotrexate–polyglutamates concentration in erythrocytes at 8 weeks in patients with rheumatoid arthritis

Abstract

Objectives: The objective of this study is to evaluate the pharmacokinetics and pharmacodynamics of methotrexate–polyglutamates (MTX-PGs) in erythrocytes in patients with rheumatoid arthritis and correlate them with the efficacy.

Methods: MTX-PG concentrations in erythrocytes were measured in 42 MTX-naïve patients repeatedly for 24 weeks by high-performance liquid chromatography. In 56 patients receiving stable MTX doses for at least 12 weeks, the correlation between MTX doses and MTX-PG concentrations was examined. The efficacy was measured by the change of DAS28CRP (ΔDAS28CRP).

Results: There were moderate correlations between MTX dose and MTX-PG 3, 4, and 5. At 24 weeks, MTX-PG2, 3, 4, and 1–5 were higher in patients with ΔDAS28CRP >1.2 than in those with ≤1.2. The cutoff value of MTX-PG1-5 to discriminate ΔDAS28CRP >1.2 from ≤1.2 at 24 weeks was 68.7 nM. Among 20 patients with MTX-PG1-5 > 50.6 nM at 8 weeks, seven already improved at 8 weeks and additional 11 improved at 24 weeks (p < 0.001). On the contrary, among the nine patients with MTX-PG1-5 ≤ 50.6 nM at 8 weeks, none improved at 8 weeks and only one improved at 24 weeks (p = 0.500).

Conclusions: Erythrocyte MTX-PGs might be a potential indicator and predictor of MTX efficacy.

Keywords:

• Biomarker
• Drug monitoring
• Methotrexate
• Methotrexate–polyglutamates
• Rheumatoid arthritis

Acknowledgements

The authors would like to thank Mika Kobayashi, Chiyomi Hayashi, Tomomi Nakamoto, and Maiko Tanaami for expert technical support.

Conflict of interest

S. M. received an unlimited research grant from Pfizer. All other authors have declared no conflicts of interest.