Abstract
Methotrexate is used to manage moderate to severe psoriasis and psoriatic arthritis. Methotrexate acts by inhibiting the enzymes involved in nucleotide synthesis. Methotrexate polyglutamates (MTXPGs) have a higher potency to inhibit Dihydrofolate reductase (DHFR), 5-aminoimidazole-4-carboxamide ribonucleotide transformylase (ATIC), and thymidylate synthase (TS), compared to naïve methotrexate. Among all the MTXPGs, methotrexate polyglutamate three (MTXPG-3) is a more potent inhibitor of DHFR, ATIC, and TS enzymes. MTXPG-3 is anticipated to allow therapeutic drug monitoring in immune-mediated inflammatory diseases. We aim to study MTXPG-3 levels as a biomarker for both efficacy and adverse events among psoriatic patients treated with methotrexate monotherapy. We used the LC-MS/MS (Liquid Chromatography Mass Spectrophotometry) system for measuring erythrocyte MTXPG-3. We recruited 106 patients with psoriasis who were treated with methotrexate. Sixty-one of them had psoriatic arthritis (concomitant or in the past). The mean age was 45.08 ± 13.04 years. After twenty-four weeks of methotrexate treatment, 73(69%) were responders, and 33(31%) were non-responders. Thirty-nine (36%) experienced adverse effects, and 67(64%) did not experience any adverse effects. We observed a significant positive correlation between erythrocyte MTXPG-3 and methotrexate dose per week at weeks 12 and 16 but not at week 24. Erythrocyte MTXPG-3 did not correlate with response or adverse effects. It can be used as a marker of compliance. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12291-024-01269-x.