Therapeutic drug monitoring of methotrexate in patients with Crohn's disease

Abstract

SummaryBackgroundTherapeutic drug monitoring (TDM) has the potential to improve efficacy and diminish side effects. Measuring methotrexate‐polyglutamate (MTX‐PG) in erythrocytes might enable TDM for methotrexate in patients with Crohn's disease (CD).AimTo investigate the relationship between MTX‐PGs and methotrexate drug survival, efficacy and toxicityMethodsIn a multicentre prospective cohort study, patients with CD starting subcutaneous methotrexate without biologics were included and followed for 12 months. Primary outcome was subcutaneous methotrexate discontinuation or requirement for step‐up therapy. Secondary outcomes included faecal calprotectin (FCP), Harvey Bradshaw Index (HBI), hepatotoxicity and gastrointestinal intolerance. Erythrocyte MTX‐PGs were analysed at weeks 8, 12, 24 and 52 or upon treatment discontinuation.ResultsWe included 80 patients with CD (mean age 55 ± 13y, 35% male) with a median FCP of 268 μg/g (IQR 73–480). After the 12‐month visit, 21 patients (26%) were still on subcutaneous methotrexate monotherapy. Twenty‐one patients stopped because of disease activity, 29 because of toxicity, and four for both reasons. Five patients ended study participation or stopped methotrexate for another reason. A higher MTX‐PG3 concentration was associated with a higher rate of methotrexate drug survival (HR 0.86, 95% CI 0.75–0.99), lower FCP (β −3.7, SE 1.3, p < 0.01) and with biochemical response (FCP ≤250 if baseline >250 μg/g; OR 1.1, 95% CI 1.0–1.3). Higher MTX‐PGs were associated with less gastrointestinal intolerance. There was no robust association between MTX‐PGs and HBI or hepatotoxicity.ConclusionsHigher MTX‐PG3 concentrations are related to better methotrexate drug survival and decreased FCP levels. Therefore, MTX‐PG3 could be used for TDM if a target concentration can be established.