Abstract
OBJECTIVES: Methotrexate is widely used at low dosages (LD-MTX) for non-oncologic indications and is associated with a variety of adverse effects (AEs). We sought to determine whether concentrations of the active metabolite, MTX polyglutamates (MTX-PGs) 1-5, correlate with AEs. METHOD: We examined data from the LD-MTX arm of the randomized double-blind Cardiovascular Inflammation Reduction Trial (CIRT). All AEs were blindly adjudicated and monitoring laboratories were tested centrally. The MTX-PGs 1-5 were assessed in one reference laboratory using liquid chromatography-tandem mass spectrometry. Based on prior literature, MTX-PGs 3-5 were chosen as the exposure of interest and quartiles of MTX-PGs 3-5 were assessed for their relationship with all AEs and each pre-specified category of AE using adjusted Cox proportional hazards regression. RESULTS: Of the 2391 subjects randomized to LD-MTX, MTX-PG levels were available for 1319 subjects (median dosage 16.1 mg/week) from the 8 month visit. We followed these subjects for a median of 2.2 years [interquartile range (IQR) 1.5-2.9]. Higher MTX-PG3-5 levels were related to an increased risk of anaemia [compared with quartile 1 (Q1); hazard ratio (HR) for Q4 1.27 (95% CI 0.98, 1.65), P for trend = 0.05] and a decreased risk of thrombocytopenia [HR for Q4 0.52 (95% CI 0.32, 0.84), P for trend = 0.05]. MTX-PG3-5 levels >134 nmol/l were associated with an increased risk of liver abnormalities [HR 1.36 (95% CI 1.08, 1.72)]. CONCLUSIONS: Higher MTX- PG3-5 levels were modestly associated with LD-MTX AEs, including anaemia and liver function abnormalities, but a reduced risk of thrombocytopenia and haemorrhage. CLINICAL TRIAL REGISTRATION: NCT01594333.