In vitro stability study of methotrexate in blood and plasma samples for routine monitoring

A study was conducted to assess the stability of methotrexate (MTX) in pooled plasma and whole blood samples during an 11-day period. The concentrations were determined by liquid chromatography with UV detection over time, in the dark or in light, at different temperatures (4 degrees C or room temperature), and for a low and a high concentration level (0.6 and 2.5 microg/mL, 1.32 and 5.5 micromol/L, respectively). The accuracy, linearity, and variability of the method were assessed. This work demonstrates that blood samples are stable for 2 days at room temperature and for 6 days at 4 degrees C. Furthermore, there is no significant loss (<17%) in plasma at any of the investigated temperatures for at least 6 days. This study shows that whole blood samples can be stored for 3 days before centrifugation and that plasma samples can be reanalyzed after 6 days without any loss.