[Urinary beta 2-microglobulin as an indicator for impaired excretion of methotrexate]

Twenty cases treated with high-dose methotrexate (MTX) infusions were studied to determine whether urinary beta 2-Microglobulin (beta 2-M) is a reliable indicator to predict impaired excretion of methotrexate. Before and after MTX infusions, the levels of urinary beta 2-M were measured along with serum creatinine, uric nitrogen, and creatinine clearance. MTX clearance was found to be impaired in four of the 20 infusions, although concentrations of serum creatinine and uric nitrogen, and creatinine clearance were normal prior to the infusions. In the four cases that resulted in impaired excretion, a significant increase of beta 2-M levels was noted before and after the high-dose MTX infusion (p less than 0.01). Although one of the four cases showed a normal level of beta 2-M before the infusion, the post-infusion level of beta 2-M extremely high. This raised level of beta 2-M was thought to be caused by impaired excretion due to decreased amounts of urine. We conclude that urinary beta 2-M is a sensitive indicator of impaired excretion of high-dose MTX infusion, and especially when levels of more than 250 ng/ml of urinary beta 2-M are found to exist, it seems to difficult to clear the drug following high-dose MTX treatment.