Delayed methotrexate elimination in a patient with primary central nervous system lymphoma: A case report

Methotrexate (MTX) is an important agent for the treatment of primary central nervous system lymphomas (PCNSL) but needs to be given in big doses by intravenous infusions to achieve therapeutic concentrations in the cerebrospinal fluid. However, co-administration with many drugs may delay the excretion of MTX which may cause serious adverse effects if the serum concentration exceeds 0.1 µmol/L 72 h after an intravenous infusion.

A 67-year-old Japanese female with PCNSL was treated with high-dose MTX-based chemotherapy. The serum MTX concentration 72 h post-infusion was 0.153 µmol/L when she was taking levofloxacin (LVFX) but <0.1 µmol/L 72 h after 4 subsequent infusions when she was not taking LVFX. She was given many other drugs but the timing of the short course of LVFX and the fact that ciprofloxacin also delays MTX excretion suggests that LVFX was the cause.

Co-administration of LVFX may delay the excretion of MTX. Therefore, serum concentrations of MTX should be monitored to help prevent and improve the management of potentially serious MTX drug-drug interaction.