Raised plasma methotrexate concentrations following intrathecal administration in children with renal dysfunction.

Plasma methotrexate (MTX) concentrations were measured following intrathecal (IT) MTX treatment in four patients with acute lymphocytic leukemia and acute renal dysfunction. All four patients had raised serum MTX concentrations to potentially cytotoxic concentrations for a prolonged period of time, (96-120 h). In contrast, serum MTX concentrations after the same dosage of IT treatment ranged from undetectable to 0.11 microM by 15-24 h in seven control patients with normal renal function, and were undetectable by 48 h in all controls. The terminal MTX T1/2 was 19-44 h in the patients with renal dysfunction. Decreased renal clearance or a rapid efflux of MTX from cerebrospinal fluid, or both, could account for the high and sustained concentrations. Plasma MTX concentrations after IT treatment were normal in two patients treated after their renal function returned to normal. Patients with renal dysfunction should be carefully monitored for plasma MTX concentrations and may require leucovorin to prevent systemic side-effects after IT MTX treatment.