Pharmacokinetics of methotrexate in plasma and cerebrospinal fluid

OBJECTIVE: To investigate the pharmacokinetics of methotrexate (MTX) in plasma and cerebrospinal fluid (CSF) during osmotic disruption of the blood-brain barrier and the intraarterial administration of combination chemotherapy postoperatively in a patient with glioblastoma. CASE SUMMARY: A 60-year-old Japanese woman with a glioblastoma received two courses of combination intraarterial chemotherapy. In the first course of treatment, 20 mL of mannitol 20%, peplomycin 10 mg, vindesine 2 mg, and MTX 500 mg were administered via the right internal carotid artery, and then via the right vertebral artery. In the second course of treatment, 20 mL of mannitol 20%, peplomycin 15 mg, vindesine 2.5 mg, and MTX 1000 mg were similarly administered. Blood samples and CSF samples from the ventricle and the space left by tumor removal were obtained; the MTX concentrations were measured from these sites by fluorescence polarization immunoassay. The pharmacokinetic parameters of MTX in plasma and CSF were estimated. DISCUSSION: The plasma concentration of MTX decreased in a biexponential decay pattern during each course of treatment. CSF concentrations of MTX in the ventricle and in the space left by tumor removal peaked at 2 and 6 hours, respectively, after drug administration and decreased monoexponentially. When the dose of MTX was doubled, the AUC for the plasma MTX concentration increased 2.4-fold and the AUCs for MTX in the ventricle and the space left by tumor removal increased 3.4- and 9.1-fold, respectively. The half-life of MTX in the CSF in the space left by tumor removal exceeded the half-lives of MTX in the plasma and in the ventricular CSF. CONCLUSIONS: The CSF AUCs of MTX in the ventricle and the space left by tumor removal increased markedly and in parallel with the MTX dosage increase during osmotic disruption of the blood-brain barrier and intraarterial combination chemotherapy. Such treatment improves the delivery of chemotherapy agents to the brain.

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