Using a sensitive radioimmunoassay, concentrations of vincristine and its products were determined in cerebrospinal fluid (CSF) and corresponding blood samples from four patients with lymphoma and two patients with leukemia who had received i.v. bolus injection of 2 mg vincristine. Serial samples of CSF were withdrawn from a CSF reservoir in two patients during a 24-hr period following injection. The first time point after injection at which measurable levels of vincristine were detected in the

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... CSF was 30 min; the concentrations were within the lower range of sensitivity of the assay and were 20- to 30-fold lower than were corresponding serum samples. Despite a prolonged terminal half-life of vincristine in the serum (14.4 to 37.5 hr) following i.v. bolus injection, concentrations of vincristine in the CSF ranged between undetectable within the limits of the assay and 1.1 X 10(-9) M during the 24-hr period of observation. The highest CSF concentration of vincristine (2.6 X 10(-9) M) has been observed in a patient receiving cranial irradiation for active meningeal lymphoma. No measurable levels of vincristine or its products were detected in spot samples of CSF from three patients. Penetration of vincristine and its products into the CSF of humans after i.v. bolus injection appears to be very poor and may account for the uncommon occurrence of central neurotoxicity following its clinical use.