Pharmacokinetics of cytosine arabinoside in cerebrospinal fluid and of its metabolite in leukemic cells

Pharmacokinetics Following Intraventricular Administration of Chemotherapy in Patients with Neoplastic Meningitis

Intraventricular administration of chemotherapy is one approach to overcoming the limited distribution of anticancer drugs and their active metabolites into the CNS. This form of regional chemotherapy has led to effective treatment of occult and overt meningeal leukaemia in humans. In contrast, the efficacy of this therapy is extremely limited in the treatment of leptomeningeal dissemination of various solid tumours. Pharmacokinetic studies of the commonly intraventricularly applied anticancer agents in humans have demonstrated that, using low drug doses, very high drug concentrations can be achieved in the cerebrospinal fluid (CSF) and relatively high concentrations in the leptomeninges but not in the brain tissue and the plasma. Therefore, this approach is not an effective treatment for bulky disease of brain tissue, and results in minimal systemic toxicity. In comparison with intralumbar administration, lower interpatient variability of CSF drug concentrations and improved clinical efficacy were observed. 'Concentration x time' schedules, i.e. frequent small drug doses over a short period, enable long-term CSF exposure to cytotoxic drug concentrations while avoiding excessively high and potentially neurotoxic drug concentrations. The technique of ventriculolumbar cerebrospinal perfusion delivers continuously high drug concentrations throughout the CSF for several hours, but its widespread use is limited by the technical complexities of this approach. In this article, the dosages, schedules and pharmacokinetic data of routinely used intraventricular agents in humans, e.g. methotrexate, cytarabine, glucocorticoids and thiotepa, are outlined in detail. In addition, pharmacokinetic data of investigational agents for intraventricular administration (diaziquone, DTC 101, mercaptopurine, mafosfamide, etoposide, topotecan, nimustine [ACNU] and bleomycin) are presented. Better understanding of the CSF pharmacology of these drugs is an essential prerequisite for safe, effective administration of these drugs. Investigational efforts are underway to verify the feasibility and efficacy of different dosages, schedules and combination therapies of these new intra-CSF agents. Current and future clinical research should also focus on methods allowing the delivery of tumoricidal drug concentrations for extended periods into the CSF and the brain tissue while minimising neurotoxicity and systemic toxicity (e.g. liposomal drug preparations, monoclonal antibodies, immunotoxins and gene therapy).

Intracellular retention of cytosine arabinoside triphosphate in blast cells from children with acute myelogenous and lymphoblastic leukemia

The importance of the cellular pharmacokinetics of cytarabine triphosphate (ara-CTP) with regard to therapeutic efficacy is well established. In vitro and in vivo monitoring of pharmacokinetic parameters of leukemic blast cells were initiated in order to contribute to the pharmacological basis of optimal ara-C treatment strategies. Peripheral or bone marrow blast cells from 66 leukemic patients [51 acute myelogenous leukemia (ALL), 15 acute lymphoblastic leukemia (AML) were separated and incubated with ara-C for 1 hour and in ara-C-free medium for another 3 hours, and the intracellular formation and retention of ara-CTP was measured. In eight children who received continuous ara-C infusion for induction treatment, the ara-CTP concentration in circulating blast cells was monitored in vivo. The in vitro values observed in this assay corresponded to the cellular levels monitored in vivo. The ara-CTP retention differed clearly among the individual groups, as classified by immunophenotype at the time of the initial diagnosis: non-T-ALL 67+/-25% (x+/-SD, n=33), T-ALL 37+/-15% (n=8), and AML 34+/-18% (n=14). The difference in ara-CTP retention between non-T-All and AML (P<0.05) as well as T-ALL (P<0.05) was significant. There was a tendency toward lower ara-CTP retention in relapsed as compared with newly diagnosed ALL, but the difference was not significant. The maximal accumulation of ara-CTP (after 1 hour incubation) was comparable in AML, T-ALL, non-T-ALL, and blast cells from children in relapse. The observed similarity of cellular accumulation in all groups and the significantly more rapid decrease in T-ALL and AML provide the pharmacokinetic rationale supporting the prolonged infusion duration for ara-C in these subgroups as an alternative to the intensification by high-dose ara-C schedules with short-term infusion.