Hematology. Individualized methotrexate dosing in primary CNS lymphoma

Diagnosis and management of primary central nervous system lymphoma: a Consensus Practice Statement from the Australasian Lymphoma Alliance

Primary central nervous system lymphoma is a clinicopathological disease entity that accounts for 1 % of all non-Hodgkin lymphoma (NHL). Advanced patient age, adverse disease biology and complexities of diagnosis and treatment render outcomes markedly inferior to systemic NHL. Despite this, an increasing evidence base including limited randomised controlled clinical trial data is informing optimal therapeutic strategies with methotrexate-based induction chemotherapy schedules and intensified consolidation in selected patients. This practice statement represents an evidence-based review of the literature and has been devised to assist healthcare professionals in the diagnosis and management of this disease. This article is protected by copyright. All rights reserved.

A minimal physiologically based pharmacokinetic model for high-dose methotrexate

Purpose

High-dose methotrexate (HDMTX) is administered for the treatment of a variety of malignant tumors. Wide intra- and inter-individual variabilities characterize the pharmacokinetics of MTX, which is mostly excreted renally. HDMTX dosages are prescribed as a function of body surface area whereas dose adjustments depending on renal function are not well defined. We develop a population pharmacokinetic model with a physiological description of renal excretion as the basis for clinical tools able to suggest model-informed dosages and support therapeutic monitoring.

Methods

This article presents a minimal physiologically based pharmacokinetic (PBPK) model for HDMTX, which specifically accounts for individual characteristics such as body weight, height, gender, age, hematocrit, and serum creatinine to provide individualized predictions. The model supplies a detailed and mechanistic description of capillary and cellular exchanges between plasma, interstitial fluid, and intracellular fluid compartments, and focuses on an individualized description of renal excretion.

Results

The minimal PBPK model is identified and validated with a literature dataset based on Chinese patients suffering from primary central nervous system lymphoma. A comparison with a pharmacokinetic model from the literature suggests that the proposed model provides improved predictions. Remarkably, the model does not present any significant bias in a wide range of degrees of renal function.

Conclusion

Results show that model predictions can capture the wide intra- and inter-individual variability of HDMTX, and highlight the role played by the individual degree of renal function. The proposed model can be the basis for the development of clinical decision-support systems for individualized dosages and therapeutic monitoring.

Dosing algorithm to target a predefined AUC in patients with primary central nervous system lymphoma receiving high dose methotrexate

AIM

There is no consensus regarding optimal dosing of high dose methotrexate (HDMTX) in patients with primary CNS lymphoma. Our aim was to develop a convenient dosing algorithm to target AUC(MTX) in the range between 1000 and 1100 µmol l(-1) h.

METHODS

A population covariate model from a pooled dataset of 131 patients receiving HDMTX was used to simulate concentration-time curves of 10,000 patients and test the efficacy of a dosing algorithm based on 24 h MTX plasma concentrations to target the prespecified AUC(MTX) . These data simulations included interindividual, interoccasion and residual unidentified variability. Patients received a total of four simulated cycles of HDMTX and adjusted MTX dosages were given for cycles two to four.

RESULTS

The dosing algorithm proposes MTX dose adaptations ranging from +75% in patients with MTX C(24) < 0.5 µmol l(-1) up to -35% in patients with MTX C(24) > 12 µmol l(-1). The proposed dosing algorithm resulted in a marked improvement of the proportion of patients within the AUC(MTX) target between 1000 and 1100 µmol l(-1) h (11% with standard MTX dose, 35% with the adjusted dose) and a marked reduction of the interindividual variability of MTX exposure.

CONCLUSIONS

A simple and practical dosing algorithm for HDMTX has been developed based on MTX 24 h plasma concentrations, and its potential efficacy in improving the proportion of patients within a prespecified target AUC(MTX) and reducing the interindividual variability of MTX exposure has been shown by data simulations. The clinical benefit of this dosing algorithm should be assessed in patients with primary central nervous system lymphoma (PCNSL).

Methotrexate area under the curve as a prognostic factor in primary central nervous system lymphoma treated with immunochemoradiotherapy

A higher methotrexate area under the curve (MTX AUC) observed during the first chemotherapy cycle has been associated with improved tumor control in patients with primary central nervous system lymphoma. To confirm these findings, we conducted a post hoc analysis of data from a prospective phase II trial of rituximab, methotrexate, procarbazine, vincristine, cytarabine, and low-dose radiotherapy. Thirty-nine patients were included (24 men; 15 women). The median age was 60 years (range 30-76) and median Karnofsky performance status (KPS) score was 70 (range 50-100). There was substantial inter-individual variability in MTX AUC (median: 795.5 µM*h/L, range 44.8-8326.44). However, there were no differences in progression-free survival (PFS) in patients below and above the median MTX AUC (2-year PFS 78% vs. 85% respectively; p = 0.51). Similarly, there were no differences in response rates or overall survival according to MTX AUC, suggesting that intra-patient dose escalation to increase MTX exposure is unnecessary when our regimen is utilized.