High-dose methotrexate: on the relationship of methotrexate elimination time vs renal function and serum methotrexate levels in 1164 courses in 264 Swedish children with acute lymphoblastic leukaemia (ALL)

Population pharmacokinetic analyses of methotrexate in pediatric patients: a systematic review

BACKGROUND AND OBJECTIVES

Methotrexate is widely utilized in the chemotherapy of malignant tumors and autoimmune diseases in the pediatric population, but dosing can be challenging. Several population pharmacokinetic models were developed to characterize factors influencing variability and improve individualization of dosing regimens. However, significant covariates included varied across studies. The primary objective of this review was to summarize and discuss population pharmacokinetic models of methotrexate and covariates that influence pharmacokinetic variability in pediatric patients.

METHODS

Systematic searches were conducted in the PubMed and EMBASE databases from inception to 7 July 2023. Reporting Quality was evaluated based on a checklist with 31 items. The characteristics of studies and information for model construction and validation were extracted, summarized, and discussed.

RESULTS

Eighteen studies (four prospective studies and fourteen retrospective studies with sample sizes of 14 to 772 patients and 2.7 to 93.1 samples per patient) were included in this study. Two-compartment models were the commonly used structural models for methotrexate, and the clearance range of methotrexate ranged from 2.32 to 19.03 L/h (median: 6.86 L/h). Body size and renal function were found to significantly affect the clearance of methotrexate for pediatric patients. There were limited reports on the role of other covariates, such as gene polymorphisms and co-medications, in the pharmacokinetic parameters of methotrexate pediatric patients. Internal and external evaluations were used to assess the performance of the population pharmacokinetic models.

CONCLUSION

A more rigorous external evaluation needs to be performed before routine clinical use to select the appropriate PopPK model. Further research is necessary to incorporate larger cohorts or pool analyses in specific susceptible pediatric populations to improve the understanding of predicted exposure profiles and covariate identification.

Factors influencing delayed clearance of high dose methotrexate (HDMTX) in pediatric, adolescent, and young adult oncology patients

Purpose

To identify modifiable risk factors associated with prolonged clearance of methotrexate in pediatric, adolescent, and young adult (AYA) oncology patients receiving high dose methotrexate (HDMTX).

Design/Method

A single institution, retrospective chart review of patients receiving HDMTX between 2010-2017. Patients had a diagnosis of either leukemia or osteosarcoma. Data included demographics, concurrent intravenous (IV) medications, IV fluids (IVF) administered, urine output (UO), and rises in serum creatinine (RSC) reflective of renal toxicity (RT). Outcome measures included 1) delayed targeted MTX clearance (DC), 2) actual time to clearance (TTC) and 3) length of stay (LOS).

Results

Data from 447 HDMTX administrations were analyzed. The sample consisted of 241 (54%) osteosarcoma encounters, and 206 (46%) leukemia encounters, with an average patient age of 12.7 years. Multivariate analysis showed that DC was associated with the diagnosis of leukemia (OR 7.64, p <.0001), and less UO on day 1 (OR 0.76, p=0.005). Increased TTC was associated with increasing age (RR 1.02, p<0.0001), higher 24-hour MTX levels (RR 1.001, p=0.012) and 48-hour MTX levels (RR 1.02, p<0.0001), RT (RR 1.004, p<0.0001), use of IV lorazepam (RR 1.08, p=0.001) and IV metoclopramide (RR 1.08, p<0.001) both on day 3. Like TTC, LOS was affected by MTX levels at 24 (RR 1.001, p=0.025) and 48 hours (RR 1.03, p<0.0001), RT (RR 1.006, p<0.0001), total IV medications on day 3 (RR 1.042, p<0.0001), and the use of leucovorin on day 2 (RR 0.93, p=0.002).

Conclusion

Multiple modifiable risk factors were identified which can be leveraged to improve HDMTX clearance. Subsequent efforts will assess whether acting on such risk factors can improve MTX clearance and shorten LOS.

Early clinical indicators of acute kidney injury caused by administering high-dose methotrexate therapy to juvenile pigs

Introduction

Early identification of compromised renal clearance caused by high-dose methotrexate (HDMTX) is essential for initiating timely interventions that can reduce acute kidney injury and MTX-induced systemic toxicity.

Methods

We induced acute kidney injury (AKI) by infusing 42 juvenile pigs with 4 g/kg (80 g/m2) of MTX over 4 hours without high-volume alkalinizing hydration therapy. Concentrations of serum creatinine and MTX were measured at 15 time points up to 148 hours, with 10 samples collected during the first 24 hours after the start of the HDMTX infusion.

Results

During the first 28 hours, 81% of the pigs had increases in the concentrations of serum creatinine in one or more samples indicative of AKI (i.e., > 0.3g/dL increase). A rate of plasma MTX clearance of less than 90% during the initial 4 hours after the HDMTX infusion and a total serum creatinine increase at 6 and 8 hours after starting the infusion greater than 0.3 g/dL were predictive of AKI at 28 hours (p < 0.05 and p < 0.001, respectively). At conclusion of the infusion, pigs with a creatinine concentration more than 0.3 g/dL higher than baseline or serum MTX greater than 5,000 μmol/L had an increased risk of severe AKI.

Conclusions

Our findings suggest that serum samples collected at conclusion and shortly after HDMTX infusion can be used to predict impending AKI. The pig model can be used to identify biological, environmental, and iatrogenic risk factors for HDMTX-induced AKI and to evaluate interventions to preserve renal functions, minimize acute kidney injury, and reduce systemic toxicity.

Rescue Therapies for AKI in Onconephrology: Rasburicase and Glucarpidase

Tumor lysis syndrome (TLS) and high-dose methotrexate (HD MTX) toxicity can present with potentially severe complications, including acute kidney injury, in patients with malignancy. Guidelines for using rasburicase and glucarpidase as rescue therapies for TLS and HD MTX toxicity, respectively, are widely used by clinicians intending to mitigate organ toxicity and decrease morbidity and mortality as a consequence of cancer therapy. This review discusses the pathogenesis of TLS and HD MTX-associated toxicity, to understand the mechanism of action of these therapeutic agents and to review the currently available evidence supporting their use.

Hypoalbuminemia and not undernutrition predicts high-dose methotrexate-induced nephrotoxicity in children with acute lymphoblastic leukemia in resource-constrained centers

BACKGROUND

The standard practice to mitigate high-dose methotrexate (HD-MTX)-induced nephrotoxicity (HMN) in acute lymphoblastic leukemia (ALL) is to monitor levels until serum MTX falls below a predefined threshold. It is not feasible in most resource-constrained centers. Literature on the various factors affecting HMN in these centers is limited, retrospective, and heterogeneous. Though hypoalbuminemia has been postulated as a risk factor for HMN, the relationship of undernutrition with HMN has not been studied.

PROCEDURE

This prospective observational study consecutively enrolled children < 12 years old with ALL receiving HD-MTX. Children with preexisting renal disease and exposed to nephrotoxic drugs two weeks preceding HD-MTX infusion were excluded. HD-MTX was administered over 24 hours (BFM-2009 protocol) with 12 hours of prehydration. Solitary MTX levels at 36 hours (MTX36) were outsourced, and 6-8 doses of leucovorin were given six-hourly. Hydration was continued till last dose of leucovorin. Various factors affecting HMN (rise in creatinine to 1.5 times baseline) were recorded: age, sex, type of ALL, risk group of ALL, first dose of MTX, dose of MTX, undernourishment, serum protein, and albumin along with C-reactive protein and MTX36 levels.

RESULTS

Forty-four children who received 150 HD-MTX cycles were analyzed. HMN was seen in 14% of cycles. On univariate analysis, undernourishment, MTX36 levels, hypoproteinemia, and hypoalbuminemia were significantly associated with HMN. On multivariate analysis, hypoalbuminemia and MTX36 levels significantly predicted the development of HMN with odds ratios of 4.71 and 1.45.

CONCLUSION

Hypoalbuminemia and solitary serum MTX levels predict HMN in centers where serial MTX level monitoring is not feasible.

Methotrexate nephrotoxicity in a patient with preserved renal function. Case report

Introduction: Methotrexate is a drug with chemotherapeutic properties frequently used for the treatment of certain types of cancer. The following is a clinical case which, to the best of the authors’ knowledge, is the first report in Colombia on nephrotoxicity caused by this drug and describes the consequences as well as the treatment provided at a quaternary care hospital. Case report: A 71-year-old patient with a diagnosis of non-Hodgkin’s lymphoma with normal renal function underwent chemotherapy (high-dose methotrexate intravenously) and developed stage 3 acute renal failure according to the KDIGO guidelines, which was most likely related to methotrexate intake. The patient received treatment with intravenous fluids and sodium bicarbonate as promoters of urine excretion of the toxin, and oral calcium folinate following the institutional protocol. The patient was discharged with recovery of kidney function and improved creatinine and urea nitrogen levels. Conclusion: The treatment given to the patient in this case report shows that although methotrexate nephrotoxicity is a potentially serious entity, it can have a good prognosis if treated promptly.

A Systematic Review of Population Pharmacokinetic Models of Methotrexate

BACKGROUND AND OBJECTIVES

Methotrexate (MTX) is widely used for the treatment of a variety of neoplastic and autoimmune diseases. However, its toxicity and efficacy varied greatly among individuals, and they could be predicted by its pharmacokinetics. Many population pharmacokinetic models have been published to describe MTX pharmacokinetics. The objective of this systematic review was to summarize and discuss covariates with significant influence on MTX pharmacokinetics.

METHODS

We searched PubMed and EMBASE databases from their inception to April 2021 for population pharmacokinetic of MTX. The articles were screened by inclusion and exclusion criteria. The characteristics of studies and information for model construction and validation were extracted, summarized and discussed.

RESULTS

Thirty-five articles were included. The two-compartment model well described the pharmacokinetic behavior of MTX. For inter-individual variability, an exponential distribution error model was usually used for high-dose MTX population pharmacokinetic models, while a proportional distribution error model was used for low-dose MTX population pharmacokinetic models. Proportional and combined proportional and additive error models were used to describe residual error. Renal function was an independent indicator of MTX clearance. Body weight, age, gene polymorphisms (SLCO1B1, ABCC2, ABCB1, ABCG2 and MTHFR) and co-medications (proton pump inhibitors, non-steroidal anti-inflammatory drug, dexamethasone, vancomycin, penicillin and salicylic acid) could influence MTX clearance. Body weight, body surface area, age and dosage regimen have significant influence on MTX central compartment volume. Internal bootstrap test, external validation and visual predictive check were used to evaluate model predictive ability.

CONCLUSIONS

Various covariates could affect MTX pharmacokinetics, and their relationships have been summarized and discussed. This review will be helpful for researchers to develop their own population pharmacokinetic models and select appropriate models for individualized therapy of MTX.

Utility of repeated drug level measurements after high dose methotrexate infusion for treatment planning in pediatric leukemia

Introduction: Although high-dose Methotrexate (MTX) is a successful chemotherapeutic agent used in the treatment of acute lymphoblastic leukemia in childhood, life-threatening toxic effects are rarely seen. Therefore, frequent follow-up of drug levels is recommended. The study researched the necessity of drug level measurement and a minimum safe number of measurements. Materials and Methods: The files of pediatric patients with Acute Lymphoblastic Leukemia receiving high-dose MTX treatment in a single center between 2018 and 2021 were retrospectively reviewed. The treatment protocol was: 3000 mL/m2 alkaline hydration fluid was continued until the 72nd hour together with 2 gr/m2 continuous MTX infusion in the low-risk group and 5 gr/m2 in moderate and high-risk groups, and 15 mg/m2 /dose folinic acid was given at the 42nd, 48thand 54th hours. Findings: 456 MTX treatments were evaluated in 114 patients. Similar results (p>0.05) were obtained in the MTX level measurements performed at the 24th, 42nd, 48th, and 54th hours after MTX administration. In the repeated measurements, the data at the 42nd hour were similar (p=0.021). The number of cases that were >150 µmol/L at the 24th hour of methotrexate infusion and above 1 µmol/L at the 42nd, 48th, and 52nd hours were found to be similar in the repeated measurements. Conclusion: Although recommended, frequent follow-up of MTX levels might not always indicate toxicity. In centers with limited laboratory facilities, the MTX level measured at the 42nd hour in the first treatment might be a practical approach to guide the management of other MTX treatments.

Reduced dose folinic acid rescue after rapid high-dose methotrexate clearance is not associated with increased toxicity in a pediatric cohort

Purpose

Low doses of folinic acid (FA) rescue after high-dose methotrexate (HD-MTX) have been associated with increased toxicity, whereas high doses may be related to a decreased antileukemic effect. The optimal dosage and duration of FA rescue remain controversial. This study was designed to investigate, whether a shorter duration of FA rescue in the setting of rapid HD-MTX clearance is associated with increased toxicity.

Methods

We reviewed the files of 44 children receiving a total of 350 HD-MTX courses during treatment for acute lymphoblastic leukemia according to the NOPHO ALL-2000 protocol. Following a 5 g/m2 HD-MTX infusion, pharmacokinetically guided FA rescue commenced at hour 42. As per local guidelines, the patients received only one or two 15 mg/m² doses of FA in the case of rapid MTX clearance (serum MTX ≤ 0.2 μmol/L at hour 42 or hour 48, respectively). Data on MTX clearance, FA dosing, inpatient time, and toxicities were collected.

Results

Rapid MTX clearance was observed in 181 courses (51.7%). There was no difference in the steady-state MTX concentration, nephrotoxicity, hepatotoxicity, neutropenic fever, or neurotoxicity between courses followed by rapid MTX clearance and those without. One or two doses of FA after rapid MTX clearance resulted in a 7.8-h shorter inpatient time than if a minimum of three doses of FA would have been given.

Conclusion

A pharmacokinetically guided FA rescue of one or two 15 mg/m² doses of FA following HD-MTX courses with rapid MTX clearance results in a shorter hospitalization without an increase in toxic effects.

Risk factors for high-dose methotrexate-induced nephrotoxicity

High-dose methotrexate (MTX) is widely used for the treatment of hematological malignancies. Despite the application of routine supportive care measures, such as intensive fluid hydration and urine alkalinization, nephrotoxicity is still a problem. The present study aimed to evaluate the risk factors for MTX-induced nephrotoxicity. We retrospectively reviewed 88 patients who received a regimen consisting of high-dose MTX (1000 mg/m²) and cytosine arabinoside between 2006 and 2018. Nephrotoxicity (≥ grade 2) was observed in 11 patients. Nephrotoxicity was observed only in patients with a high MTX concentration. Other than the MTX concentration, the serum uric acid level and urine pH at day 1 were associated with nephrotoxicity. A multivariate analysis revealed that urine pH was an independent risk factor for MTX-induced nephrotoxicity. Urine pH < 7.0 at day 1 was a significant risk factor for nephrotoxicity (odds ratio, 8.05; 95% confidence interval 1.95-33.3) and was also a predictor of delayed MTX elimination at 72 h after injection. Among pre-treatment factors, a low serum calcium level predicted urine pH < 7.0 at day 1. In conclusion, the present study suggests that low urine pH at day 1 is an independent risk factor for MTX-induced nephrotoxicity.

Risk prediction for delayed clearance of high-dose methotrexate in pediatric hematological malignancies by machine learning

This study aimed to establish a predictive model to identify children with hematologic malignancy at high risk for delayed clearance of high-dose methotrexate (HD-MTX) based on machine learning. A total of 205 patients were recruited. Five variables (hematocrit, risk classification, dose, SLC19A1 rs2838958, sex) and three variables (SLC19A1 rs2838958, sex, dose) were statistically significant in univariable analysis and, separately, multivariate logistic regression. The data was randomly split into a "training cohort" and a "validation cohort". A nomogram for prediction of delayed HD-MTX clearance was constructed using the three variables in the training dataset and validated in the validation dataset. Five machine learning algorithms (cart classification and regression trees, naïve Bayes, support vector machine, random forest, C5.0 decision tree) combined with different resampling methods were used for model building with five or three variables. When developed machine learning models were evaluated in the validation dataset, the C5.0 decision tree combined with the synthetic minority oversampling technique (SMOTE) using five variables had the highest area under the receiver operating characteristic curve (AUC 0.807 [95% CI 0.724-0.889]), a better performance than the nomogram (AUC 0.69 [95% CI 0.594-0.787]). The results support potential clinical application of machine learning for patient risk classification.

Evaluation of body-surface-area adjusted dosing of high-dose methotrexate by population pharmacokinetics in a large cohort of cancer patients

Background

The aim of this study was to identify sources of variability including patient gender and body surface area (BSA) in pharmacokinetic (PK) exposure for high-dose methotrexate (MTX) continuous infusion in a large cohort of patients with hematological and solid malignancies.

Methods

We conducted a retrospective PK analysis of MTX plasma concentration data from hematological/oncological patients treated at the University Hospital of Cologne between 2005 and 2018. Nonlinear mixed effects modeling was performed. Covariate data on patient demographics and clinical chemistry parameters was incorporated to assess relationships with PK parameters. Simulations were conducted to compare exposure and probability of target attainment (PTA) under BSA adjusted, flat and stratified dosing regimens.

Results

Plasma concentration over time data (2182 measurements) from therapeutic drug monitoring from 229 patients was available. PK of MTX were best described by a three-compartment model. Values for clearance (CL) of 4.33 [2.95–5.92] L h^− 1 and central volume of distribution of 4.29 [1.81–7.33] L were estimated. An inter-occasion variability of 23.1% (coefficient of variation) and an inter-individual variability of 29.7% were associated to CL, which was 16 [7–25] % lower in women. Serum creatinine, patient age, sex and BSA were significantly related to CL of MTX. Simulations suggested that differences in PTA between flat and BSA-based dosing were marginal, with stratified dosing performing best overall.

Conclusion

A dosing scheme with doses stratified across BSA quartiles is suggested to optimize target exposure attainment. Influence of patient sex on CL of MTX is present but small in magnitude.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08443-x.

Relationship Between the Free and Total Methotrexate Plasma Concentration in Children and Application to Predict the Toxicity of HD-MTX

High-dose methotrexate (HD-MTX) can be highly effective as well as extremely toxic. Many drug molecules can bind to plasma proteins to different extents in vivo, whereas only the free drug can reach the site of action to exert a pharmacological effect and cause toxicity. However, free MTX concentrations in plasma have not been reported. Traditional analyses of free drugs are both cumbersome and inaccurate. We collected 92 plasma samples from 52 children diagnosed with ALL or NHL or other lymphomas that were treated with HD-MTX. The hollow fiber centrifugal ultrafiltration (HFCF-UF) was used to prepare plasma samples for analysis of the free MTX concentration. Protein precipitation was employed to measure the total MTX concentration. The HFCF-UF is a simple method involving a step of ordinary centrifugation; the validation parameters for the methodological results were satisfactory and fell within the acceptance criteria. A linearity coefficient r² of 0.910 was obtained for the correlation between the free and total MTX plasma concentrations in 92 plasma samples. However, the free and total MTX concentrations was only weakly correlated in 16 clinical plasma specimens with total MTX concentrations >2 μmol L⁻¹ (r² = 0.760). Both the free and total MTX concentrations at 42 h were negatively correlated with the creatinine clearance (CCr) level (P = 0.023, r = −0.236 for total MTX and P = 0.020, r = −0.241for free MTX, respectively). The free MTX concentration could not be accurately estimated from the total MTX concentration for patients with high MTX levels which are conditions under which toxic reactions are more likely to occur. High plasma MTX levels could become a predictor of the occurrence of MTX nephrotoxicity to draw people's attention. The proposed HFCF-UF method is a simple and accurate way to evaluate efficacy and toxicity in clinical therapeutic drug monitoring.

Risk factors for delayed elimination of high-dose methotrexate in childhood acute lymphoblastic leukemia and lymphoma

High-dose methotrexate (HD-MTX) therapy is widely used in patients with acute lymphoblastic leukemia (ALL) and lymphoma. However, some patients experience delayed MTX elimination, which requires treatment suspension or dose reduction to avoid organ damage. This single-center retrospective analysis reviewed the clinical data of 88 children with ALL or non-Hodgkin lymphoma who received a total of 269 courses of HD-MTX therapy between April 2008 and April 2019. HD-MTX was defined as MTX administration at 2.0, 3.0, or 5.0 g/m² over a 24-h period, and delayed MTX elimination was defined as a serum MTX concentration ≥ 1.0 µmol/L at 48 h after the start of HD-MTX. Clinical factors were compared between courses with and without delayed MTX elimination. MTX elimination was delayed in 21 of the 269 courses (7.8%). Multivariate analysis showed that first HD-MTX course (OR 4.04), lower urine volume per BSA on the first day of HD-MTX administration (< 2,675 mL/m², OR 5.10), higher total bilirubin (> 0.5 mg/dL, OR 5.11), lower eGFR (< 136 mL/min/1.73 m², OR 3.90), higher dose of MTX(> 3.0 g/m², OR 10.8), and lower urine volume per BSA on the next day of starting HD-MTX (< 2,107 mL/m², OR 3.43) were independent risk factors for delayed MTX elimination.

Safe administration of high-dose methotrexate with minimal drug level monitoring: Experience from a center in north India

BACKGROUND

High-dose methotrexate (HDMTX) is recommended to be administered with serial monitoring of methotrexate (MTX) levels, which may not be universally feasible in resource-limited settings. In this study, we evaluated the overall experience of administration of HDMTX at our center by monitoring a single drug level at 54 h from the start of MTX infusion.

METHODS

This retrospective study was performed at a tertiary level hospital in north India, over a 5-year period (2011-2015). All patients <18 years of age with newly diagnosed acute lymphoblastic leukemia (ALL) and T-non-Hodgkin lymphoma (T-NHL) were enrolled in the study. Details of HDMTX and all significant toxicities requiring prolonged or repeat hospitalization were retrieved from the medical records. All eligible patients received HDMTX as per the recommendations followed by at least three doses of leucovorin rescue, before drug levels were sent at 54 h. Subsequent leucovorin doses were adjusted accordingly.

RESULTS

The records of 598 cycles of HDMTX in 184 patients were reviewed. A total of 531 of 598 cycles (88.7%) were managed with monitoring only a single plasma drug level at 54 h from the beginning of infusion. Delayed MTX clearance was seen in 260 of 598 cycles (43.5%). Only three episodes (0.5%) were associated with significant toxicity. There were no deaths.

CONCLUSIONS

The strategy of monitoring MTX concentration at 54 h was safe in our cohort. Although recommended, dynamic monitoring of plasma drug levels may not always predict toxicity.

MTXPK.org: A Clinical Decision Support Tool Evaluating High-Dose Methotrexate Pharmacokinetics to Inform Post-Infusion Care and Use of Glucarpidase

Methotrexate (MTX), an antifolate, is administered at high doses to treat malignancies in children and adults. However, there is considerable interpatient variability in clearance of high‐dose (HD) MTX. Patients with delayed clearance are at an increased risk for severe nephrotoxicity and life‐threatening systemic MTX exposure. Glucarpidase is a rescue agent for severe MTX toxicity that reduces plasma MTX levels via hydrolysis of MTX into inactive metabolites, but is only indicated when MTX concentrations are > 2 SDs above the mean excretion curve specific for the given dose together with a significant creatinine increase (> 50%). Appropriate administration of glucarpidase is challenging due to the ambiguity in the labeled indication. A recent consensus guideline was published with an algorithm to provide clarity in when to administer glucarpidase, yet clinical interpretation of laboratory results that do not directly correspond to the algorithm prove to be a limitation of its use. The goal of our study was to develop a clinical decision support tool to optimize the administration of glucarpidase for patients receiving HD MTX. Here, we describe the development of a novel 3‐compartment MTX population pharmacokinetic (PK) model using 31,672 MTX plasma concentrations from 772 pediatric patients receiving HD MTX for the treatment of acute lymphoblastic leukemia and its integration into the online clinical decision support tool, MTXPK.org. This web‐based tool has the functionality to utilize individualized demographics, serum creatinine, and real‐time drug concentrations to predict the elimination profile and facilitate model‐informed administration of glucarpidase.

Identifying risk factors for high-dose methotrexate-induced toxicities in children with acute lymphoblastic leukemia

Background

Whether monitoring of the methotrexate (MTX) concentrations after high-dose MTX (HD-MTX) infusion can predict toxicities is still controversial, especially when HD-MTX therapy is used in the treatment of children with acute lymphoblastic leukemia (ALL), which is different than the previous schedules. The relationship between patient characteristics and severe adverse events (AEs) has yet to be determined.

Objective

To analyze the relationship between the MTX concentration and toxicities and to identify the risk predictors from patient characteristics for severe AEs during HD-MTX therapy in children with ALL.

Methods

We conducted a retrospective study on children with ALL who were treated with 388 HD-MTX infusions. The chi-square test and univariate and logistic regression analyses were used to analyze the relationship between the MTX concentrations and toxicities and to identify predictors for severe AEs.

Results

Febrile neutropenia (P=0.000) and vomiting (P=0.034) were more likely to occur if the infusion had an MTX level ≥1 μmol/L at 44 h, but other toxicities had no correlations with MTX concentration. Predictive factors for toxicities were as follows: higher risk stratification and higher values of albumin (ALB) for leucopenia, higher values of white blood cell count (WBC) for anemia, higher values of ALB and creatinine (Cr) for neutropenia, higher risk stratification and higher 44-h MTX concentration for febrile neutropenia, higher values of alanine transferase (ALT) for elevated ALT, higher values of ALT for elevated aspartate transferase (AST), and higher values of total bilirubin (TBil) for vomiting.

Conclusion

Routine monitoring of 44-h MTX concentrations is essential to identify patients at high risk of developing febrile neutropenia and vomiting. This study may provide a reference for clinicians to distinguish patients with a relatively high risk of severe AEs based on certain characteristics before HD-MTX infusion.

The Population Pharmacokinetics of High-Dose Methotrexate in Infants with Acute Lymphoblastic Leukemia Highlight the Need for Bedside Individualized Dose Adjustment: A Report from the Children's Oncology Group

BACKGROUND

Infants with acute lymphoblastic leukemia (ALL) treated with high-dose methotrexate may have reduced methotrexate clearance (CL) due to renal immaturity, which may predispose them to toxicity.

OBJECTIVE

The aim of this study was to develop a population pharmacokinetic (PK) model of methotrexate in infants with ALL.

METHODS

A total of 672 methotrexate plasma concentrations were obtained from 71 infants enrolled in the Children's Oncology Group (COG) Clinical Trial P9407. Infants received methotrexate 4 g/m2 intravenously for four cycles during weeks 4-12 of intensification. A population PK analysis was performed using NONMEM® version 7.4. The final model was evaluated using a non-parametric bootstrap and a visual predictive check. Simulations were performed to evaluate methotrexate dose and the utility of a bedside algorithm for dose individualization.

RESULTS

Methotrexate was best characterized by a two-compartment model with allometric scaling. Weight was the only covariate included in the final model. The coefficient of variation for interoccasion variability (IOV) on CL was relatively high at 25.4%, compared with the interindividual variability for CL and central volume of distribution (10.7% and 13.2%, respectively). Simulations identified that 21.1% of simulated infants benefitted from bedside dose adjustment, and adjustment of methotrexate doses during infusions can avoid supratherapeutic concentrations.

CONCLUSION

Infants treated with high-dose methotrexate demonstrated a relatively high degree of IOV in methotrexate CL. The magnitude of IOV in the CL of methotrexate suggests that use of a bedside algorithm may avoid supratherapeutic methotrexate concentrations resulting from high IOV in methotrexate CL.

Plasma creatinine as predictor of delayed elimination of high-dose methotrexate in childhood acute lymphoblastic leukemia: A Danish population-based study

BACKGROUND

Severely delayed elimination of methotrexate (MTX) is difficult to predict in patients treated with high-dose MTX (HD-MTX), but it may cause life-threatening toxicity. It has not been defined how an increase in plasma creatinine can be best used as a predictor for severely delayed MTX elimination, thus providing a guide for therapeutic interventions to minimize renal toxicity.

METHODS

Pharmacokinetic data were retrospectively collected on 218 Danish children with acute lymphoblastic leukemia treated with HD-MTX 5 or 8 g/m² on the NOPHO2000 protocol. Moderately delayed MTX elimination was defined as 42-hour plasma MTX ≥ 4.0-9.9 μM, and severely delayed elimination was defined as 42-hour plasma MTX ≥ 10 μM.

RESULTS

Median 42-hour plasma MTX was 0.61 μM (interquartile range, 0.4-1.06 μM). Of 1295 MTX infusions with 5 g/m² (n = 140 patients) or 8 g/m² (n = 78 patients), 5.1% were severely (1.5%) or moderately (3.6%) delayed. The risk of having delayed elimination was highest in the first of eight infusions with MTX 5 g/m² (7.4% vs 0.0 to 4.1% for subsequent MTX infusions) (P < 0.02). A 25 μM increase or a 1.5-fold increase in plasma creatinine within 36 hours from start of the MTX infusion had a sensitivity of 92% (95% CI, 82%-97%) and a specificity of 85% (95% CI, 83%-87%) for predicting 42-hour MTX ≥4.0 μM.

CONCLUSIONS

A 25 μM increase or a 1.5-fold in plasma creatinine within 36 hours after start of an HD-MTX infusion can predict delayed MTX elimination, thus allowing intensification of hydration and alkalization to avoid further renal toxicity and promote the elimination of MTX.

Improving the safety of high-dose methotrexate for children with hematologic cancers in settings without access to MTX levels using extended hydration and additional leucovorin

BACKGROUND

A lack of access to methotrexate levels is common in low- and middle-income countries (LMIC), relevant for 80% of children with cancer worldwide. We evaluated whether high-dose methotrexate (HD-MTX) can be administered safely with extended hydration and leucovorin rescue, with monitoring of serum creatinine and urine pH.

METHODS

The prospective study was conducted at a single centre in Chandigarh, India in 2015. Patients with B-cell acute lymphoblastic leukemia (ALL) or with T-cell ALL or non-Hodgkin lymphoma (T-NHL) were administered 3 and 5 gm/m² of MTX (24 hr infusion), respectively. Six doses of leucovorin (15 mg/m² /dose), instead of recommended three (for optimally reduced levels) at standard timing (42 hr from start of HD-MTX) were administered. Hydration (125 ml/m² /hr) was continued for 72 hr, instead of the recommended 30 hr. Hydration fluid consisted of 0.45% sodium chloride, 5% dextrose, 7.5% sodium bicarbonate (50 mmol/l) and potassium chloride (20 mmol/l). Serum creatinine and urine pH were measured at baseline, 24 and 48 hr. The volume of hydration was increased (200 ml/m² /hr) for a serum creatinine > 1.25 times the baseline.

RESULTS

The study included 100 cycles of HD-MTX in 53 patients: B-ALL 25 patients (51 cycles), T-ALL 16 patients (28 cycles), T-NHL 10 patients (18 cycles), and relapsed ALL 2 patients (3 cycles). The mean age was 6.8 ± 3.2 years. Patients were underweight in 15 (15%) cycles. Patients in 23% of cycles had a rise in creatinine to >1.25 times the baseline. Toxicities (NCI CTCAE v4.0) included mucositis (32%), diarrhoea (10%), and febrile neutropenia (9%). One patient died from dengue shock syndrome.

CONCLUSIONS

It is safe to administer 3 or 5 gm/m² of MTX (24 hr infusion) without measuring MTX levels, with extended hydration, additional doses of leucovorin, and monitoring of serum creatinine and urine pH.

Consensus Guideline for Use of Glucarpidase in Patients with High-Dose Methotrexate Induced Acute Kidney Injury and Delayed Methotrexate Clearance

An expert panel was convened to provide specific, expert consensus guidelines for the use of glucarpidase in patients who develop high‐dose methotrexate (HDMTX)‐induced nephrotoxicity and delayed methotrexate excretion. This guideline provides recommendations to identify the population of patients who would benefit from glucarpidase rescue by more precisely defining the absolute methotrexate concentrations associated with risk for severe or life‐threatening toxicity at several time points after the start of a HDMTX infusion.

Acute kidney injury due to high‐dose methotrexate (HDMTX) is a serious, life‐threatening toxicity that can occur in pediatric and adult patients. Glucarpidase is a treatment approved by the Food and Drug Administration for high methotrexate concentrations in the context of kidney dysfunction, but the guidelines for when to use it are unclear. An expert panel was convened to provide specific, expert consensus guidelines for the use of glucarpidase in patients who develop HDMTX‐induced nephrotoxicity and delayed methotrexate excretion. The guideline provides recommendations to identify the population of patients who would benefit from glucarpidase rescue by more precisely defining the absolute methotrexate concentrations associated with risk for severe or life‐threatening toxicity at several time points after the start of an HDMTX infusion. For an HDMTX infusion ≤24 hours, if the 36‐hour concentration is above 30 µM, 42‐hour concentration is above 10 µM, or 48‐hour concentration is above 5 µM and the serum creatinine is significantly elevated relative to the baseline measurement (indicative of HDMTX‐induced acute kidney injury), glucarpidase may be indicated. After a 36‐ to 42‐hour HDMTX infusion, glucarpidase may be indicated when the 48‐hour methotrexate concentration is above 5 µM. Administration of glucarpidase should optimally occur within 48–60 hours from the start of the HDMTX infusion, because life‐threatening toxicities may not be preventable beyond this time point.

Implications for Practice.

Glucarpidase is a rarely used medication that is less effective when given after more than 60 hours of exposure to high‐dose methotrexate, so predicting early which patients will need it is imperative. There are no currently available consensus guidelines for the use of this medication. The indication on the label does not give specific methotrexate concentrations above which it should be used. An international group of experts was convened to develop a consensus guideline that was specific and evidence‐based to identify the population of patients who would benefit from glucarpidase.

Non-infectious chemotherapy-associated acute toxicities during childhood acute lymphoblastic leukemia therapy

During chemotherapy for childhood acute lymphoblastic leukemia, all organs can be affected by severe acute side effects, the most common being opportunistic infections, mucositis, central or peripheral neuropathy (or both), bone toxicities (including osteonecrosis), thromboembolism, sinusoidal obstruction syndrome, endocrinopathies (especially steroid-induced adrenal insufficiency and hyperglycemia), high-dose methotrexate-induced nephrotoxicity, asparaginase-associated hypersensitivity, pancreatitis, and hyperlipidemia. Few of the non-infectious acute toxicities are associated with clinically useful risk factors, and across study groups there has been wide diversity in toxicity definitions, capture strategies, and reporting, thus hampering meaningful comparisons of toxicity incidences for different leukemia protocols. Since treatment of acute lymphoblastic leukemia now yields 5-year overall survival rates above 90%, there is a need for strategies for assessing the burden of toxicities in the overall evaluation of anti-leukemic therapy programs.

Pharmacokinetics of high-dose methotrexate in infants aged less than 12 months treated for aggressive brain tumors

PURPOSE

In infants aged less than 12 months, there are few data on pharmacokinetics of high-dose methotrexate (MTX) for brain tumors at the dose of 8 g/m(2). Consolidated knowledges are present only with the dose of 5 g/m(2) in acute lymphoblastic leukemia.

METHODS

We collected data on 8 infants at the time of their first treatment with high-dose MTX, 8 g/m(2), to evaluate the pharmacokinetic profile. All children had a dose adjustment with a weight-based prescription (1 m(2) = 30 kg).

RESULTS

The median age was 4.5 months (range 0-9). The median weight was 5.63 kg (range 3.12-9.0). The median steady-state MTX concentration at the end of 6-hr infusion was 486 µM/L (range 227-790). The median systemic MTX clearance was 4.14 L/h/m(2) (range 1.98-9.35). The median MTX concentration after 24 h from the beginning of infusion was 3.29 µM/L (range 1.14-100.44). Three (37.5 %) patients had a delayed elimination of MTX (delayed early, delayed late, or total delayed: one for each). These altered elimination occurred principally in children weighing less than 4 kg (p: 0.0179). Moreover, a systemic MTX clearance at the end of infusion minor than 3 L/h/m(2) can predict a delayed elimination (p: 0.0179). Patients with altered elimination underwent rescue measures (leucovorin supplement and/or exchange transfusion).

CONCLUSIONS

Our data suggest that a higher dose of MTX for the treatment of aggressive brain tumors in early infants had an acceptable pharmacokinetic profile. Greater attention must be used in the treatment of children weighing less than 4 kg.

Performance characteristics between TDx®FLx and TBA™-25FR for the therapeutic drug monitoring of methotrexate

Background

High-dose methotrexate (HDMTX) is used in the treatment of certain malignancies, including leptomeningeal metastases, systemic non-Hodgkin lymphoma, acute lymphoblastic leukemia, and osteosarcoma. High circulating levels of methotrexate can cause severe myelosuppression. The present study aimed to examine the differences in plasma MTX concentrations measured by two immunoassay systems currently available in the Japanese market, a TD_X/FL_X analyzer and a TBA-25FR analyzer.

Methods

A total of 69 plasma samples from 16 patients were assayed by a fluorescence polarization immunoassay technique using a TDx/FLx analyzer (Abbott Diagnostics, Chicago, Illinois, U.S.A.) and a homogeneous enzyme immunoassay technique using a TBA-25FR analyzer (Toshiba Medical Systems, Tokyo, Japan).

Results

Assay results were very consistent between the two systems, with good correlation 24 h after the start of treatment (TBA-25FR = 1.06・TD_X/FL_X, −1.31, r = 0.99), 48 h after the start of treatment (TBA-25FR = 1.00・TD_X/FL_X, +0.027, r > 0.99), and 72 h after the start of treatment (TBA-25FR = 1.09・TD_X/FL_X, +0.011, r > 0.99).

Conclusions

The calibration curve spanned one order of magnitude with a linear working range from the lowest to the highest standard. The standard deviations show the excellent reproducibility of repeated measurements at each standard level for both immunoassay systems. However, when using the TBA-25FR, it is necessary to perform measurements in the low-concentration range with care.

N-acetylcysteine renoprotection in methotrexate induced nephrotoxicity and its effects on B-cell lymphoma

Background:

Nephrotoxicity is one of the known side effects of methotrexate (MTX) therapy despite the use of conventional protective measures. Our objectives were to evaluate the effects of N-acetylcysteine (NAC) on MTX-induced toxicity in renal tubular cells and to evaluate whether adjunctive use of NAC interferes with MTX antitumor activity in the B-cell lymphoma.

Methods:

Kidney Epithelial (Madin-Darby canine kidney [MDCK]) cells were exposed to MTX (10 μM or 100 μM) alone and with NAC (0.2 mM or 0.4 mM). Reactive oxygen species (ROS) generation at 1, 2, 4, and 24 h was measured by flow cytometer. Quantification of total glutathione (GSH) was performed by using GSH assay kit. To measure the impact of NAC on the antitumor activity of MTX, B lymphoma cells were exposed to MTX alone and with NAC. A percentage of apoptosis was measured using fluorescein isothiocyanate in both cell lines. Quantitative data was presented as a means ± standard deviation, and P values were analyzed using the Student's t-test.

Results:

Apoptosis in MDCK cells were observed after 24 h of incubation with both 10 μM and 100 μM MTX. Maximum ROS generation was observed at 4 h and corresponded to GSH production. Treatment with 0.2 and 0.4 mM of NAC led to decrease percentages of apoptotic MDCK cells. NAC did not change either proliferation or apoptosis of B-cell lymphoma.

Conclusion:

Using NAC for kidney protection may not interfere with the antitumor activity of MTX. Further in vivo studies are warranted to confirm noninterference between MTX and NAC and assess synergistic antitumor effects.

Methotrexate Associated Renal Impairment Is Related to Delayed Elimination of High-Dose Methotrexate

Although Methotrexate (MTX) is an effective drug for the treatment of acute lymphoblastic leukemia (ALL), the toxicity remains a significant problem. In this prospective study, fifty-four patients with ALL were enrolled. 3 g or 5 g MTX/m² was administered over 24 hours. Serum MTX concentrations were determined in 24, 48, and 96 hours after MTX infusion. Serum creatinine concentrations and creatinine clearance rate (CCR) were determined before and 24 and 48 hours after MTX infusion. A total of 173 courses of MTX infusion were administered. The serum creatinine concentrations did not change much after MTX infusion while the CCR was gradually decreased. MTX clearance status was independently related to CCR decrease, with the risk of 8.07 to develop renal impairment in patients with delayed MTX elimination. Serum creatinine concentration, serum creatinine ratio, CCR, and CCR ratio at 24 hours were all related to MTX elimination delay. Patients with serum creatinine level >35.0 μmol/L, creatinine ratio >1.129, or CCR <100.0 mL/min were more likely to undergo MTX elimination delay. In conclusion, MTX could induce transient renal impairment and compromised renal function will delay MTX clearance. The serum creatinine concentration and the ratio and CCR are useful tools for evaluating MTX elimination status.

Assessment of renal function during high-dose methotrexate treatment in children with acute lymphoblastic leukemia

BACKGROUND

High-dose methotrexate (HD-MTX) is potentially nephrotoxic. The feasibility of novel biomarkers to indicate renal injury due to HD-MTX infusion was studied in children with acute lymphoblastic leukemia (ALL).

PROCEDURE

Markers for glomerular and tubular injury were evaluated prospectively after HD-MTX infusion in 20 children with ALL. Plasma creatinine, cystatin C, and neutrophil gelatinase-associated lipocalin (NGAL) were measured 24-48 hr before MTX-infusion and 24, 36, 48, and 72 hr after starting the HD-MTX treatment, and thereafter daily until the MTX concentration was below 0.1 µmol/L. Urine NGAL, β2 -microglobulin, and creatinine concentrations as well as dipstick and urinalysis were performed at the same time points.

RESULTS

In children with ALL, HD-MTX treatment at 5 g/m(2) over 24 hr was well tolerated and none of the patients developed significant glomerular or tubular dysfunction. The mean plasma cystatin C level increased significantly (P < 0.001) from 0.83 mg/L at baseline to 0.94 mg/L at 36 hr after starting the HD-MTX treatment. The cystatin C concentration remained within reference range in all but two patients (10%). There was no significant change in plasma creatinine level during or after HD-MTX treatment, the values being normal in all patients. Plasma and urea NGAL did not increase during or after the HD-MTX treatment.

CONCLUSIONS

Our results suggest that plasma cystatin C concentration alone is a sensitive marker to monitor renal function during and after HD-MTX infusion in pediatric ALL patients. Plasma or urine NGAL do not provide any further advantage in the follow-up of these patients.

Extended duration of prehydration does not prevent nephrotoxicity or delayed drug elimination in high-dose methotrexate infusions: a prospectively randomized cross-over study

BACKGROUND

Alkalized hydration is used as supportive care to prevent renal toxicity during infusions with high-dose methotrexate (HDMTX). In children with acute lymphoblastic leukemia (ALL), the hydration is commonly initiated 4 hours before start of the methotrexate (MTX) infusion. To test if longer duration of prehydration would prevent MTX-induced renal toxicity, we preformed a randomized cross-over study comparing 12-4 hours of hydration before the infusion of HDMTX.

PROCEDURES

Children with ALL and non-Hodgkin lymphoma that were treated with infusions of HDMTX 5 or 8 g/m(2) were randomized to receive intravenous prehydration 12 or 4 hours before the first HDMTX infusion. Patients alternated between 12 and 4 hours of prehydration in the subsequent HDMTX infusions. Renal toxicity was defined as 50% increase in plasma creatinine after the HDMTX infusion. The plasma MTX concentration was measured during and after the HDMTX infusion to determine if the duration of prehydration would influence the systemic MTX clearance.

RESULTS

A total of 47 patients (224 HDMTX infusions) with a median age of 4.9 years were included in the study. The duration of prehydration had no effect on MTX induced renal toxicity that occurred in 18.5% of all HDMTX 5 g/m(2) infusions and in 40.0% of all HDMTX 8 g/m(2) infusions. Similar the duration of prehydration had no impact on the systemic clearance of MTX.

CONCLUSION

Extending prehydration beyond 4 hours does not reduce the risk of renal toxicity or delayed MTX clearance after infusions with HDMTX 5-8 g/m(2).

Serum creatinine and creatinine clearance for predicting plasma methotrexate concentrations after high-dose methotrexate chemotherapy for the treatment for childhood lymphoblastic malignancies

PURPOSE

Monitoring of plasma methotrexate (MTX) concentrations allows for therapeutic adjustments in treating childhood acute lymphoblastic leukemia (ALL) or non-Hodgkin lymphoma (NHL) with high-dose MTX (HDMTX). We tested the hypothesis that assessment of creatinine clearance (CrCl) and/or serum Cr may be a suitable means of monitoring plasma MTX concentrations.

METHODS

All children in the study had ALL or NHL, were in complete remission, and received HDMTX (3 or 5 g/m(2))+leucovorin. Plasma MTX concentrations were measured at 24, 48, and 96 h. CrCl was determined at 24 and 48 h. Correlations between 24- and 48-h plasma MTX concentrations and CrCl and serum Cr concentrations were determined. CrCl and serum Cr concentrations were compared over time between children who had delayed and non-delayed MTX elimination.

RESULTS

A total of 105 children were included. There were significant negative correlations between CrCl at 24 and 48 h and plasma MTX concentrations at 24 (both p < 0.001) and 48 h (both p < 0.001). There were significant positive correlations between serum Cr concentrations at both 24 and 48 h and plasma MTX concentrations at 24 (both p < 0.001) and 48 h (both p < 0.001). There were 88 (30.2 %) instances of elimination delay. Children with elimination delay had significantly lower CrCl and higher Cr concentrations at 24 and 48 h compared with children without elimination delay (all p < 0.05).

CONCLUSION

Our findings suggest that, with further refinement, assessment of renal function may be a useful means of monitoring plasma MTX concentrations during HDMTX for ALL and NHL.

Comparison of pharmacokinetics and toxicity after high-dose methotrexate treatments in children with acute lymphoblastic leukemia

We carried out a detailed comparative study of the pharmacokinetics and toxicity of methotrexate (MTX) and 7-hydroxy-methotrexate (7-OH-MTX) after high-dose intravenous methotrexate (HD-MTX) in children with acute lymphoblastic leukemia (ALL). Overall, 65 children were treated with 5 g/m2/24 h MTX and 88 children were treated with 2 g/m2/24 h MTX according to ALL-BFM 95 and ALL IC-BFM 2002 protocols (mean age: 6.4 years, range 1.0-17.9 years). A total of 583 HD-MTX courses were analyzed. Serum MTX and 7-OH-MTX levels were measured at 24, 36, and 48 h, and cerebrospinal fluid (CSF) MTX levels were determined 24 h after the initiation of the infusion. The area under the concentration-time curve was calculated. Hepatotoxicity, nephrotoxicity, and bone marrow toxicity were estimated by routine laboratory tests. We investigated pharmacokinetics and toxicity in distinct age groups (< 6 and > 14 years). 5 g/m2/24 h treatments resulted in higher serum and CSF MTX and 7-OH-MTX levels (P < 0.05). The CSF penetration rate of MTX was independent of the MTX dose [2.3% (95% confidence interval: 1.7-2.5%) vs. 2.8% (95% confidence interval: 2.4-3%)]. The CSF MTX concentration was correlated with the 24 h MTX serum level (r = 0.38, P < 0.0001). Repeated treatments did not alter MTX or 7-OH-MTX levels. 7-OH-MTX levels were correlated with nephrotoxicity (r = 0.36, P < 0.0001). Higher MTX levels and toxicity occurred more frequently in children aged older than 14 years (P < 0.05). Therapeutic serum and CSF MTX concentrations can be achieved more reliably with 5 g/m2/24 h treatments. To predict the development of toxicity, monitoring of the level of the 7-OH-MTX is useful. Monitoring of pharmacokinetics is essential to prevent the development of severe adverse events in adolescents.

[Pharmacokinetic analysis of high-dose methotrexate treatments in children with hematologic malignancies]

Monitoring the pharmacokinetic parameters of different anticancer drugs is necessary because they might have several side effects.

AIM

Pharmacokinetic and toxicity evaluation of high-dose methotrexate treatments in children with acute lymphoblastic leukemia.

PATIENTS AND METHODS

43 children (28 boys, 15 girls, mean age: 7.03 years) in 147 cases were treated with 5 g/m2/24h MTX according to ALL-BFM 1995 and 2002 protocols. Methotrexate and 7-hydroxi-methotrexate levels were measured with high pressure liquid chromatography at 24, 36, 48 hours. Authors registered the development of hepatotoxicity, nephrotoxicity, grade III/IV oral mucositis.

RESULTS

Therapeutic methotrexate serum concentrations (30-100µmol/l) were achieved in 72.5% of the cases. Repeated treatments resulted similar serum levels. Hepatotoxicity and hypoproteinemia occurred in 17% and in 48.9% of the cases. There was significant correlation between serum 7-hydroxi-methotrexate and creatinine levels (p<0.05).

CONCLUSION

5 g/m2 methotrexate resulted reliable therapeutic serum levels with mild and reversible toxicity. 7-hydroxi-methotexate measurements might be more useful than methotrexate levels to detect toxicity.

High dose methotrexate treatment in children with acute lymphoblastic leukaemia may be optimised by a weight-based dose calculation

BACKGROUND

The inter-individual variation in exposure to methotrexate is considerable after intravenous high dose methotrexate (HDMTX) administration and both under- and over exposures may have dire consequences. Thus, optimal dose individualisation is of paramount importance.

PROCEDURE

We studied how pharmacokinetic parameters were related to outcome in 340 patients with acute lymphoblastic leukaemia (ALL). A population pharmacokinetic model was developed with data from 1284 HDMTX courses in 304 children evaluating age, height, weight, body surface area (BSA), sex, serum creatinine and serum alanine aminotransferase as potential covariates.

RESULT

Body weight improved the population pharmacokinetic model significantly more than any of the other patient characteristics, indicating that body weight may be the better way of dose normalisation. In a logistic regression analysis, higher values of clearance as well as volume of distribution were related to increased relapse risk in the standard (SR) and intermediate risk (IR) groups as well as in the entire cohort. A higher weight was strongly associated with worse outcome in the SR and IR groups, (P = 0.0186 and 0.0121, respectively).

CONCLUSIONS

We conclude that dose normalisation of methotrexate according to body weigh may give more predictable pharmacokinetics of methotrexate and may also improve the outcome for children with ALL.

Challenges in implementing individualized medicine illustrated by antimetabolite therapy of childhood acute lymphoblastic leukemia

Predicting the response to medical therapy and subsequently individualizing the treatment to increase efficacy or reduce toxicity has been a longstanding clinical goal. Not least within oncology, where many patients fail to be cured, and others are treated to or beyond the limit of acceptable toxicity, an individualized therapeutic approach is indicated. The mapping of the human genome and technological developments in DNA sequencing, gene expression profiling, and proteomics have raised the expectations for implementing genotype-phenotype data into the clinical decision process, but also multiplied the complex interaction of genetic and other laboratory parameters that can be used for therapy adjustments. Thus, with the advances in the laboratory techniques, post laboratory issues have become major obstacles for treatment individualization. Many of these challenges have been illustrated by studies involving childhood acute lymphoblastic leukemia (ALL), where each patient may receive up to 13 different anticancer agents over a period of 2-3 years. The challenges include i) addressing important, but low-frequency outcomes, ii) difficulties in interpreting the impact of single drug or single gene response data that often vary across treatment protocols, iii) combining disease and host genomics with outcome variations, and iv) physicians' reluctance in implementing potentially useful genotype and phenotype data into clinical practice, since unjustified downward or upward dose adjustments could increase the of risk of relapse or life-threatening complications. In this review we use childhood ALL therapy as a model and discuss these issues, and how they may be addressed.

Clinical pharmacology in the adolescent oncology patient

Numerous studies have documented that adolescents and young adults (AYAs) experience a significant cancer burden as well as significant cancer mortality compared with other age groups. The reasons for the disparate outcomes of AYAs and other age groups are not completely understood and are likely to be multifactorial, including a range of sociodemographic issues unique to these individuals as well as differences between adolescents, younger pediatric patients, and adults in the pharmacology of anticancer agents. Because adolescence is a period of transition from childhood to early adulthood, numerous physical, physiologic, cognitive, and behavioral changes occur during this time. In this review, we provide an overview of the unique developmental physiology of the adolescent and explain how these factors and the behavioral characteristics of adolescents may affect the pharmacology of anticancer agents in this patient population. Finally, we describe examples of studies that have assessed the relation between drug disposition and age, focusing on the AYA age group.

High dose methotrexate population pharmacokinetics and Bayesian estimation in patients with lymphoid malignancy

The purpose of present study was to develop a population pharmacokinetic model of high dose methotrexate (HD-MTX) infusion in patients with lymphoid malignancy, to investigate the biological and clinical covariates related to the drug distribution and elimination. It is also the purpose to propose a limited sampling strategy (LSS) for the estimation of the time above the threshold (0.2 micromol.L(-1)). A total 82 patients with lymphoid malignancy were involved in the study. A pharmacokinetic model was developed using nonlinear mixed-effect model. The influence of demographic characteristics, biological factors, and concurrent administration were investigated. The final predictive performance was validated by bootstrap and cross-validation. Bayesian estimation was evaluated. The pharmacokinetics of HD-MTX was described by a two-compartment model. The pharmacokinetic parameters and the inter-individual variability were as follows: the clearance CL, 7.45 L.h(-1) (inter-individual variability 50.6%), the volume of the central and peripheral compartment V(1), 25.9 L (22.5%), V(2), 9.23 L (97.8%), respectively, and the intercompartmental clearance Q, 0.333 L.h(-1) (70.4%). The influence of serum creatinine on CL and weight on V(1) was retained in the final model. The protocol involved one sampling time at 44 h after the start of the infusion, allowing one to predict the time at which the MTX concentration reached the expected threshold (0.2 micromol.L(-1)). Serum creatinine and weight showed significant influence on methotrexate CL and V(1), respectively. Furthermore, a Bayesian estimation based on the covariates and 44 h sample was developed, allowing prediction of the individual methotrexate pharmacokinetic parameters and the time to 0.2 micromol.L(-1).

Advances in individual prediction of methotrexate toxicity: a review

As the cure rates for haematological malignancies have improved, the exploration of the balance between efficacy and side effects has become a major research target. The antifolate methotrexate is widely used in the treatment of acute lymphoblastic leukaemia, non-Hodgkin lymphoma, and osteosarcoma. Even when given identical methotrexate doses, patients vary significantly in their response and pattern of toxicities. This diversity can, to some extent, be linked to sequence variations in genes involved in drug absorption, metabolism, excretion, cellular transport, and effector targets or target pathways. In the coming years pharmacogenomics is expected to change our approaches to individualised therapy with methotrexate. However, genetic polymorphisms affect the pharmacokinetics and dynamics of all the drugs a patient receive as well as the normal tissues tolerance to a given drug exposure. Thus, although high-throughput techniques will allow mapping of tens of thousands of genetic polymorphisms in one run, it will be a major challenge to dissect out which of these have the strongest impact on efficacy and toxicity and hence should be the targets for intervention. This paper discusses the pharmacology of methotrexate and reviews studies on haematological malignancies that have attempted to predict the risk of toxicity by specific clinical or genetic features.

Pharmacokinetics of high-dose methotrexate in infants treated for acute lymphoblastic leukemia

BACKGROUND

Interfant-99 was an international collaborative treatment protocol for infants with acute lymphoblastic leukemia (ALL).

PROCEDURE

We collected data on 103 infants at the time of their first treatment with high-dose methotrexate (HD MTX), 5 g/m(2). Children <6 months of age received two-third of the calculated dose based on body surface area (BSA), children 6-12 months three-fourth of the calculated dose, and children >12 months full dose.

RESULTS

The median steady-state MTX concentration at the end of the 24-hr infusion was 57.8 microM (range 9.5-313). The median systemic clearance was 6.22 L/hr/m(2) BSA, and tended to increase with age (P = 0.099). Boys had higher clearance than girls, 6.77 and 5.28 L/hr/m(2) (P = 0.030), and tended to have lower median MTX concentration at 24 hr. Eight infants had MTX levels below 20 microM, a level judged to be sufficient in B-lineage ALL in children >1 year of age. All infants tolerated the dose well enough to receive a second dose of HD MTX without dose reduction. We found no significant effect on disease-free survival for MTX steady-state concentration, MTX clearance, or time to MTX below 0.2 microM.

CONCLUSIONS

Our data provide no support for a change in the dosing rules for MTX used in Interfant-99. However, in view of the poor treatment results for infants, one might consider increase in the dose for patients who reach plasma levels below median after the first MTX dose.

Methotrexate concentrations in cerebrospinal fluid and serum, and the risk of central nervous system relapse in children with acute lymphoblastic leukaemia

The aim of the study was to characterize the relationship between the pharmacokinetics of methotrexate in serum and concentrations in the cerebrospinal fluid, and to analyse the association to risk of a central nervous system relapse in children with acute lymphoblastic leukaemia. In this retrospective study, 353 children with acute lymphoblastic leukaemia treated with high-dose methotrexate according to the Nordic Society of Pediatric Haematology and Oncology-92 acute lymphoblastic leukaemia protocol were studied. Data from 18 patients with a subsequent central nervous system relapse and 335 event-free patients were available. In 34 patients the methotrexate concentrations were monitored repeatedly during each 24-h methotrexate intravenous infusion and a cerebrospinal fluid sample was taken at the end of the infusion. Using statistics separating interindividual and intraindividual variability, methotrexate concentration in cerebrospinal fluid was found to be significantly dependent upon both serum concentrations at the end of infusion and the area under the concentration curve in serum (P<0.0017 and <0.002, respectively). The logistic regression analysis revealed that high patient median serum methotrexate concentrations at the end of infusion were significantly associated with decreased risk for a central nervous system relapse in the standard risk group (P=0.02) and the number of courses with a calculated cerebrospinal fluid concentration of more than 1 mumol/l (P=0.048) with a decreased risk of a central nervous system relapse in the combined (standard risk and intermediate) risk group. In conclusion, methotrexate concentrations in cerebrospinal fluid are dependent on methotrexate concentrations in serum and serum area under the concentration curve. Multivariate analysis indicates that an increased exposure to methotrexate is related to decreased risk for central nervous system relapse.

A limited sampling strategy to estimate individual pharmacokinetic parameters of methotrexate in children with acute lymphoblastic leukemia

PURPOSE

The objectives of this study were to characterize the population pharmacokinetics of MTX in patients with acute lymphoblastic leukemia (ALL) with ages ranging from 2 to 16 years and to propose a limited sampling strategy to estimate individual pharmacokinetic parameters.

METHODS

Seventy-nine children were enrolled in this study; they received 1-4 courses of chemotherapy. MTX was administered at a dose of 5 g/m2. MTX population parameters were estimated from 61 patients (231 courses; age range: 2-16 years). The data were analyzed by nonlinear mixed-effect modeling with use of a two-compartment structural model. The interoccasion variability was taken into account in the model. Eighteen additional patients (70 courses) were used to evaluate the predictive performances of the Bayesian approach and to devise a limited sampling strategy.

RESULTS

The following population parameters were obtained: total clearance (CL) = 8.8 l/h (inter-individual variability: 43%), initial volume of distribution (V1) = 17.3 l (48%), k12 = 0.0225 h(-1) (41%), and k21 = 0.0629 h(-1) (24%). The inter-individual variability in the initial volume of distribution was partially explained by the fact that this parameter was weight-dependent. Intercourse variability was limited, with a mean variation of 13.2%. The protocol involving two sampling times, 24 and 48 h after the beginning of infusion, allows precise and accurate determination of individual pharmacokinetic parameters and consequently, it was possible to predict the time at which the MTX concentration reached the predicted threshold (0.2 microM) below which the administration of folinic acid could be stopped.

CONCLUSION

The results of this study combine the relationships between the pharmacokinetic parameters of MTX and patient covariates that may be useful for dose adjustment, with a convenient sampling procedure that may aid in optimizing pediatric patient care.

Methotrexate induces cell swelling and necrosis in renal tubular cells

BACKGROUND

The present study was carried out to investigate if methotrexate (MTX) has a direct lethal effect in renal tubular cells, and if so, to further clarify the mechanisms of cell death.

MATERIALS AND METHODS

Renal tubular cells (LLC-PK(1) cells) were incubated with MTX (0.01 microM, 0.1 microM, and 1 microM), either alone or in combination with 0.1 microM amiloride (Na(+)/H(+) antiporter inhibitor) or 1 microM carbachol (M-cholinergic agonist). Cell viability was then determined by means of trypan blue (TB) exclusion tests and MTT assays.

RESULTS

After 4 hr incubation with 0.1 microM MTX the number of viable cells was decreased by 18% in comparison with control cells, and the proportion of dead cells was increased by 38%. Cell death induced by MTX was time-dependent and did not show apoptotic features. On the contrary, cell swelling was discovered. This cell death was prevented by co-incubating the cells with amiloride or carbachol.

CONCLUSIONS

MTX induces cell swelling and cell death in renal tubular LLC-PK(1) cells. The tubular cell death induced by MTX is time-dependent. Cell death can be prevented by co-incubating with amiloride, thus indicating that the Na(+)/H(+) antiporter and possibly other volume regulatory factors in renal tubular cells are involved in MTX-induced renal failure.

Population pharmacokinetic study of methotrexate in patients with lymphoid malignancy

PURPOSE

A population pharmacokinetic model was developed to describe dose-exposure relationships of methotrexate (MTX) in adults with lymphoid malignancy; this is in order to explore the interindividual variability in relationship with the different physiopathological variables. The final model was applied to the Bayesian estimation of MTX concentrations using two blood samples.

METHODS

Fifty-one patients receiving 136 courses of MTX (1-6 per patient) were included in this study. The data was analysed using NONMEM software. A linear two-compartment model with linear elimination best described the data. Setting mean parameters values and variabilities to population values, we obtained Bayesian prediction of MTX pharmacokinetic parameters and concentrations. The predictive performance was evaluated by comparing the Bayesian estimated and observed concentrations and the Bayesian estimated parameters with the individual final model estimated parameters.

RESULTS

The population pharmacokinetic parameters and the inter-subject variablities expressed as coefficient of variation were: the total body clearance CL, 7.1 l h-1 (22%), the volume of the central and peripheral compartments V1, 25.1 l (22.5%), V2, 2.7 l (64%), respectively, and the transfer constant Q, 2.7 (51%) l h-1. Inter-course variability was only significant on CL. Age and serum creatinine had significant effects on CL and was included in the final model. A good correlation was obtained between Bayesian estimated and experimental concentrations (r2=0.85).

Population Pharmacokinetics of High-Dose Methotrexate in Children with Acute Lymphoblastic Leukaemia

OBJECTIVE

To develop and a priori validate a methotrexate population pharmacokinetic model in children with acute lymphoblastic leukaemia (ALL), receiving high-dose methotrexate followed by folinic acid rescue, identifying the covariates that could explain part of the pharmacokinetic variability of methotrexate.

METHODS

The study was carried out in 49 children (aged 6 months to 17 years) who received high-dose methotrexate (3 g/m(2) per course) in long-term treatment. In an index group (37 individuals; 1236 methotrexate plasma concentrations), a population pharmacokinetic model was developed using a nonlinear mixed-effects model. The remaining patients' data (12 individuals; 278 methotrexate plasma concentrations) were used for model validation. Age, sex, total bodyweight (TBW), height, body surface area, lowest urine pH during infusion, serum creatinine, ALT, AST, folinic acid dose and length of rescue were analysed as possible covariates. The final predictive performance of the pharmacokinetic model was tested using standardised mean prediction errors.

RESULTS

The final population pharmacokinetic model (two-compartmental) included only age and total bodyweight as influencing clearance (CL) and volume of distribution of central compartment (V(1)). For children aged < or =10 years: CL (L/h) = 0.287 . TBW(0.876); V(1) (L) = 0.465 . TBW, and for children aged >10 years: CL (L/h) = 0.149 . TBW; V(1) (L) = 0.437 . TBW. From the base to the final model, the inter-individual variabilities for CL and V(1) were significantly reduced in both age groups (30-50%). The coefficients of variation of the pharmacokinetic parameters were <30%, while residual and inter-occasional coefficients maintained values close to 40%. Validation of the proposed model revealed the suitability of the model.

CONCLUSION

A methotrexate population pharmacokinetic model has been developed for ALL children. The proposed model could be used in Bayesian algorithms with a limited sampling strategy to estimate the systemic exposure of individual patients to methotrexate and adapt both folinic acid rescue and methotrexate dosing accordingly.