Individualized methotrexate dosing in children with relapsed acute lymphoblastic leukemia

Model-informed precision dosing: State of the art and future perspectives

Model-informed precision dosing (MIPD) stands as a significant development in personalized medicine to tailor drug dosing to individual patient characteristics. MIPD moves beyond traditional therapeutic drug monitoring (TDM) by integrating mathematical predictions of dosing, and considering patient-specific factors (patient characteristics, drug measurements) as well as different sources of variability. For this purpose, rigorous model qualification is required for the application of MIPD in patients. This review delves into new methods in model selection and validation, also highlighting the role of machine learning in improving MIPD, the utilization of biosensors for real-time monitoring, as well as the potential of models integrating biomarkers for efficacy or toxicity for precision dosing. The clinical evidence of TDM and MIPD is discussed for various medical fields including infection medicine, oncology, transplant medicine, and inflammatory bowel diseases, thereby underscoring the role of pharmacokinetics/pharmacodynamics and specific biomarkers. Further research, particularly randomized clinical trials, is warranted to corroborate the value of MIPD in enhancing patient outcomes and advancing personalized medicine.

Methotrexate level discrepancy post-glucarpidase: A pediatric case series and review of literature

Methotrexate is a common component of pediatric oncology treatment and delayed clearance increases risk of significant toxicities. Glucarpidase is indicated for patients with toxic plasma methotrexate concentrations with renal toxicity. Laboratory interference with immunoassay measurement post-glucarpidase administration is well established, with current product labeling indicating this persists for 48 h. However, recent experience in pediatric patients supports this discrepancy persists beyond 48 h. Three cases experienced delayed methotrexate clearance and received glucarpidase with subsequent measurement of methotrexate levels by liquid chromatography tandem mass spectrometry (LC-MS/MS) and/or immunoassay. Within this case series, discrepancies between LC-MS/MS and immunoassay levels persisted significantly longer than 48 h.

External evaluation and systematic review of population pharmacokinetic models for high-dose methotrexate in cancer patients

Several population pharmacokinetic (PPK) models have been established to optimize the therapeutic regimen and reduce the toxicity of high-dose methotrexate (HDMTX) in patients with cancer. However, their predictive performance when extrapolated to different clinical centers was unknown. In this study, we aimed to externally evaluate the predictive ability of HDMTX PPK models and determine the potential influencing factors. We searched the literature and determined the predictive performance of the selected models using methotrexate concentrations in 721 samples from 60 patients in the First Affiliated Hospital of the Navy Medical University. Prediction-based diagnostics and simulation-based normalized prediction distribution errors (NPDE) were used to evaluate the predictive performance of the models. The influence of prior information was also assessed using Bayesian forecasting, and the potential factors affecting model predictability were investigated. Thirty models extracted from published PPK studies were assessed. Prediction-based diagnostics showed that the number of compartments potentially influenced model transferability, and simulation-based NPDE indicated model misspecification. Bayesian forecasting significantly improved the predictive performance of the models. Various factors, including bioassays, covariates, and population diagnosis, influence model extrapolation. The published models were unsatisfactory for all prediction-based diagnostics, except for the 24 h methotrexate concentration monitoring and simulation-based diagnostics, making them inappropriate for direct extrapolation. Moreover, Bayesian forecasting combined therapeutic drug monitoring could improve the predictive performance of the models.

Interplay of Breast Cancer Resistance Protein (Bcrp/Abcg2), Sex, and Fed State in Oral Pharmacokinetic Variability of Furosemide in Rats

Poor and variable oral bioavailability of furosemide (FUR) presents critical challenges in pharmacotherapy. We investigated the interplay of breast cancer resistance protein (Bcrp)-mediated transport, sex, and fed state on FUR pharmacokinetics (PK) in rats. A crossover PK study of FUR (5 mg/kg, oral) was performed in Sprague-Dawley rats (3 males and 3 females), alone or with a Bcrp inhibitor, novobiocin (NOV) (20 mg/kg, oral), in both fed and fasted states. Co-administration of NOV significantly increased FUR extent (AUC) and rate (C_max) of exposure by more than two-fold, which indicates efficient Bcrp inhibition in the intestine. The female rats showed two-fold higher AUC and C_max, and two-fold lower renal clearance of FUR compared to the male rats. The latter was correlated with higher renal abundance of Bcrp and organic anion transporters (Oats) in the male rats compared to age-matched female rats. These findings suggest that the PK of Bcrp and/or Oat substrates could be sex-dependent in rats. Moreover, allometric scaling of rat PK and toxicological data of Bcrp substrates should consider species and sex differences in Bcrp and Oat abundance in the kidney. Considering that Bcrp is abundant in the intestine of rats and humans, a prospective clinical study is warranted to evaluate the effect of Bcrp inhibition on FUR PK. The potential confounding effect of the Bcrp transporter should be considered when FUR is used as a clinical probe of renal organic anion transporter-mediated drug-drug interactions. Unlike human data, no food-effect was observed on FUR PK in rats.

Leucovorin (folinic acid) rescue for high-dose methotrexate: A review

High-dose methotrexate (HDMTX) is active against various malignancies; it possesses serious toxicities and is associated with patient characteristics, dosage regimens, comedications, and physiological status. There are many strategies to overcome HDMTX-induced toxicities, such as hydration, alkalization, leucovorin rescue, and haemodialysis. Leucovorin rescue is a cornerstone for toxicity prevention in HDMTX treatment. However, the leucovorin dose adjustment and the existence of leucovorin overrescue are still controversial. At present, various methods for calculating leucovorin doses in different tumour types have been proposed, including empirical calculations based on MTX plasma concentration, the Bleyer nomogram, and other methods. Nonetheless, leucovorin rescue protocols differ greatly across tumour types and medical institutions. Further studies are needed to investigate the optimal dosage regimen for leucovorin rescue in various tumours using HDMTX.

Evaluation and Application of Population Pharmacokinetic Models for Identifying Delayed Methotrexate Elimination in Patients With Primary Central Nervous System Lymphoma

Objective: Several population pharmacokinetic (popPK) models have been developed to determine the sources of methotrexate (MTX) PK variability. It remains unknown if these published models are precise enough for use or if a new model needs to be built. The aims of this study were to 1) assess the predictability of published models and 2) analyze the potential risk factors for delayed MTX elimination.

Methods: A total of 1458 MTX plasma concentrations, including 377 courses (1–17 per patient), were collected from 77 patients who were receiving high-dose MTX for the treatment of primary central nervous system lymphoma in Huashan Hospital. PopPK analysis was performed using the NONMEM® software package. Previously published popPK models were selected and rebuilt. A new popPK model was then constructed to screen potential covariates using a stepwise approach. The covariates were included based on the combination of theoretical mechanisms and data properties. Goodness-of-fit plots, bootstrap, and prediction- and simulation-based diagnostics were used to determine the stability and predictive performance of both the published and newly built models. Monte Carlo simulations were conducted to qualify the influence of risk factors on the incidence of delayed elimination.

Results: Among the eight evaluated published models, none presented acceptable values of bias or inaccuracy. A two-compartment model was employed in the newly built model to describe the PK of MTX. The estimated mean clearance (CL/F) was 4.91 L h⁻¹ (relative standard error: 3.7%). Creatinine clearance, albumin, and age were identified as covariates of MTX CL/F. The median and median absolute prediction errors of the final model were -10.2 and 36.4%, respectively. Results of goodness-of-fit plots, bootstrap, and prediction-corrected visual predictive checks indicated the high predictability of the final model.

Conclusions: Current published models are not sufficiently reliable for cross-center use. The elderly patients and those with renal dysfunction, hypoalbuminemia are at higher risk of delayed elimination.

Clinical pharmacology of cytotoxic drugs in neonates and infants: Providing evidence-based dosing guidance

Cancer in neonates and infants is a rare but challenging entity. Treatment is complicated by marked physiological changes during the first year of life, excess rates of toxicity, mortality, and late effects. Dose optimisation of chemotherapeutics may be an important step to improving outcomes. Body size-based dosing is used for most anticancer drugs used in infants. However, dose regimens are generally not evidence based, and dosing strategies are frequently inconsistent between tumour types and treatment protocols. In this review, we collate available pharmacological evidence supporting dosing regimens in infants for a wide range of cytotoxic drugs. A systematic review was conducted, and available data ranked by a level of evidence (1-5) and a grade of recommendation (A-D) provided on a consensus basis, with recommended dosing approaches indicated as appropriate. For 9 of 29 drugs (busulfan, carboplatin, cyclophosphamide, daunorubicin, etoposide, fludarabine, isotretinoin, melphalan and vincristine), grade A was scored, indicating sufficient pharmacological evidence to recommend a dosing algorithm for infants. For busulfan and carboplatin, sufficient data were available to recommend therapeutic drug monitoring in infants. For eight drugs (actinomycin D, blinatumomab, dinutuximab, doxorubicin, mercaptopurine, pegaspargase, thioguanine and topotecan), some pharmacological evidence was available to guide dosing (graded as B). For the remaining drugs, including commonly used agents such as cisplatin, cytarabine, ifosfamide, and methotrexate, pharmacological evidence for dosing in infants was limited or non-existent: grades C and D were scored for 10 and 2 drugs, respectively. The review provides clinically relevant evidence-based dosing guidance for cytotoxic drugs in neonates and infants.

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.

Population Pharmacokinetics of High-Dose Methotrexate in Chinese Pediatric Patients With Acute Lymphoblastic Leukemia

High-dose methotrexate (HD-MTX) is widely used in pediatric acute lymphoblastic leukemia (ALL) treatment regimens. In this study, we aimed to develop a population pharmacokinetic (PK) model of HD-MTX in Chinese pediatric patients with ALL for designing personalized dosage regimens. In total, 4,517 MTX serum concentration data for 311 pediatric patients with ALL, aged 0.75–15.2 years and under HD-MTX treatment, were retrospectively collected at a tertiary Children’s Hospital in China. The non-linear mixed-effect model was used to establish the population PK model, using NONMEM software. The potential covariate effects of age, body weight, and biochemical measurements (renal and liver function) on MTX PK disposition were investigated. The model was then evaluated using goodness-of-fit, visual predictive check. MTX PK disposition was described using a three-compartment model reasonable well. Body weight, implemented as a fixed allometric function on all clearance and volume of distribution parameters, showed a substantial improvement in model fit. The final population model demonstrated that the MTX clearance estimate in a typical child with body weight of 19 kg was 6.9 L/h and the central distribution of volume estimate was 20.7 L. The serum creatinine significantly affected the MTX clearance, with a 0.97% decrease in clearance per 1 μmol/L of serum creatinine. Other covariates (e.g., age, sex, bilirubin, albumin, aspartate transaminase, concomitant medication) did not significantly affect PK properties of MTX. The proposed population PK model could describe the MTX concentration data in Chinese pediatric patients with ALL. This population PK model combined with a maximum a posteriori Bayesian approach could be used to estimate individual PK parameters, and optimize personalized MTX therapy in target patients, thus aiming to reduce toxicity and improve treatment outcomes.

Direct control of CAR T cells through small molecule-regulated antibodies

Antibody-based therapeutics have experienced a rapid growth in recent years and are now utilized in various modalities spanning from conventional antibodies, antibody-drug conjugates, bispecific antibodies to chimeric antigen receptor (CAR) T cells. Many next generation antibody therapeutics achieve enhanced potency but often increase the risk of adverse events. Antibody scaffolds capable of exhibiting inducible affinities could reduce the risk of adverse events by enabling a transient suspension of antibody activity. To demonstrate this, we develop conditionally activated, single-module CARs, in which tumor antigen recognition is directly modulated by an FDA-approved small molecule drug. The resulting CAR T cells demonstrate specific cytotoxicity of tumor cells comparable to that of traditional CARs, but the cytotoxicity is reversibly attenuated by the addition of the small molecule. The exogenous control of conditional CAR T cell activity allows continual modulation of therapeutic activity to improve the safety profile of CAR T cells across all disease indications.

Effect of Body Fat on Population Pharmacokinetics of High-Dose Methotrexate in Pediatric Patients With Acute Lymphoblastic Leukemia

Nearly all international regimens for pediatric acute lymphoblastic leukemia (ALL) incorporate intravenous "high-dose" methotrexate (HDMTX, ≥1 g/m² ) to penetrate the central nervous system. Dosing is routinely adjusted for body surface area (BSA), but limited data describe the pharmacokinetics of HDMTX, particularly in obese and/or large patients. To understand the impact of body size (BSA) and body fat percentage (BFP) on HDMTX pharmacokinetics, we performed a secondary analysis of 36 children and adolescents 10-21 years old treated for newly diagnosed ALL and who were enrolled in a prospective study examining body composition. All patients received 5 g/m² of HDMTX infused over 24 hours. Plasma methotrexate concentrations were measured at 24, 42, and 48 hours. At 48 hours, ≥0.4 μmol/L was defined as "delayed elimination," necessitating prolonged supportive care. BFP was measured using dual-energy x-ray absorptiometry. A nonparametric population pharmacokinetic model was constructed with subsequent simulations to explore effects of BSA and BFP extremes. Despite standard BSA-adjusted dosing, we found significant intrapatient variability in mean MTX concentration (38%; range, 1.2%-86%). BSA and BFP were not linearly associated with increased area under the curve (AUC, P = 0.74 and P = 0.12), but both larger size (BSA) and greater obesity (BFP) were associated with an approximately 2-fold higher risk for delayed elimination at 48 hours. HDMTX AUC was not associated with toxicity. MTX pharmacokinetics vary among and even within patients despite BSA-adjusted dosing. Obesity and large size are identified as new risk factors for delayed elimination, requiring further investigation.

Development and Validation of UHPLC-MS/MS Assay for Therapeutic Drug Monitoring of High-dose Methotrexate in Children with Acute Lymphoblastic Leukemia

Purpose

Precise and timely detection of methotrexate (MTX) concentration played a key role in high-dose MTX individualization therapy in acute lymphoblastic leukemia (ALL) children to avoid serious adverse effects or nonresponse. This report described a sensibility and validation of ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method for therapeutic drug monitoring (TDM) of methotrexate concentration in children's plasma.

Methods

One-step protein precipitation of samples was accomplished by adding 200 μL of acetonitrile to 100 μL of plasma sample. The separation of plasma samples was carried out on a ZORBAX Eclipse Plus C18 Rapid Resolution HD column with gradient elution using a mobile phase constituted of acetonitrile and 1% formic acid. The detection was executed by electrospray ionization (ESI) of triple quadrupole tandem mass spectrometer (TQMS) in the multiple reaction monitoring (MRM) mode with the transitions m/z 455.2 → 307.9 for methotrexate and m/z 458.2 → 311.2 for IS, separately. Linear concentration range of the calibration curve was 44-11,000 nmol/L and 44 nmol/L was the lower limit of quantification.

Results

The methotrexate elution time was at 1.577 min, and the overall running time was only 3.3 min. The intra- and interday precision for all the analysis results was within 11.24%, and mean recoveries rate of methotrexate exceeded 87.98%.

Conclusion

The described and fully validated UHPLC-MS/MS method was successfully applied in clinical TDM after infusion of high-dose methotrexate 1-5 g/m² to 41 childpatients.

Do intravenous fluid substitutions influence methotrexate clearance? An unanticipated impact of an intravenous sodium bicarbonate drug shortage

BACKGROUND

National drug shortages of essential medications for childhood cancer have increasingly posed a challenge in the treatment of patients. The efficacy of standardized supportive care practices to avoid treatment-related toxicities may be limited during these drug shortages. High-dose methotrexate (HDMTX) plays a critical role in modern treatment protocols for acute lymphoblastic leukemia and requires stringent supportive care measures to mitigate toxicity. As the result of a national intravenous (IV) sodium bicarbonate shortage, institutional standard HDMTX supportive care guidelines had to be modified. We describe the unanticipated consequences on HDMTX clearance.

METHODS

We performed a retrospective chart review assessing the impact of alternative compositions of IV fluids on the mean 24-h methotrexate levels (Cp_ss ) of 25 patients receiving 76 total HDMTX infusions at Texas Children's Hospital Cancer Center from March to October 2017. During the sodium bicarbonate drug shortage, all patients received IV hydration consisting of either dextrose 5%, 0.45% normal saline (D5 ½ NS-Group A) or dextrose 5%, 0.2% normal saline (D5 ¼ NS-Group B).

RESULTS

Patients receiving a higher total sodium dose demonstrated significantly lower Cp_ss (25.36 ± 16.6 μMol) compared to patients receiving less sodium (53.9 ± 37.9 μMol; P < .001).

CONCLUSIONS

Our report shows that in the setting of IV sodium bicarbonate shortage, the composition of hydration IV fluids may affect methotrexate clearance. Patient who received a higher sodium load had a lower 24-h methotrexate level. This demonstrates the potential for unanticipated outcomes resulting from national drug shortages.

Association of GGH Promoter Methylation Levels with Methotrexate Concentrations in Chinese Children with Acute Lymphoblastic Leukemia

BACKGROUND

It is known that γ-glutamyl hydrolase (GGH) is involved in the disposition of methotrexate (MTX), and GGH activity is regulated by DNA methylation in acute lymphoblastic leukemia (ALL) cells. The present study explores the methylation status of the GGH promoter in peripheral blood and its association with MTX levels and toxicities in Chinese children with ALL.

METHODS

Serum MTX concentrations were determined by fluorescence polarization immunoassay. Methylation quantification and genotyping for GGH rs3758149 and rs11545078 was performed by Sequenom MassARRAY in 50 pediatric patients with ALL.

RESULTS

Overall, the investigated region of the GGH promoter was in hypomethylated status. The methylation levels of cytosine phosphate guanine (CpG)_7, CpG_12, CpG_17, and CpG_20 were significantly higher in patients with B-cell ALL than other immunotypes (p<0.05). The methylation levels of CpG_13.14, CpG_17, and CpG_19 showed a significant negative correlation with MTX C_24 hr (p<0.05). The methylation level of CpG_8.9 correlated significantly with MTX C_42 hrs (p<0.05). The methylation level of CpG_19 was significantly lower in patients with MTX toxicities (p<0.05).

CONCLUSIONS

The methylation levels of the GGH promoter might affect MTX exposure and toxicities. These findings provided reasonable explanations for the variability of MTX responses in patients with childhood ALL.

Clinical implementation of pharmacogenetics and model-informed precision dosing to improve patient care

Providing maximal therapeutic efficacy without toxicity is a universal goal of rational drug therapy. However, substantial between-patient variability in drug response often impedes such successful treatments and brings the necessity of tailoring drug dose to individual needs for more precise therapy. In many cases plenty of patient characteristics, such as body size, genetic makeup and environmental factors, need to be taken into consideration to find the optimal dose in clinical practice. A pharmacokinetics and pharmacodynamics (PK/PD) model-informed approach offers integration of various patient information to provide an expectation of drug response and derive practical dose estimates to support clinicians' dosing decisions. Such an approach was pioneered in the late 1970s, but its broad clinical acceptance and implementation have been hampered by the lack of widespread computer technology, including user-friendly software tools. This has significantly changed in recent years. With the advent of electronic health records (EHRs) and the ubiquity of user-friendly software tools, we now experience a convergence of clinical information, pharmacogenetics, systems pharmacology and pharmacometrics, and technology. Advanced pharmacometrics research is now more appliable and implementable to improve health care. This article presents examples of successful development and implementation of pharmacogenetics-guided and PK/PD model-informed decision support to facilitate precision dosing, including the development of an EHR-embedded decision support tool. Through the integration of clinical decision support tools in EHRs, clinical pharmacometrics support can be brought directly to the clinical team and the bedside.

Doxorubicin induces cytotoxicity and miR-132 expression in granulosa cells

Doxorubicin (DOX) is one of the most commonly used drugs for the treatment of childhood cancers, including leukemia and lymphomas. Despite the high survival rate, female leukemia survivors are at higher risk of ovarian failure and infertility later in life. Treatment with chemotherapeutic drugs like DOX is associated with damage in ovarian follicles, but the affectation grade of granulosa cells remains unclear. To assess and avoid the possible side-effects of DOX, early biomarkers of ovarian injury and chemotherapy-induced ovarian toxicity should be identified. MicroRNAs (miRNAs) have emerged in recent years as a promising new class of biomarkers for drug-induced tissue toxicity. In this study, the effects of DOX on cell viability, steroidogenesis, and miRNA expression were studied in primary granulosa cells (GCs) and in two cellular models (COV434 and KGN cells). We report that compared to other chemotherapeutic drugs, DOX treatment is more detrimental to granulosa cells as observed by decrease of cell viability. Treatment with DOX changes the expression of the aromatase gene (CYP19A1) and the secretion of 17β-estradiol (E2) in a cell-specific manner. miR-132-3p is dose-dependently increased by DOX in all cellular models. In absence of DOX, miR-132-3p overexpression in COV434 cells has no effect on E2 secretion or CYP19A1 expression. Altogether, these findings contribute to understanding the hormonal disbalance caused by DOX in human ovarian cells and suggest miR-132 as a putative sensor to predict DOX-induced ovarian toxicity.

The role of therapeutic drug monitoring in the management of safety of anticancer agents: a focus on 3 cytotoxics

Introduction: Therapeutic drug monitoring in oncology is used to prevent major toxicities of selected anticancer agents due to overexposure by individualizing the dose based on a pharmacokinetic target. Areas covered: Numerous studies relating a relation between pharmacokinetic variability and toxicity have been reported since the eighties but very few have been implemented in clinical practice due to a lack of validation and harmonization, logistical constraints and reluctance from oncologists. Following recent recommendations, this paper highlights the current-validated applications of pharmacokinetic monitoring in oncology focusing on the safety of anticancer therapies. Expert opinion: Paradoxically given the oldness of the agents, guidelines of dose adjustment have been recently available for intravenous busulfan, 5-fluorouracil, and high-dose methotrexate. Interestingly, besides the enhancement of tolerability, it applies to potential curative clinical situations. In an era of personalized oncology that integrates complex molecular factors in the treatment of cancer, education is needed for oncologists to show the benefits of this valuable (even old) resource for the safety of patients. Therapeutic drug monitoring for busulfan, 5-fluorouracil and methotrexate will still hold in the future unless more active agents are available in the concerned indications.

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.

Methotrexate Disposition in Pediatric Patients with Acute Lymphoblastic Leukemia: What Have We Learnt From the Genetic Variants of Drug Transporters

Background:

Methotrexate (MTX) is one of the leading chemotherapeutic agents with the bestdemonstrated efficacies against childhood acute lymphoblastic leukemia (ALL). Due to the narrow therapeutic range, significant inter- and intra-patient variabilities of MTX, non-effectiveness and/or toxicity occur abruptly to cause chemotherapeutic interruption or discontinuation. The relationship between clinical outcome and the systemic concentration of MTX has been well established, making the monitoring of plasma MTX levels critical in the treatment of ALL. Besides metabolizing enzymes, multiple transporters are also involved in determining the intracellular drug levels. In this mini-review, we focused on the genetic polymorphisms of MTX-disposition related transporters and the potential association between the discussed genetic variants and MTX pharmacokinetics, efficacy, and toxicity in the context of MTX treatment.

Methods:

We searched PubMed for citations published in English using the terms “methotrexate”, “transporter”, “acute lymphoblastic leukemia”, “polymorphisms”, and “therapeutic drug monitoring”. The retrieval papers were critically reviewed and summarized according to the aims of this mini-review.

Results:

Solute carrier (SLC) transporters (SLC19A1, SLCO1A2, SLCO1B1, and SLC22A8) and ATP-binding cassette (ABC) transporters (ABCB1, ABCC2, ABCC3, ABCC4, ABCC5, and ABCG2) mediate MTX disposition. Of note, the influences of polymorphisms of SLC19A1, SLCO1B1 and ABCB1 genes on the clinical outcome of MTX have been extensively studied.

Conclusion:

Overall, the data critically reviewed in this mini-review article confirmed that polymorphisms in the genes encoding SLC and ABC transporters confer higher sensitivity to altered plasma levels, MTX-induced toxicity, and therapeutic response in pediatric patients with ALL. Pre-emptive determination may be helpful in individualizing treatment.

Delayed methotrexate clearance in patients with acute lymphoblastic leukemia concurrently receiving dasatinib

We aimed to determine whether patients receiving dasatinib or imatinib concurrently with high-dose methotrexate (HDMTX) had slower methotrexate clearance than patients not receiving a tyrosine kinase inhibitor (TKI) during the HDMTX infusion. Patients concurrently receiving dasatinib and HDMTX (N = 7) had significantly slower MTX clearance (P = 0.008) than patients not receiving a TKI (N = 111). Two patients receiving a TKI during a HDMTX infusion required glucarpidase. In vitro studies showed that dasatinib significantly inhibited methotrexate uptake by SLCO1B1-expressing cells (P = 0.009). There may be an interaction between dasatinib and HDMTX, mediated by the transporter SLCO1B1, that causes a delay in MTX clearance.

Evaluation of the Novel Methotrexate Architect Chemiluminescent Immunoassay: Clinical Impact on Pharmacokinetic Monitoring

BACKGROUND

Fluorescence polarization immunoassay (FPIA) has probably been the most widely used technique for the determination of methotrexate (MTX) concentrations in clinical laboratories. After its replacement by a novel architect chemiluminescent microparticle immunoassay (CMIA), it is essential to verify that there are no differences between the methods that can induce an error in leucovorin rescue with dire consequences for the patient. The objective of our study was to compare plasma/serum MTX measurements between CMIA and FPIA (reference method in this study) in the work conditions of a clinical pharmacokinetics unit to determine whether any difference would affect clinical decisions on the management of this drug.

METHODS

FPIA on TDx/FLx and CMIA on Architect ci8200 were simultaneously used to evaluate 127 clinical samples. Within-run (20 repetitions on same day) and between-run (20 repetitions on different days) imprecision was evaluated using 6 control samples provided by the manufacturer and diluting 2 of them by 50% for 0.03 and 0.22 μmol/L, respectively. The Passing-Bablok regression method, Bland-Altman plot, and concordance correlation coefficient (CCC) were used in the statistical analysis.

RESULTS

Within-run imprecision was <5% (3.6%-4.39%) and between-run imprecision <11% (2.42%-10.65%). Between-assay correlation for the studied concentration range (0.05-250 μmol/L) was CMIA = -0.026 + 1.033 FPIA (n = 127), r = 0.9963, and CCC = 0.9946. For samples <1.5 μmol/L (nondiluted) included in the assay calibration curve, the correlation was CMIA = -0.009 + 0.955 FPIA (n = 54), r = 0.9819, and CCC = 0.9807. No significant difference was observed between the measurements by the 2 assays, given that the 95% confidence interval of the ordinate at the origin included "0" (-0.020 to 0.0007), and the 95% confidence interval of the slope included 1 (0.923-1.020). The interchangeability of these assays was confirmed by Bland-Altman plot results, which showed a mean difference insignificant at concentrations <10 μmol/L.

CONCLUSIONS

The correlation between methods was excellent, and Passing-Bablok regression analysis detected no virtually difference in their results. Utilization of the CMIA-Architect assay to measure MTX concentrations would therefore not affect clinical decisions on MTX management, supporting its employment in routine MTX monitoring.

Association between a microRNA binding site polymorphism in SLCO1A2 and the risk of delayed methotrexate elimination in Chinese children with acute lymphoblastic leukemia

Organic anion-transporting polypeptide 1A2 (OATP1A2) is involved in the cellular uptake of methotrexate (MTX). Genetic variation in solute carrier organic anion transporter family member 1A2 (SLCO1A2, the coding gene of OATP1A2) has important implications for the elimination of MTX. We investigated the association between a microRNA (miRNA) binding site polymorphism (rs4149009 G > A) in the 3'-untranslated region (3'-UTR) of SLCO1A2 with the serum MTX concentrations in Chinese children with acute lymphoblastic leukemia (ALL). Genotyping for SLCO1A2 rs4149009 G > A in 141 children with ALL was performed using the Sequenom MassARRAY system. Serum MTX concentrations were determined by fluorescence polarization immunoassay. The percentages of MTX level ≥1 μmol/L at 42 h were compared among the AA, GA, and GG genotypes. The minor allele frequency observed in this study (33.0%) was significantly lower than that in the African samples reported in the 1000 Genomes Project (57.4%, P = 0.00). The incidence rate of delayed MTX elimination was significantly higher in patients with the GG genotype (23.1%) compared with the AA genotype (0.0%, P = 0.03). Bioinformatics tools predicted that the rs4149009 A allele would disrupt the putative binding sites of hsa-miR-324-3p and hsa-miR-1913. These results indicate that the rs4149009 G > A polymorphism might affect MTX pharmacokinetics by interfering with the function of miRNAs.

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.

Using a Bedside Algorithm to Individually Dose High-dose Methotrexate for Patients at Risk for Toxicity

We developed a bedside algorithm for individually adjusting the high-dose methotrexate (HDMTX) dose (5 g/m) given to patients with acute lymphoblastic leukemia at high risk for methotrexate toxicity. Data were reviewed for 8 patients receiving 21 cycles of HDMTX as per our algorithm. Eleven cycles began with 5 g/m, 10 cycles began with a preinfusion 20% to 25% dose reduction. Neither mean MTX AUC (2320.5±179.1 vs. 2080.4±161.7 μmol×h/L), mean Cpss (64.3±7.9 vs. 60.8±6.1 μM), nor toxicities were statistically different between groups. Our algorithm allowed the safe administration of HDMTX to patients at risk of MTX toxicities and obviated the need for preinfusion dose reduction.

Delayed methotrexate excretion in infants and young children with primary central nervous system tumors and postoperative fluid collections

PURPOSE

High-dose methotrexate (HD-MTX) has been used to treat children with central nervous system tumors. Accumulation of MTX within pleural, peritoneal, or cardiac effusions has led to delayed excretion and increased risk of systemic toxicity. This retrospective study analyzed the association of intracranial post-resection fluid collections with MTX plasma disposition in infants and young children with brain tumors.

METHODS

Brain MRI findings were analyzed for postoperative intracranial fluid collections in 75 pediatric patients treated with HD-MTX and for whom serial MTX plasma concentrations (MTX) were collected. Delayed plasma excretion was defined as (MTX) ≥1 μM at 42 hours (h). Leucovorin was administered at 42 h and then every 6 h until (MTX) <0.1 μM. Population and individual MTX pharmacokinetic parameters were estimated by nonlinear mixed-effects modeling.

RESULTS

Fifty-eight patients had intracranial fluid collections present. Population average (inter-individual variation) MTX clearance was 96.0 ml/min/m² (41.1 CV %) and increased with age. Of the patients with intracranial fluid collections, 24 had delayed excretion; only 2 of the 17 without fluid collections (P < 0.04) had delayed excretion. Eleven patients had grade 3 or 4 toxicities attributed to HD-MTX. No significant difference was observed in intracranial fluid collection, total leucovorin dosing, or hydration fluids between those with and without toxicity.

CONCLUSIONS

Although an intracranial fluid collection is associated with delayed MTX excretion, HD-MTX can be safely administered with monitoring of infants and young children with intracranial fluid collections. Infants younger than 1 year may need additional monitoring to avoid toxicity.

Association of -24CT, 1249GA, and 3972CT ABCC2 gene polymorphisms with methotrexate serum levels and toxic side effects in children with acute lymphoblastic leukemia

Acute lymphoblastic leukemia patients after being treated with methotrexate, have differences in methotrexate serum levels and toxic side effects. One of the main determinants of these toxic side effects is the host pharmacogenetics. The aim of this study was to evaluate the association of -24CT, 1249GA, and 3972CT ABCC2 gene polymorphisms with serum levels, and toxic side effects of methotrexate in childhood acute lymphoblastic leukemia. Applying polymerase chain reaction and restriction fragment length polymorphism techniques, the prevalence of -24CT, 1249GA, and 3972CT ABCC2 gene polymorphisms was evaluated in 65 acute lymphoblastic leukemia patients. The relationship between polymorphisms and methotrexate serum levels and toxicities was studied. A reverse significant relationship was detected between 3972T allele carriers and hepatotoxicity (P = 0.01, OR = 0.25, 95% CI = 0.09-0.72). Also, 1249A allele carriers had increased rate of gastrointestinal toxicity (P = 0.05, OR = 3.47, 95% CI = 1.04-11.57). No significant relationship was detected between -24CT polymorphism and methotrexate toxic side effects. There was no significant relationship between these three polymorphisms and methotrexate serum levels. Genotyping for 3972CT and 1249GA ABCC2 gene variants maybe useful in acute lymphoblastic leukemia to optimize methotrexate therapy and reducing the associated toxicity.

Between-course targeting of methotrexate exposure using pharmacokinetically guided dosage adjustments

PURPOSE

It is advantageous to individualize high-dose methotrexate (HDMTX) to maintain adequate exposure while minimizing toxicities. Previously, we accomplished this through within-course dose adjustments.

METHODS

In this study, we evaluated a strategy to individualize HDMTX based on clearance of each individual's previous course of HDMTX in 485 patients with newly diagnosed acute lymphoblastic leukemia. Doses were individualized to achieve a steady-state plasma concentration (Cpss) of 33 or 65 μM (approximately 2.5 or 5 g/m(2)/day) for low- and standard-/high-risk patients, respectively.

RESULTS

Individualized doses resulted in 70 and 63 % of courses being within 20 % of the targeted Cpss in the low- and standard-/high-risk arms, respectively, compared to 60 % (p < 0.001) and 61 % (p = 0.43) with conventionally dosed therapy. Only 1.3 % of the individualized courses in the standard-/high-risk arm had a Cpss greater than 50 % above the target compared to 7.3 % (p < 0.001) in conventionally dosed therapy. We observed a low rate (8.5 % of courses) of grade 3-4 toxicities. The odds of gastrointestinal toxicity were related to methotrexate plasma concentrations in both the low (p = 0.021)- and standard-/high-risk groups (p = 0.003).

CONCLUSIONS

Individualizing HDMTX based on the clearance from the prior course resulted in fewer extreme Cpss values and less delayed excretion compared to conventional dosing.

Involvement of Multiple Transporters-mediated Transports in Mizoribine and Methotrexate Pharmacokinetics

Mizoribine is administered orally and excreted into urine without being metabolized. Many research groups have reported a linear relationship between the dose and peak serum concentration, between the dose and AUC, and between AUC and cumulative urinary excretion of mizoribine. In contrast, a significant interindividual variability, with a small intraindividual variability, in oral bioavailability of mizoribine is also reported. The interindividual variability is mostly considered to be due to the polymophisms of transporter genes. Methotrexate (MTX) is administered orally and/or by parenteral routes, depending on the dose. Metabolic enzymes and multiple transporters are involved in the pharmacokinetics of MTX. The oral bioavailability of MTX exhibits a marked interindividual variability and saturation with increase in the dose of MTX, with a small intraindividual variability, where the contribution of gene polymophisms of transporters and enzymes is suggested. Therapeutic drug monitoring of both mizoribine and MTX is expected to improve their clinical efficacy in the treatment of rheumatoid arthritis.

ABCB1 C3435T genetic polymorphism on population pharmacokinetics of methotrexate after hematopoietic stem cell transplantation in Korean patients: a prospective analysis

BACKGROUND

Methotrexate (MTX) is often used to prevent graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (HSCT). However, MTX has great pharmacokinetic variability and its use can result in fatal complications and/or infections after HSCT.

OBJECTIVES

The purposes of this study were to build a population pharmacokinetic model of MTX treatment in Korean patients who have undergone HSCT and to identify covariates, including genetic polymorphisms, that affect the pharmacokinetic properties of MTX.

METHODS

Clinical characteristics and MTX concentration data for 20 post-HSCT patients were collected. For each patient, ABCB1, ABCC2, ATIC, GGH, MTHFR, and TYMS genotyping was performed. Population pharmacokinetic analysis was performed using the NONMEM program. Analysis of MTX pharmacokinetic properties was accomplished using a 2-compartment pharmacokinetic model that incorporated first-order conditional estimation methods with interaction. The effects of a variety of demographic and genetic factors on MTX disposition were investigated.

RESULTS

The study population consisted of 12 men (60%) and 8 women (40%). Median age and body weight were 28 years (range, 18-49 years) and 55.6 kg (range, 44.8-80.8 kg), respectively. Within the study population, the estimated mean MTX clearance (CL) was 7.08 L/h, whereas the mean central compartment volume (V(1)) of MTX distribution was 19.4 L. MTX CL was significantly affected by glomerular filtration rate (GFR), penicillin use, and the ABCB1 3435 genotype. Interindividual variabilities for CL and V(1) were 21.6% and 73.3%. A 10-mL/min GFR increase was associated with a 32% increase in mean MTX CL, whereas penicillin use was associated with a decrease in MTX CL of 61%. MTX CL was significantly greater (by ∼21%) in patients with the ABCB1 3435 CC and CT genotype than in those with the ABCB1 3435 TT genotype (P < 0.001).

CONCLUSIONS

There was great interindividual variation in MTX pharmacokinetic properties in patients who had undergone HSCT. GFR, concurrent penicillin use, and the presence of the ABCB1 3435 C<T genotypes significantly affected MTX CL. The MTX population pharmacokinetic model developed here may provide useful information for individualizing MTX therapy after HSCT.

A population pharmacokinetic/pharmacodynamic model of methotrexate and mucositis scores in osteosarcoma

Methotrexate, when used in high doses (12 g/m²) in the treatment of osteosarcoma, shows wide between-subject variability (BSV) in its pharmacokinetics. High-dose methotrexate is associated with severe toxicity; therefore, therapeutic drug monitoring (TDM) is carried out to guide rescue therapy and monitor for nephrotoxicity. Mucositis is a commonly encountered dose-limiting toxicity that often leads to delays in subsequent courses of chemotherapy. This, in turn, results in a reduction in the dosing intensity, which is essential in the treatment of osteosarcoma. The aims of this study were to develop a population pharmacokinetic (PK) model from TDM using physiologically relevant covariates and to investigate the correlation between mucositis scores and methotrexate pharmacokinetics. In total, 46 osteosarcoma patients (30 men and 16 women; age, 4-51 years) were recruited, and blood samples were collected for routine TDM once every 24 hours. Mucositis scores, graded according to the National Cancer Institute Common Toxicity Criteria, were recorded for 28 of the patients (18 men and 10 women; age, 8-51 years) predose and postdose. A population PK model was developed in NONMEM VI. A 2-compartment PK model was chosen, and clearance (CL) was divided into filtration and secretion/metabolism components. All parameters were scaled with body weight, and, in addition, total CL was scaled with age- and sex-adjusted serum creatinine. Between-subject variability was modeled for all parameters, and between-occasion variability was included in CL. For a typical 70 kg man of 18 years or older, the parameter estimates for the final model were CL(filt) = 2.69 L/h/70 kg, CL(sec) = 10.9 L/h/70 kg, V₁ = 74.3 L/70 kg, Q = 0.110 L/h/70 kg, and V₂ = 4.10 L/70 kg. Sequential pharmacodynamic modeling consisted of mucositis scores as 5-point ordered categorical data. A significant linear relationship between individual area under the curve (AUC) and mucositis score probability was found, and the probability of having mucositis score ≥ 1 increased with increasing AUC and was almost 50% at the average cumulative AUC after 2 consecutive methotrexate doses.

Evaluation of destructive effects of exposure to cisplatin during developmental stage: no profound evidence for sex differences in impaired motor and memory performance

We have elucidated the alteration in hippocampal and cerebellum function following chronic cisplatin treatment in male and female rats. Hippocampus and cerebellum related behavioral dysfunction in cisplatin-treated [intraperitoneally, 5 mg/(kg/week) for 5 weeks from 23-day-old] rats were analyzed using explorative, motor function, learning, and memory tasks (grasping, rotarod, open field, and Morris water maze tests). Exposure to cisplatin impaired the motor coordination in male and female rats. Exposure to cisplatin was reflected by a decrease in grasping time compared to vehicle-treated controls (saline) only in male rat while there were not any differences in female rats. When the rearing frequency, total distance moved and velocity of their recorded in open fieldtest, both males and females were dramatically affected by exposure to cisplatin. Compared to the saline, male and female rats trained 5 weeks after cisplatin injection showed significant memory deficits in the Morris water maze test. However, hippocampal and cerebellum functions of male and female rats were profoundly affected by exposure to cisplatin while no sex differences in the most variable were evident.

Profound destructive effects of adolescent exposure to vincristine accompanied with some sex differences in motor and memory performance

Vincristine, an anticancer drug, is known to induce neuronal cell damage. We have elucidated the alteration in performance of the hippocampus and cerebellum following chronic vincristine treatment (0.2 mg·(kg body mass)–1·week–1) in male and female rats. Intraperitoneal injection of vincristine in adolescent rats caused impairment of motor and cognitive behavior. In the probe test, the length of path traveled and percent swimming time for vincristine-treated rats in the correct quadrant was significantly less than for the saline-treated (control) groups. The path length and time latency at the 2nd and 3rd blocks of trials for the male vincristine-treated group was significantly higher than that for the female saline- and the vincristine-treated rats. In the rod test, vincristine exposure impaired the motor coordination in both male and female rats. Exposure to vincristine caused a significant decrease in hanging time in male rats, compared with the saline- and the vincristine-treated female rats, while there were no differences between the female vincristine-treated rats and the saline-treated rats of both sexes. The rearing frequency, total distance moved, and velocity for both male and female rats were dramatically affected by exposure to vincristine. We have observed that the hippocampal and cerebellar functions of male and female rats were profoundly affected by exposure to vincristine, especially the male rats, suggesting a sexual dimorphism in the developing central nervous system that is affected by chemicals such as anticancer drugs.

Influence of folate pathway polymorphisms on high-dose methotrexate-related toxicity and survival in childhood acute lymphoblastic leukemia

The prediction of high-dose methotrexate (HD-MTX) toxicity is a key issue in the individualization of treatment in childhood acute lymphoblastic leukemia (ALL). Our aim was to evaluate the influence of MTX pathway polymorphisms on HD-MTX treatment outcome in children with ALL. In total, 167 children with ALL were genotyped for methylenetetrahydrofolate dehydrogenase (MTHFD1) 1958G > A, methylenetetrahydrofolate reductase (MTHFR) 677C > T and 1298A > C and thymidylate synthase (TYMS) 2R > 3R polymorphisms. The MTHFD1 1958A allele significantly reduced the odds of hepatotoxicity (adjusted p = 0.009), while the TYMS 3R allele significantly reduced the odds of leukocytopenia and thrombocytopenia (adjusted p = 0.005 and adjusted p = 0.002, respectively). MTHFR polymorphisms did not influence HD-MTX-related toxicity, but a significant effect of MTHFR 677C > T-TYMS 2R > 3R and MTHFD1 1958G > A-MTHFR 677C > T interactions on HD-MTX-related toxicity was observed. None of the investigated polymorphisms influenced survival. Our study suggests an important role of polymorphisms and gene-gene interactions within the folate pathway in HD-MTX-related toxicity in childhood ALL.

Methotrexate-induced side effects are not due to differences in pharmacokinetics in children with Down syndrome and acute lymphoblastic leukemia

BACKGROUND

Children with Down syndrome have an increased risk of developing acute lymphoblastic leukemia and a poor tolerance of methotrexate. This latter problem is assumed to be caused by a higher cellular sensitivity of tissues in children with Down syndrome. However, whether differences in pharmacokinetics play a role is unknown.

DESIGN AND METHODS

We compared methotrexate-induced toxicity and pharmacokinetics in a retrospective case-control study between patients with acute lymphoblastic leukemia who did or did not have Down syndrome. Population pharmacokinetic models were fitted to data from all individuals simultaneously, using non-linear mixed effect modeling.

RESULTS

Overall, 468 courses of methotrexate (1-5 g/m(2)) were given to 44 acute lymphoblastic leukemia patients with Down syndrome and to 87 acute lymphoblastic leukemia patients without Down syndrome. Grade 3-4 gastrointestinal toxicity was significantly more frequent in the children with Down syndrome than in those without (25.5% versus 3.9%; P=0.001). The occurrence of grade 3-4 gastrointestinal toxicity was not related to plasma methotrexate area under the curve. Methotrexate clearance was 5% lower in the acute lymphoblastic leukemia patients with Down syndrome (P=0.001); however, this small difference is probably clinically not relevant, because no significant differences in methotrexate plasma levels were detected at 24 and 48 hours.

CONCLUSIONS

We did not find evidence of differences in the pharmacokinetics of methotrexate between patients with and without Down syndrome which could explain the higher frequency of gastrointestinal toxicity and the greater need for methotrexate dose reductions in patients with Down syndrome. Hence, these problems are most likely explained by differential pharmaco-dynamic effects in the tissues between children with and without Down syndrome. Although the number of patients was limited to draw conclusions, we feel that it may be safe in children with Down syndrome to start with intermediate dosages of methotrexate (1-3 g/m(2)) and monitor the patients carefully.

Benefits of the Intermittent Use of 6-Mercaptopurine and Methotrexate in Maintenance Treatment for Low-Risk Acute Lymphoblastic Leukemia in Children: Randomized Trial From the Brazilian Childhood Cooperative Group—Protocol ALL-99

Purpose

To describe event-free survival (EFS) and toxicities in children with low-risk acute lymphoblastic leukemia (ALL) assigned to receive either continuous 6-mercaptopurine (6-MP) and weekly methotrexate (MTX) or intermittent 6-MP with intermediate-dose MTX, as maintenance treatment.

Patients and Methods

Between October 1, 2000, and December 31, 2007, 635 patients with low-risk ALL were enrolled onto Brazilian Childhood Cooperative Group for ALL Treatment (GBTLI) ALL-99 protocol. Eligible children (n = 544) were randomly allocated to receive either continuous 6-MP/MTX (group 1, n = 272) or intermittent 6-MP (100 mg/m2/d for 10 days, with 11 days resting) and MTX (200 mg/m2every 3 weeks; group 2, n = 272).

Results

The 5-year overall survival (OS) and EFS were 92.5% ± 1.5% SE and 83.6% ± 2.1% SE, respectively. According to maintenance regimen, the OS was 91.4% ± 2.2% SE (group 1) and 93.6% ± 2.1% SE (group 2; P = .28) and EFS 80.9% ± 3.2% SE (group 1) and 86.5% ± 2.8% SE (group 2; P = .089). Remarkably, the intermittent regimen led to significantly higher EFS among boys (85.7% v 74.9% SE; P = .027), while no difference was seen for girls (87.0% v 88.8% SE; P = .78). Toxic episodes were recorded in 226 and 237 children, respectively. Grade 3 to 4 toxic events for groups 1 and 2 were, respectively, 273 and 166 for hepatic dysfunction (P = .002), and 772 and 636 for hematologic episodes (P = .005). Deaths on maintenance were: seven (group 1) and one (group 2).

Conclusion

The intermittent use of 6-MP and MTX in maintenance is a less toxic regimen, with a trend toward better long-term EFS. Boys treated with the intermittent schedule had significantly better EFS.

Pharmacokinetics and Drug Dosing in Obese Children

OBJECTIVES

To review pharmacokinetics in obese children and to provide medication dosing recommendations.

METHODS

EMBASE, MEDLINE, and International Pharmaceutical Abstracts databases were searched using the following terms: obesity, morbid obesity, overweight, pharmacokinetics, drug, dose, kidney function test, creatinine, pediatric, and child.

RESULTS

We identified 10 studies in which the authors examined drug dosing or pharmacokinetics for obese children. No information was found for drug absorption or metabolism. Obese children have a higher percent fat mass and a lower percent lean mass compared with normal-weight children. Therefore, in obese children, the volume of distribution of lipophilic drugs is most likely higher, and that of hydrophilic drugs is most likely lower, than in normal-weight children. Serum creatinine concentrations are higher in obese than normal-weight children. Total body weight is an appropriate size descriptor for calculating doses of antineoplastics, cefazolin, and succinylcholine in obese children. Initial tobramycin doses may be determined using an adjusted body weight, although using total body weight in the context of monitoring serum tobramycin concentrations would also be an appropriate strategy. We found no information for any of the opioids; antibiotics such as penicillins, carbapenems, vancomycin, and linezolid; antifungals; cardiac drugs such as digoxin and amiodarone; corticosteroids; benzodiazepines; and anticonvulsants. In particular, we found no information about medications that are widely distributed to adipose tissue or that can accumulate there.

CONCLUSIONS

The available data are limited because of the small numbers of participating children, study design, or both. The number and type of drugs that have been studied limit our understanding of the pharmacokinetics in obese children. In the absence of dosing information for obese children, it is important to consider the nature and severity of a child's illness, comorbidities, organ function, and side effects and physiochemical properties of the drug. Extrapolating from available adult data is possible, as long as practitioners consider the effects of growth and development on the pharmacokinetics relevant to the child's age.

Effect of allopurinol versus urate oxidase on methotrexate pharmacokinetics in children with newly diagnosed acute lymphoblastic leukemia

BACKGROUND

Allopurinol and urate oxidase are both effective in preventing or treating hyperuricemia during remission induction therapy for lymphoid malignancies, but to the authors' knowledge, their effects on concomitant anticancer drug therapy have not been compared.

METHODS

The authors compared plasma methotrexate pharmacokinetics in pediatric patients with newly diagnosed acute lymphoblastic leukemia who received concomitant allopurinol (n = 20) versus those treated with nonrecombinant or recombinant urate oxidase (n = 96) during high-dose methotrexate administration before conventional remission induction therapy.

RESULTS

The minimum plasma concentration of uric acid was significantly (P < .0001) lower after urate oxidase treatment than the concentration after allopurinol treatment. Methotrexate clearance was significantly higher (median, 117.1 mL/minute/m(2) vs 91.1 mL/minute/m(2); P = .019) in patients who received urate oxidase. A higher proportion of patients in the allopurinol group had elevated methotrexate plasma concentrations (36% vs 7%; P = .003) and experienced mucositis (45% vs 16%; P = .003) after methotrexate treatment compared with the urate oxidase group.

CONCLUSIONS

The lower rate of methotrexate clearance in patients who received allopurinol likely reflected a less potent hypouricemic effect of allopurinol, leading to precipitation of uric acid in renal tubules. Hence, during remission induction therapy for lymphoid malignancies, the authors concluded that renally excreted drugs should be monitored closely, especially in patients who are receiving allopurinol.

Pharmacogenomics of MRP transporters (ABCC1-5) and BCRP (ABCG2)

Elucidation of the key mechanisms that confer interindividual differences in drug response remains an important focus of drug disposition and clinical pharmacology research. We now know both environmental and host genetic factors contribute to the apparent variability in drug efficacy or in some cases, toxicity. In addition to the widely studied and recognized genes involved in the metabolism of drugs in clinical use today, we now recognize that membrane-bound proteins, broadly referred to as transporters, may be equally as important to the disposition of a substrate drug, and that genetic variation in drug transporter genes may be a major contributor of the apparent intersubject variation in drug response, both in terms of attained plasma and tissue drug level at target sites of action. Of particular relevance to drug disposition are members of the ATP Binding Cassette (ABC) superfamily of efflux transporters. In this review a comprehensive assessment and annotation of recent findings in relation to genetic variation in the Multidrug Resistance Proteins 1-5 (ABCC1-5) and Breast Cancer Resistance Protein (ABCG2) are described, with particular emphasis on the impact of such transporter genetic variation to drug disposition or efficacy.

Pharmacogenomics of acute leukemia

Pharmacogenomics provides knowledge regarding how genetic polymorphisms affect treatment responses. Such an approach is particularly needed in cancer therapy, as most chemotherapeutics drugs affect both tumor and normal cells, are ineffective in many patients and exhibit serious side effects. Leukemia exists in two different forms, myeloid and lymphoid. Acute lymphoblastic leukemia more frequently occurs in children, whereas the risk of acute myeloid leukemia is more common in adults. Despite significant progress in the treatment of these diseases, therapy is still unsuccessful in many patients. Prognosis is particularly poor in adult acute myeloid leukemia. Treatment failure in childhood acute lymphoblastic leukemia due to drug resistance remains the leading cause of cancer-related death in children. Here, we provide an overview of pharmacogenetics studies carried out in children and adults with acute lymphoblastic leukemia and acute myeloid leukemia, attempting to find the associations between treatment responses and polymorphisms in the genes whose products are needed for metabolism, and effects of drugs used in the treatment of leukemia.

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.

Body mass index does not influence pharmacokinetics or outcome of treatment in children with acute lymphoblastic leukemia

There is conflicting information about the influence of body mass index (BMI) on the pharmacokinetics, toxicity, and outcome of chemotherapy. We compared pharmacokinetics, outcome, and toxicity data across 4 BMI groups (underweight, BMI < or = 10th percentile; normal; at risk of overweight, BMI > or = 85th and < 95th percentile; overweight, BMI > or = 95th percentile) in 621 children with acute lymphoblastic leukemia (ALL) treated on 4 consecutive St Jude Total Therapy studies. Chemotherapy doses were not adjusted to ideal BMI. Estimates of overall survival (86.1% +/- 3.4%, 86.0% +/- 1.7%, 85.9% +/- 4.3%, and 78.2% +/- 5.5%, respectively; P = .533), event-free survival (76.2% +/- 4.2%, 78.7% +/- 2.1%, 73.4% +/- 5.5%, and 72.7% +/- 5.9%, respectively; P = .722), and cumulative incidence of relapse (16.0% +/- 3.7%, 14.4% +/- 1.8%, 20.6% +/- 5.1%, and 16.7% +/- 5.1%, respectively; P = .862) did not differ across the 4 groups. In addition, the intracellular levels of thioguanine nucleotides and methotrexate polyglutamates did not differ between the 4 BMI groups (P = .73 and P = .74, respectively). The 4 groups also did not differ in the overall incidence of grade 3 or 4 toxicity during the induction or postinduction periods. Further, the systemic clearance of methotrexate, teniposide, etoposide, and cytarabine did not differ with BMI (P > .3). We conclude that BMI does not affect the outcome or toxicity of chemotherapy in this patient population with ALL.

Experimental and clinical evidence for loss of effect (tolerance) during prolonged treatment with antiepileptic drugs

Development of tolerance (i.e., the reduction in response to a drug after repeated administration) is an adaptive response of the body to prolonged exposure to the drug, and tolerance to antiepileptic drugs (AEDs) is no exception. Tolerance develops to some drug effects much more rapidly than to others. The extent of tolerance depends on the drug and individual (genetic?) factors. Tolerance may lead to attenuation of side effects but also to loss of efficacy of AEDs and is reversible after discontinuation of drug treatment. Different experimental approaches are used to study tolerance in laboratory animals. Development of tolerance depends on the experimental model, drug, drug dosage, and duration of treatment, so that a battery of experimental protocols is needed to evaluate fully whether tolerance to effect occurs. Two major types of tolerance are known. Pharmacokinetic (metabolic) tolerance, due to induction of AED-metabolizing enzymes has been shown for most first-generation AEDs, and is easy to overcome by increasing dosage. Pharmacodynamic (functional) tolerance is due to "adaptation" of AED targets (e.g., by loss of receptor sensitivity) and has been shown experimentally for all AEDs that lose activity during prolonged treatment. Functional tolerance may lead to complete loss of AED activity and cross-tolerance to other AEDs. Convincing experimental evidence indicates that almost all first-, second-, and third-generation AEDs lose their antiepileptic activity during prolonged treatment, although to a different extent. Because of diverse confounding factors, detecting tolerance in patients with epilepsy is more difficult but can be done with careful assessment of decline during long-term individual patient response. After excluding confounding factors, tolerance to antiepileptic effect for most modern and old AEDs can be shown in small subgroups of responders by assessing individual or group response. Development of tolerance to the antiepileptic activity of an AED may be an important reason for failure of drug treatment. Knowledge of tolerance to AED effects as a mechanism of drug resistance in previous responders is important for patients, physicians, and scientists.

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.

Sex-dependent expression and activity of the ATP-binding cassette transporter breast cancer resistance protein (BCRP/ABCG2) in liver

The breast cancer resistance protein (BCRP/ABCG2) is an ATP-binding cassette drug efflux transporter present in the liver and other tissues that affects the pharmacological behavior of many compounds. To assess the possible role of BCRP in sex-dependent pharmacokinetics, we studied the in vivo disposition of several murine Bcrp1 substrates in male and female wild-type and Bcrp1 knockout mice. After oral administration of the antibiotic nitrofurantoin, the area under the plasma concentration-time curve in wild-type female mice was approximately 2-fold higher than in wild-type male mice. Moreover, after i.v. administration of nitrofurantoin, the antiulcerative cimetidine, the anticancer drug topotecan, and the carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), the plasma levels in wild-type female mice were all significantly higher than those in wild-type male mice. Analysis of the expression of murine Bcrp1 in several pharmacokinetically important tissues showed that only the hepatic Bcrp1 expression was higher in male mice compared with female mice. In line with this difference, the hepatobiliary excretion for nitrofurantoin and PhIP was, respectively, 9-fold higher and approximately 2-fold higher in male compared with female wild-type mice. No significant sex differences were observed in plasma levels or hepatobiliary excretion for any of the tested compounds in Bcrp1-/- mice, indicating that Bcrp1 was the main cause of the sex difference in wild-type mice. Analysis of hepatic expression of human BCRP also indicated a higher expression in men compared with women. In conclusion, sex-dependent expression of BCRP/Bcrp1 in the liver may be a cause of sex-specific variability in the pharmacokinetics of BCRP substrates, with potential impact on the clinical-therapeutic applications and toxicity risks of drugs.

Individualised Cancer Chemotherapy: Strategies and Performance of Prospective Studies on Therapeutic Drug Monitoring with Dose Adaptation

Therapeutic drug monitoring (TDM) is increasingly used in clinical practice for the optimisation of drug treatment. Although pharmacokinetic variability is an established factor involved in the variation of therapeutic outcome of many chemotherapeutic agents, the use of TDM in the field of oncology has been limited thus far. An important reason for this is that a therapeutic index for most anticancer agents has not been established; however, in the last 20 years, relationships between plasma drug concentrations and clinical outcome have been defined for various chemotherapeutic agents. Several attempts have been made to use these relationships for optimising the administration of chemotherapeutics by applying pharmacokinetically guided dosage. These prospective studies, individualising chemotherapy dose during therapy based on measured drug concentrations, are discussed in this review. We focus on the way a target value is defined, the methodologies used for dose adaptation and the way the performance of the dose-adaptation approach is evaluated. Furthermore, attention is paid to the results of the studies and the applicability of the strategies in clinical practice. It can be concluded that TDM may contribute to improving cancer chemotherapy in terms of patient outcome and survival and should therefore be further investigated.