High-dose Methotrexate Pharmacokinetics Research Articles

High-dose methotrexate pharmacokinetics and its impact on prognosis of paediatric acute lymphoblastic leukaemia patients: A population pharmacokinetic study.

This study delivers a comprehensive evaluation of the efficacy and pharmacokinetics of high-dose methotrexate (HDMTX) in a large cohort of Chinese paediatric acute lymphoblastic leukaemia patients. A total of 533 patients were included in the prognostic analysis. An association was observed between lower steady-state MTX concentrations (<56 μmol/L) and poorer outcomes in intermediate-/high-risk (IR/HR) patients. Subgroup analysis further revealed that this relationship between concentrations and prognosis was even more pronounced in patients with MLL rearrangements. In contrast, such an association did not emerge within the low-risk patient group. Additionally, utilizing population pharmacokinetic modelling (6051 concentrations from 815 patients), we identified the significant impact of physiological maturation, estimated glomerular filtration rate, sex and concurrent dasatinib administration on MTX pharmacokinetics. Simulation-based recommendations include a reduced dosage regimen for those with renal insufficiency and a specific 200 mg/kg dosage for infants under 1 year. The findings underscore the critical role of HDMTX in treating IR/HR populations and call for a reassessment of its application in lower-risk groups. An individualized pharmacokinetic dosage regimen could achieve the most optimal results, ensuring the largest proportion of steady-state concentrations within the optimal range.

Impact of Anticonvulsant - Methotrexate Interactions on High Dose Methotrexate Clearance and Outcomes in Patients with Primary CNS Lymphoma

Background: Patients with primary CNS Lymphoma (PCNSL) often present with neurologic complications such as focal defects, neuropsychiatric symptoms, increased intracranial pressure, aphasia, seizures, and ocular symptoms which require initiation of prophylactic or therapeutic anticonvulsants. Most anticonvulsants are notorious for their pharmacodynamic and pharmacokinetic drug interactions. The cornerstone of PCNSL therapy is the utilization of high-dose methotrexate (HD-MTX). The pharmacokinetics of HD-MTX are uniquely sensitive to both disease biology and drug interactions. Due to the importance of both HD-MTX and anticonvulsants in PCNSL patients, these medications are frequently given in concert with one another despite theoretical and proven drug interactions published in the literature. This is a retrospective analysis of patients treated with a modified R-MPV regimen (rituximab, methotrexate, procarbazine, vincristine alternating with intrathecal methotrexate) and the effects of various anticonvulsants on HD-MTX clearance.Methods: Patients ≥18 years of age with a biopsy proven diagnosis of PCNSL at Roswell Park Comprehensive Cancer Center who received R-MPV between January 2002 and December 2019 were included in this retrospective analysis. The electronic health record of each patient was reviewed for specific patient demographics, laboratory results, confounding drug interactions, toxicity, and treatment outcomes. Descriptive statistics were computed for all categorical variables. The time to MTX clearance in hours and the potential impact of concomitant use of various anticonvulsants were assessed using the Wilcoxon Rank Sum test in the case of ordinal responses and the Pearson chi-square test or Fisher's Exact test for categorical variables where appropriate.Results: A total of 67 patients met the inclusion criteria of which 53 patients (79.1%) received anticonvulsants (189 cycles of R-MPV) and 14 did not (69 cycles of R-MPV). Patients who had seizures or frontal brain PCNSL were more likely to receive anticonvulsants (p <0.001). When considering all possible medication interactions with HD-MTX, use of any interacting medication within 48 hours prior to HD-MTX was a predictor of delayed clearance (p = 0.0398). The most common confounding interaction seen in this population were with proton pump inhibitors. Levetiracetam was the most common anticonvulsant used at any point in time during treatment (83.1%). Compared to no anticonvulsant, levetiracetam did not significantly prolong HD-MTX clearance (52.6h v. 72.7h, p = 0.1586). Other anticonvulsants utilized included phenytoin (24.5%), gabapentin (3.8%), valproate (3.8%), carbamazepine (1.9%), lacosamide (1.9%), lamotrigine (1.9%), and phenobarbital (1.9%). Of the patients who received an anticonvulsant, 11 received more than one over the treatment period. Time to clearance of HD-MTX for patients not on an anticonvulsant was 53.8 hours compared to a clearance time of 68.2 hours for those who received an anticonvulsant (p = 0.0571). Patients who received anticonvulsants had a significantly higher complete response rate (79.2% vs 35.7%, p = 0.009), longer progression free survival (25.4 mo vs 3 mo, p = 0.014) and overall survival (56.6 mo vs 4.6 mo, p = 0.002) compared to those who did not (Table 1). There was no difference in grade 3/4 toxicities between anticonvulsants and no anticonvulsants except for thrombocytopenia (p = 0.047) and respiratory side effects (p = 0.035).Conclusion: Anticonvulsants are an essential component to PCNSL therapy in patients on HD-MTX. They are well tolerated, do not alter HD-MTX clearance in a clinically significant manner and may help improve patient outcomes. [Display omitted] DisclosuresTorka: TG Therapeutics: Membership on an entity's Board of Directors or advisory committees.

Urine volume to hydration volume ratio is associated with pharmacokinetics of high-dose methotrexate in patients with primary central nervous system lymphoma.

High‐dose methotrexate (HD‐MTX)‐based chemotherapy is the first‐line treatment for primary central nervous system lymphoma (PCNSL), but is associated with severe adverse effects, including myelosuppression and renal impairment. MTX is primarily excreted by the kidneys. Renal function calculated using serum creatinine (Scr) derived from muscle may be overestimated in elderly PCNSL patients. Therefore, we aimed to construct a population pharmacokinetic model in PCNSL patients and explore the factors associated with MTX clearance. Sixteen PCNSL patients (median age, 66 years) treated with HD‐MTX were included, and serum MTX concentrations were measured at 193 points in 49 courses. A population pharmacokinetic analysis was performed using NONMEM. A Monte Carlo simulation was conducted, in which serum MTX concentrations were stratified into three groups of creatine clearance (Ccr) (50, 75, and 100 ml/min) with three groups of the urine volume to hydration volume (UV/HV) ratio (<1, 1–2, and >2). The final model was constructed as follows: MTX clearance = 4.90·(Ccr/94.5)0.456·(UV/HV)0.458. In the Monte Carlo simulation, serum MTX concentrations were below the standard values (10, 1, and 0.1 µM at 24, 48, and 72 h, respectively, after the start of the MTX administration) in most patients with UV/HV >2, even with Ccr of 50 ml/min. Conversely, half of the patients with UV/HV <1 and Ccr of 50 ml/min failed to achieve the standard values. The present results demonstrated that the UV/HV ratio was useful for describing the pharmacokinetics of MTX in PCNSL patients.

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The cover image is based on the Original Article* Population Pharmacokinetics of High-Dose Methotrexate in Chinese Pediatric Patients with Medulloblastoma by Dan Yan** et al., https://doi.org/10.1002/bdd.2221.***

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.

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. The aim of this study was to develop a population pharmacokinetic (PK) model of methotrexate in infants with ALL. 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 4g/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. 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. 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.

Pharmacogenetic analysis of high-dose methotrexate treatment in children with osteosarcoma.

Inter-individual differences in toxic symptoms and pharmacokinetics of high-dose methotrexate (MTX) treatment may be caused by genetic variants in the MTX pathway. Correlations between polymorphisms and pharmacokinetic parameters and the occurrence of hepato- and myelotoxicity were studied. Single nucleotide polymorphisms (SNPs) of the ABCB1, ABCC1, ABCC2, ABCC3, ABCC10, ABCG2, GGH, SLC19A1 and NR1I2 genes were analyzed in 59 patients with osteosarcoma. Univariate association analysis and Bayesian network-based Bayesian univariate and multilevel analysis of relevance (BN-BMLA) were applied. Rare alleles of 10 SNPs of ABCB1, ABCC2, ABCC3, ABCG2 and NR1I2 genes showed a correlation with the pharmacokinetic values and univariate association analysis. The risk of toxicity was associated with five SNPs in the ABCC2 and NR1I2 genes. Pharmacokinetic parameters were associated with four SNPs of the ABCB1, ABCC3, NR1I2, and GGH genes, and toxicity was shown to be associated with ABCC1 rs246219 and ABCC2 rs717620 using the univariate and BN-BMLA method. BN-BMLA analysis detected relevant effects on the AUC0-48 in the following SNPs: ABCB1 rs928256, ABCC3 rs4793665, and GGH rs3758149. In both univariate and multivariate analyses the SNPs ABCB1 rs928256, ABCC3 rs4793665, GGH rs3758149, and NR1I2 rs3814058 SNPs were relevant. These SNPs should be considered in future dose individualization during treatment.

Effect of single agent high-dose methotrexate-related acute kidney injury on length of hospitalization and relative dose intensity in adult patients with central nervous system lymphoma.

Purpose Grade ≥3 adverse effects prolong hospitalization and reduce chemotherapy dose intensity. The purpose of this study was to evaluate the rate and severity of high-dose methotrexate-related acute kidney injury and analyze its effect on hospital length of stay and relative chemotherapy dose intensity. Methods This was a retrospective cohort analysis. Patients receiving ≥1 dose of high-dose methotrexate were analyzed for acute kidney injury and length of stay. Patients receiving ≥6 cycles of induction therapy were included in the analysis of relative chemotherapy dose intensity. Chi squared analysis was used to determine the differences between dichotomous data; Student's t-test for parametric data and Mann-Whitney U test for non-parametric data for continuous variables. Statistical analyses were performed with IBM SPSS Statistics (version 21). Results Twenty-six patients and 194 treatment encounters were identified. Thirteen patients were evaluated for relative chemotherapy dose intensity. Grade ≥3 acute kidney injury occurred in four patients (15% of patients; 2% of encounters). There were no grade 5 adverse events. Mean length of stay for encounters with grade ≥3 acute kidney injury was almost three times longer than for those with ≤ grade 2 acute kidney injury (p = 0.041). Mean relative chemotherapy dose intensity was reduced approximately in half for patients experiencing grade ≥3 acute kidney injury (p < 0.01). The most common adverse events were hypokalemia and nausea. Proton pump inhibitors were the most frequently co-administered medications with the potential to affect high-dose methotrexate pharmacokinetics. Conclusion At our cancer program, the rate of grade ≥3 acute kidney injury with high-dose methotrexate is similar to that reported by others. Grade ≥3 acute kidney injury following high-dose methotrexate administration significantly prolonged length of stay and reduced relative chemotherapy dose intensity.

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

In infants aged less than 12months, there are few data on pharmacokinetics of high-dose methotrexate (MTX) for brain tumors at the dose of 8g/m(2). Consolidated knowledges are present only with the dose of 5g/m(2) in acute lymphoblastic leukemia. We collected data on 8 infants at the time of their first treatment with high-dose MTX, 8g/m(2), to evaluate the pharmacokinetic profile. All children had a dose adjustment with a weight-based prescription (1m(2)=30kg). The median age was 4.5months (range 0-9). The median weight was 5.63kg (range 3.12-9.0). The median steady-state MTX concentration at the end of 6-hr infusion was 486µM/L (range 227-790). The median systemic MTX clearance was 4.14L/h/m(2) (range 1.98-9.35). The median MTX concentration after 24h from the beginning of infusion was 3.29µM/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 4kg (p: 0.0179). Moreover, a systemic MTX clearance at the end of infusion minor than 3L/h/m(2) can predict a delayed elimination (p: 0.0179). Patients with altered elimination underwent rescue measures (leucovorin supplement and/or exchange transfusion). 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 4kg.

The pharmacokinetics of high-dose methotrexate in people living with HIV on antiretroviral therapy.

Purpose Clinical outcomes for lymphoma in people living with HIV (PLWH) are similar to those in the general public. However, a number of concerns remain including pharmacological interactions between cytotoxic chemotherapy and antiretroviral therapy (ARVs). Much attention has focussed on pharmacokinetic interactions attributable to effects on hepatic microsomal enzymes, but not on competition for the renal organic anion transport system. High-dose (3 g/m2) intravenous methotrexate (MTX) is part a of (R)-CODOX-M/IVAC chemotherapy regimen for HIV-associated Burkitt/Burkitt-like lymphoma (BL/BLL). We investigated MTX pharmacokinetics and evaluated the effects of renal function (eGFR), age and use of different classes of ARVs.MethodsForty-three PLWH treated with ARVs and (R)-CODOX-M/IVAC are included in the analysis. Plasma MTX concentration was measured (ARK TM MTX assay, VITROS® 5600) daily after administration until levels were <0.04/mmol/L. MTX elimination half-life was correlated with age, renal function and antiretroviral regimen.ResultsOne hundred and fifty timed plasma MTX levels were collected. The median MTX elimination half-life was 21.7 h (range 9.4–204.4). MTX elimination half-life was not influenced by age (p = 0.71), eGFR (p = 0.67) or use of non-nucleoside reverse transcriptase inhibitors (NNRTIs) or integrase inhibitors (p = 0.15). Similarly, different NRTI backbones did not affect MTX elimination kinetics (p = 0.68), despite the potential overlapping competition for active renal tubular transporters between MTX and tenofovir.ConclusionAlthough there is potential competition for active renal tubular transporters between MTX and tenofovir, no prolongation of MTX half-life was observed. These findings are reassuring to clinicians managing patients with dual diagnoses.

Population pharmacokinetics of high-dose methotrexate after intravenous administration in Chinese osteosarcoma patients from a single institution.

Background:High-dose methotrexate (HD-MTX) with folinic acid (leucovorin) rescue is the gold standard therapy in the treatment of osteosarcoma. The plasma concentration of MTX is closely related to efficacy and toxicity. There are large individual differences. Many authors have described the pharmacokinetic (PK) profile of MTX regarding osteosarcoma under a variety of circumstances. However, no data concerning Chinese osteosarcoma patient PKs using the nonlinear mixed effects models (NONMEM) have been previously reported. The goals of this study were to establish the population pharmacokinetics (PPK) of HD-MTX treatment in Chinese osteosarcoma patients, and to explore the influence of patient covariates and between-occasion variability on drug disposition.Methods:An intravenous HD-MTX solution (10 g/m2) was given 274 times to 148 osteosarcoma patients. MTX plasma concentrations were measured at 0, 6, 12, 24, 48 and 72 h after commencement of the infusion, and the fluorescence polarization immunoassay was used to determine MTX plasma concentrations. The PPK model and parameters were estimated using NONMEM software. The effects of fixed-effect factors were evaluated, and the final regression model was obtained.Results:The following population parameters were obtained using a two-compartment model: CL1 (clearance of central compartment):(CL1)i = CL1TV × [1- θCL1 −MTXNUM × MTXNUM]×[1-θCL1 −CrCI1 × (CrCl1 −1.89)]×eηCL1i (L/h). V1 (central volume):(V1)i = V1TV × eηV1i (L). CL2 (clearance of peripheral compartment):(CL2)i = CL2TV ×[1- θCL2 −BODYAREA × (bodyarea − 1.62)]×eηCL2i (L/h). V2(peripheral compartment):(V2)i = V2TV ×[1 − θV2−bodyarea × (bodyarea-1.62)]× eηV2i (L). The PPK parameters (RSD%) were CL1, V1, CL2 and V2 with values of 6.20 L/h (8.48%), 19.6 L (extremely small), 0.0172 L/h (50.9%) and 0.515 L (39.1%), respectively. Creatinine clearance and the number of methotrexate chemotherapy cycles before MTX infusion had a significant effect on the CL1, and body surface area had a significant effect on the CL2 and the V2 (P < 0. 01).Conclusions:A good fit was derived for the PPK. The model could be used to provide guidance for MTX treatment and reduce adverse effects.

SLCO1B1c. 521T>C gene polymorphisms are associated with high-dose methotrexate pharmacokinetics and clinical outcome of pediatric acute lymphoblastic leukemia

To provide guidance for the high-dose methotrexate (HD-MTX) treatment of pediatric acute lymphoblastic leukemia (ALL), and to understand the impact of SLCO1B1c.521T>C (rs4149056) variant on methotrexate (MTX) pharmacokinetics and clinical outcome in children with ALL. Eighty-two children with ALL in Division of Hematology of Wuhan Children's Hospital from January 2008 to February 2013 were enrolled. All patients were genotyped for rs4149056 single nucleotide polymorphism (SNP) into wild-type group (TT genotype) and variant group (TC/CC genotype). According to the ALL-BFM 2000 protocol, all patients received intravenous infusion of MTX every ten days at 3 to 5 g/m(2). Leucovorin rescue was performed after 36 hours of the MTX administration and its dose was adjusted according to the MTX plasma concentration at 48 hours. The concentrations of MTX and its metabolite at 24, 48 and 72 h were determined by high performance liquid chromatography with solid phase extraction. Population pharmacokinetic parameters were estimated by the NLME software. The pharmacokinetics, toxicity and leucovorin rescue was compared. The relapse rate within 5 years and event-free survival were followed up. Eighty-two pediatric patients were classified into two groups: variant group including 20 TC genotype carriers and one CC genotype carrier, wild-type group included 61 patients with TT genotype. Compared with wild-type group, plasma concentration of MTX at 48 and 72 h increased significantly [48 h: (1.00±1.41) vs.(0.34±0.17) µmol/L, t=2.131, P=0.046; 72 h: (0.31±0.26) vs.(0.08±0.04) µmol/L; t=3.995, P=0.001]. Area under the concentration time curve (AUC48-∝) of MTX significantly increased in variant group [(23.18±19.91) vs.(5.66±2.01) h·µmol/L] (t=4.025, P=0.001). Time above the MTX safety threshold (TC>0.1 µmol/L) increased significantly in variant group [(95.3±22.0) vs.(67.1±7.5) h, t=5.880, P<0.001]. Rescue dosage of leucovorin in variant group was higher than that in wild-type group [(312.7±287.8) vs.(140.6±27.5) mg/m2, t=2.614, P=0.017]. The children carrying rs4149056 C allele suffered from a higher frequency of serious adverse effect [gastrointestinal toxicity: 33% (7/21) vs. 5% (3/61);hepatic toxicity: 24% (5/21) vs. 2% (1/61)]. The difference was statistically significant (χ2=9.275, 8.289, all P<0.05). Hospital stay of variant group was significantly longer than that of wild-type [(4.95±1.43) vs. (4.05±0.22) d, t=2.881, P=0.009]. The relapse rate within 5 years of variant group and wild-type group were 9% (2/21) and 13% (8/61), respectively. There were no significant differences in the event-free survival between the two groups (χ2=0.001, P=0.971). The SLCO1B1 c.521T>C variant was an important determinant of MTX pharmacokinetics. An appropriate leucovorin dose raise in variant group was beneficial to reducing the serious toxicity and did not affect the long-term clinical outcome.

Fractional model for pharmacokinetics of high dose methotrexate in children with acute lymphoblastic leukaemia

The aim of this study is to promote a model based on the fractional differential calculus related to the pharmacokinetic individualization of high dose methotrexate treatment in children with acute lymphoblastic leukaemia, especially in high risk patients.We applied two-compartment fractional model on 8 selected cases with the largest number (4–19) of measured concentrations, among 43 pediatric patients received 24-h methotrexate 2–5g/m2 infusions. The plasma concentrations were determined by fluorescence polarization immunoassay. Our mathematical procedure, designed by combining Post’s and Newton’s method, was coded in Mathematica 8.0 and performed on Fujicu Celsius M470-2 PC.Experimental data show that most of the measured values of methotrexate were in decreasing order. However, in certain treatments local maximums were detected. On the other hand, integer order compartmental models do not give values which fit well with the observed data. By the use of our model, we obtained better results, since it gives more accurate behavior of the transmission, as well as the local maximums which were recognized in methotrexate monitoring. It follows from our method that an additional test with a small methotrexate dose can be suggested for the fractional system parameter identification and the prediction of a possible pattern with a full dose in the case of high risk patients.A special feature of the fractional model is that it can also recognize and better fit an observed non-monotonic behavior. A new parameter determination procedure can be successfully used.

Impact of ABCC2 polymorphisms on high-dose methotrexate pharmacokinetics in patients with lymphoid malignancy

Human multidrug resistance-related protein 2 (MRP2, encoded by ABCC2) is involved in the transport of anionic drugs such as methotrexate (MTX). We prospectively investigated the influence of four common ABCC2 genetic variants (rs717620, rs2273697, rs8187694 and rs8187710) on MTX pharmacokinetics parameters. MTX concentrations were monitored in 50 patients with lymphoid malignancy (27 males; mean age: 53±17 years) receiving high-dose MTX (5.13±1.88 g m(-)(2) in a 4-h perfusion). The population pharmacokinetics modelling showed that ABCC2 -24T allele (rs717620) had a combined influence on both MTX elimination and distribution. The MTX clearance and distribution volume were significantly higher in carriers of at least one copy of the -24T allele as compared with noncarriers: 8.6±2.2 vs 6.7± 2.5 l h(-1), P<0.01 and 30.7±7.7 vs 22.1±8.8 l, P<0.001, respectively. Consequently, -24T allele carriers were more prone to reach MTX nontoxic levels, 48 h after administration.

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).

Population pharmacokinetics of high-dose methotrexate in Japanese adult patients with malignancies: a concurrent analysis of the serum and urine concentration data

This study aimed to develop a population pharmacokinetic model for high-dose methotrexate (MTX), specifically focusing on the drug urinary excretion process. Three hundred and forty-eight serum samples and 416 urine samples from 51 Japanese adult patients with malignancies were concurrently fitted into a multi-compartment model using the nonmem program. In the final model, creatinine clearance (CCR, mL/min) and the MTX dose (DOSE10G; 0 when <10 g, 1 when >or=10 g) were the most significant factors that affected the renal clearance (CL(r)) and non-renal clearance (CL(nr)), respectively: CL(r)(L/h) = 5.57 x (CCR/80.0)(0.112), V(1)(L) = 26.9, Q(L/h) = 0.0778, V(2)(L) = 2.27, CL(nr)(L/h) = 0.567 x 3.39(DOSE10G), where V(1) and V(2) are the volumes of distribution of the central and peripheral compartments, respectively, and Q is the inter-compartmental (central-peripheral) clearance. For another nine patients, the model enabled a satisfactory Bayesian estimation using two time-point serum concentrations. The newly developed population pharmacokinetic model should improve the quality of serum concentration monitoring of high-dose MTX to predict and control toxic events.

High-dose methotrexate in pediatric acute lymphoblastic leukemia: Impact of ABCC2 polymorphisms on plasma concentrations

The adenosine triphosphate-binding cassette (ABC) class transporter ABCC2 (MRP2 [multidrug resistance related protein 2] or cMOAT [canalicular multispecific organic anion transporter]) is involved in the cellular outward transport and elimination of methotrexate. We hypothesized that common genetic variations may contribute to the variability of high-dose methotrexate pharmacokinetics. Polymorphisms in all 32 exons of the ABCC2 gene were analyzed in a reference group of 59 healthy white subjects by polymerase chain reaction, single-strand conformation polymorphism, and sequencing. Subsequently, we assessed the association of polymorphisms with the methotrexate plasma concentrations in 44 pediatric patients with acute lymphoblastic leukemia (ALL) (29 male and 15 female patients; mean age, 6.8+/-4.8 years). Patients received 4 cycles of 5000 mg/m2 body surface area according to the ALL-Berlin-Frankfurt-Muenster (BFM) 95 or ALL-BFM 2000 protocol. In the reference group we detected 8 frequent single-nucleotide polymorphisms. Five of these were in complete linkage disequilibrium. Overall, 5 new polymorphisms are described. The genotype distribution of the patient cohort was not significantly different from the reference collective. The mean plasma methotrexate area under the curve from 36 to 48 hours after the start of the infusion was significantly 2-fold higher in female patients carrying at least 1 -24T allele as compared with all other patients (14.2+/-12.8 h.micromol/L versus 6.9+/-4.2 h.micromol/L, P<.001). The risk to have 2 or more cycles necessitating an intensification of folinate rescue was 9-fold (95% confidence interval, 1.8- to 44-fold) in female patients carrying at least 1 T allele (P=.0067). The data suggest a hitherto unknown gender-specific impact of the -24C>T ABCC2 gene polymorphism on high-dose methotrexate pharmacokinetics. Whereas a nonfunctional MRP2 variant has been described in a patient with severe impairment of methotrexate excretion, our study is the first to suggest that a frequent ABCC2 polymorphism contributes to variability of methotrexate kinetics.

Implication of clinical and paraclinical covariates in the pharmacokinetics of high dose MTX (HD-MTX) in patients with osteosarcoma

12022 Background: Methotrexate (MTX) is a mainstay in the treatment of ostosarcoma. MTX is characterized by a narrow therapeutic window, combined with high intra- and inter-patient variabilities. In our institute, safe administration of high dose MTX is ensured by using bayesian, adaptive dosing with feedback strategy. In patients with osteosarcoma, up to 20g/patient MTX is administred following an 8h infusion. From the 6th hour, the dose is tailored according to individual pharmacokinetics parameters, determined in real-time from two early sampling times (T3.5, T4.5) and a reference population. This method enables accurate adjustment of most patients around a target Cend of 10−3 M/L. Still, 15–20% of the patients show reduced MTX elimination rate, thus leading to an overlasting hospitalization time with folate rescue required to prevent severe toxicities. In this work, we studied the relevance of clinical or pareaclinical covariates likely to be associated with the MTX clearance so as to identify patients at risk of impaired elimination with subsequent increase in iatrogeny. Methods: This retrospective study was performed on 49 patients treated with HD-MTX. Population PK parameters were computed using Apis and NonMem routines. The second objective was to predict for how long MTX plasma concentration would remain above 0.2 μM/L, the threshold associated with toxicity, upper which folinic acid is required. Finally, simplified sampling strategy for folate rescue protocol was developed. Results: two covariates (creatinemia and ALAT) have been identified as being correlated with MTX clearance. Besides, simulation of the 0.2μM/L threshold reaching showed that it was possible to predict accurately the time most patients can leave the hospital safely. This, would have led to reduce the hospitalization stay by at least one day in 25% of the patients, thus optimizing their life quality while being cost-effective. Conclusions: in this study, we showed that high dose MTX can be administred safely using an adaptive dosing with drug monitoring strategy. Besides, modelling of MTX PK parameters leads to an accurate estimation of the elimination pattern of this drug, thus enabling a planification of the time patients leave the hospital. No significant financial relationships to disclose.

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

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. 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. 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. 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.

High dose methotrexate in adult patients with osteosarcoma: Clinical and pharmacokinetic results

High dose methotrexate (HDMTX) with folinic acid rescue is widely used to treat osteosarcoma, which predominantly afflicts children; the study investigated HDMTX pharmacokinetics (pk) in adult subjects in neoadjuvant/adjuvant settings. Twenty five patients with advanced osteosarcoma (11 females – 14 males, median age 26.0 years) were treated by 12 g/m2 HDMTX 4 hour iv infusion (64 total courses, range 1 – 7 courses). Pk was determined by non-compartmental analysis and population pk modeling. Median (range) bioavailability pk parameters were: Cmax (maximum MTX concentration) 1149.5 µM (692 – 2 200), AUCtot (total area under curve) 6 955.1 µmol*h/l (3 477 – 12 681). Cmax>1 000 µM gave increased histological responses (p < 0.05). Six covariates (height-weight-hemoglobin-AST-ALT-creatinine) were found to influence MTX volume of distribution (V) and elimination rate constant (Kel). Toxicity was mild: only two reversible G4 events were observed, related to AUCtot >12 000 µmol*h/l (p < 0.001). HDMTX pk and interpatient variability in adults are comparable to those in children. No correlation between Cmax/AUCtot and subject age/sex was found, even in the population pk model. The excretion mechanism is not affected by sex/age differences. HDMTX can safely be administered to adults: as in younger patients, a good clinical response can be predicted by Cmax, while severe toxicity depends on highest AUCtot values.

ACRAL ERYTHEMA CAUSED BY HIGH-DOSE METHOTREXATE THERAPY IN PATIENTS WITH OSTEOGENIC SARCOMA

High doses of methotrexate (MTX) have been incorporated in the treatment of osteogenic sarcoma since the 1970s. Unfortunately, high-dose MTX (HD-MTX) can cause untoward side effects that may complicate the proper management of these patients. Two cases of MTX-induced acral erythema are described and the possible implications of this complication are reviewed, with a discussion of the pathophysiology of this adverse effect. Two young female patients suffering from osteogenic sarcoma received HD-MTX (12 g/m2) according to the chemotherapeutic protocol. A 17-year-old patient with osteogenic sarcoma of the head developed painful acral erythema of her palms and soles after the fifth dose of MTX, and a 22-year-old patient with osteosarcoma of the femur developed severe acral erythema after the sixth dose. The severity of the reaction was significant enough to cancel further treatment with HD-MTX in both patients. All symptoms resolved without sequellae several weeks later in both cases. Acral erythema may pose a significant albeit transient phenomenon adversely influencing chemotherapy in patients suffering from osteosarcoma and treated with HD-MTX. The pathophysiology of this side effect is not completely understood and further investigation of the pharmacokinetics of HD-MTX in this patient population is needed.