Methotrexate pharmacokinetics in childhood ... - Wiley Online Library

Journal of Clinical Pharmacy and Therapeutics (2011) 36, 237–245

doi:10.1111/j.1365-2710.2010.01179.x

PHARMACOKINETICS

Methotrexate pharmacokinetics in childhood acute lymphoblastic leukaemia: a prognostic value ? N. Martelli* PharmD , O. Mathieu* PharmD , G. Margueritte MD , M. C. Bozonnat BSC , J.-P. Daure` s MD PhD , F. Bressolle§ PharmD PhD , D. Hillaire-Buys* MD PhD and H. Peyrie` re* PharmD PhD *Medical Pharmacology and Toxicology Department, Lapeyronie Hospital, University Hospital of Montpellier, Department of Pediatric Oncology, Arnaud de Villeneuve Hospital, University Hospital of Montpellier, Department of Statistics and Epidemiology, University Institute for Clinical Research, Biostatistic Laboratory, University Hospital of Montpellier, and §Clinical Pharmacokinetic Laboratory, Faculty of Pharmacy, University of Montpellier 1, Montpellier, France SUMMARY

What is known and Objective: In industrialized countries, acute lymphoblastic leukaemia (ALL) is the most frequent cancer in children aged less than 15 years. High-dose methotrexate is a common component of many chemotherapeutic protocols for childhood with ALL. Our objective was to retrospectively evaluate the pharmacokinetics and plasma levels of high-dose methotrexate as it relates to event-free survival (EFS) in children with ALL. Methods: Relapsed patients and subjects in EFS were compared for MTX serum concentrations 24, 36, 48 and 72 h after the start of 24 h infusion. Clearance (Cl), area under the curve (AUC) and volume of distribution (Vd) of the drug were estimated by the NONMEM computer program and also compared between both groups. Results and Discussion: Among 69 children included, 54 (78Æ3%) were still in EFS, whereas 15 (21Æ7%) relapsed. The difference between relapsed and EFS patients for the pharmacokinetic parameters studied was not significant. On the contrary, the cohort studied was representative and known prognostic factors for relapse in ALL were significantly associated with relapse.

Received 10 July 2009, Accepted 16 March 2009 Correspondence: He´le`ne Peyrie`re, Service de Pharmacologie Me´dicale et Toxicologie, Hoˆpital Lapeyronie, 371 avenue du doyen Gaston Giraud, 34295 Montpellier Cedex 5, France. Tel.: +33 46 7336753; fax: +33 46 7336751; e-mail: [email protected] 2010 Blackwell Publishing Ltd

What is new and Conclusion: Serum concentrations and pharmacokinetic parameters of MTX are not associated with outcome in ALL. Prognoses based on single-drug pharmacokinetic estimates within a complex multiple-agent protocol appear to be unreliable. However, therapeutic drug monitoring of high-dose methotrexate remains a useful tool for early detection of impaired elimination and for avoiding systemic toxicity. Keywords: acute lymphobastic leukemia, children, methotrexate, pharmacokinetics, relapse

INTRODUCTION

In France, as in other industrialized countries, acute lymphoblastic leukaemia (ALL) is the most frequent cancer in children aged less than 15 years. About 5000 children in the US and 400 in France are diagnosed with ALL each year (1). High-dose methotrexate (HDMTX, i.e., higher than 1 g ⁄ m2), is a common component of many chemotherapeutic protocols for childhood with ALL. As the first trial of HDMTX in children with ALL, the survival rate of patients has gradually increased (2). After MTX infusion, monitoring of MTX plasma levels allows the rapid detection of delayed MTX elimination and the prevention of MTX toxicity (3). MTX plasma level is monitored from 24 h after the start of MTX infusion until the concentration falls below 0Æ2 lM. Although the relationship between MTX plasma level and toxicity is well-documented, the relationship between systemic exposure to 237

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HDMTX and clinical response in childhood with ALL is unclear and few studies have addressed this issue (4). One study concluded that patients with a median 24-hour plasma MTX level less than 16 lM had a higher probability of relapse (5). A correlation between MTX pharmacokinetics and the risk of relapse in patients receiving 6–8 g ⁄ m2 MTX has also been reported (6). However, in patients receiving 5 g ⁄ m2, systemic MTX clearance (ClMTX) was not related to disease outcome in a way that can be exploited for individual prognosis (7). A prospective study, published 10 years later, indicated that adjusting the MTX dose to account for the patient’s ability to clear the drug could improve the outcome in children with B-ALL (8). Our objective was to study the relationship between MTX exposure level MTX (plasma levels and MTX area under the curve, total clearance and volume of distribution) with event-free survival (EFS) in children with ALL. MATERIALS AND METHODS

We undertook a retrospective study of children with ALL, hospitalized in the Arnaud de Villeneuve Hospital (Montpellier, France) during the 1996–2004 period, treated with HDMTX infusions. Patients and protocols Sixty-nine children with ALL were enrolled, at the time of diagnosis, in the European Organization for Research and Treatment of Cancer (EORTC) protocol 58881 (9), or in the EORTC protocol 58951 (ongoing evaluation). These protocols were approved by the Ethics Committee of the Montpellier University hospital. Children were treated in the Department of Paediatric Onco-hematology of the Arnaud de Villeneuve Hospital (Montpellier, France) between November 1996 and November 2004. Briefly, the EORTC protocols consisted of four phases: induction (including a prephase with corticosteroid therapy), consolidation, interval and maintenance therapies. Children with a low or a standard risk received four HDMTX courses while those with a high risk received nine HDMTX courses. Urinary alkalinization through intravenous sodium bicarbonate administration and hydration were performed during MTX adminis-

tration and urine pH was monitored closely. MTX was administered as a 24-h infusion of 5 g ⁄ m2. One-tenth of the dose (500 mg ⁄ m2) was given over the first hour and the remaining dose (4500 mg ⁄ m2) was given over the following 23 h at a constant rate. Triple intrathecal therapy (methotrexate, cytarabine, prednisolone) was administered as central nervous system prophylactic treatment, at the end of each MTX infusion. Leucovorin (12 mg ⁄ m2 every 6 h) was initiated 36 h after start of the MTX infusion and continued until MTX concentrations were below 0Æ2 lM. The following patient characteristics were collected: age, gender, weight, height, serum creatinine level, leukocyte count, immunophenotype of leukaemic cells, clinical signs at diagnosis, corticoid resistance, induction therapy resistance and clinical outcome. The Du Bois’s formula was used to estimate body surface area (BSA) from height and weight (10). Creatinine clearance (ClCR) was estimated using Schwartz’s formula for children less than 12 years old and Cockcroft and Gault’s formula for the older patients (11, 12). Measurement of MTX concentrations As part of the routine patient management, blood samples were collected from all patients at the following times: 24, 36, 48 and 72 h after the beginning of the infusion. If MTX plasma levels were higher than 0Æ2 lM 72 h after the start of infusion, additional blood samples were drawn. After collection, blood samples were immediately centrifuged at 2000 g for 10 min, and MTX plasma levels were measured the same day in order to adjust leucovorin administration. The database consisted of four to eight MTX cycles per patient. Plasma MTX concentrations were measured by fluorescence polarization immunoassay (MTXTDX, Abbott Laboratories, Rungis, France). The limit of quantification for the assay was 0Æ01 lM. Pharmacokinetic analysis A methodology to estimate individual MTX pharmacokinetic parameters, from a limited sampling strategy in patients with ALL (age ranging from 2 to 16 years), has previously been developed (13). The predictive performances of the Bayesian procedure were validated using an independent

2010 Blackwell Publishing Ltd, Journal of Clinical Pharmacy and Therapeutics, 36, 237–245

Methotrexate pharmacokinetics in childhood ALL

group of patients. Population pharmacokinetic analysis was performed using the NONMEM computer program (Version 5.1, ICON Development solutions, San Francisco, CA, USA) through the Visual–NM graphical interface. An open twocompartment pharmacokinetic model with zeroorder input rate was used to describe the pharmacokinetics of MTX. The inter-occasion variability was taken into account in the model. The interindividual variability in the initial volume of distribution was partially explained by the fact that this parameter was weight-dependent. The population approach developed previously enabled the estimation of individual MTX pharmacokinetic parameters with good accuracy and without bias from two sampling times taken 24 and 48 h after the beginning of infusion (13). Thus, in the present study, individual pharmacokinetic parameters [total plasma clearance (Cl, mL ⁄ min ⁄ m2) and volume of distribution (Vd, l ⁄ m2)] were estimated using a Bayesian methodology and MTX concentrations at 24 and 48 h. Clearance and volume of distribution were reported in mL ⁄ min ⁄ m2 and in l ⁄ m2 respectively to improve the comparison between subjects. These calculations were possible because body area surface is a weight-dependent parameter such as the volume of distribution. From the resulting individualized parameter values, the elimination half-life (t1 ⁄ 2elim) and the area under the plasma concentration–time curve (AUC) were estimated. Statistical calculations Acute lymphoblastic leukaemia prognostic factors were assessed for the 69 enrolled patients. Tested covariates were age, gender, white cell blood count, ALL lineage and treatment response after prephase and induction therapies. Event free survival (EFS) was defined as the period lasting from the date of diagnosis to the date of the first observation of progressive disease. Survival data was updated on July 01 2007. The probability of EFS was estimated by the Kaplan–Meier method. Associations between putative prognostic variables and EFS were tested using a Cox proportional hazard model. The selection of variables to be tested in the Cox model was made using the results of univariate analyses, and variables reaching at least a P level less than 5% with the log-rank test were

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included. The stepwise procedure was used to perform the multivariate regression Cox model. For each variable, the proportional hazard assumption was tested graphically and statistically using time-dependent variables. Mean MTX concentrations at H24, H36, H48 and H72 from all courses were measured for each patient. Moreover, for each patient, we collected the highest MTX plasma level at H24 (MTX CH24 MAX) during the first four chemotherapy courses; mean and median values were then calculated for all patients. The median value of the MTX CH24 MAX was used as the statistical cut-off to assemble the two groups for comparison using the log-rank test. Finally, the influence of ClMTX, AUCMTX and VdMTX, estimated using a population approach during the first four courses, on EFS was assessed. We used Kaplan–Meier method to estimate EFS probabilities. Median values of each pharmacokinetic parameter were used as the statistical calculation cut-off. A P level less than 0Æ05 was considered as significant. The SAS software packages (8th edition, SAS Institute Inc., Cary, NC, USA) were used.

RESULTS

Patient characteristics at the time of diagnosis of ALL Sixty-nine patients [36 boys (52Æ2%)] received HDMTX according to the EORTC protocols 58951 (57 patients) and 58881 (12 patients). Among all included patients, 23 (33Æ3%) had a hyperleukocytosis over 50 000 ⁄ mm3 and 13 (18Æ8%) over 100 000 ⁄ mm3. Fifty-five patients (79Æ7%) suffered from B-cell ALL, 11 (15Æ9%) from T-cell ALL and 3 (4Æ4%) from biphenotypic ALL. Among the 57 patients included in the EORTC protocol 58951, 4 patients were classified as very low risk (VLR), 28 as average risk 1 (AR1), 7 as average risk 2 (AR2) and 18 as very high risk (VHR) based on blast count, immunophenotype of leukaemic cells and clinical signs. Seventeen patients (24Æ6%) showed a corticoid resistance after the prephase and 12 (17Æ4%) were resistant to the induction therapy. Outcome Of the 69 patients included in the study, with a mean follow-up length of 6Æ6 years (range


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Table 1. Patient characteristics at diagnosis

At diagnosis Mean age, years (range) Sex Female, % (no.) Male, % (no.) Mean weight, kg (range) Mean height, cm (range) Mean BSA, m2 (range) Mean ClCR, mL ⁄ min (range) EORTC 58951 Risk group, % (no.) VLR, % (no.) AR1, % (no.) AR2, % (no.) VHR, % (no.)

Total (n = 69) 6Æ7 (1–15) 47Æ8 52Æ2 29Æ1 122Æ9 0Æ98 152Æ4 82Æ6 7 49Æ1 12Æ3 31Æ6

(33) (36) (10–80) (74–179) (0Æ47–1Æ87) (76Æ3–247) (57) (4) (28) (7) (18)

Patients in EFS (n = 54)

Relapsed patients (n = 15)

6Æ0 (1–15) 50 50 26Æ8 119Æ4 0Æ93 152Æ4 87 8Æ5 55Æ3 12Æ8 23Æ4

9Æ3 (1–14)

(27) (27) (10–78) (77–179) (0Æ48–1Æ87) (70–245) (47) (4) (26) (6) (11)

40 60 37Æ4 135Æ8 1Æ17 152Æ5 66Æ7 0 20 10 70

(6) (9) (10–80) (74–168) (0Æ47–1Æ87) (72–267) (10) (0) (2) (1) (7)

BSA, body surface area; ClCR, creatinine clearance; EFS, event-free survival; VLR, very low risk; AR1, average risk 1; AR2, average risk 2; VHR, very high risk.

4Æ4–10Æ6 years) from diagnosis, 54 patients (78Æ3%) were still in EFS and 15 (21Æ7%) relapsed (Table 1). The time from diagnosis to disease recurrence in the relapsed group ranged from 0Æ8 to 7Æ8 years (mean ± SD, 2Æ6 ± 1Æ8). Twelve children had a very early relapse (100 000 ⁄ mm3 5

1Æ35–14 2Æ5–29Æ8 1Æ33–19

0Æ0007 0Æ0008 0Æ009

After prephase and induction therapies. A corticoid resistance during the prephase was more frequent in patients with relapse than in EFS patients (Plog rank = 0Æ0007, Table 4). In addition, a resistance during the induction therapy was associated with a higher risk for relapse (Plog rank = 0Æ04, Table 3). Data are reported in Fig. 1a, b.

Event free survival according to corticoresistance

(a) 1

Plog rank

88 (78–99) 93 (85–1)

0Æ44

95 (89–1) 84 (69–98)

0Æ0025

0.9 0.8 0.7 0.6 0.5 0.4

CR CS

0.3 0.2 0.1 0

0

2

4

6

8

10

12

Years since diagnosis

100 (100–100) 73 (55–91) 98 (95–100) 58 (30–86)

0Æ0024 Event free survival according to chemoresistance

(b)

0Æ01

66 (13–100) 72 (46–99) 96 (91–1)

0Æ01

76 (56–96) 96 (90–1)

0Æ0007

83 (62–1) 92 (86–99)

0Æ04

Probabilty of free survival

Gender Male Female Age At least 9 years old Older than 9 years White cell blood count At least 50,000 ⁄ mm3 Higher than 50,000 ⁄ mm3 White cell blood count At least 100 000 ⁄ mm3 Higher than 100,000 ⁄ mm3 Type of ALL Biphenotypic T-cell ALL B-cell ALL Corticoid resistance Yes No Induction therapy resistance Yes No Protocol EORTC 58881 AR1 AR2 VHR VLR

Hazard 95% Confidence ratio Interval P-value


Event-free survival Probability percent (95% confidence interval)

241

1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

ITR ITS

0

83 100 85 83 100

(62–100) (100–100) (59–100) (66–100) (100–100)

0Æ03

2

4

6

8

10

12


Fig. 1. (a) Kaplan–Meier curves of event-free survival among the 69 patients included in the study between CR and CS patients (CR: patients with a corticoid resistance after the prephase; CS: patients with a corticoid sensibility after the prephase). (Plog rank = 0Æ0007). (b) Kaplan– Meier estimates of event-free survival among the 69 patients enrolled in the study between ITR and ITS patients (ITR, patients with an induction therapy resistance; ITS, patients with an induction therapy sensibility) (Plog rank = 0Æ04).


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N. Martelli et al. Table 5. Event-free survival probability according to methotrexate parameters


Event free survival according to protocol 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

2

4

6

8

10

12


Fig. 2. Kaplan–Meier curves of event-free survival according to the risk groups of the 57 patients included in the EORTC 58951 protocol (Plogrank = 0Æ03).

Risk groups. Rate and early relapse were strongly associated with the risk groups defined by the EORTC protocol 58951 (n = 57). The risk of relapse was significantly higher in the poor prognosis groups (VHR ⁄ AR2, Plog rank = 0Æ03). For these patients, the risk of relapse was 9-fold that of children in the VLR ⁄ AR1 group (P = 0Æ006). According to the risk group, the cumulative probability of EFS in the 57 patients included in the EORTC 58951 protocol was reported in Fig. 2. Influence of methotrexate plasma levels. There was no significant relationship between MTX plasma levels and EFS of patients at 2 years. Moreover, there was no significant difference in mean MTX CH24 MAX values between patients in EFS and relapsed patients (Plog rank = 0Æ39). MTX CH24 MAX were also compared between relapsed patients and patients in EFS in the different risk groups, and no significant difference was found (Table 5). Influence of methotrexate estimated pharmacokinetic parameters. The influence of MTX pharmacokinetic parameters, estimated during the first four chemotherapy courses (276 courses), on the EFS was assessed and the difference was not significative (Table 5). Safety and tolerability Among our studied population, 83 adverse-effects (ADEs) related to MTX were observed in 44 ⁄ 69 patients (63Æ8%). Some patients presented more than one adverse effect. Main ADEs reported were digestive disorders (31Æ3%), cutaneous–mucous disorders (25Æ3%, especially mucositis), haemato-

2 years

Even-free survival Probability percent (95% confidence Plog interval) rank

EORTC 58881 EORTC 58951 AR1 EORTC 58951 AR2 EORTC 58951 VHR EORTC 58951 VLR 0

at

MTX total dose Less than 20 g Higher than 20 g CH24 MAX Higher than 92 lM Less than 92 lM VdMTX Higher than 100 L ⁄ m2 Less than 100 L ⁄ m2 AUCMTX Higher than 1586 lM · h Less than 1586 lM · h ClMTX Higher than 118 mL ⁄ min ⁄ m2 Less than 118 mL ⁄ min ⁄ m2

97 (91–1) 85 (73–97)

0Æ013

87 (76–99) 94 (86–1)

0Æ64

85 (73–97) 97 (91–100)

0Æ63

88 (78–99) 94 (86–1)

0Æ90

91 (82–1) 90 (81–1)

0Æ80

Medians of each pharmacokinetic parameter means were used as the statistical calculation cut-off.

logical abnormalities (20Æ5%), liver function test disturbances (6%), and neurological disturbances (3Æ6%). Moreover, 14 patients (20Æ3%) presented at least 1 MTX plasma level higher than 0Æ2 lM 72 h after the start of MTX infusion. Among these 14 patients, only 2 systemic toxicities (1 neurotoxicity and 1 renal failure) were related to this delayed MTX elimination. DISCUSSION

MTX plasma levels or MTX pharmacokinetic parameters were not associated with outcome in our study of children with ALL. By referring to the last publication of the American Cancer Society about trends in childhood cancer, our cohort appears to be a representative childhood ALL population, especially in terms of age and gender distributions (1). We found a median MTXH24 of 56 lM (range 10–380 lM) and a median MTXH48 of 0Æ38 lM (range 0Æ03–19Æ6). These values are similar to those reported elsewhere, where a large variability in plasma


Methotrexate pharmacokinetics in childhood ALL

levels of MTX measured at H24 or H48, ie 26–470 lM and 0Æ1–6Æ8 lM respectively, were found (14). In our study, the pharmacokinetics of methotrexate were estimated using population pharmacokinetic modelling, previously used in a study of a cohort of patients similar to ours (13). Several studies on MTX pharmacokinetics in children are available in the literature and the clearance (118 mL ⁄ min ⁄ m2), and terminal half-life (12Æ6 h) found in our study are comparable to those reported in studies with comparable MTX administration protocols (24 h infusion of 5 g ⁄ m2) (13, 15, 16). In our study, 21Æ7% of patients relapsed, a rate similar to that observed in childhood ALL, elsewhere (17). Moreover, among the major initial factors determining the risk of relapse (WBC, age, gender, cytogenetic and immunphenotypic subtypes), we found that age higher than 9 years, high WBC (>50 000 ⁄ mm3 and >100 000 ⁄ mm3), T-cell ALL, and late achievement of complete remission were significantly associated with relapse (9, 18). Gender has long been recognized as a significant prognostic factor in childhood ALL, with boys having a worse prognosis than girls. This difference is partially attributable to a higher incidence of T-cell ALL in boys (19). In our population, we did not find gender difference, although out of 11 (15Æ9%) children suffering from T-cell ALL, 8 were boys. With regard to the risk groups as defined in EORTC 58951 protocol, in our study, relapse rate was associated with the initial risk level. Indeed, 18 patients were classified as very high risk (VHR), and among the 10 VHR patients who relapsed, 7 were classified as higher risk. Whatever the protocol, all patients who died (n = 12) were from the

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relapse group, and 6 of them (50%) were considered to be at high risk of relapse. Patients in EFS group can also change depending on the clinical outcome, thus influencing the results. In our study, such influence was unlikely, because of the long period of follow-up (an average of 6Æ6 years), and the consequential minimization of the probability of new relapses. Nevertheless, the two treatment protocols (protocol EORTC 58881 and protocol EORTC 58951) were not exactly the same and could have introduced a bias in our study. Actually, protocol EORTC 58951 replaced protocol EORTC 58881, which studied a new risk group with VHR patients. For this group, the treatment has been partly modified and intensified. Few studies have aimed to investigate the relationship between MTX plasma levels and ⁄ or pharmacokinetic parameters (AUCMTX, ClMTX, and VdMTX) and clinical outcome. In one study, the authors found that patients with median steadystate MTX plasma levels below 16 lM had a lower probability of remaining in remission than patients with levels of 16 lM or more (5). In our study, no such relationship was found between MTX plasma levels (at different sampling times) and patient clinical outcome. The median MTX plasma level at the end of infusion (H24) was 56 lM, and showed high interpatient variability (10–380 lM). A steadystate level (defined as level at 24 h after the start of infusion) at 16 lM below which the risk of relapse is increased, has been proposed (5). However, in that study, intermediate MTX dose (1 g ⁄ m2 over 24 h) was administered, whereas in our study, all patients received strictly the same dose of MTX (5 g ⁄ m2) (Table 6). Thus, the high variability observed in MTX plasma levels in our study cannot

Table 6. Published studies on the relationship between serum MTX concentrations and relapse rate

Reference

Year

Number of patients

Evans et al. (5) Borsi et al. (6) Seidel et al. (7) Evans et al. (8) Our study

1987 1987 1997 1998 2008

108 58 42 188 69

Mean age of patients, years (range)

MTX dose ⁄ course, g ⁄ m2

MTX clearance, mL ⁄ min ⁄ m2

Relationship between MTX concentrations and relapse rate

Statistical test used

4Æ2 6Æ9 5Æ7 ? 6Æ7

1 6–8 6–8 1Æ5 5

78Æ4 61Æ8 70Æ7 103 118

Yes Yes No Yes No

Kaplan–Meier t Student Kaplan–Meier Kaplan–Meier Kaplan–Meier

(5 m–17) (1–19) (0Æ8–13Æ1) (4Æ3 m–18Æ8 years) (1–15)


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be explained by a bias in patient enrolment. Moreover, in our study, only 10 patients had methotrexate CH24 levels below 20 lM, among whom, 3 relapsed. Other studies have investigated the influence of MTX pharmacokinetic parameters on the relapse rate. Relapsed children were reported to have significantly lower steady-state MTX concentrations (faster systemic clearance) than those who remained in continuous complete remission, whatever the administered dose (6). These authors used a Student’s t-test to compare the two groups of patients (relapsed and EFS). This test is not robust enough for such an analysis. Seidel et al., also found a relationship between MTX clearance and prognosis when using a Student’s t-test, but they concluded that patients with higher median ClMTX values did not have a significantly poorer outcome when using a more appropriate statistical analysis method, such as the Kaplan–Meier procedure (7). The intra-individual course-to-course variability of MTX pharmacokinetics suggests that first MTX courses may not be predictive for the pharmacokinetics in subsequent cycles. Given the high interindividual variability, MTX monitoring clearly cannot be used to predict patients’ clinical outcomes. Approximately, 80% of children with ALL are cured (18). Adverse drug reaction is one of the main reasons for interruption or discontinuation of MTX therapy, which may increase the risk of relapse. Identifying genetic polymorphisms in folate-metabolizing enzymes may modify the therapeutic effectiveness and toxicity of MTX, and may allow a prospective identification of patients with suboptimal drug responses (20). There is also interest in human reduced folate carrier (RFC) gene expression as a prognostic factor of outcome in pediatric ALL (21). It has been shown that children with the genetic polymorphism G80A of RFC had a higher risk for relapse (P = 0Æ03), and higher MTX plasma levels (P = 0Æ02) (22). However, these authors did not observe an association between MTX levels and disease outcome. Recently, Costea et al., analysed the relationship between genotypes and the frequency of hematologic and liver toxicity in pediatric ALL patients treated with MTX (23). They showed that homozygous individuals for cyclin D1 (CCND1) A870 allele and carriers of at least one methylenetetrahydrofolate reductase

(MTHFR) T677 variant, genes showed reduced EFS, and had significantly lower hematologic and liver toxicities. In our study, HDMTX was well tolerated by the majority of patients. Only 14 patients (20Æ3%) experienced MTX plasma levels higher than 0Æ2 lM 72 h after the start of MTX infusion (corresponding to a delayed elimination) and two of them suffered from toxicities. In these patients, additional measures were required, with the continuation of folinic acid rescue. In the case of neurotoxicityinduced by HDMTX, aminophylline was successfully administered and led to a rapid reversal (24). In this case, MTX plasma level measured at the end of 24 h infusion, during the cycle with neurotoxicity was higher (94 lM) than those found during the other cycles (mean of 41Æ2 ± 7 lM). Thus, MTX plasma level at the end of the infusion could be a predictive factor for toxicity. Therefore, while our study does not highlight the benefits of therapeutic drug monitoring in terms of EFS, the benefits of this type of intervention in terms of drug safety seems obvious. None of our patients stopped MTX therapy because of toxicity. Moreover, in regard the two patients with neurotoxicity and acute renal failure, MTX treatment was reintroduced without recurrence of toxicity or delayed elimination. Potential limitations of our study include the retrospective analysis and the relatively small sample size. The protocols used to treat all our patients have changed with stratification according to risk factors and the intensification of chemotherapy in patients at high risk. Moreover, the management of ALL is based on the use of concomitant or sequential chemotherapy with drugs, which all have their useful place. Our study has estimated only one component of the management of this disease, and could therefore be biased. What is new and conclusion Serum concentrations and pharmacokinetic parameters of MTX were not associated with outcome in children with ALL. Prognoses based on single-drug pharmacokinetic estimates within a complex multiple-agent protocol appear to be unreliable. However, therapeutic drug monitoring of high-dose methotrexate remains an indispensable tool for early detection of a delayed elimination and avoid systemic toxicities.


Methotrexate pharmacokinetics in childhood ALL CONFLICT OF INTEREST

The authors have no conflicts in interest to declare. 14. REFERENCES 1. Linabery AM, Ross JA (2008) Trends in childhood cancer incidence in the U.S. (1992-2004). Cancer, 112, 416–432. 2. Goubin A, Auclerc MF, Auvrignon A et al. (2006) Survival in France after childhood acute leukaemia and non-Hodgkin’s lymphoma (1990-2000). European Journal of Cancer, 42, 534–541. 3. Sterba J, Valik D, Bajciova V et al. (2005) High-dose methotrexate and ⁄ or leucovorin rescue for the treatment of children with lymphoblastic malignancies: do we really know why, when and how? Neoplasma, 52, 456–463. 4. Evans WE, Pratt CB, Taylor RH, Barker LF, Crom WR (1979) Pharmacokinetic monitoring of high-dose methotrexate. Early recognition of high-risk patients. Cancer Chemotherapy and Pharmacology, 3, 161–166. 5. Evans WE, Abromowitch M, Crom WR et al. (1987) Clinical pharmacodynamic studies of high-dose methotrexate in acute lymphocytic leukemia. NCI Monographs, 5, 81–85. 6. Borsi JD, Moe PJ (1987) Systemic clearance of methotrexate in the prognosis of acute lymphoblastic leukemia in children. Cancer, 60, 3020–3024. 7. Seidel H, Nygaard R, Moe PJ et al. (1997) On the prognostic value of systemic methotrexate clearance in childhood acute lymphocytic leukemia. Leukemia Research, 21, 429–434. 8. Evans WE, Relling MV, Rodman JH et al. (1998) Conventional compared with individualized chemotherapy for childhood acute lymphoblastic leukemia. The New England Journal of Medicine, 338, 499–505. 9. Vilmer E, Suciu S, Ferster A et al. (2000) Long-term results of three randomized trials (58831, 58832, 58881) in childhood acute lymphoblastic leukemia: a CLCG-EORTC report. Children Leukemia Cooperative Group. Leukemia, 14, 2257–2266. 10. Du Bois D, Du Bois EF (1989) A formula to estimate the approximate surface area if height and weight be known. 1916. Nutrition, 5, 303–311. 11. Schwartz GJ, Haycock GB, Edelmann CM Jr, Spitzer A (1976) A simple estimate of glomerular filtration rate in children derived from body length and plasma creatinine. Pediatrics, 58, 259–263. 12. Cockcroft DW, Gault MH (1976) Prediction of creatinine clearance from serum creatinine. Nephron, 16, 31–41. 13. Piard C, Bressolle F, Fakhoury M et al. (2007) A limited sampling strategy to estimate individual

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