Pharmacokinetics of methotrexate and 7-hydroxy-methotrexate in rabbits

Summary In rabbits the IV kinetics of MTX (1.33, 4 and 12 mg/kg) could be described by a linear three-compartment model with a terminal half-life between 2.4 and 3.6 h. During 8 h 50% of the dose was excreted into urine in unchanged form and 15% as the metabolite 7-OH-MTX. These fractions remained constant with increasing dose. In continuous infusion experiments (9–900 g/kg x min MTX IV) a decrease of the renal MTX clearance with increasing plasma concentration was observed. This effect was nearly compensated by an increase of the extrarenal MTX clearance. After short-term infusion of 7-OH-MTX (4 mg/kg) a biexponential decline of 7-OH-MTX plasma concentrations was observed with a terminal half-life of 0.45 h. About 80% of the dose was regained from urine during 5 h. From the combined pharmacokinetic data a linear model was constructed for the calculation of 7-OH-MTX plasma concentrations after short-term MTX infusion. For the first 4 h after MTX application the predicted values were in good accordance with the 7-OH-MTX concentrations actually measured.     

Pharmacokinetics of low-dose methotrexate in children receiving maintenance therapy for acute lymphoblastic leukaemia

Summary Serum methotrexate (MTX) concentrations were measured by immunoassay in 28 children receiving maintenance therapy for acute lymphoblastic leukaemia. Patients were studied either after a single weekly dose or on the first day of a 5-day course of treatment. A standard dose (15 mg/m²) was given PO and/or IV.After PO dose the peak serum MTX concentration and its timing varied widely between cases and there was a significant positive correlation between the rate of serum concentration rise and the area under the concentration curve up to 4 h. The absorption rate constant showed a biphasic distribution and correlated less closely with early serum concentrations.After IV and PO administration drug disposition was triphasic with an initial rapid distribution phase, an intermediate phase, and a prolonged terminal elimination phase. The intermediate phase half-life was significantly longer after PO than after an IV dose. The MTX clearance rate was consistently lower than the glomerular filtration rate and there was no significant correlation between the two.The mean bioavailability (PO/IV) was 42%, but bioavail-ability was as low as 6% in some cases due to prolonged high serum concentrations after an IV dose, which was not seen with the equivalent PO dose.     

Pharmacokinetics of oral methotrexate in children

The absorption and disposition kinetics of p.o. methotrexate were studied in 15 children. Serum levels and urinary excretion of methotrexate, as measured by the dihydrofolate reductase inhibition assay, were monitored following a routine p.o. dose (6.3 to 28.1 mg/sq m) administered after an overnight fast. Significant interindividual variability was noted in peak levels (range, 0.27 to 1.1 microM), time to peak (1 to 5 hr), area under the serum concentration-time curve (1.08 to 5.00 microM . hr), and the fraction of the dose absorbed (23 to 95%). Patients taking doses greater than 12 mg/sq m had a more prolonged absorptive phase and absorbed a smaller fraction of their dose, indicating that the mechanism of absorption may be saturable in some patients within the commonly administered dosage range. Urinary excretion was rapid, and the mean renal clearance of methotrexate was 1.6 times greater than was creatinine clearance, consistent with renal tubular secretion of the drug. While the marked degree of variability observed suggests a potential role for therapeutic drug monitoring in optimizing p.o. methotrexate therapy, the critical time points to monitor, the therapeutic and toxic ranges, and the intrapatient consistency of absorption must be defined before it will be practical and useful.     

Kinetics of 7-hydroxy-methotrexate after high-dose methotrexate therapy

Summary Kinetics of 7-hydroxy-methotrexate (7-OH-MTX) excretion after high-dose methotrexate (MTX) (12 g/m²) therapy were monitored in 93 consecutive drug cycles of 19 adolescent patients with osteosarcoma. A reversed-phase HPLC method was used. Serum elimination was found to be monophasic with a mean half-life of 5.5 h. Shortly after the 4-h MTX infusion period 7-OH-MTX levels exceeded those of the parent compound. By 12 h after MTX infusion 7-OH-MTX levels were 16.5 times higher than those of MTX itself.Autostimulation of MTX metabolism leading to enhanced 7-OH-MTX production after repeated drug cycles was not observed. The production of 7-OH-MTX decreased significantly from the first to the last high-dose MTX cycle of the adjuvant chemotherapy protocol.     

Pharmacokinetics of oral and intramuscular methotrexate in children with acute lymphoblastic leukaemia

Summary Repeated methotrexate absorption studies were performed under standard conditions in 127 children receiving either oral or intramuscular methotrexate for acute lymphoblastic leukaemia. There was marked variability in peak concentration, area under the serum concentration curve and clearance both between patients and in repeated studies on the same patient. Although the intramuscular route produced higher serum concentrations and AUC than the oral route, variability within and between patients was considerable and was most marked at higher concentrations. Neither age or sex could account for variation in methotrexate absorption or clearance.Intramuscular methotrexate, although producing higher serum concentrations and AUC, does not reduce the variability observed with oral administration. Prediction of subsequent methotrexate concentrations from the knowledge of one absorption profile is not possible.     

Pharmacokinetics of high-dose oral CCNU in bone marrow transplant patients

 Purpose: CCNU (lomustine) and other nitrosourea compounds are rapidly metabolized to alkylating moieties, which are active against various malignancies. In humans, CCNU undergoes biotransformation to the geometric isomers of 4′-hydroxyCCNU. The pharmacokinetics of trans- and cis-4′-hydroxyCCNU were determined in five patients with Hodgkin’s or non-Hodgkin’s lymphoma receiving sequential doses of CCNU (15 mg/kg), etoposide (60 mg/kg) and cyclophosphamide (100 mg/kg) prior to autologous bone marrow transplantation. Methods: Plasma concentrations of the isomeric forms of the metabolites were determined by high-performance liquid chromatography. Data were analysed using noncompartmental pharmacokinetic methods. Results: Formation of the trans-isomer predominated over that of the cis-isomer, with an average exposure ratio of 1.4 (range 1.0–2.1). Peak plasma concentrations occurred between 1 and 4.1 h postdosing and averaged 1.56 mg/l for the trans-isomer and 1.10 mg/l for cis isomer. Peak plasma concen- trations and systemic exposures varied approximately six- and ninefold, respectively, reflecting significant interindividual variability in alkylating activity after high doses of CCNU. Plasma half-lives of the metabolites were 3.1 h (range 1.1–4.5 h) for the trans-isomer and 3.5 h (range 1.3–6.4 h) for the cis- isomer, and varied linearly with increasing patient body weight. There was no significant difference in plasma half-lives after high-dose CCNU administration observed in this study and those reported previously after the administration of substantially lower doses of CCNU. Conclusion. Despite linearity in the pharmacokinetics of the isomeric forms of 4′-hydroxyCCNU at high doses, large interindividual variability in exposure to the CCNU metabolites was observed. Potential saturation of metabolic pathways to the isomers at these doses may manifest as toxic symptoms since alkylating moieties formed directly from the parent, CCNU, may be associated with greater toxicity than those formed from the isomeric forms of the 4′-hydroxylated metabolite. Received: 11 August 1995/Accepted: 2 January 1996     

Methotrexate and 7-hydroxy-methotrexate pharmacokinetics following intravenous bolus administration and high-dose infusion of methotrexate

The pharmacokinetics of methotrexate and 7-hydroxy-methotrexate were studied in patients undergoing very high-dose methotrexate monotherapy. The patients received, first, two methotrexate intravenous bolus test doses (50 mg/m²) one with and one without concomitant administration of folinic acid (15 mg every 6 h) in a random sequence, and, second, an 8 h infusion, individualized to achieve a peak plasma concentration of 5 × 10⁻⁴M methotrexate (infusion rates > 1000 mg/h). Methotrexate and 7-hydroxy-methotrexate concentrations were measured by specific radioimmunoassays and the data were analysed simultaneously by an integrated pharmacokinetic model. Following test dose administration, methotrexate and 7-hydroxy-methotrexate plasma concentration kinetics were best described by assuming that methotexate elimination (and 7-hydroxy-methotrexate formation) occurred from a peripheral compartment reaching rapid equilibrium with the plasma. Folinic acid administration did not influence the disposition of either compound. Following the infusion, a significant (P < 0.01) decrease of methotrexate total plasmatic clearance occurred without modification of 7-hydroxy-methotrexate formation and elimination.     

Maximum tolerated doses of methotrexate and 7-hydroxy-methotrexate in a model of acute toxicity in rats

Purpose: After more than 50 years of methotrexate (MTX) treatment of acute lymphoblastic leukaemia (ALL), it is currently believed that as long as dose escalations are followed by adequate leucovorin rescue guided by monitoring MTX serum concentrations, hydration and urinary alkalinization, high-dose MTX (HD-MTX) can be tolerated without life-threatening toxicity. However, our recent experimental animal studies of the major metabolite of MTX, 7-OH-MTX, indicate that this concept may have some limitations. Animals with levels of 7-OH-MTX of 1 mM, which is below the levels routinely found in patients on HD-MTX, demonstrate intolerable toxicity and some animals die within 8 h. Electron microscopy indicates that endothelial cell and platelet functions are perturbed. Since animal data are lacking, and interspecies differences not known, we wanted to investigate the maximum tolerated doses of MTX and 7-OH-MTX in a rat model of short-term effects. The maximum tolerated dose was chosen instead of LD₅₀ for reasons of animal welfare. Methods: We infused MTX and 7-OH-MTX into anaesthetized male Wistar rats and monitored the animals for 8 h. The drugs were given as a bolus plus continuous infusion. The dose-finding ranges were 1.8–11.3 g/kg MTX and 0.1–1.2 g/kg 7-OH-MTX. Results: The maximum tolerated dose was between 3 and 5 g/kg for MTX and lower than 0.1 g/kg for 7-OH-MTX. The mean serum concentrations of MTX and 7-OH-MTX in animals that did not survive the 8-h period were 21.9 and 1.6 mM, respectively. The animals that received the highest MTX or 7-OH-MTX doses and concentrations died after sudden reductions in heart rate and blood pressure. Conclusions: We demonstrated a lower maximum tolerated dose of 7-OH-MTX than of MTX in rats after 8 h. The 7-OH-MTX concentrations were in the therapeutic range after HD-MTX. If the rat/human interspecies differences are not large, our data may indicate that HD-MTX regimens should not be further dose intensified, due not so much to the effects of MTX as to those of 7-OH-MTX. Received: 28 July 1999 / Accepted: 25 January 2000     

Methotrexate test-dose protocol in the presence of 7-hydroxy-methotrexate

Methotrexate (MTX) and 7-hydroxy-methotrexate (7-OH-MTX) plasma concentration-time curves (AUC) have been analyzed in 24 patients after different routes of MTX administration. After an i.v. bolus (50 mg/m²), the AUC for 7-OH-MTX is correlated with that for MTX and inversely correlated with the MTX plasma clearance. When MTX is administered with plasma steady level standardization, using the test-dose protocol, at a level of 10⁻⁵ M over 36 hr (10⁻⁵, 36 hr), 7-OH-MTX-AUC is still correlated with the i.v. bolus pharmacokinetic parameters. The dose prediction using the classical test-dose protocol provides a less efficient MTX dose adjustment at 5 × 10⁻⁴M over 8 hr (5.10⁻⁴, 8 hr) and the hydroxylation process is no more correlated with the i.v. parameters.On the opposite, upon 6 successive infusions with 10⁻⁵, 36 hr or 5.10⁻⁴, 8 hr protocols, the plasma concentrations of 7-OH-MTX are not significantly modified. This suggests that the hydroxylation process is not inducible.     

Methotrexate and its polyglutamate derivatives in erythrocytes during and after weekly low-dose oral methotrexate therapy of children with acute lymphoblastic leukemia

Summary Methotrexate and methotrexate polyglutamates were quantitatively determined in red blood cells from 12 children with acute lymphoblastic leukemia who were treated with MTX (15–20 mg/m² per week) and daily 6-mercaptopurine orally during the steady-state period of erythrocyte MTX concentration (ery-MTX). The terminal decline of the ery-MTX and its polyglutamate metabolites were determined for up to 15 weeks after cessation of MTX treatment. Methotrexate polyglutamates with 2–4 extra glutamyl derivatives (MTX-glu_2-5) constituted 75% of the MTX in the entire red blood cell population. MTX-glu₃ was the principal metabolite; no MTX-glu_6-7 was identified. After discontinuation of MTX therapy, the ery-MTX declined in a non-linear manner because of different half-lives for the individual polyglutamates. From about 5 weeks until 13–15 weeks after the last MTX dose, the erythrocyte MTX elimination curve was linear. The approximate half-life of MTX-glu₁ was 2–3 days; for MTX-glu₂ it was 4–15 days. The concentration of MTX-glu_3-5 remained constant in the erythrocyte throughout its life span and declined only with age-dependent destruction of the red blood cell. It was calculated that 80%–90% of MTX in newly formed reticulocytes was MTX-glu₁₊₂, the remainder being MTX-glu_3-5. Mature red blood cells did not form methotrexate polyglutamates to any significant degree. There was a significant correlation between the amount of MTX-glu_3-5 and the steady-state ery-MTX, which to some extent explained the interindividual variation of the ery-MTX in children with ALL in maintenance therapy.     

Modification of oral methotrexate absorption in children with leukemia

Summary The effect of administering oral methotrexate in different formulations to children with acute lymphoblastic leukemia was evaluated. Methotrexate tablets alone achieved higher mean plasma levels and larger area under the absorption curve than either methotrexate liquid alone of methotrexate tablets taken concurrently with metoclopramide.     

Anabolic steroids and bone marrow toxicity during therapy with methotrexate

The effect of the anabolic steroids nandrolone decanoate and oxymetholone on the peripheral blood haemoglobin, total leucocyte and platelet counts was studied in a controlled trial in which patients received standardized chemotherapy for one form of malignant disease. The results indicate that these agents have no protective effect on bone marrow suppression during cytotoxic chemotherapy. It was observed that the time interval between the initial nadir total leucocyte count and the return to pre-treatment values in those patients receiving the anabolic steroids was significantly shorter than in the control group.     

Changes in plasma methionine and total homocysteine levels in patients receiving methotrexate infusions

Methotrexate reduces intracellular pools of 5-methyltetrahydrofolate and could result in reduced conversion of homocysteine to methionine by methionine synthetase. This study was designed to investigate the effects of moderate dose to very high dose methotrexate on methionine and total homocysteine as reflections of methotrexate induced intracellular events. Methionine and total homocysteine were measured prior to, during, and following twenty-six 24-h i.v. infusions of 33.6 g/m2 methotrexate (very high dose methotrexate) in 16 children with acute lymphocytic leukemia and seven 4-h i.v. infusions of 8 g/m2 methotrexate (high dose methotrexate) in 5 children with osteogenic sarcoma. Amino acids were measured by gas chromatography/mass spectrophotometry. Mean methionine levels decreased by 70.0 +/- 3.1% (SE) with very high dose methotrexate and 72.6 +/- 5.9% with high dose methotrexate at 24 and 4.5 h, respectively, after beginning methotrexate infusions. Mean total homocysteine levels increased by 61.7 +/- 3.1% with very high dose methotrexate and 55.6 +/- 17.5% with high dose methotrexate at 36 and 24 h, respectively, after beginning methotrexate infusions. No consistent or significant changes were noted in levels of total cysteine, leucine, isoleucine, or valine. Similar changes did not occur in patients receiving prednisone, vincristine, daunomycin, and intrathecal methotrexate as therapy for acute lymphocytic leukemia. These changes in homocysteine and methionine may reflect biological effects of methotrexate that may predict cytotoxicity of methotrexate.     

Pharmacokinetics of high-dose methotrexate in dogs

Summary The usefulness of a diffusion chamber method for determination of concentrations of cytostatic drugs in the interstitial fluid of tissues was tested. Chambers with a permeable membrane (pore size: 0.45 m) were implanted in the liver, kidney, bladder wall, and prostate of dogs. After administration of high doses of methotrexate (100 mg/kg body wt) the concentrations in the chamber fluid and in serum were measured simultaneously and repeatedly for 72 h.The method proved to be effective for collecting data on the distribution of drugs in different organs. The results show that knowledge of the serum concentration does not permit predictions of the drug concentration in the interstitial fluid of various tissues to be made.     

Pharmacokinetics of erythrocyte methotrexate in children with acute lymphoblastic leukemia during maintenance treatment

The concentration of methotrexate (MTX) in erythrocytes (E-MTX) was measured in 47 children with acute lymphoblastic leukemia during maintenance treatment with MTX 1.7-21.6 mg/m2/week and 6-mercaptopurine 25-75 mg/m2/day. At the time of measurement the plasma MTX concentration was less than 2 nmol/l. The steady state E-MTX varied between 51 and 202 nmol/l erythrocytes. Alterations in the E-MTX took place over 8-12 weeks after a change in dosage. A significant correlation was found between the E-MTX and the weekly dose of MTX administered. Noncompliance was revealed in two patients. A very low E-MTX was found in one patients, probably caused by inhibition of erythropoiesis. No correlation was found between E-MTX and the total amount of MTX administered or the length of treatment. A terminal half-life of 2-5 weeks after discontinuation of the drug showed that the erythrocytes functioned as a slow-changing compartment for MTX. Unexpectedly low E-MTX could mean noncompliance, impaired erythropoiesis, altered metabolism, or poor drug absorption.     

Absorption of oral aminoglycosides following bone marrow transplantation

Four patients with severe gastrointestinal reactions receiving oral "nonabsorbable" antibiotics for gut sterilization following bone marrow transplantation absorbed clinically significant amounts of aminoglycoside (gentamicin and/or tobramycin). Serum concentrations of 2.2, 2.6, 5.8, and 12.0 micrograms/ml were measured. Two of these patients had acute graft versus host reactions and two had severe mucositis following cytoreduction with intensive chemotherapy and irradiation. Nephrotoxicity occurred in the latter patients. One patient was studied in detail. Her hospital course and investigative results are presented. Four additional patients with mild gastrointestinal reactions following cytoreduction did not absorb gentamicin when their toxicity was maximal. Serum aminoglycoside determinations are necessary in patients receiving oral aminoglycosides for gut sterilization following bone marrow transplantation if moderate to severe gastrointestinal reactions occur.     

Association of plasma methotrexate, neutropenia, hepatic dysfunction, nausea/vomiting and oral mucositis in children with cancer

Oral mucositis is a major toxicity associated with high-dose methotrexate (HD-MTX) therapy in the treatment of children with acute lymphoblastic leukaemia and osteosarcoma. This pilot matched case-control study investigated the associations between plasma concentration of MTX at 42 (p-MTX(42h)) and 66 (p-MTX(66h)) h, absolute neutrophil count (ANC) < or = or >1.0 x 10(9)/l, serum transaminases (ASAT/ALAT) < or > or =58 U/l, WHO < or > or =grade 2 nausea/vomiting and WHO < or > or =grade 2 oral mucositis. In this study, 11 children with WHO > or =grade 2 oral mucositis were compared with 17 control children matched for age, diagnosis and MTX-dosage. The results indicated that children with p-MTX(42h) > or = 1.0 micromol/l had an odds ratio (OR) of 4.3 of developing oral mucositis when compared with the referent group of children who had p-MTX(42h) < 1.0 micromol/l. Children with p-MTX(66h) >= 0.2 micromol/l had an OR of 8.2 of developing oral mucositis when compared with the referent group of children who had p-MTX(66h) < 0.2 micromol/l. Children with ANC < or = 1.0 x 10(9)/l had an OR of 1.2 of developing oral mucositis when compared with the referent group of children who had ANC > 1.0 x 10(9)/l. In comparison with the referent group of children, who had <58 U/l ASAT/ALAT, those with ASAT/ALAT > or = 58 U/l had an OR of 1.2 of developing oral mucositis. Finally, children with WHO grade > or =2 nausea/vomiting had an elevated risk of developing oral mucositis when compared with the referent group of children who had WHO grade <2 nausea/vomiting (OR = 8.7). In conclusion, the results in this preliminary study provide support for the hypothesis that the risk of oral mucositis is associated with the plasma MTX concentration at 66 h and the level of nausea/vomiting.     

Avascular necrosis of bone in children undergoing allogeneic bone marrow transplantation

Avascular necrosis of bone (AVNB) is reported in two children after allogeneic bone marrow transplantation. Preparation therapy for transplantation included cyclophosphamide and total body irradiation. Corticosteroids, cyclosporine A, and methotrexate were used for graft-versus-host-disease prophylaxis. The possible role of combination therapy in development of AVNB is discussed, but a direct relationship with single agents was not found. However, an early diagnosis is important to institute conservative treatment and prevent irreversible damage to affected joints. Magnetic resonance imaging was found to be more sensitive than plain radiography in early detection of AVNB.