Theoretically required urinary flow during high-dose methotrexate infusion

Summary The renal excretion of methotrexate (MTX) and its major metabolite 7-hydroxymethotrexate (7-OH-MTX) was analysed in 12 children with malignancies during 52 courses of high-dose methotrexate (H-D-MTX) infusion at dosages ranging from 0.7 to 8.4 g/m².The peak concentrations of both MTX and 7-OH-MTX exceeded the aqueous solubilities of these compounds at low pH (6.0). The cumulative MTX excretion in urine was 75%–98% of the administered amount of MTX, and the cumulative 7-OH-MTX excretion in the urine was 3%–15%. The theoretically required urinary flow (TRUF) was estimated as the minimum urine volume needed for complete resolution of MTX and its metabolites in urine. TRUF during MTX infusion from 0 to 6 h and from 6 to 12 h was correlated with the dosage of MTX, and these values were 0.1–1.8 ml/min/m² at pH 7.0, 0.5–11.1 ml/min/m² at pH 6.0, and 1.9–42.2 ml/min/m² at pH 5.0 with dosages of 0.7 to 8.4 g/m². The value of the theoretically required urinary flow is important to ensure adequate hydration and the optimum alkalinization schedule for massive MTX infusion.     

Dose-dependent pharmacokinetics of methotrexate and 7-hydroxymethotrexate in the rat in vivo

The pharmacokinetics of methotrexate (MTX) and 7-hydroxymethotrexate (7-OH-MTX) in bile, urine, and serum was studied in rats in vivo after short-time infusions of 10, 50, 250, and 1000 mg/kg MTX. All animals were anesthetized and drained of bile during experiments. The biliary secretion rate of MTX approached saturation when serum MTX levels surpassed 700-800 microM, causing a significant reduction in biliary recovery as the parent compound (49 to 32%) at MTX doses exceeding 50 mg/kg. The hepatic metabolism of MTX to the 7-hydroxy metabolite was not saturated at the doses used. Serum MTX pharmacokinetics demonstrated dose dependency, inasmuch as doses exceeding 10 mg/kg were accompanied by a reduced total body clearance (Clr) and biliary clearance (ClB). A significant finding in relation to acute hepatotoxicity reported after high-dose MTX in humans was the occurrence of cholestasis 30-90 min after drug infusion and the observation of macroscopic precipitations in the bile duct in five of six animals treated with 1000 mg/kg MTX. In these five animals, cessation of bile secretion occurred at similar bile 7-OH-MTX levels [9800 +/- 1100 (SD) microM], while the single rat that secreted bile throughout the experiment had a 5-fold lower peak 7-OH-MTX concentration in bile. Analysis of biliary precipitates formed in vivo and in vitro found 7-OH-MTX to constitute 97% and MTX 3% of the drug content of the precipitated material.     

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     

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.     

Cephalosporins increase the renal clearance of methotrexate and 7-hydroxymethotrexate in rabbits

Summary Anaesthetized rabbits were infused with methotrexate (MTX; 30 μg × kg⁻¹ × min⁻¹ for 4h. Constant plasma concentrations of MTX and its main metabolite 7-hydroxymethotrexate (7-OH-MTX) were achieved 40–60 min after the start of the infusion. In all, 50% of the infused MTX was eliminated by the kidney; another 15%–30% was hydroxylated and excreted as 7-OH-MTX in the urine. A concomitant infusion of penicillin G (3.96 mg × kg⁻¹ × min⁻¹) decreased the renal clearance of MTX and 7-OH-MTX, probably by competitive antagonism at the common tubular secretion site. In contrast, the four cephalosporins ceftriaxone, ceftazidime, ceftizoxime and cefoperazone all increased the renal clearance of MTX and 7-OH-MTX. At similar plasma concentrations, ceftriaxone and ceftazidime were almost equipotent, ceftizoxime was less effective and cefoperazone seemed to have a biphasic effect, depressing the clearance of MTX and 7-OH-MTX at higher drug concentrations. The effects are best explained by an inhibition of the tubular reabsorption of the cytostatic and its metabolite. The results suggest that cephalosporins are a better choice than penicillin for antibiotic treatment during MTX therapy.     

The effects of antibiotics and uricosuric drugs on the renal elimination of methotrexate and 7-hydroxymethotrexate in rabbits

Summary In anesthetized rabbits, continuous infusion of methotrexate (MTX; 30 g kg^-1 min^-1) established steadystate plasma concentrations for MTX and the metabolite 7-hydroxymethotrexate (7-OH-MTX) within 40 min. Fifty percent of the infused dose was eliminated unchanged by the kidneys and the renal MTX clearance was slightly higher than the inulin clearance. Another 15%–30% was metabolized and excreted as 7-OH-MTX in the urine. Infusions of 7-OH-MTX, furosemide or benzarone had no influence on the clearance of MTX or 7-OH-MTX. Infusions of probenecid or piperacillin decreased the renal clearance of MTX and 7-OH-MTX mainly by reducing the tubular secretion of both compounds. In contrast, infusions of the antibiotics ceftriaxone and sulfamethoxazole increased the renal elimination of MTX and 7-OH-MTX. An increase was also observed during the infusion of the uricosuric drugs sulfinpyrazone and benzbromarone. These results are consistent with competition for tubular reabsorption between MTX, ceftriaxone and sulfamethoxazole. The pharmacokinetic drug interactions observed occurred with therapeutic drug concentrations and thus may be clinically relevant.     

High-dose 7-hydroxymethotrexate: Acute toxicity and lethality in a rat model

To elucidate mechanisms for methotrexate (MTX)-induced renal and hepatic toxicity, we investigated the acute effects of bolus plus continuous infusion of up to 0.4 g/kg 7-hydroxymethotrexate (7-OH-MTX) in the rat. We demonstrate for the first time in any species the occurrence of acute lethal toxicity within a few hours after 7-OH-MTX administration. Serum concentrations of 7-OH-MTX measured at the time of death were 1.4 mM (mean), about one-half of those achieved in some patients after infusion of high-dose MTX (HD-MTX) in the clinic. The data suggest an approximate LD50 (the dose lethal to 50% of the study population) of 0.3 g/kg and a steep dose/ lethality curve for 7-OH-MTX. Moreover, acute renal and hepatic toxicity occurred as evidenced by severe morphological findings and increased serum levels of creatinine and liver transaminases. In all rats subjected to continuous infusion of 7-OH-MTX, yellow microscopic precipitations were apparent in the kidney tubules. Crystallization was also seen in bile ducts of the liver in some of the rats. These results further support that the formation of 7-OH-MTX is disadvantageous and that reported attempts to prevent its formation during MTX treatment are warranted.     

Influence of piperacillin on the pharmacokinetics of methotrexate and 7-hydroxymethotrexate

The influence of concomitant administration of piperacillin (PIP) on the pharmacokinetic parameters of methotrexate (MTX) and 7-hydroxymethotrexate (7-OH-MTX) was studied in rabbits. Six rabbits received an initial i.v. bolus (0.21 mg kg⁻¹) followed by a constant-rate i.v. infusion of the drug (5 μg min⁻¹ kg⁻¹) for 240 min. The PIP dose (30 mg kg⁻¹) was repeated every 30 min until the end of the infusion period. The control group consisted of four rabbits treated the same way except for the addition of PIP. There were significant increases in the mean residence times found for MTX (MRT_inf) and 7-OH-MTX (MRT_m,inf) following PIP administration. Concomitant administration of PIP with MTX also produced significant 1.5- and 2.8-fold increases in the area under the curve of MTX and 7-OH-MTX, respectively. The total body clearance of MTX and the operative total body clearance of 7-OH-MTX significantly decreased, but in a less than proportional manner. The study demonstrates that the interaction between MTX and PIP is mainly due to the reduced clearance of both MTX and 7-OH-MTX combined with a slight increase in the formation clearance of the metabolite. Received: 9 March 1998 / Accepted: 14 May 1998     

Serum monitoring of methotrexate (MTX) and 7-hydroxymethotrexate concentrations in patients treated with MTX using high-pressure liquid chromatography (HPLC) and comparison of serum MTX levels between HPLC method and fluorescence polarization immunoassay (FPIA)

In order to measure simultaneously the serum levels of methotrexate (MTX) and its major metabolite, 7-hydroxymethotrexate (7-OH-MTX), in samples obtained from patients treated with MTX, we have investigated the reversed-phase high-pressure liquid chromatographic assay using ion-pairing reagents. The mobile phase consisted of 77.5% solution of 0.005M tetrabutylammonium and 22.5% acetonitrile. SEP-PAK C18 Cartridges were used for the precolumn. The detectable range of MTX and 7-OH-MTX were 0.02-0.03 and 1.0 mumol/l respectively. A significant positive correlation was observed (r = 0.983) between FPIA and HPLC methods. Serum MTX levels with FPIA were significantly (p less than 0.05) higher than those of HPLC method. The serum 7-OH-MTX levels at 24 hr and 48 hr were 4.857 +/- 1.383 (n = 10) and 1.835 +/- 0.286 (n = 6) mumol/l respectively with the dosage of 400 mg/m2. The serum 7-OH-MTX levels at 48 hr were 6.254 +/- 3.053 mumol/l (n = 5) with the dosage of 3,000 mg. The serum half lives of MTX and 7-OH-MTX were 8.05 +/- 1.03 (n = 4) and 14.8 +/- 1.35 (n = 6) hours respectively between 24 hr and 48 hr after administration. The T1/2 7-OH-MTX/MTX ratio was 1.8. Percent cross-reactivity of 7-OH-MTX with concentrations ranging from 1-10 mumol/l were 0.6-2.0% by FPIA. However, patients' serum levels of 7-OH-MTX were 15-85 times (n = 21) higher than those of MTX. MTX levels of containing both MTX and 7-OH-MTX (7-OH-MTX/MTX ratio was 50/1) were significantly higher than those of containing MTX alone by FPIA.     

Formation and elimination of 7-hydroxymethotrexate in the rat in vivo after methotrexate administration

Bile, urine, and serum concentrations of methotrexate (MTX) and 7-hydroxy-methotrexate (7-OH-MTX) were monitored in rats in vivo following a short-time infusion of 10 mg/kg [3H]MTX. The experiments were performed in one group of anesthetized, bile-drained rats and in two control groups, one anesthetized and one unanesthetized, that were not bile-drained. Peak biliary levels of MTX (3.8 x 10(-3) M) and 7-OH-MTX (1.8 x 10(-4) M) appeared within 15 min after cessation of infusions. For two log ranges of serum MTX concentrations, biliary levels remained 180-fold higher. High bile 7-OH-MTX levels appeared few min after start of MTX administration, and were 720 times higher than the peak serum concentrations, indicating that the liver is a major site of 7-OH-MTX formation in the rat. 7-OH-MTX concentrations in bile declined monophasically with a half-life of 29.4 min, while MTX showed a biphasic elimination with initial and second phase half-lives of 23.1 and 86.4 min, respectively. Bile was the major excretory route for MTX and 7-OH-MTX, with 50% of the dose recovered as the parent compound and 3.6% as the metabolite. There was no difference in urinary recovery of MTX in bile-drained and control animals, indicative of insignificant enterohepatic circulation of MTX. This was further corroborated by the finding of just 2.1% urinary recovery of MTX in rats who received previously collected MTX-containing bile through a duodenal catheter. Serum concentration curves were analyzed according to a three-compartment open model with an initial elimination half-life of 1.7-3.3 min, a second phase half-life of 15.4-21.0 min, and a terminal phase half-life of 119-240 min. Our finding of 7-OH-MTX formation and high biliary levels of the metabolite in the rat, can be used as basis for studies of interactions with in vivo MTX conversion to the 7-hydroxy metabolite.     

Protection against cisplatin nephrotoxicity by prochlorperazine

Summary In pentobarbital anesthetized rats that received 4 mg/kg i.v. methotrexate (MTX) or 7-hydroxymethotrexate (7-OH-MTX), the pharmacokinetics of the two drugs were similar. Plasma concentrations of both drugs declined biexponentially, with terminal half-lives of 90.6 min for MTX and 97.2 min for 7-OH-MTX. The total clearance values were 9.2 and 9.6 mlxkg^-1xmin^-1, respectively. With MTX, 48.2% of the dose was excreted in the urine within 200 min and another 31.6% was recovered from the bile; 5.8% was metabolized to 7-OH-MTX and appeared in the bile. Plasma concentrations of the metabolite 7-OH-MTX after MTX administration were below the detection limit. Injected 7-OH-MTX was predominantly excreted into the bile (72.8% of the dose); only 11.2% could be recovered from the urine. Differences between the physicochemical properties of MTX and 7-OH-MTX or different affinities for active transport systems may account for the unequal importance of these two excretion pathways for the two compounds.     

7-Hydroxymethotrexate concentrations in serum and cerebrospinal fluid of children with acute lymphoblastic leukemia

Summary Concentrations of methotrexate (MTX) and 7-hydroxymethotrexate (7-OH-MTX) were determinded by HPLC in the serum and cerebrospinal fluid (CSF) of 29 children with acute lymphoblastic leukemia. CSF and serum samples were obtained at the end of 104 infusions of MTX given in a dose range of 0.5–8.0 g/m². Concentrations, distribution ratios in serum and CSF for MTX and 7-OH-MTX, and the metabolic index were analyzed with regard to the MTX dose, age and clinical state of the patients. A wide inter-patient (2- to 12-fold) but narrower (1,1- to 3,5-fold) intra-patient variability of the concentrations was observed. A dose-proportional increase in the metabolite concentration was found in serum. On the other hand, the elevation of the level of metabolite in CSF was less than porportional to the dose. The CSF/serum distribution data suggest the existence of a saturable carrier system for MTX and 7-OH-MTX between serum and CSF that has lower affinity for 7-OH-MTX. No correlation was found between concentrations of MTX and 7-OH-MTX in the serum of patients receiving the same dose of MTX. No significant difference was observed in the values for metabolic index between relapsed patients and those who were in continuous complete remission. A significant correlation was found between age and metabolic index: the younger the patient, the higher the metabolite concentration measured in serum.     

Plasma levels of 7-hydroxymethotrexate after high-dose methotrexate treatment

Summary Thirteen patients with cancer being treated with high-dose methotrexate (MTX) chemotherapy (350–5,000 mg/6 h IV were entered in this study. Plasma levels of MTX and 7-OHMTX, its main circulating metabolite, were measured by an HPLC technique. 7-OHMTX appears rapidly in the blood, reaching a maximum 6–12 h after the beginning of treatment.The elimination of 7-OHMTX is slower than that of MTX, but the elimination half-lives (24–48 h) are not significantly different: 25.2 h for 7-OHMTX versus 20.3 h for MTX. In all cases, 24 h after starting infusion plasma levels of 7-OHMTX exceeded those of MTX. There was a positive and significant correlation between the dose administered and peak plasma 7-OHMTX. Finally, 7-OHMTX formation was shown to be relatively stable throughout the treatment.     

CSF drug levels for children with acute lymphoblastic leukemia treated by 5 g/m2 methotrexate: A study from the EORTC childrens' leukemia cooperative group

A multicenter EORTC study was conducted in children with acute lymphocytic leukemia to determine whether 5 g/m² of methotrexate (MTX) (24 h i.v. infusion, four cycles) is an appropriate dosage for obtaining CSF drug concentrations approaching the critical cytotoxic level of 10⁻⁶ M. A total of 193 cycles were analyzed for 58 patients. At the end of the 24 h infusion, the mean MTX serum level was 65.27 ± 33.11 μM; the mean CSF MTX level was 1.47 ± 1.1 μM; no significant difference in CSF MTX levels was observed between patients with (n = 20) and those without i.v. Ara-C (n = 38). The mean CSF MTX/serum MTX ratio was 0.029 ± 0.027. CSF drug concentrations greater than or equal to 10⁻⁶ M were achieved in 81% of the courses. The highest level was 8.4 × 10⁻⁶ M. Only 5% of patients failed to achieve this drug concentration in at least one cycle. No significant correlation was observed between blood and CSF MTX levels. Mean CSF MTX levels were comparable from one cycle to another.     

Renal and hepatic toxicity after high-dose 7-hydroxymethotrexate in the rat

To examine directly the hepatic and renal toxicity of 7-hydroxymethotrexate (7-OH-MTX) without interference of the parent compound methotrexate (MTX), we purified and gave 100 mg/kg 7-OH-MTX to rats, a dose resulting in serum levels of 7-OH-MTX comparable with those achieved in the clinic after the administration of high-dose MTX (HD-MTX). After only 5 h, the 7-OH-MTX-treated rats demonstrated 2.6-fold increases in serum creatinine values and 2-fold elevations in serum aspartate aminotransferase (ASAT) levels as compared with the controls. Morphologic evidence of toxicity, however, was apparent only in the kidneys. Intraluminal cellular debris containing membranous material and deteriorated organelles was seen, but no precipitate of the delivered drug. The peak serum concentration of 7-OH was up to 939 M, and concentrations of 7-OH-MTX declined triphasically, showing at1/2 value of 2.45 min, at1/2 value of 30.5 min, and a terminal half-life (t1/2) of 240 min. The total clearance value was 14.5 ml min^–1 kg, and the postdistributional volume of distribution (V) was 5070 ml/kg. Our results may indicate a direct toxic effect of 7-OH-MTX on kidney and liver cells.This study was supported financially by the Norwegian Cancer Society     

Interactions between 7-hydroxymethotrexate and methotrexate at the cellular level in the Ehrlich ascites tumor in vitro

Studies were undertaken to characterize the cellular pharmacology of 7-hydroxymethotrexate (7-OH-MTX) in Ehrlich ascites tumor cells, compare it to that of methotrexate (MTX), and define the interactions between the parent compound and its catabolite. Transport of 7-OH-MTX is mediated by the MTX-tetrahydrofolate cofactor carrier, with a Km of 9 microM in comparison to the MTX Km of 5 microM. Both compounds mutually inhibit their influx and steady-state levels of free drug accumulated. While influx of 7-OH-MTX is slower than influx of MTX, 7-OH-MTX efflux is likewise slower, so that the steady-state level of 7-OH-MTX achieved is comparable to that of MTX. Influx of 7-OH-MTX is inhibited by extracellular 5-formyltetrahydrofolate and trans-stimulated in cells preloaded with this tetrahydrofolate cofactor. The energetics of 7-OH-MTX transport is similar to that of MTX in the influx and net transport are stimulated by sodium azide, while net transport is reduced by glucose. As observed for MTX, 7-OH-MTX transport is sensitive to the anionic composition of the extracellular compartment and was shown to be inhibited by organic and inorganic phosphates. 7-OH-MTX does not, alone, inhibit [3H]deoxyuridine incorporation into DNA at concentrations of up to 50 microM. However, the catabolite reduces MTX inhibition of deoxyuridine metabolism, presumably due to the reduction in the free level of intracellular MTX achieved. These findings support the possibility that when 7-OH-MTX accumulates to high levels relative to MTX in clinical regimens, it may modulate the pharmacological effects of MTX.     

大剂量甲氨蝶呤静脉给药时间对淋巴瘤患者脑脊液中药物浓度的影响

背景与目的:甲氨蝶呤(methotrexate,MTX)在脑脊液中高于最小有效治疗浓度是治疗中枢淋巴瘤的必要条件,目前尚不明确大剂量MTX(high doseMTX,HD-MTX)静脉给药时间对MTX穿透血脑屏障的影响.本研究探索HD-MTX静脉不同给药时间对脑脊液中MTX浓度的影响,以获得更好的中枢淋巴瘤防治效果并尽可能减少MTX外周毒性.方法:34例非霍奇金淋巴瘤患者分别接受MTX 1～3g/m2 6 h持续静脉给药或24 h持续静脉给药,其中17例交替使用两种给药方法;采用高效液相色谱法检测MTX停药0 h、24 h、48 h的MTX血清浓度,及停药0 h后脑脊液中MTX浓度;比较两组血中和脑脊液中MTX浓度以及毒性反应,并对影响MTX浓度的因素进行相关分析.结果:给药结束时6 h给药组的MTX血清浓度显著高于24 h给药组:自身对照结果6 h给药组的脑脊液中MTX浓度为0.70 Ixmol/L,明显高于24 h给药组的0.49 Ixmol/L(校正值,P=0.044).MTX的脑脊液浓度与血清浓度呈正相关,中枢侵犯患者脑脊液MTX浓度显著高于无中枢侵犯的患者.自身对照结果6 h组和24 h组Ⅱ～Ⅳ度粘膜炎的发生率分别15.4%和37.8%.Ⅲ～Ⅳ度骨髓抑制的发生率分别为46.2%和67.6%.结论:在提高MTX的中枢浓度和降低外周毒性方面,HD-MTX 6 h给药方案优于24 h给药方案.     

Continuous intratumoral microdialysis during high-dose methotrexate therapy in a patient with malignant fibrous histiocytoma of the femur: a case report

 We used a microdialysis technique to assay intratumoral methotrexate (MTX) levels during high-dose (12 g/m² given as a 4-h infusion) therapy in a 43-year-old man with a malignant fibrous histiocytoma in the medial femoral condyle. Additional microdialysis probes were implanted in muscle tissue contralateral to the tumor and in an antecubital vein. Microdialysis was attempted during the initial two high-dose courses, but the two latter probes were removed at the start of the second treatment cycle due to leakage. No attempt to correct for microdialysis recovery was made. The intratumorally localized probe gave reproducible data on tumor MTX exposure of 9.3–14% of unbound systemic MTX. There was a close correlation between tumor and systemic levels for both MTX and its major extracellular metabolite 7-hydroxymethotrexate. Although limited to the study of MTX pharmacokinetics in a single subject, the experiment demonstrates that intratumoral microdialysis may provide data on tumor drug exposure, although of an indirect nature and dependent on the probe characteristics, the flow rate, and, possibly, the time after probe implantation. We propose that the application of microdialysis may prove useful for elucidation of the relationship between local drug exposure and the therapeutic response in normally inaccessible compartments during cancer pharmacotherapy. Received: 5 May 1996/Accepted: 25 July 1996     

Inhibition of 7-hydroxymethotrexate formation by amsacrine

Summary The inhibition of methotrexate (MTX) biotransformation to 7-hydroxymethotrexate (7-OH-MTX) by 4-(9-acridinylamino)-methanesulfon-m-anisidide (mAMSA) was studied in bile-drained rats in vivo and in incubates of isolated rat hepatocytes and rat-liver homogenate in vitro. In vivo, i.v. administration of 10 mg/kg mAMSA prior to [³H]-MTX infusion (50 mg/kg) led to a significant alteration in 7-OH-MTX kinetics. 7-OH-MTX peak concentrations and AUC in bile and serum were reduced by 75% and the recovery of MTX as 7-OH-MTX in bile and urine decreased by 70%, whereas MTX pharmacokinetics remained unaltered. In suspensions of isolated hepatocytes. 10 m mAMSA led to a 54% decrease in 7-OH-MTX formation. However, the hepatocellular influx and efflux of MTX was not perturbed by mAMSA. Preincubation of rat-liver homogenates with 1.25–10 m mAMSA reduced the formation of 7-OH-MTX by up to 73%. mAMSA appeared to inhibit MTX hydroxylation competitively, exhibiting aK _iof 3 m. Due to its inhibition of the MTX-oxidizing system, mAMSA may be beneficial in combination chemotherapy with MTX by reducing 7-OH-MTX-associated toxicity and, possibly, enhancing the cytotoxic effects of MTX.This study was financially supported by the Norwegian Cancer Society and the Erna and Olav Aakre Foundation for Cancer Research     

大剂量甲氨蝶呤化疗的脑脊液药代动力学研究

Objective: To study the cerebrospinal fluid pharmacokinetics of intravenously administered high dose-methotrexate (HD-MTX) and provide a solid fundament for clinical practice. Methods: MTX at a high dose ranging from 1.0 to 3.0 g per course was intravenously administered to 30 patients with malignant tumors. Blood and CSF samples were consecutively collected up to 36 h after the initiation of infusion (6 h). MTX concentrations were measured by using a reversed phase high-performance liquid chromatography (RP-HPLC) assay. Results: CSF MTX concentrations were (1.65±1.52)×10^-6, (4.3±3.34)×10^-7, (1.46±1.10)×10^-7 and (3.19±4.38)×10^-8 mol/L, respectively, at 0, 6, 12 and 24 h post infusion, and became undetectable at 36 h post infusion. The concentration-time curve of CSF MTX closely resembled that of the plasma MTX and fitted with the following linear regression equation: Ŷ=0.057 97+0.010 82X (Ŷ: CSF MTX concentration, X: Plasma MTX concentration, r=0.8357). Conclusion: CSF MTX was metabolized in a linear two-compartment model. Additionally, pharmacokinetic analysis of MTX levels indicated a positive correlation between CSF MTX and plasma MTX levels.