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.     

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.     

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.     

Pharmacokinetics and toxicity of high-dose intravenous methotrexate in the treatment of leptomeningeal carcinomatosis

Purpose: To evaluate the pharmacokinetics and toxicity of high-dose intravenous (i.v.) methotrexate (MTX) with leucovorin in patients with meningeal carcinomatosis. Methods: Of 16 eligible patients entered on this study, 13 with meningeal carcinomatosis from breast cancer, lung cancer, or osteosarcoma were treated with MTX at loading doses of 200–1500 mg/m², followed by a 23-h infusion of 800–6000 mg/m². Three patients without meningeal disease were also treated and the cerebrospinal fluid (CSF) MTX concentrations were compared in patients with and without central nervous system (CNS) disease. Results: Patients without CNS disease had lower CSF MTX concentrations relative to the plasma MTX levels than those with CNS disease, who all had CSF MTX concentrations above the target cytotoxic concentration (1 μM). The CSF MTX concentrations correlated better with the free and the total plasma MTX concentrations than with the doses. The mean half-life of CSF MTX was 8.7 ± 3.4 h. The mean plasma clearance of MTX was not significantly different in patients with CNS disease (84 ± 41 ml/min per m²) versus without CNS disease (59 ± 38 ml/min per m²). All toxicities were grade 2 or less except grade 3 hematologic toxicity. No patient had an objective response in the CSF. Conclusion: This trial demonstrates that potentially cytotoxic CSF MTX concentrations (>1 μM) are delivered safely by i.v. infusion, a less invasive and better distributed CSF therapy compared with intrathecal MTX. Because of the excellent pharmacokinetics and toxicity, high-dose i.v. MTX should be evaluated at a loading dose of 700 mg/m² and a 23-h infusion of 2800 mg/m² with leucovorin in less heavily pretreated patients with carcinomatous meningitis. Received: 4 May 1999 / Accepted: 14 February 2000     

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.     

Preclinical pharmacology and antitumour activity of the novel sequence-selective DNA minor-groove cross-linking agent DSB-120

 We examined the in vitro cytotoxicity, antitumour activity and preclinical pharmacokinetics of the novel sequence-selective, bifunctional alkylating agent DSB-120, a synthetic pyrrolo[1, 4][2, 1-c]benzodiazepine dimer. DSB-120 was shown to be a potent cytotoxic agent in vitro against a panel of human colon carcinomas [50% growth-inhibitory concentration (IC₅₀) 42±7.9 nM, mean±SE, n=7] and two rodent tumours (L1210 and ADJ/PC6). Antitumour activity was assessed in the bifunctional alkylating-agent-sensitive murine plasmacytoma ADJ/PC6 using a variety of administration protocols. The maximal antitumour eff- ects were observed following a single i.v. dose but the therapeutic index was only 2.6. DSB-120 was less effective when given i.p. either singly or by a daily+5 schedule. After a single i.v. dose at the maximum tolerated dose (MTD, 5 mg kg⁻¹) the plasma elimination was biphasic, with a short distribution phase (t _1/2α 4 min) being followed by a longer elimination phase (t _1/3β 38 min). Peak plasma concentrations were 25 μg ml⁻¹, the clearance was 1.3 ml g⁻¹ h⁻¹ and the AUC_0-∞ was 230 μg ml⁻¹ min. Concentrations of DSB-120 in ADJ/PC6 tumours were very low, showing a peak of 0.4 μg g⁻¹at 5 min. The steady-state tumour/plasma ratio was about 5% and the AUC was only 2.5% of that occurring in the plasma. DSB-120 appeared to be unstable in vivo, with only 1% of an administered dose being recovered unchanged in 24-h urine samples. Plasma protein binding was extensive at 96.6%. In conclusion, the poor antitumour activity of DSB-120 may be a consequence of low tumour selectivity and drug uptake as a result of high protein binding and/or extensive drug metabolism in vivo. Received: 5 November 1995/Accepted: 30 January 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     

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.     

Impact of the simultaneous administration of the (+)- and (−)-forms of formyl-tetrahydrofolic acid on plasma and intracellular pharmacokinetics of (−)-tetrahydrofolic acid

Purpose: To detect possible interactions between (−)-formyl-tetrahydrofolic acid (leucovorin, (−)-fTHF) and (+)-formyl-tetrahydrofolic acid ((+)-fTHF) on the plasma and intracellular pharmacokinetics following their simultaneous administration. Methods: Plasma levels of (−)-fTHF, (−)-methyl-THF, and (+)-fTHF were determined in samples from four volunteers following the administration of both (−)-fTHF and (±)-fTHF and in seven patients during a 5-fluorouracil (5-FU)/fTHF combination chemotherapy. In addition, the intracellular uptake of ¹⁴C-(−)-mTHF in the presence of (+)-mTHF at increasing concentrations was measured in vitro. Analyses were performed using a highly specific high-performance liquid chromatography procedure. Results: The pharmacokinetic parameters obtained for (−)-fTHF following the administration of (−)-fTHF only were: terminal half-life, 1.2 h; area under the curve, 10 μg · h/ml; maximum concentration, 12 μg/ml; clearance, 305 ml/min; volume of distribution, 19 l. The parameters did not differ significantly as compared with those obtained following the administration of (±)-fTHF to both volunteers and patients. There were no differences in the pharmacokinetics of (−)-mTHF or in the protein binding of both substances with the different forms of administration. The intracellular uptake of ¹⁴C-(−)-mTHF did not depend on the presence of (+)-mTHF at either concentration. Conclusions: These data suggest that (−)-fTHF is not therapeutically superior to (±)-fTHF and that the latter is appropriate during combination chemotherapy with 5-FU/fTHF in patients with colorectal cancers. Received: 12 March 1999 / Accepted: 9 August 1999     

Pharmacokinetics of oxaliplatin in patients with normal versus impaired renal function

Purpose: The pharmacokinetics (PK) of platinum was investigated and compared in patients with normal (NRF) and impaired renal function (IRF), after they had received oxaliplatin at the recommended dose and delivery modality. Methods: Oxaliplatin was administered at 130 mg/m² as a 2-h infusion without hydration. Patients were recruited and classified according to their creatinine clearance (CrCl > or < 60 ml/min), calculated using the Cockcroft and Gault formula. Blood was taken for PK analysis during and after the infusion. Twenty-three patients were included in the PK analysis (13 NRF and 10 IRF). At inclusion, the median CrCls were 70.5 ml/min (range 63–136) for the NRF group and 42 ml/min (range 27–57) for the IRF group. Three patients underwent a second course of treatment and additional blood sampling for analysis. Platinum levels in the plasma, ultrafiltrate and red blood cells (RBCs) were measured using flameless atomic absorption spectrophotometry (FAAS). Results: Following the administration of oxaliplatin, platinum binding to plasma proteins and RBCs was rapid and extensive; at the end of the 2-h infusion, 27% of the platinum in the plasma remained free (40% bound to RBCs, 33% bound to plasma proteins). Neither the mean maximal concentration (C_max) of total platinum in the plasma, the mean C_max of ultrafilterable platinum in the plasma, nor the maximal platinum content in the RBCs differed significantly between the two groups (2.59 vs 2.58 μg/ml, 1.09 vs 1.28 μg/ml and 2.06 vs 2.17 μg/ml, respectively, for patients with NRF vs IRF). After the end of the infusion, levels of total and free (ultrafilterable) platinum in the plasma declined biexponentially. The plasma clearance of both total and free platinum as well as the area under the curve (AUC) of the free platinum fraction correlate with the calculated CrCl (P=9 × 10⁻³, P=3.1 × 10⁻⁵ and P=9 × 10⁻⁶, respectively). After a single course of oxaliplatin, toxicities reported in the two groups of patients were similar. Conclusions: Our results are in agreement with the in vitro data concerning the extensive binding of oxaliplatin to plasma proteins and RBCs. They also reveal a strong negative correlation between free drug plasma availability and renal function, with a corresponding positive correlation between clearance of the plasmatic platinum and renal function. Thus, renal impairment entails a greater overall exposure to platinum in the plasma. However, this study failed to elicit any relationship between moderate renal impairment and the acute toxicity associated with oxaliplatin. Received: 8 April 1999 / Accepted: 30 July 1999     

Renal toxicity of the anticancer drug fostriecin

Purpose: Fostriecin is an inhibitor of topoisomerase II catalytic activity. In a phase I trial we observed renal toxicity, documented as a rise in serum creatinine, which was reversible and non-dose-limiting. The purpose of this study was a detailed analysis of this toxicity. Methods: A total of 20 patients received fostriecin as a 1-h i.v. infusion daily × 5 at doses ranging from 2 to 20 mg/m² per day. Serum creatinine determination and urinalysis were performed daily during drug administration. Renal hemodynamics were measured by means of clearance studies using ¹²⁵I-iothalamate and ¹³¹I-hippuran in eight patients at doses of ≥4 mg/m² per day at baseline, on day 3 or 4 during the first course, and 3 weeks after the second course. Results: The rise in serum creatinine was maximal after one to two doses despite continued administration. This increase showed no correlation with the dose level at fostriecin doses of ≥4 mg/m² per day. Urinary β₂-microglobulin concentrations increased 150-fold (median), which is compatible with impaired tubular reabsorption. The median change in the glomerular filtration rate (GFR) was −36% (range −28% to −44%), that in effective renal plasma flow (ERPF) was −23% (range −11% to −36%), and the filtration fraction (FF) decreased in all patients during the first course of treatment. The values measured 3 weeks after the second course, however, did not differ from baseline. Conclusions: Fostriecin induces reversible renal hemodynamic changes compatible with renal tubular damage. Received: 1 June 1997 / Accepted: 14 November 1997     

A limited sampling strategy to estimate individual pharmacokinetic parameters of methotrexate in children with acute lymphoblastic leukemia

Purpose The objectives of this study were to characterize the population pharmacokinetics of MTX in patients with acute lymphoblastic leukemia (ALL) with ages ranging from 2 to 16 years and to propose a limited sampling strategy to estimate individual pharmacokinetic parameters. Methods Seventy-nine children were enrolled in this study; they received 1–4 courses of chemotherapy. MTX was administered at a dose of 5 g/m2. MTX population parameters were estimated from 61 patients (231 courses; age range: 2–16 years). The data were analyzed by nonlinear mixed-effect modeling with use of a two-compartment structural model. The interoccasion variability was taken into account in the model. Eighteen additional patients (70 courses) were used to evaluate the predictive performances of the Bayesian approach and to devise a limited sampling strategy. Results The following population parameters were obtained: total clearance (CL) = 8.8 l/h (inter-individual variability: 43%), initial volume of distribution (V ₁) = 17.3 l (48%), k ₁₂ = 0.0225 h⁻¹ (41%), and k ₂₁ = 0.0629 h⁻¹ (24%). The inter-individual variability in the initial volume of distribution was partially explained by the fact that this parameter was weight-dependent. Intercourse variability was limited, with a mean variation of 13.2%. The protocol involving two sampling times, 24 and 48 h after the beginning of infusion, allows precise and accurate determination of individual pharmacokinetic parameters and consequently, it was possible to predict the time at which the MTX concentration reached the predicted threshold (0.2 μM) below which the administration of folinic acid could be stopped. Conclusion The results of this study combine the relationships between the pharmacokinetic parameters of MTX and patient covariates that may be useful for dose adjustment, with a convenient sampling procedure that may aid in optimizing pediatric patient care. An erratum to this article can be found at     

A clinical pharmacokinetics study of carzelesin given by short-term intravenous infusion in a phase I study

We investigated the pharmacokinetic behavior of carzelesin in 31 patients receiving this drug by 10-min intravenous infusion in a Phase I clinical trial, which was conducted at institutions in Nijmegen (institution 1) and Brussels (institution 2). The dose steps were 24, 48, 96, 130, 150, 170, 210, 250, and 300 μg/m². Carzelesin is a cyclopropylpyrroloindole prodrug that requires metabolic activation via U-76,073 to U-76,074. The lower limit of quantitation (LLQ) of the high-performance liquid chromatography (HPLC) method used in this study was 1 ng/ml for the parent drug and its metabolic products. Carzelesin was rapidly eliminated from plasma (elimination half-life 23 ± 9 min; mean value ± SD). At all dose levels, U-76,073 was found as early as in the first samples taken after the start of the infusion. However, the concentration of U-76,074 exceeded the LLQ for only short periods and only at the higher dose levels. Although the plasma levels of all three compounds were well above the respective IC₅₀ values obtained by in vitro clonogenic assays, they were much lower than those observed in a preclinical study in mice. There was a substantial discrepancy in the mean plasma clearance␣observed between patients from institution 1 (7.9 ± 2.1 l h⁻¹ m⁻²) and those from institution 2 (18.4 ± 13.6 l h⁻¹ m⁻²; P = 0.038), probably reflecting problems with drug administration in the latter institution. The results recorded for patients in institution 1 indicated that the AUC increased proportionately with increasing doses. There was a good correlation between the maximal plasma concentration and the AUC, enabling future monitoring of drug exposure from one timed blood sample. Urinary excretion of carzelesin was below 1% of the delivered dose. Received: 6 May 1997 / Accepted: 5 September 1997     

In vivo microdialysis to characterize drug transport in brain tumors: analysis of methotrexate uptake in rat glioma-2 (RG-2)-Bearing rats

 Brain microdialysis was applied to sample free methotrexate (MTX) concentrations in brain extracellular fluid of normal and RG-2 glioma-bearing rats. All animals received 50 mg/kg of MTX intraarterially following which serial blood and interstitial fluid samples were collected for 3 h and measured for MTX by an HPLC assay. Retrodialysis was used to estimate the in vivo recovery of MTX from brain. A linear two-compartment model was fitted to the plasma MTX concentration-time data in both the normal and RG-2 groups. The mean total body clearance and volume of distribution at steady state of MTX varied from 0.90±0.3 to 0.24±0.02 l h^-1 kg^-1 (P<0.05) and from 0.58±0.24 to 0.21±0.16 l kg^-1 (P<0.05) in control and tumor rats, respectively. The significant reductions in clearance and volume of distribution at steady-state were attributed in part to a cachectic state in the RG-2 animals in which total body water was reduced. The mean MTX area under the interstitial fluid concentration-time curve (AUC) was 171.6±69.14 μg min ml^-1(control) and 583.5±296.7 μg min ml^-1 (brain tumor-bearing rats). The significantly higher AUC values obtained with RG-2 rats compared with control rats may have resulted from high plasma MTX concentrations and a more permeable blood–tumor barrier (BTB). A hybrid physiologically based pharmacokinetic model was used to characterize the mechanisms responsible for the high MTX brain tumor concentrations. In conclusion, a microdialysis technique was successfully utilized to examine the extracellular uptake of MTX in brain. This technique can be a powerful tool to evaluate intracerebral drug kinetics and the delivery of drugs to brain tumors. Received: 11 July 1995/Accepted: 1 February 1996     

Phase I dose escalation pharmacokinetics of O-(chloroacetylcarbamoyl) fumagillol (TNP-470) and its metabolites in AIDS patients with Kaposi's sarcoma

The pharmacokinetics of TNP-470 and its major metabolites were investigated in AIDS patients enrolled in a phase I dose escalation trial for the treatment of Kaposi's sarcoma. The patients received TNP-470 by 1-h intravenous infusion in dose cohorts of 10, 20, 30, 40, 50 and 70 mg/m². The parent drug and metabolites, MII and MIV, were measured by high-performance liquid chromatography/mass spectrometry (HPLC/MS) in plasma samples collected during and out to 168 h after the beginning of the infusion. Both metabolites were detected in all patients' plasma, while the parent drug was undetectable at time-points as early as 5 min after the end of infusion for some patients. A large interpatient variability of pharmacokinetic parameters among the dosing cohorts was observed for TNP-470, with a mean (±SD) plasma elimination half-life (t_1/2) of 0.06 ± 0.04 h, plasma clearance (CL) of 1487 ± 1216 l/h and an area under the concentration versus time curve (AUC) of 49.9 ± 35.8 ng/ml · h. Time to maximum plasma concentration (Tmax) typically occurred before the end of the infusion. The predominant plasma metabolite was MII with a t_1/2 of 1.21 ± 0.43 h, AUC of 1226 ± 2303 l/h and a Tmax occurring between 5 and 15 min after infusion. The reported active metabolite MIV had a t_1/2 of 0.24 ± 0.13 h, AUC of 24.9 ± 32.6 ng/ml · h and a Tmax occurring between the midpoint of the infusion and 15 min after infusion. The parent drug was undetectable by HPLC/MS/MS in urine samples collected and pooled between 0–6 and 6–24 h from the beginning of drug administration. Metabolite MIV was present in the 0–6-h urine pool of two patients enrolled in the highest dosing cohorts, equivalent to 0.4% of the administered dose. Metabolite MII was present in all 0–6-h samples analyzed and represented 1.12 ± 0.9% of the administered dose. Renal clearance (CL_R) for MII was 140 ± 70 ml/h. Received: 16 September 1999 / Accepted: 5 April 2000     

Pharmacokinetics of paclitaxel administered in combination with cisplatin, etoposide and bleomycin in patients with advanced solid tumours

 Purpose: To evaluate the pharmacokinetics of paclitaxel and cisplatin administered in combination with bleomycin and etoposide and Granulocyte Colony-Stimulating Factor (G-CSF) in patients with advanced solid tumours. Methods: Patients were recruited to a phase I trial where escalating doses of paclitaxel (125 to 200 mg/m²) were administered in combination with etoposide 100 or 120 mg/m², and fixed dose of cisplatin 20 mg/m² and bleomycin 30 mg, with the concomitant use of G-CSF. Paclitaxel (3-h infusion) was followed by 1-h etoposide, 4-h cisplatin and 30-min bleomycin infusions, respectively. Pharmacokinetics sampling for paclitaxel analysis was performed in ten patients from dose levels II–V. Results: The mean paclitaxel area under the plasma concentration-versus-time curves (AUC) for the 125-mg/m² dose level (II) was 7.0 ± 3.6 h μmol⁻¹ l⁻¹, for the 175-mg/m² dose level (III) 10.6 ± 2.8 h μmol⁻¹ l⁻¹, for the 200-mg/m² dose level (IV) it was 16.0 ± 5.0 h μmol⁻¹ l⁻¹, and for the 175-mg/m² dose level (V) it was 12.5 ± 6.1 h μmol⁻¹ l⁻¹. The mean peak plasma concentration (C_max) values for dose levels II–V were 1.9 ± 1.1 μmol/l, 3.4 ± 1.2 μmol/l, 4.3 ± 1.0 μmol/l and 3.8 ± 1.2 h μmol/l, respectively. Conclusion: In this study, relevant pharmacokinetic parameters of paclitaxel like AUC, C_max and the paclitaxel plasma concentration above the pharmacologically relevant 0.1-μmol/l threshold concentration (t > 0.1 μM) when administered in combination with cisplatin, etoposide and bleomycin (PEB) were not statistically different from paclitaxel data of historical controls. However, given the trial design, pharmacokinetic interactions between the agents cannot be excluded. Received: 29 June 1998 / Accepted: 29 January 1999     

Pharmacokinetics of 2-chloro-2′-deoxyadenosine administered subcutaneously or by continuous intravenous infusion

Purpose: Cladribine (2-chlorodeoxyadenosine, 2-CDA) is effective in the treatment of various lymphoproliferative disorders. In the standard protocol the compound is administered by continuous intravenous (i.v.) infusion. In order to allow outpatient therapy alternative modes of administration such as subcutaneous (s.c.) injection would be desirable. The aim of the present study was to compare the pharmacokinetics of 2-CDA after i.v. and s.c. administration. Patients and methods: Nine patients received 0.1 mg/kg 2-CDA per 24 h on one occasion by continuous i.v. infusion and on another occasion as a bolus subcutaneously. The concentrations of 2-CDA in the plasma and urine were determined by HPLC. Results: During i.v. infusion the concentration of 2-CDA in the plasma reached a plateau after 4–8 h, whereas with s.c. administration almost ten times higher peak concentrations were reached within 20 to 60 min. A two-compartment model was fitted to the data points whereby the goodness-of-fit statistics showed R ² values of >0.98. The calculated rate of elimination, k_elim, averaged 0.336 h⁻¹ with s.c. and 0.397 h⁻¹ with i.v. administration. The estimated volumes of distribution were 1.67 and 1.58 l/kg. The areas under the concentration time curves (608 ± 65 pmol · h/ml after s.c. administration vs 571 ± 50 pmol · h/ml during i.v. infusion) and the urinary excretion of 2-CDA in 24 h (4.75 ± 0.95 vs 3.55 ± 0.53 μmol/24 h) were similar in both groups, indicating identical bioavailability. Conclusions: Although the pharmacokinetic profile of 2-CDA administered s.c. differs substantially from the profile of a continuous i.v. infusion the areas under the plasma concentration time curves, the urinary excretion of unchanged drug and the estimated pharmacokinetic variables were similar with both modes of administration, indicating that the different time-courses of the plasma concentration did not influence the fraction metabolized or eliminated. Received: 3 November 1999 / Accepted: 3 March 2000     

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.