Photochemically stabilized formulation of dacarbazine with reduced production of algogenic photodegradants.

The present study aimed to develop a photochemically stabilized formulation of dacarbazine [5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide; DTIC] for reducing the production of algogenic photodegradant (5-diazoimidazole-4-carboxamide; Diazo-IC). Photochemical properties of DTIC were characterized by UV-visible light spectral analysis, reactive oxygen species (ROS) assay, and photostability testing. A pharmacokinetic study was conducted after intravenous administration of DTIC formulations (1 mg-DTIC/kg) to rats. DTIC exhibited strong absorption in the UVA range, and photoirradiated DTIC exhibited marked ROS generation. Thus, DTIC had high photoreactive potential. After exposure of DTIC (1 mM) to simulated sunlight (250 W/m2) for 3 min, remaining DTIC and yielded Diazo-IC were estimated to be ca. 230 µM and 600 µM, respectively. The addition of radical scavenger (1 mM), including l-ascorbic acid, l-cysteine (Cys), l-histidine, D-mannitol, l-tryptophan, or l-tyrosine, to DTIC (1 mM) could attenuate DTIC photoreactions, and in particular, the addition of Cys to DTIC brought ca. 34% and 86% inhibition of DTIC photodegradation and Diazo-IC photogeneration, respectively. There were no significant differences in the calculated pharmacokinetic parameters of DTIC between DTIC and DTIC with Cys (0.67 mg/kg). From these findings, the supplementary use of Cys would be an effective approach to improve the photostability of DTIC with less production of Diazo-IC.

Pharmacokinetics of dacarbazine (DTIC) in pregnancy.

PURPOSE: The purpose of this report is to describe, for the first time, the pharmacokinetics of dacarbazine (DTIC) and its metabolites [5-[3-methyl-triazen-1-yl]-imidazole-4-carboxamide (MTIC), 5-[3-hydroxymethyl-3-methyl-triazen-1-yl]-imidazole-4-carboxamide (HMMTIC) and 5-aminoimidazole-4-carboxamide (AIC)] during pregnancy (n = 2) and postpartum (n = 1). METHODS: Non-compartmental DTIC, MTIC, HMMTIC, and AIC pharmacokinetics (PK) were estimated in one case at 29 week gestation and 18 day postpartum and a second case at 32 week gestation, in women receiving DTIC in combination with doxorubicin, bleomycin, and vinblastine for treatment of Hodgkin's lymphoma. Drug concentrations were measured by HPLC. RESULTS: In the subject who completed both pregnancy and postpartum study days, DTIC area under the concentration-time curve (AUC) was 27% higher and metabolite AUCs were lower by 27% for HMMTIC, 38% for MTIC, and 83% of AIC during pregnancy compared to postpartum. At 7 and 9 year follow-up, both subjects were in remission of their Hodgkin's lymphoma. CONCLUSIONS: Based on these two case reports, pregnancy appears to decrease the metabolism of the pro-drug dacarbazine, likely through inhibition of CYP1A2 activity. Lower concentrations of active metabolites and decreased efficacy may result, although both these subjects experienced long-term remission of their Hodgkin's lymphoma.

Temozolomide analogs with improved brain/plasma ratios - Exploring the possibility of enhancing the therapeutic index of temozolomide.

Temozolomide is a chemotherapeutic agent that is used in the treatment of glioblastoma and other malignant gliomas. It acts through DNA alkylation, but treatment is limited by its systemic toxicity and neutralization of DNA alkylation by upregulation of the O6-methylguanine-DNA methyltransferase gene. Both of these limiting factors can be addressed by achieving higher concentrations of TMZ in the brain. Our research has led to the discovery of new analogs of temozolomide with improved brain:plasma ratios when dosed in vivo in rats. These compounds are imidazotetrazine analogs, expected to act through the same mechanism as temozolomide. With reduced systemic exposure, these new agents have the potential to improve efficacy and therapeutic index in the treatment of glioblastoma.

The effect of regadenoson-induced transient disruption of the blood-brain barrier on temozolomide delivery to normal rat brain.

The blood-brain barrier (BBB) significantly reduces the delivery of many systemically administered agents to the central nervous system. Although temozolomide is the only chemotherapy to improve survival in patients with glioblastoma, its concentration in brain is only 20 % of that in blood. Regadenoson, an FDA approved adenosine receptor agonist used for cardiac stress testing, transiently disrupts rodent BBB allowing high molecular weight dextran (70 kD) to enter the brain. This study was conducted to determine if regadenoson could facilitate entry of temozolomide into normal rodent brain. Temozolomide (50 mg/kg) was administered by oral gavage to non-tumor bearing F344 rats. Two-thirds of the animals received a single dose of intravenous regadenoson 60-90 min later. All animals were sacrificed 120 or 360 min after temozolomide administration. Brain and plasma temozolomide concentrations were determined using HPLC/MS/MS. Brain temozolomide concentrations were significantly higher at 120 min when it was given with regadenoson versus alone (8.1 ± 2.7 and 5.1 ± 3.5 µg/g, P < 0.05). A similar trend was noted in brain:plasma ratios (0.45 ± 0.08 and 0.29 ± 0.09, P < 0.05). Brain concentrations and brain:plasma ratios were not significantly different 360 min after temozolomide administration. No differences were seen in plasma temozolomide concentrations with or without regadenoson. These results suggest co-administration of regadenoson with temozolomide results in 60% higher temozolomide levels in normal brain without affecting plasma concentrations. This novel approach to increasing intracranial concentrations of systemically administered agents has potential to improve the efficacy of chemotherapy in neuro-oncologic disorders.

Double-salting out assisted liquid-liquid extraction (SALLE) HPLC method for estimation of temozolomide from biological samples.

The role of temozolomide (TMZ) in treatment of high grade gliomas, melanomas and other malignancies is being defined by the current clinical developmental trials. Temozolomide belongs to the group of alkylating agents and is prescribed to patients suffering from most aggressive forms of brain tumors. The estimation techniques for temozolomide from the extracted plasma or biological samples includes high-performance liquid chromatography with UV detection (HPLC-UV), micellar electrokinetic capillary chromatography (MKEC) and liquid chromatography coupled to mass spectroscopy (LC-MS). These methods suffer from disadvantages like low resolution, low sensitivity, low recovery or cost involvement. An analytical method possessing capacity to estimate low quantities of TMZ in plasma samples with high extraction efficiency (%) and high resolution with cost effectiveness needs to be developed. Cost effective, robust and low plasma component interfering HPLC method using salting out liquid-liquid extraction (SALLE) technique was developed and validated for estimation of drug from plasma samples. The extraction efficiency (%) with conventional LLE technique with methanol, ethyl acetate, dichloromethane and acetonitrile was found to be 5.99±2.45, 45.39±4.56, 46.04±1.14 and 46.23±3.67 respectively. Extraction efficiency (%) improved with SALLE where sodium chloride was used as an electrolyte and was found to be 6.80±5.56, 52.01±3.13, 62.69±2.11 and 69.20±1.18 with methanol, ethyl acetate, dichloromethane and acetonitrile as organic solvent. Upon utilization of two salts for extraction (double salting liquid-liquid extraction) the extraction efficiency (%) was further improved and was twice of LLE. It was found that double salting liquid-liquid extraction technique yielded extraction efficiency (%) of 11.71±5.66, 55.62±3.44, 77.28±2.89 and 87.75±0.89. Hence a method based on double SALLE was developed for quantification of TMZ demonstrating linearity in the range of 0.47-20 µg/ml. The LOQ and LOD for the developed method were 0.4 µg/ml and 0.1 µg/ml, respectively. Thus, plasma non-interfering SALLE-HPLC method that is precise, robust, accurate, specific and cost effective for estimation of temozolomide from plasma samples was developed and validated.

Irinotecan and temozolomide brain distribution: a focus on ABCB1.

Glioblastoma (GBM), the most common primary brain tumor in adults, is usually rapidly fatal with median survival duration of only 15 months and a 3-year survival rate of <7 %. Temozolomide (TMZ) is the only anticancer drug that has improved survival in GBM when administered with concomitant radiotherapy. Irinotecan (CPT-11) has also shown efficacy in recurrent gliomas monotherapy with moderate response. As the efficacy of GBM treatments relies on their brain distribution through the blood-brain barrier (BBB), the aim of the present work was to study, on an in vivo model, the brain distribution of TMZ, CPT-11 and its active metabolite, SN-38. We have focussed on the role of ABCB1, the main efflux transporter at the BBB level, through pharmacokinetics studies in CF1 mdr1a(+/+) and mdr1a(-/-) mice. Our results show that TMZ, CPT-11 and SN-38 are transported by ABCB1 at the BBB level with brain/plasma ratios of 1.1, 2.1 and 2.3, respectively.

Development of a new UPLC-MSMS method for the determination of temozolomide in mice: application to plasma pharmacokinetics and brain distribution study.

A sensitive and accurate liquid chromatography method with mass spectrometry detection was developed and validated for the quantification of temozolomide in mouse plasma and brain. Theophyllin was used as the internal standard. A single-step protein precipitation was used for plasma and brain sample preparation. The method was validated with respect to selectivity, extraction recovery, linearity, intra- and inter-day precision and accuracy, limit of quantification and stability. The method has a limit of quantification of 50 ng/mL for temozolomide in plasma and 125 ng/g in brain. This method was used successfully to perform brain and plasma pharmacokinetic studies of temozolomide in mice after intraperitoneal administration.

A phase I study of temozolomide and everolimus (RAD001) in patients with newly diagnosed and progressive glioblastoma either receiving or not receiving enzyme-inducing anticonvulsants: an NCIC CTG study.

PURPOSE: This phase I trial was designed to determine the recommended phase II dose(s) of everolimus (RAD001) with temozolomide (TMZ) in patients with glioblastoma (GBM). Patients receiving enzyme-inducing antiepileptic drugs (EIAEDs) and those not receiving EIAEDs (NEIAEDs) were studied separately. PATIENTS AND METHODS: Enrollment was restricted to patients with proven GBM, either newly diagnosed or at first progression. Temozolomide was administered at a starting dose of 150 mg/m(2)/day for 5 days every 28 days, and everolimus was administered continuously at a starting dose of 2.5 mg orally on a daily schedule starting on day 2 of cycle 1 in 28-day cycles. RESULTS: Thirteen patients receiving EIAEDs and 19 not receiving EIAEDs were enrolled and received 83 and 116 cycles respectively. Everolimus 10 mg daily plus TMZ 150 mg/m(2)/day for 5 days was declared the recommended phase II dose for the NEIAEDs cohort. In the EIAEDs group, doses were well tolerated without DLTs, and pharmacokinetic parameters indicated decreased everolimus exposure. Temozolomide pharmacokinetic parameters were unaffected by EIAEDs or everolimus. In the subset of 28 patients with measurable disease, 3 had partial responses (all NEIAEDs) and 16 had stable disease. CONCLUSION: A dosage of 10 mg everolimus daily with TMZ 150 mg/m(2)/day for five consecutive days every 28 days in patients is the recommended dose for this regimen. Everolimus clearance is increased by EIAEDs, and patients receiving EIAEDs should be switched to NEIAEDs before starting this regimen.

Validated HPLC method for determination of temozolomide in human plasma.

The aim of the study was to develop a bioanalytical method for the determination of temozolomide (TMZ) in human plasma. Plasma concentration of TMZ was determined on a C18 column after liquid-liquid extraction. Isocratic elution was applied with the mixture of aqueous acetic acid and methanol. Theophylline was used as the internal standard. To prevent chemical degradation of TMZ at physiological pH, plasma samples were acidified to pH < 3. All validation parameters met the acceptance criteria. Calibration curve, prepared using freshly spiked plasma samples, was linear within the range of 0.10-20.00 microg/mL. The method was found to be sufficiently accurate and precise over the studied range of concentrations. TMZ was stable in the acidified plasma samples for at least 50 days at < or = -14 degrees C and < or = -65 degrees C. The method recovery of TMZ from human plasma was consistent and ranged 37.1-41.1%. The developed method is suitable for pharmacokinetic studies in humans after oral administration of TMZ.

Interaction of dacarbazine and imexon, in vitro and in vivo, in human A375 melanoma cells.

AIM: We evaluated mechanisms of interaction between the alkyating agent dacarbazine (DTIC) and the pro-oxidant, imexon, in the human A375 melanoma cell line. MATERIALS AND METHODS: The effect of DTIC and imexon, alone and in combination, was evaluated for growth inhibition (MTT), radiolabeled drug uptake, cellular thiol content (HPLC), and DNA strand breaks (Comet assay). Pharmacokinetic and antitumor effects were evaluated in mice. RESULTS: Growth inhibition in vitro was additive with the two drugs. There was no effect on drug uptake or on the number of DNA strand breaks. There was a >75% reduction in cellular glutathione and cysteine with imexon but not DTIC. Co-administration of the two drugs in mice caused an increase in the area under the curve of both drugs, but the combination was not effective in reducing human A375 melanoma tumors in vivo. CONCLUSION: Imexon and dacarbazine show additive effects in vitro but not in vivo in human A375 melanoma cells.

Determination of temozolomide in serum and brain tumor with micellar electrokinetic capillary chromatography.

Micellar electrokinetic capillary chromatographic (MEKC) with photodiode-array detection was applied to determine temozolomide (TMZ) in human serum and brain tumor. The limit of quantitation (LOQ) was 0.096 µg/mL using 325 nm as detection wavelength. The method made possible that the TMZ could be detected in in vivo serum samples without sample pretreatment. In order to detect TMZ at lower concentration, an extraction with ethyl acetate was applied to preconcentrate the analyte. Small amount of brain tumor tissues (less than 1g) were lyophilized and pretreated using extraction as a clean up and concentrating step. After removing the organic solvent a final sample volume of only 10 µL was analyzed. The obtained peak concentrations (8.2-10.1 µg/mL) and T(max) (44-65 min) of TMZ in serum were similar to the data reported by others, the in vivo TMZ concentrations found in brain tumor ranged between 0.061 and 0.117 µg/g.

Pharmacokinetic results of a phase I trial of sorafenib in combination with dacarbazine in patients with advanced solid tumors.

PURPOSE: Sorafenib, a multikinase inhibitor of Raf and several growth factor receptors, is under investigation in combination with dacarbazine, a commonly used chemotherapeutic agent for the treatment of many cancers. The current phase I study investigates the effects of sorafenib on the pharmacokinetic (PK) profile of dacarbazine and its metabolite 5-amino-imidazole-4-carboxamide (AIC). (AIC is formed in amounts equimolar to the active alkylating moiety, methane diazohydroxide, which is undetectable by known validated assays.) METHODS: Patients with advanced solid tumors received intravenous dacarbazine 1,000 mg/m(2) on day 1 of a 21-day cycle to evaluate the PK of dacarbazine alone. Sorafenib 400 mg was administered twice daily continuously starting at day 2 of cycle 1. The PK of dacarbazine in the presence of sorafenib was assessed on day 1 of cycle 2. Sorafenib PK was also assessed at steady state. RESULTS: PK data were available for 15 of 23 patients. With concomitant administration of sorafenib, the mean AUC and C (max) values of dacarbazine were reduced by 23 and 16%, respectively. Mean AUC and C (max) values of AIC were increased by 41 and 45%, respectively, with individual increases of up to 106 and 136%, respectively. The apparent terminal half-lives of the two compounds were not significantly influenced by sorafenib. Based on coefficients of variation, the AUC and C (max) values for sorafenib and its three metabolites were highly variable with dacarbazine coadministration. CONCLUSIONS: Concomitant administration of sorafenib and dacarbazine as described above may result in decreased dacarbazine exposure but increased AIC exposure.

Transplacental transfer of anthracyclines, vinblastine, and 4-hydroxy-cyclophosphamide in a baboon model.

OBJECTIVE: The paucity of data on the fetal effects of prenatal exposure to chemotherapy prompted us to study transplacental transport of chemotherapeutic agents. METHODS: Fluorouracil-epirubicin-cyclophosphamide (FEC) and doxorubicin-bleomycin-vinblastine-dacarbazine (ABVD) were administered to pregnant baboons. At predefined time points over the first 25 h after drug administration, fetal and maternal blood samples, amniotic fluid (AF), urine, fetal and maternal tissues, and cerebrospinal fluid (CSF) were collected. High-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) were used for bioanalysis of doxorubicin, epirubicin, vinblastine, and cyclophosphamide. RESULTS: In nine baboons, at a median gestational age of 139 days (range, 93-169), FEC 100% (n = 2), FEC 200% (n=1), ABVD 100% (n = 5), and ABVD 200% (n = 1) were administered. The obtained ratios of fetal/maternal drug concentration in the different simultaneously collected samples were used as a measure for transplacental transfer. Fetal plasma concentrations of doxorubicin and epirubicin averaged 7.5 ± 3.2% (n = 6) and 4.0 ± 1.6% (n = 8) of maternal concentrations, respectively. Fetal tissues contained 6.3 ± 7.9% and 8.7 ± 8.1% of maternal tissue concentrations for doxorubicin and epirubicin, respectively. Vinblastine concentrations in fetal plasma averaged 18.5 ± 15.5% (n=9) of maternal concentrations. Anthracyclines and vinblastine were neither detectable in maternal nor in fetal brain/CSF. 4-Hydroxy-cyclophosphamide concentrations in fetal plasma and CSF averaged 25.1 ± 6.3% (n = 3) and 63.0% (n = 1) of the maternal concentrations, respectively. CONCLUSION: This study shows limited fetal exposure after maternal administration of doxorubicin, epirubicin, vinblastine, and 4-hydroxy-cyclophosphamide.

Analysis and stability study of temozolomide using capillary electrophoresis.

The applicability of micellar electrokinetic capillary chromatography (MEKC) for the analysis of temozolomide (TMZ) and its degradants, 3-methyl-(triazen-1-yl)imidazole-4-carboxamide (MTIC) and 5-amino-imidazole-4-carboxamide (AIC) has been studied. Using short-end injection, the analysis of TMZ and its degradants could be performed within 1.2 min. The obtained precision of migration times was better than 1.6 RSD%, and the limit of quantitation (LOQ) was 0.31-0.93 microg/mL. The therapeutic concentration of TMZ in blood samples can be determined after direct sample injection and conventional on-capillary UV detection. The proposed MEKC method was applied to study the stability of TMZ in water and serum at different pH values. It was established that the half-life of the TMZ in vitro serum at room temperature was 33 min, close to the half-life (28 min) obtained in water at pH 7.9.

A new model for prediction of drug distribution in tumor and normal tissues: pharmacokinetics of temozolomide in glioma patients.

Difficulties in direct measurement of drug concentrations in human tissues have hampered the understanding of drug accumulation in tumors and normal tissues. We propose a new system analysis modeling approach to characterize drug distribution in tissues based on human positron emission tomography (PET) data. The PET system analysis method was applied to temozolomide, an important alkylating agent used in the treatment of brain tumors, as part of standard temozolomide treatment regimens in patients. The system analysis technique, embodied in the convolution integral, generated an impulse response function that, when convolved with temozolomide plasma concentration input functions, yielded predicted normal brain and brain tumor temozolomide concentration profiles for different temozolomide dosing regimens (75-200 mg/m(2)/d). Predicted peak concentrations of temozolomide ranged from 2.9 to 6.7 microg/mL in human glioma tumors and from 1.8 to 3.7 microg/mL in normal brain, with the total drug exposure, as indicated by the tissue/plasma area under the curve ratio, being about 1.3 in tumor compared with 0.9 in normal brain. The higher temozolomide exposures in brain tumor relative to normal brain were attributed to breakdown of the blood-brain barrier and possibly secondary to increased intratumoral angiogenesis. Overall, the method is considered a robust tool to analyze and predict tissue drug concentrations to help select the most rational dosing schedules.

Disposition of temozolomide in a patient with glioblastoma multiforme after gastric bypass surgery.

Temozolomide, used for anaplastic gliomas and glioblastoma multiforme, is an oral drug that is stable under acidic, but labile under neutral and basic conditions. Although the bioavailability of temozolomide is approximately 100%, pathology or anatomical changes of the gastrointestinal tract may adversely affect absorption, and consequently therapeutic response. HPLC-UV was used to evaluate temozolomide plasma pharmacokinetics in a patient with unresponsive glioblastoma multiforme who had previously undergone gastric bypass as part of a weight-loss strategy. Temozolomide plasma pharmacokinetics were comparable to values reported for patients with normal gastrointestinal anatomy. These data imply that progression of disease in this patient was not due to inadequate temozolomide concentrations. Physicians need to become aware of the rapidly increasing population of patients who have had a gastric bypass and require oral therapy, of which our case is representative. The effect of gastric bypass on pharmacokinetics will need to be evaluated on a drug-by-drug basis.

Validated hydrophilic interaction LC-MS/MS method for simultaneous quantification of dacarbazine and 5-amino-4-imidazole-carboxamide in human plasma.

A hydrophilic interaction high performance liquid chromatography-tandem mass spectrometric method has been developed and validated for simultaneous quantification of dacarbazine (DTIC) and its terminal metabolite, 5-amino-4-imidazole-carboxamide (AIC) in human plasma. The plasma samples are first extracted by a C8+SCX mixed-mode 96-well plate to extend the extraction stability of DTIC and AIC. The extracted residues are further cleaned by a primary and secondary amine (PSA) adsorbent for minimization of matrix effect. Analyses are done on an Amide-80 HPLC column coupled to a tandem mass spectrometer fitted with an atmospheric pressure turbo ion spray ionization interface in the positive-ion mode. Both DTIC and AIC have reproducible retention times on the Amide-80 HPLC column. This type of column not only has an excellent column life (over 4000 injections), but also has zero carryover effect. The injection volume should be limited at 10 microL or less to avoid the peak splitting. The validated concentration ranges are from 0.5 to 500 ng/mL for DTIC and from 2.0 to 500 ng/mL for AIC. The validated method has been successfully applied to determine the pharmacokinetic profiles for human patients receiving DTIC infusions.

Pharmacokinetic study of temozolomide on a daily-for-5-days schedule in Japanese patients with relapsed malignant gliomas: first study in Asians.

BACKGROUND: Temozolomide (TMZ) is widely used in Europe and the United States. For the safe use of TMZ in the Japanese, as representative of Asians, the pharmacokinetics of TMZ was investigated in Japanese patients and compared to that in Caucasians. METHODS: The pharmacokinetics and safety of TMZ following oral administration of 150 and 200 mg/m2 per day for the first 5 days of a 28-day treatment cycle were investigated in six Japanese patients with relapsed gliomas. RESULTS: The time-to-maximum plasma concentration (tmax) of TMZ was about 1 h and the elimination half-life of terminal excretion phase (t 1/2lambda z) was about 2 h. A dose-dependent increase was observed in maximum plasma concentration (Cmax) and AUC, while values for t 1/2lambda z, apparent total body clearance (CL/F), and apparent distribution volume (Vz/F) were independent of dose. After administration for 5 days, changes in pharmacokinetics and accumulation were not observed. The plasma 5-(3-methyl)1-triazen-1-yl-imidazole-4-carboxamide (MTIC) concentration changed in parallel with the TMZ plasma concentration, and the Cmax and AUC of MTIC were about 2% of those of TMZ. The pharmacokinetic parameters of TMZ and MTIC in Japanese patients in this study were comparable to those previously determined in Caucasian subjects. Adverse events occurred in all patients, but toxicities were mostly mild or moderate, and continuation of administration was possible by adjusting the dose and by delaying the start of the next treatment cycle. CONCLUSION: The pharmacokinetic and safety profile of TMZ in Japanese patients was comparable to that in Caucasians. The treatment regimen used in Europe and the United States will be suitable for Asian patients, including Japanese.

Development of a pharmacokinetic limited sampling model for temozolomide and its active metabolite MTIC.

PURPOSE: To develop a pharmacokinetic limited sampling model (LSM) for temozolomide and its metabolite MTIC in infants and children. METHODS: LSMs consisting of either two or four samples were determined using a modification of the D-optimality algorithm. This accounted for prior distribution of temozolomide and MTIC pharmacokinetic parameters based on full pharmacokinetic sampling from 38 patients with 120 pharmacokinetic studies (dosage range 145-200 mg/m(2) per day orally). Accuracy and bias of each LSM were determined relative to the full sampling method. We also assessed the predictive performance of the LSMs using Monte-Carlo simulations. RESULTS: The four strategies generated from the D-optimality algorithm were as follows: LSM 1=0.25, 1.25, and 3 h; LSM 2=0.25, 1.25, and 6 h; LSM 3=0.25, 0.5, 1.25, and 3 h; LSM 4=0.25, 0.5, 1.25, and 6 h. LSM 2 demonstrated the best combination of low bias [0.1% (-8.9%, 11%) and 11% (4.3%, 15%)] and high accuracy [-1.0% (-12%, 24%) and 14% (7.9%, 37%)] for temozolomide clearance and MTIC AUC, respectively. Furthermore, adding a fourth sample (e.g., LSM 4) did not substantially decrease the bias or increase the accuracy for temozolomide clearance or MTIC AUC. Results from Monte-Carlo simulations also revealed that LSM 2 had the best combination of lowest bias (0.1+/-6.1% and -0.8+/-6.5%), and the highest accuracy (4.5+/-4.1% and 5.0+/-4.3%) for temozolomide clearance and MTIC apparent clearance, respectively. CONCLUSIONS: Using data derived from our population analysis, the sampling times for a limited sample pharmacokinetic model for temozolomide and MTIC in children are prior to the temozolomide dose, and 15 min, 1.25 h and 6 h after the dose.

Plasma and cerebrospinal fluid population pharmacokinetics of temozolomide in malignant glioma patients.

PURPOSE: Scarce information is available on the brain penetration of temozolomide (TMZ), although this novel methylating agent is mainly used for the treatment of malignant brain tumors. The purpose was to assess TMZ pharmacokinetics in plasma and cerebrospinal fluid (CSF) along with its inter-individual variability, to characterize covariates and to explore relationships between systemic or cerebral drug exposure and clinical outcomes. EXPERIMENTAL DESIGN: TMZ levels were measured by high-performance liquid chromatography in plasma and CSF samples from 35 patients with newly diagnosed or recurrent malignant gliomas. The population pharmacokinetic analysis was performed with nonlinear mixed-effect modeling software. Drug exposure, defined by the area under the concentration-time curve (AUC) in plasma and CSF, was estimated for each patient and correlated with toxicity, survival, and progression-free survival. RESULTS: A three-compartment model with first-order absorption and transfer rates between plasma and CSF described the data appropriately. Oral clearance was 10 liter/h; volume of distribution (V(D)), 30.3 liters; absorption constant rate, 5.8 h(-1); elimination half-time, 2.1 h; transfer rate from plasma to CSF (K(plasma-->CSF)), 7.2 x 10(-4)h(-1) and the backwards rate, 0.76 h(-1). Body surface area significantly influenced both clearance and V(D), and clearance was sex dependent. The AUC(CSF) corresponded to 20% of the AUC(plasma). A trend toward an increased K(plasma-->CSF) of 15% was observed in case of concomitant radiochemotherapy. No significant correlations between AUC in plasma or CSF and toxicity, survival, or progression-free survival were apparent after deduction of dose-effect. CONCLUSIONS: This is the first human pharmacokinetic study on TMZ to quantify CSF penetration. The AUC(CSF)/AUC(plasma) ratio was 20%. Systemic or cerebral exposures are not better predictors than the cumulative dose alone for both efficacy and safety.