Influence on Busilvex pharmacokinetics of clonazepam compared to previous phenytoin historical data.

This study investigated the effect of seizure prophylaxis on busulfan (Bu) plasma exposure. Twenty-four adult patients received an intravenous Bu-cyclophoshamide conditioning regimen prior to bone marrow transplantation. Busilvex (0.8 mg/kg) was administered every six hours during four consecutive days. Clonazepam (0.025 to 0.03 mg/kg/day as a continuous 12-h i.v. infusion) was administered at least 12 hours prior to i.v. Bu dosing and continued until 24 hours after the last dose. Pharmacokinetic (PK) data were compared with those previously collected in patients (n=127) treated with phenytoin for seizure prophylaxis. Through population PK analysis, a 10% average increase (coefficient of variation, RSE=5.35%) in total clearance of Bu was quantified when Bu was associated with clonazepam as compared to phenytoin, which was considered as not being clinically relevant. The suspected induction on Bu metabolism by phenytoin should have resulted in the opposite effect. The patient efficacy and safety profiles were comparable between the two cohorts.

Exposure equivalence between IV (0.8 mg/kg) and oral (1 mg/kg) busulfan in adult patients.

OBJECTIVE: This study was conducted to retrospectively compare the area under the curve (AUC) and the total clearance of busulfan (Bu) following oral and intravenous (IV) administrations and to determine which intravenous dose generated equivalent exposure to that of the oral form that has been marketed for decades. METHODS: Patient pharmacokinetics were assessed at dose 9 during a conditioning regimen for stem-cell transplantation and included data from 277 patients for oral Bu (71 from fixed-dose studies and 206 from studies with dose adjustment allowed) and 120 patients for IV Bu (fixed dose). AUCs were compared between patients with fixed dose of oral Bu (n = 71, 1 mg/kg) and those of IV Bu (n = 120, 0.8 mg/kg). Total clearances were calculated for all 277 patients with oral Bu and compared to those with IV Bu, with the ratio of IV-to-oral clearance representing the absolute bioavailability of the oral form. RESULTS: Oral and IV populations differed on disease-type distribution but presented comparable demography parameters. IV Bu dosing was mostly based on the ideal body weight index while actual body weight or adjusted ideal body weight indexes were mostly used for oral. When normalised to comparable indexes, bioequivalent AUCs were achieved between oral and IV populations. Oral Bu bioavailability was about 80% when calculated from the ratio of IV-to-oral total clearances. CONCLUSION: This retrospective study carried out on a large set of data showed that similar plasma exposures were achieved with 1.0 mg/kg oral Bu or 0.8 mg/kg IV Bu.

Metabolism pathway of vinorelbine (Navelbine) in human: characterisation of the metabolites by HPLC-MS/MS.

The biotransformation of vinorelbine (VRL), an anti-neoplastic vinca-alkaloid derivate already marketed for nonsmall cell lung cancer and advanced breast cancer as an i.v. form and currently registered in several countries as an oral form, was investigated in human. Biological specimen from several human sources constituted the material for the metabolic identification in human. An isocratic liquid chromatographic system composed of 40 mM ammonium acetate (pH 3) and acetonitrile was used for separation of the potential metabolites of VRL. Tandem mass spectrometry with positive electrospray ionisation was used to enable the structural identification of the metabolites. A total of 17 metabolites (12 directly obtained from VRL and 5 involving sequential step pathways) were characterised with proposed structures for most of the metabolites. All metabolites went through phase I reactions by the way of deacetylation, dealkylation, oxidation and hydroxylation. No conjugates were observed. Despite the high number of metabolites quantified, VRL was the major compound observed whatever the matrix. Most of the metabolites rapidly disappeared from blood, except 4-O-deacetyl vinorelbine which was slowly cleared. Most of the enzymatic pathways involved in the metabolites strongly suggested the major role of cytochrome P450 in the biotransformation of vinorelbine.

Prospective validation of a novel IV busulfan fixed dosing for paediatric patients to improve therapeutic AUC targeting without drug monitoring.

INTRODUCTION: Oral busulfan clearance is age-dependent and children experience a wide variability in plasma exposure. BSA- or age-based dosing is used with therapeutic drug monitoring (TDM) to reduce this variability. PURPOSE: A new intravenous (IV) dosing of busulfan (Bu) based on body weight, designed to improve AUC targeting without TDM and dose-adjustment, was prospectively evaluated. METHOD: Bu was administered as a 2 h IV infusion every 6 h over 4 days (16 administrations). Five dose levels were defined on body weight as follows: 1.0 mg/kg for <9 kg; 1.2 mg/kg for 9 to <16 kg; 1.1 mg/kg for 16-23 kg; 0.95 mg/kg for >23-34 kg; 0.80 mg/kg for >34 kg. Bu treatment was followed by Cyclophosphamide or Melphalan prior to allogeneic or autologous transplantation in 55 children aged 0.3-17.2 years (median 5.6 years). RESULTS: No difference in AUC values was observed between weight strata (mean +/- SD 1248 +/- 205 micromol.min), whereas a significant difference in Bu clearance was demonstrated. This new dosing enabled to achieve a mean exposure comparable to that in adults. At dose 1, 91% of patients achieved the targeted AUC range (900-1500 micromol.min) while no patients were underexposed. At doses 9 and 13, over 75% of patients remained within that target whilst most of the others were slightly above. Successful engraftment was achieved in all patients. In conclusion, from infants to adults this new dosing enabled, without TDM and dose adjustment, to successfully target a therapeutic AUC window.

Evaluation of oral versus intravenous dose of vinorelbine to achieve equivalent blood exposures in patients with solid tumours.

Patient's preference is for oral chemotherapy when both oral and i.v. are available, provided that efficacy is equivalent. Reliable switch from oral to i.v. is possible if correspondence between respective doses has been established. Vinorelbine oral was developed as a line extension of VRL i.v. on the basis that similar AUCs result in similar activities. From a first crossover study on 24 patients receiving VRL 25 mg/m2 i.v. and 80 mg/m2 oral data extrapolation concluded on AUCs bioequivalence between Vinorelbine 30 mg/m2 i.v. and 80 mg/m2 oral. A new trial was performed to support this calculation. In a crossover design study on patients (PS 0-1) with advanced solid tumours (44% breast carcinoma), VRL was administered (30 mg/m2 i.v., 80 mg/m2 oral) with a standard meal and 5-HT3 antagonists, at 2 weeks interval. Pharmacokinetics was performed over 168 h and VRL was measured by LC-MS/MS. Statistics included bioequivalence tests. Forty-eight patients were evaluable for PK: median age 58 years (25-71), PS0/PS1: 20/28, M/F: 11/37. Mean AUCs were 1,230 +/- 290 and 1,216 +/- 521 ng/ml for i.v. and oral, respectively. The confidence interval of the AUC ratio (0.83-1.03) was within the required regulatory range (0.8-1.25) and proved the bioequivalence between the two doses. The absolute bioavailability was 37.8 +/- 16.0%, and close to the value from the first study (40%). Patient tolerability was globally comparable between both forms with no significant difference on either haematological or non-haematological toxicities (grade 3-4). This new study, conducted on a larger population, confirmed the reliable dose correspondence previously established between vinorelbine 80 mg/m2 oral and 30 mg/m2 i.v.

Development of a sensitive liquid chromatography method coupled with a tandem mass spectrometric detection for the clinical analysis of vinflunine and 4-O-deacetyl vinflunine in blood, urine and faeces.

A sensitive and specific liquid chromatographic method coupled with tandem mass spectrometric detection was set up and fully validated for the simultaneous quantification of vinflunine (VFL) and its pharmacologically active metabolite, 4-O-deacetyl vinflunine (DVFL). The two compounds, as well as vinblastine (used as internal standard), were deproteinised from blood and faeces, analysed on a cyano type column and detected on a Micromass Quattro II system in the positive ion mode after ionisation using an electrospray ion source. In blood, linearity was assessed up to 200 ng/ml for vinflunine and 100 ng/ml for 4-O-deacetyl vinflunine. The lower limit of quantification was validated at 250 pg/ml for both compounds. In other biological media, the linearity was assessed within the same range; the limit of quantification was adjusted according to the expected concentration levels of each compound. This method was first developed in order to identify the structures and to elucidate the metabolic pathway of vinflunine. Thanks to its high sensitivity and specificity, the method has enabled the quantification of vinflunine and 4-O-deacetyl vinflunine in blood at trace levels, and has contributed to the knowledge of vinflunine metabolism by monitoring up to 10 metabolites.

A high performance liquid chromatography method for vinorelbine and 4-O-deacetyl vinorelbine: a decade of routine analysis in human blood.

A sensitive high performance liquid chromatographic method was developed and validated for the simultaneous quantification of vinorelbine and its active metabolite, 4-O-deacetyl vinorelbine, in human biological fluids. These two compounds together with vinblastine, used as internal standard, were extracted from blood and urine by a liquid-liquid process using diethyl ether, and followed by a back-extraction in acidic conditions. Then, they were analysed through a cyano column and detected in ultraviolet at 268 nm. The assay linearity was validated up to 2000 ng/ml. The lower limit of quantification was set at 2.5 ng/ml. The between-run precision and accuracy were always higher than 94%. Biological samples were stable when stored at -80 degrees C over 2 years. The long-term reproducibility and the suitability of this analytical method were demonstrated within the last decade through the analysis of about 7000 samples during the clinical development of i.v. and oral formulations of vinorelbine. Because vinorelbine binds mainly to platelets and blood cells and because this binding is rapidly reversible and highly influenced by environmental conditions, drug concentration in plasma may be highly influenced by the sampling conditions and the centrifugation process used to separate blood cells from plasma. Therefore, this method was developed in blood and then used for sample analyses in routine. The major benefit was that it was easy for nurses to directly collect blood instead of plasma and that reduced volume of sampling could be withdrawn from frail patients. Furthermore, the analysis in blood enabled to quantify vinorelbine and 4-O-deacetyl vinorelbine concentrations for a longer period of time, which resulted in a more accurate evaluation of pharmacokinetic parameters.

Intravenous busulfan in adults prior to haematopoietic stem cell transplantation: a population pharmacokinetic study.

An IV form of busulfan (IV Bu) has recently become available for high dose conditioning regimen before haematopoietic stem cell transplantation (HSCT). This IV form is expected to reduce the high pharmacokinetic variability exhibited with oral busulfan and as a result, to better target the plasma area under the curve (AUC). Pharmacokinetics (PK) of IV Bu was investigated on 127 adult patients (333 PK administrations) who received 0.8 mg.kg-1 of Bu as a 2-h infusion every 6 h over 4 days, followed by cyclophosphamide (60 mg.kg-1 day-1x2). A retrospective population PK analysis was carried out to search for important predictive factors of IV Bu PK and to develop a limited sampling strategy (LSS) through Bayesian methodology. The analysis was conducted using the Non Linear Mixed Effect methodology and included a validation process on an independent data set. Adjusted Ideal Body Weight (AIBW) and Body Surface Area (BSA) were the best covariates to explain the inter-patient variability. The final inter-patient variability (CV=16%) in IV Bu clearance (Cltot) was estimated close to the intra-patient variability (CV=13%). There was neither age-dependency nor gender effect. IV Bu Cltot was not affected by elevated hepatic enzymes or by co-administration of either fluconazole or acetaminophen, and was not altered in heavily pre-treated or pre-transplanted patients. Normalised Cltot based on either AIBW or BSA was comparable between normal and obese patients (BMI=18-26.9 kg.m-2, >26.9 kg.m-2, respectively) whereas significant differences existed when based on either actual (ABW) or ideal body weight (IBW). As a consequence, no dose adjustment is required in obese patients when using a AIBW- or BSA-based dose calculation. A fixed dose of 0.80 mg.kg-1 of AIBW or 29 mg.m-2 of BSA yielded an average AUC of 1,200 microM.min, with 80% of patients within the "therapeutic" AUC range of 900-1,500 microM.min. Alternatively, 0.80 mg.kg-1 based on either ABW or IBW for normal patients and on AIBW for obese patients would achieve the same performance. A limited sampling strategy based on a Bayesian methodology was developed and validated on an independent dataset: AUCs obtained from one to two samplings were demonstrated to be reliably estimated.

I.V. busulfan in pediatrics: a novel dosing to improve safety/efficacy for hematopoietic progenitor cell transplantation recipients.

A retrospective population pharmacokinetic (PPK) analysis was performed in 24 pediatric patients (PEDS) (0.45-16.7 years old) receiving i.v. busulfan/cyclophosphamide (i.v. Bu/Cy 4) regimen prior to allogeneic hematopoietic stem cell transplantation. I.V. Bu doses were given as a 2-hour infusion every 6 h over 4 days. Initial dosing of i.v. Bu was 1 mg/kg for children < or =4 years old and 0.8 mg/kg for patients >4 years old. Bu plasma concentrations at doses 1, 9 and 13 were analyzed through a multivariate NONMEM analysis. A close log-linear relationship between body weight (BW) and i.v. Bu clearance was demonstrated with no further age-dependency or gender effect. The interpatient coefficient of variation (CV) in Bu clearance significantly decreased from 56% (covariate-free model) to 19% (BW covariate model) and reproducible i.v. Bu exposure between doses was illustrated (intraindividual CV=9%). Based on the PPK model, a novel Bu dosing regimen (ie: doses in mg/kg adjusted to discrete weight categories) for a better AUC targeting was developed by simulation on 1000 patients. Age-based dosing was demonstrated not to be clinically relevant with i.v. Bu. Use of the new BW-based dosing appears to be more appropriate for the PEDS.

Phase I and pharmacokinetic study of the new vinca alkaloid vinflunine administered as a 10-min infusion every 3 weeks in patients with advanced solid tumours.

BACKGROUND: Vinflunine is a novel vinca alkaloid obtained by semi-synthesis using super-acidic chemistry to selectively introduce two fluorine atoms at the 20' position of vinorelbine. In human tumour xenografts, vinflunine showed definite antitumour activity in seven out of 11 tumours tested compared with three out of 11 for vinorelbine. PATIENTS AND METHODS: In this phase I study, vinflunine was administered to 31 patients with advanced malignancies as a 10-min i.v. infusion every 3 weeks according to an escalating schedule of doses between 30 and 400 mg/m(2). RESULTS: Pharmacokinetic parameters and toxicities were assessed and, at 400 mg/m(2), three out of five patients experienced dose-limiting toxicity. At the maximum tolerated dose (MTD), i.e. 400 mg/m(2), the toxicity profile of vinflunine consisted mainly of mucositis, constipation and neutropenia of short duration. Vinflunine area under the curve increased as a proportion of the administered dose whereas no saturation of elimination was observed. CONCLUSION: The MTD of vinflunine was achieved at 400 mg/m(2) every 3 weeks. According to protocol rules, the recommended dose was established at 350 mg/m(2). A preliminary assessment of first patients included in early phase II trials led to reduction of the recommended dose to 320 mg/m(2) every 3 weeks for further development of vinflunine. Three partial responses (two in breast carcinoma, one in renal cell carcinoma) suggest that activity is likely to be seen in less heavily pretreated patient populations.

New sensitive liquid chromatography method coupled with tandem mass spectrometric detection for the clinical analysis of vinorelbine and its metabolites in blood, plasma, urine and faeces.

A new sensitive and specific liquid chromatographic method coupled with tandem mass spectrometric detection was set up and validated for the simultaneous quantitation of vinorelbine, its main metabolite, 4-O-deacetylvinorelbine and two other minor metabolites, 20'-hydroxyvinorelbine and vinorelbine 6'-oxide. All these compounds, including vinblastine (used as internal standard) were deproteinised from blood, plasma and faeces (only diluted in urine), analysed on a cyano column and detected on a Micromass Quattro II system in the positive ion mode after ionisation, using an electrospray ion source. Under tandem mass spectrometry conditions, the specific product ions led one to accurately quantify vinorelbine and its metabolites in all biological fluids. In whole blood, linearity was assessed up to 200 ng/ml for vinorelbine and up to 50 ng/ml for the metabolites. The limit of quantitation was validated at 250 pg/ml for both vinorelbine and 4-O-deacetylvinorelbine. In the other biological media, the linearity was assessed within a same range and the limit of quantitation was adjusted according to the expected concentrations of each compound. This method was initially developed in order to identify the metabolite structures and to elucidate the metabolic pathway of vinorelbine. Thanks to its high sensitivity, this method has enabled the quantitation of vinorelbine and all its metabolites in whole blood over 168 h (i.e., 4-5 elimination half lives) whilst the previous liquid chromatographic methods allowed their measurement for a maximum of 48-72 h. Therefore, using this method has improved the reliability of the pharmacokinetic data analysis of vinorelbine.

Information tools for exploratory data analysis in population pharmacokinetics.

For a group of individuals, population pharmacokinetic studies describe the interindividual variability through a statistical distribution. These studies conducted during the drug development serve as a useful marker of the safety of the drug, provide information that might be decisive for future experiments and, in a clinical context, help establish guidelines for optimal use in each patient. As complementary tools to the existing statistical and graphical techniques for population pharmacokinetic data analysis, indexes derived from information theory were used to select the most appropriate modelfor the statistical distribution, to detect atypical individuals, and to screen influential covariates. The rationale for using these indexes is shown using simulated and real data.

Oral vinorelbine pharmacokinetics and absolute bioavailability study in patients with solid tumors.

BACKGROUND: Vinorelbine is a vinca alkaloid obtained by hemisynthesis, which makes the molecule more lipophilic than the other vincas. An injectable formulation is already marketed for the treatment of non small cell lung cancer (NSCLC) and advanced breast cancer (ABC). A new oral form has been developed and its file registration is being submitted. As part of its development, a clinical study was conducted to determine the absolute bioavailability and pharmacokinetics of oral vinorelbine administered as softgel capsules, and to evaluate its safety profile compared with intravenous administration. PATIENTS AND METHODS: Thirty-two patients with solid tumours were included in the study. Patients fasted and were randomised to receive vinorelbine on day 1, either as a 20 minute intravenous (i.v.) infusion of 25 mg/m2 or as softgel capsules at a dose of 80 mg/m2. Patients were treated with the alternate route after a one week wash-out period. Blood and urine samples for pharmacokinetic analysis were collected during each vinorelbine administration. Safety was assessed after each administration using the CALGB/expanded CTC classification. RESULTS: Twenty-four patients were eligible for pharmacokinetic evaluation. Oral vinorelbine was rapidly absorbed at 80 mg/m2 (Tmax 1.4 +/- 0.7 h) and showed a bioavailability of 43 +/- 14, and close to 40% based on AUC(last) and AUC(inf), respectively. A bioequivalence analysis was conducted on dosage-normalised blood exposures. Equivalence was demonstrated between 80 mg/m2 oral and 30 mg/m2 i.v., and between 60 mg/m2 oral and 25 mg/m2 i.v. The inter-individual variability was equivalent for both routes (CV: 38% and 39% for oral and i.v., respectively). A correlation was found in both methods between AUClast and % nadir variation in white blood cells (WBC) and polymorphonuclears (PMN). More cases of neutropenia (all grades pooled), leucopenia (grades 3-4 only) and nausea (grades 2-3) were induced by 80 mg/m2 oral vinorelbine than by 25 mg/m2 i.v. The greatest intensity of these effects, following oral administration, probably reflects the higher, observed drug exposure. CONCLUSION: At therapeutic dosage levels, pharmacokinetic behaviour and safety profiles were similar for both routes. The absolute bioavailability of the oral vinorelbine (new, soft gelatine capsule) was close to 40%. Inter-individual variability in drug exposure was equivalent in both routes. The pharmacokinetic/pharmacodynamic (PK/PD) relationship in haematological toxicity was independent of the routes of administration. Reliable, corresponding doses between oral and i.v. vinorelbine were established, which will result in bioequivalent AUC.

Which bioequivalence study for a racemic drug? Application to milnacipran.

Milnacipran, a new non tricyclic antidepressant drug, is a racemic mixture (F2207) composed of two enantiomers: F2695 and F2696, both demonstrated to be active. A randomized open label, single-dose latin square study was undertaken in 24 healthy volunteers to compare, based on racemate data, the relative bioavailability of two new formulations to that of a reference formulation. Later on, as suggested by actual regulatory trend, analysis was carried out on enantiomer data, although in a supportive way. Bioequivalence was assessed on calculation of 90% confidence intervals for log-transformed Cmax and AUC(0-infinity) and on Wilcoxon test for Tmax with a 5% level of significance. Based on racemate data, both test formulations were demonstrated to be equivalent to the reference capsule in terms of Cmax and AUC-(0-infinity). Differences in Tmax reached statistical significance, although their mean magnitude was small, and probably not relevant when related to antidepressant long-term therapy. When considering the test capsule - reference capsule comparison, the equivalence demonstrated for the racemate reflect that of each enantiomer. On the contrary, equivalence between the test tablet and the reference capsule demonstrated for the racemate, is not supported by both enantiomers as Cmax of F2696 fails to reach bioequivalence criteria, making more uncertain the conclusion of bioequivalence. From this experience, it seems than when equivalence is demonstrated close to the limits for the racemate, it is difficult, especially for a low variability drug such as milnacipran, to comply with equivalence criteria for both enantiomers.

Pharmacokinetics of milnacipran in liver impairment.

The pharmacokinetics of single 50 mg oral and intravenous doses of milnacipran, a new non tricyclic antidepressant drug, were compared in 11 chronic liver impaired (LI) subjects and in 6 control subjects. Hepatic impairments, classified according to the PUGH scale were moderate (1 grade A), intermediate (6 grade B) and severe (4 grade C). Concentrations of unchanged drug and its conjugated form (its main metabolite) were measured in plasma and urines. In control subjects, milnacipran present high absolute bioavailability (mean value of 90%). Around 50% of the dose are excreted in urines as unchanged, while around 14% are excreted as glucuroconjugate. The remaining is composed of free and conjugated phase I inactive metabolites. Administration of milnacipran in LI subjects results in non significant changes in its pharmacokinetics, although its variability is increased. Unchanged drug exposure is not modified in LI subjects, while plasma levels of the conjugate are slightly decreased compared to the control group. This could either be due to a slight reduction in the conjugation process, or to a change in the distribution of the drug as urine excretion of both unchanged and conjugated forms are not modified compared to the control group. A few LI subjects present supra-bioavailability resulting in higher drug exposure after oral administration than after intravenous infusion. These modifications are not clinically relevant as drug exposure of the parent drug is not modified. As the unchanged drug is the only compound responsible for the activity of milnacipran, no dosage adjustment is needed in patients presenting liver impairment.

Pharmacokinetics of milnacipran in renal impairment.

The pharmacokinetics of a single 50 mg dose of milnacipran, a new non tricyclic antidepressant drug, were compared in 8 chronic renal failure subjects (Clc(reat) between 9 to 84.5 ml.min(-1)) and in 6 healthy volunteers. Concentrations of unchanged (F2207 racemate and F2695 and F2696, enantiomers) and glucuroconjugated drug (main metabolite) were measured using HPLC and GC-MS. As for drugs mainly eliminated via renal route, the pharmacokinetics of milnacipran were markedly affected by impaired renal function with the elimination half-life of severely impaired subject being approximately three times that of the control group. Milnacipran apparent total clearance and renal clearance were positively correlated with glomerular filtration rate, while non-renal clearance and apparent volume of distribution were unaffected by renal impairment. Plasma concentrations of the glucuroconjugate were gradually increased in plasma, while its total urine excretion remained unchanged. As for the racemate, pharmacokinetics of each enantiomer were modified by renal failure, although, as predictable from its higher renal clearance value, it was more marked for F2696 than for F2695. Considering that modifications were shown to be proportional to the degree of renal impairment and that milnacipran presents low variability, the necessary dose adjustment is therefore easy to predict.

Validated method for the determination of idazoxan in human plasma by liquid chromatography with tandem mass spectrometric detection.

A liquid chromatography-tandem mass spectrometry method for the determination of idazoxan in human (heparin) plasma is presented, which was developed and validated using 500 microl of sample. Sample preparation consisted of the addition of fluoroidazoxan as the internal standard, extraction at alkaline conditions into tert.-butyl methyl ether, followed by centrifugation, evaporation of the solvent and reconstitution in methanol. After a short chromatographic run, detection took place by ionspray tandem mass spectrometry in positive ion mode. Validation results on linearity, specificity, accuracy, precision and stability, as well as application of the method to samples from a clinical trial, are shown. The validated calibration range is from 0.300 to 100 ng/ml, with accuracy (bias) and precision (coefficient of variation) being below 15% at all levels. A sample throughput of, typically, 150 per day can be achieved.

Pharmacokinetics of milnacipran in comparison with other antidepressants.

Despite the large number of antidepressants currently available, it is still necessary to develop new drugs that combine the efficacy of the older antidepressant with improved safety, tolerability and therapeutic profile that will allow them to be used in depressed patients who are elderly or with cardiac, renal or hepatic disease. This article reviews the pharmacokinetic characteristics of the tricyclic antidepressants, the selective serotonin reuptake inhibitors (SSRIs) and more recently introduced antidepressants such as venlafaxine and nefazodone. Milnacipran (Ixel), a novel drug, combines antidepressant efficacy with some unique pharmacokinetic features. A summary of its pharmacokinetic profile shows that milnacipran has a high bioavailability, low plasma protein binding and that it is largely eliminated in the urine as parent drug or as a glucuronide. These features suggest that the likelihood of interactions with other drugs given concurrently is lower than would occur with most second generation antidepressants and the tricyclic antidepressants. Furthermore, studies in patients with liver dysfunction, and in the elderly, suggest that dose adjustment is not necessary when milnacipran is administered to these patients. The decrease in milnacipran elimination is correlated to the degree of renal impairment, allowing adjustment of schedules. In comparison to earlier antidepressants, milnacipran combines efficacy and a relatively low side-effect profile with the added advantage of fewer interactions with drugs that may be given concurrently.

Involvement of P-glycoprotein in an in vitro blood-brain barrier model.

The P-glycoprotein (P-gp) multidrug transporter is present at the luminal face of the brain capillary endothelial cells that contribute to the blood-brain barrier. To study its role in transendothelial anticancer drug transport, we made use of a co-culture system formed of bovine brain capillary endothelial cells and astrocytes which allows the in vitro maintenance of specialized properties of the brain endothelial cells, including expression of P-gp as assessed by Northern and Western blot analyses. Vinblastine, an anticancer drug substrate for P-gp and known not to enter the brain, was found to be poorly transferred across the endothelial cell monolayer. This low vinblastine transport was however strongly increased in the presence of verapamil, a well known P-gp blocker. Moreover, verapamil was shown to increase the accumulation of the anticancer drug in the brain endothelial cells through inhibition of drug efflux. These results suggest that P-gp activity evidenced in the co-culture model is involved in the low transendothelial transport of vinblastine, thus supporting the conclusion that P-gp expressed at the blood-brain barrier level may prevent xenobiotics, including anticancer drugs, from entering the central nervous system.

Selective drug transport and P-glycoprotein activity in an in vitro blood-brain barrier model.

To determine whether compounds are able to reach the neural microenvironment, a blood-brain barrier (BBB) co-culture model has been recently developed with bovine brain capillary endothelial cells and newborn rat astrocytes. In this study, the permeability of confluent endothelial cells to various compounds and the functional activity of P-glycoprotein (P-gp), an ATP-dependent pump known to efflux drugs from multidrug-resistant tumoral cells, was assessed. The permeability of the lipophilic compounds imipramine and sulpiride differed in relation to their structure. A good correlation was observed with in vivo brain extraction levels. P-gp activity was estimated by measuring the uptake of [(3)H]vinblastine by the endothelial cells, with or without verapamil, which is known to reverse drug resistance. Intracellular accumulation of the vinca alkaloid was strongly increased after addition of verapamil, suggesting that P-gp is active in these cells. These results provide further support for the use of the co-culture model of bovine brain endothelial cells and rat astrocytes to screen new centrally active drugs.