A Sensitive Triple Quadrupole Liquid Chromatography Mass Spectrometric Method for the Estimation of Valproic Acid in K2EDTA Human Plasma using Furosemide as the Internal Standard

A valproic acid is primarily being used in the treatment of epilepsy is a histone deacetylase inhibitor and it is under investigation for treatment of HIV and various cancer indications. A specific, sensitive and fast bioanalytical LC-MS/MS method was developed with furosemide as an internal standard (IS) and thoroughly validated for the quantitation of valproic acid using turbo ion spray in negative ion mode. The analyte and IS was extracted using protein precipitation. The chromatographic separation of analytes from extracted matrix was achieved using a Chromolith RP 18e (2.0×50 mm) column with a gradient mobile phase comprising of acetonitrile and purified water with acetic acid. The elution of both peaks was achieved within 5.2 min, with retention times of 2.55 min and 1.67 min for valproic acid and IS, respectively. Quantitation of valproic acid was achieved by the pseudo SRM transition pairs (m/z 142.8→m/z 142.8), and SRM transition pair (m/z 328.8 →m/z 204.6) for internal standard.The calibration standards of valproic acid showed linear over a range from 50 to 40 000 ng/mL, with a lower limit of quantitation of 50 ng/mL with accuracy of 3.74% and precision of 5.06%. The bias for inter- and intra-batch assays was 1.24-6.14% and 3.85-11.84%, respectively; while the corresponding precision was 2.56-16.37% and 1.29-11.34%, respectively. The developed method was used to monitor valproic acid levels in clinical samples. Because of higher sensitivity, this method can be used for therapeutic drug monitoring in pediatric subjects.

Infusion Rate Dependent Pharmacokinetics of Bendamustine with Altered Formation of γ-hydroxybendamustine (M3) Metabolite Following 30- and 60-min Infusion of Bendamustine in Rats

Bendamustine is an alkylating agent administered as 1 h intravenous infusion in the clinic for the treatment of malignant haematological cancers. The aim of the study was to evaluate the pharmacokinetics of bendamustine and its key cytochrome P 450 (CYP) 1A2 mediated γ-hydroxybendamustine (M3) metabolite after 30- and 60-min intravenous infusion of bendamustine in rats. 2 groups were assigned to receive bendamustine either as 30- or 60-min infusion and doses were normalized to 15 mg/kg for the sake of statistical evaluation. Serial pharmacokinetic samples were collected and were analysed for the circulatory levels of bendamustine and its M3 metabolite. Standard pharmacokinetic parameters were generated for bendamustine and its M3 metabolite. Regardless of the intravenous regimens, Cmax coincided with end of infusion for both bendamustine and its M3 metabolite. Immediately after stoppage of infusion, a rapid decline in the plasma levels occurred for both bendamustine and M3 metabolite. The Cmax and AUC0-∞ parameters for bendamustine after 60-min infusion were 1.90 and 1.34-fold higher; while CL was lower by 1.32-fold as compared to the 30-min infusion. In contrast, the Cmax and AUC0-∞ after 30-min infusion for the M3 metabolite was 2.15- and 2.78-fold greater; while CL was 2.32-fold lower when compared to the 60-min infusion. However, T1/2 and Vz values were similar between the 2 intravenous treatments for bendamustine or the M3 metabolite. The data unequivocally confirmed the existence of differential pharmacokinetics of bendamustine and its M3 metabolite as the function of the duration of intravenous infusion.

Limited Sampling Strategy for the Prediction of Area Under the Curve (AUC) of Statins: Reliability of a Single Time Point for AUC Prediction for Pravastatin and Simvastatin

Statins are widely prescribed medicines and are also available in fixed dose combinations with other drugs to treat several chronic ailments. Given the safety issues associated with statins it may be important to assess feasibility of a single time concentration strategy for prediction of exposure (area under the curve; AUC). The peak concentration (Cmax) was used to establish relationship with AUC separately for pravastatin and simvastatin using published pharmacokinetic data. The regression equations generated for statins were used to predict the AUC values from various literature references. The fold difference of the observed divided by predicted values along with correlation coefficient (r) were used to judge the feasibility of the single time point approach. Both pravastatin and simvastatin showed excellent correlation of Cmax vs. AUC values with r value ≥ 0.9638 (p<0.001). The fold difference was within 0.5-fold to 2-fold for 220 out of 227 AUC predictions and >81% of the predicted values were in a narrower range of >0.75-fold but <1.5-fold difference. Predicted vs. observed AUC values showed excellent correlation for pravastatin (r=0.9708, n=115; p<0.001) and simvastatin (r=0.9810; n=117; p<0.001) suggesting the utility of Cmax for AUC predictions. On the basis of the present work, it is feasible to develop a single concentration time point strategy that coincides with Cmax occurrence for both pravastatin and simvastatin from a therapeutic drug monitoring perspective.

Pharmacokinetics, tissue distribution and identification of putative metabolites of JI-101 - a novel triple kinase inhibitor in rats

JI-101, chemically 1-[1-(2-amino-pyridin-4-ylmethyl)-1H-indol-4-yl]-3-(5-bromo-2-methoxy-phenyl)-urea hydrochloride, is a novel orally active kinase inhibitor, which has shown potent in vitro and in vivo anticancer activity against a variety of cancer cell lines and xenografts. It is currently entering Phase II clinical development for the treatment of solid tumors. The aim of the study is to assess the metabolic stability of JI-101 in various pre-clinical and human liver microsomes, to identify the major CYPs (cytochrome β450) involved in the metabolism of JI-101 and identification of putative metabolites. We have also studied the pharmacokinetics, tissue distribution and excretion of JI-101 in Sprague Dawley rats. JI-101 was found to be stable in various liver microsomes tested. JI-101 is highly permeable and not a substrate for P-gp (permeability glycoprotein). JI-101 excreted through bile along with its mono- and di-hydroxy metabolites. Following oral administration, JI-101 was rapidly absorbed, reaching Cmax within 2 h. The t½ of JI-101 with intravenous and oral route was found to be 1.75 ± 0.79 and 2.66 ± 0.13 h, respectively. The Cl and Vd by intravenous route for JI-101 were found to be 13.0 ± 2.62 mL/min/kg and 2.11 ± 1.42 L/kg, respectively. The tissue distribution of JI-101 was extensive with rapid and preferred uptake into lung tissue. Overall, the oral bioavailability of JI-101 is 55% and the primary route of elimination for JI-101 is feces.

Baicalin, an emerging multi-therapeutic agent: pharmacodynamics, pharmacokinetics, and considerations from drug development perspectives

Baicalin was extensively researched for utility in a number of therapeutic areas owing to its anti-inflammatory, anti-oxidant, anti-bacterial, and anti-cancer properties. A number of preclinical studies, in vitro work, and mechanistic studies were performed to understand the absorption, distribution, metabolism, and excretion profiles of baicalin. The absorption of baicalin involved several complexities: the restriction to two distant sites; the conversion of baicalin to baicalein; the possible role of transporter(s); and enhanced absorption due to breakdown of conjugates by beta-glucuronidase. Limited distribution data suggest that baicalin reached several sites such as the brain, eye lens, thymus, etc. Hepatobiliary recycling also served as a distribution phase for sustained delivery of baicalin. Metabolism data suggest the rapid conversion of baicalin to baicalein, which was extensively subjected to Phase 2 metabolism, conjugates baicalein glucuronide/sulfate have been identified. Limited excretion data suggest involvement of renal and faecal routes--glucuronide and sulfate conjugates were excreted in urine and faeces (via biliary excretion). The published data on baicalin suggest imminent challenges for developing baicalin and/or during co-administration with other agents. These challenges are absorption related (transporter or changes in the microenvironment), metabolism related (CYP2B6 induction and/or CYP2E1 inhibition), and excretion/efflux related (competitive biliary pathway and/or OATP1B1 transport).

Altered intravenous pharmacokinetics of topotecan in rats with acute renal failure (ARF) induced by uranyl nitrate: Do adenosine A1antagonists (selective/non-selective) normalize the altered topotecan kinetics in ARF?

A series of exploratory investigations with multiple agents was carried out in normal rats and in rats with uranyl nitrate-induced acute renal failure to understand the disposition characteristics of intravenous topotecan (TPT) used as a model substrate. The disposition of TPT was unaltered in normal rats when treated with methotrexate, whereas treatment with probenecid increased the systemic exposure of TPT. In case of uranyl nitrate-induced acute renal failure (UN-ARF) rats, the systemic exposure of TPT was increased when compared with normal rats, whereas in UN-ARF rats treated with probenecid a further reduction in renal clearance of TPT was noted as compared with that of UN-ARF induced rats. Thus, TPT may be involved in the tubular secretory pathway when a passive glomerular filtration pathway for elimination was not possible. The disposition of TPT did not normalize in UN-ARF rats when treated with caffeine, a non-selective adenosine A1 receptor antagonist, whereas the selective adenosine A1 receptor antagonist (1,3-dipropyl-8-phenylxanthine, DPPX) normalized TPT pharmacokinetic disposition by improving renal function. Renal excretion studies demonstrated that CLR improved by almost fivefold following DPPX treatment in ARF rats. In addition, the qualitative stability/metabolism pattern of TPT in liver microsomes prepared from various groups of rats (normal rats, UN-ARF rats, rats treated with DPPX, and UN-ARF rats treated with DPPX) was found to be similar. In summary, using a pharmacokinetic tool as a surrogate, it has been shown that the pharmacokinetic disposition of TPT improved considerably upon treatment with DPPX, a selective adenosine A1 antagonist.

Drug-drug interaction studies in preclinical species: should metabolite(s) kinetics be studied?

Drug-drug interaction studies are important building blocks in drug development to understand the perceived risk of a purported interaction due to the differing clinical pharmacology attributes of the co-administered drugs. Two case studies are presented that justify the importance of evaluating the metabolite kinetics data along with the parent in a preclinical model. Atorvastatin and verapamil have interesting clinical pharmacology attributes in that both agents are substrates and/or inhibitors of the dual cytochrome P450 (CYP) 3A4 and P-glycoprotein (Pgp) efflux transporter interplay. As articulated by the two case studies, the presence of metabolite kinetic data (i.e., norverapamil) provided unequivocal evidence in order to tease out the actual pathway responsible for the interaction between atorvastatin and verapamil. Therefore, consideration for metabolite kinetics, wherever feasible, appears to be prudent in defining the interaction liability between the two agents in a preclinical model.

Effect of 1-aminobenzotriazole on thein vitrometabolism and single-dose pharmacokinetics of chlorzoxazone, a selective CYP2E1 substrate in Wistar rats

The aim of this study was to study the effect of 1-aminobenzotriazole (ABT) on in vitro metabolism, oral, and intravenous (IV) pharmacokinetics of chlorzoxazone (CZX) in rats. Enzyme kinetics of CZX was performed with rat and human liver microsomes and pure isozyme (CYP2E1) with and without ABT. The enzyme kinetics (V(max) and K(m)) of the formation of 6-hydroxychlorzoxazone (OH-CZX) was found to be similar among rat liver microsomes (3486 pmol mg protein(-1) min(-1) and 345 microM), human liver microsomes (3194 pmol mg protein(-1) min(-1) and 335 microM) and pure isozyme (3423 pmol mg protein(-1) min(-1) and 403 microM), but K(I) and K(inact) values for ABT towards the ability to inhibit the formation of OH-CZX from CZX varied between liver microsomes (rat: 32.09 microM and 0.12 min(-1); human: 27.19 microM and 0.14 min(-1)) and pure isozyme (3.18 microM and 0.29 min(-1)). The novel robust analytical method was capable of quantifying CZX, OH-CZX, and ABT simultaneously in a single run, and the method was used for both in vitro and in vivo studies. Pre-treatment of rats with ABT prior to oral and IV administration of CZX significantly decreased the clearance (threefold) and consequently increased the AUC of CZX (approx. three- to fourfold). When rats were pre-treated with ABT, the formation of OH-CZX was completely blocked after oral and IV administration; however, we were able to measure OH-CZX in rats administered with CZX by oral and IV routes without pre-treatment of ABT. The oral bioavailability of CZX was approximately 71% when dosed alone and reached 100% under pre-treatment with ABT. The t(1/2) values of CZX was significantly prolonged for oral dosing compared with IV dosing under pre-treated conditions with ABT, suggesting an involvement of pre-systemic component in the disposition of CZX. The pharmacokinetic parameters of ABT did not change when it was dosed along with CZX (oral and IV), indicating that either CZX or OH-CZX had no effect on disposition of ABT. The plasma concentrations of ABT were above and beyond the required levels to inhibit CYP2E1 enzyme for at least 36 h post-treatment.

Prediction of clinical pharmacokinetic parameters of linezolid using animal data by allometric scaling: applicability for the development of novel oxazolidinones

1. Allometric scaling has previously been used as an effective tool for the prediction of human pharmacokinetic data. The pharmacokinetic data for linezolid, a novel oxazolidinone to treat Gram-positive pathogens, in mice, rats and dogs were subjected to simple allometric scaling. Generated allometric equations for parameters such as clearance (CL), volume of distribution (Vss) and elimination rate constant (K10) were used to predict human pharmacokinetic parameters including elimination half-lives. In addition, the human plasma concentration-time curve was simulated using a one-compartmental model. 2. Application of simple allometry (Y = aWb) for animal parameters such as CL, Vss, and K10 showed excellent allometric fit (r > or = 0.98). The allometric equations for CL, Vss, and K10 were -0.5465W(0.6595), -0.1369W(0.9246), and -0.4117W(-0.3139), respectively. The confidence in predictability of CL and Vss parameters was particularly high since the allometric exponents of CL and Vss almost approached the suggested values of 0.75 and 1.00, respectively. 3. Animal pharmacokinetic parameters generated in the present authors' laboratories for linezolid were in close agreement with reported literature values. The predicted human values for CL (4.68 l h(-1)), Vss (37.07 litres), and K10 (0.10 h(-1)) were within the range observed for linezolid in the literature (CL = 4-10.5 l h(-1); Vss = 21-53 litres; K10 = 0.09-0.3 h(-1)). The human half-life (t(1/2)) predicted using allometry (6.9 h) was similar to reported values in humans of 5 h. In summary, the retrospective analysis for linezolid suggests that allometric scaling can be used as a prospective tool for predicting human pharmacokinetic parameters of novel oxazolidinones.

Influence of cholestyramine on the pharmacokinetics of rosiglitazone and its metabolite, desmethylrosiglitazone, after oral and intravenous dosing of rosiglitazone: impact on oral bioavailability, absorption, and metabolic disposition in rats

The possible influence of the bile acid-sequestering agent cholestyramine (CSA), which is a basic co-medication in hypercholesterolemic patients, on the pharmacokinetics of rosiglitazone (RGL) and its circulating metabolite desmethylrosiglitazone (DMRGL) was investigated following a single oral and intravenous dose of RGL to Wistar rats. The pharmacokinetic parameters of RGL and DMRGL were evaluated following oral or intravenous administration of RGL to rats at 10 mg kg-1 with and without pre-treatment (0.5 h before RGL administration) of CSA at 0.057, 0.115, 0.23 and 0.34 g kg-1 doses. With an increase in CSA dose there was dose-dependent decrease in area under the curve (AUC)(0-infinity) and Cmax with no change in Tmax, Kel and t1/2 values for both RGL and DMRGL following oral administration of RGL. The oral bioavailability of RGL was reduced by 19.9, 35.6, 53.8 and 72.0% in rats following pre-treatment with CSA at 0.057, 0.115, 0.230 and 0.340 g kg-1, respectively. There was no change in the above-mentioned pharmacokinetic parameters for RGL and DMRGL in rats when RGL was given intravenously following pre-treatment with the above-mentioned oral doses of CSA. Another objective of the study was to determine the effect of staggered oral CSA dosing at 1, 2 and 4 h after oral RGL administration at 10 mg kg-1. AUC(0-infinity) of RGL and DMRGL was reduced following CSA staggered administration at 1 h, whereas 2- and 4-h staggered dose administration of CSA had no effect on the AUC(0-infinity) of RGL and DMRGL. Irrespective of CSA staggered dose administration there was no change in other pharmacokinetic parameters, namely Cmax, Tmax, Kel and t1/2. The apparent formation rate constant (Kf) of DMRGL was also calculated to show that only the absorption of RGL was affected, not the apparent formation rate of DMRGL. The authors also studied the in vitro adsorption of RGL (100, 250, 500 microg ml-1) at various pH conditions (pH 2, 4 and 7) and different concentrations of CSA (15, 30, 60 and 120 mg ml-1). The percentage binding of CSA was in the range 50-72% (at pH 2), 74-89% (at pH 4) and 97-100% (at pH 7). In conclusion, we carried out a systematic investigation demonstrating mechanistically the interaction potential of RGL when co-administered with CSA. The applicability of the metabolite data after intravenous and oral dosing and pH-based binding experiments further adds credence to the key findings.

Pre-clinical assessment of DRF 4367, a novel COX-2 inhibitor: evaluation of pharmacokinetics, absolute oral bioavailability and metabolism in mice and comparative inter-species in vitro metabolism

The aim of this study was to characterize the pharmacokinetics and determine the absolute bioavailability and metabolism of DRF 4367, a novel COX-2 inhibitor, in mice. In addition, the in vitro metabolism of DRF 4367 was studied in mouse, rat, dog, monkey and human liver microsomes. Following oral administration, maximum concentrations of DRF 4367 were achieved after about 1 h. Upon intravenous (IV) administration, the concentration of DRF 4367 declined in a bi-exponential fashion with a terminal elimination half-life of 4.0 h. The elimination half-life was unchanged with route of administration. The volume of distribution and systemic clearance of DRF 4367 in mice were 0.80 l h(-1) kg(-1) and 0.14 l kg(-1), respectively, after IV administration. The absolute oral bioavailability of DRF 4367 was 44%. In all species of liver microsomes examined, the primary route of metabolism for DRF 4367 was demethylation of benzyl methoxy to form a hydroxy metabolite (M1). The formation of this metabolite was mediated by CYP2D6 and CYP2C19 enzymes. M1 was not found to possess COX-2 inhibitory activity. Chemical-inhibition studies showed that quinidine (selective for CYP2D6) and ticlopidine (selective for CYP2C19) inhibited the formation of the hydroxy metabolite of DRF 4367, whereas potent inhibitors selective for other forms of CYP did not inhibit this oxidative reaction. Upon oral or IV administration of DRF 4367 to mice, unchanged DRF 4367, M1, the O-glucuronide conjugate of M1 (M1-G) and the O-sulfate conjugate of M1 (M1-S) were identified in bile.

'Open access' generic method for continuous determination of major human CYP450 probe substrates/metabolites and its application in drug metabolism studies

1. An 'open access' generic high-performance liquid chromatography method was developed for different combination sets each containing specific cytochrome P450 probe substrate and the corresponding metabolite. Method development, optimization and validation were carried out with the following combinations: phenacetin + paracetamol + internal standard (IS, celecoxib), bufuralol + hydroxybufuralol + IS, testosterone + 6beta-hydroxytestosterone + IS, chlorzoxazone + 6-hydroxychlorzoxazone + IS, coumarin + 7-hydroxycoumarin + IS, tolbutamide + hydroxytolbutamide + IS, and diazepam + desmethyldiazepam + IS. 2. The assay procedure involved a simple one-step liquid/liquid extraction followed by reverse phase chromatography (Inertsil ODS 3V column) employing a ternary gradient system and the eluate was monitored by a photodiode array/fluorescence detector. The standard curve for each compound, in the concentration range 0.1-10 microg ml(-1), in various sets was linear (r(2)>0.99) and absolute recoveries of all analytes were >90%. The lower limit of quantification was 0.1 microg ml(-1). The intraday precision and accuracy in the measurements of quality control were <15% relative standard deviation and <15% deviation from nominal values, respectively. 3. Each combination set was tested with individual chemical inhibitors (furafylline, quinidine, ketoconazole, disulfiram, diethyldithiocarbamate, sulphaphenazole and tranylcypromine) and all analytes were well resolved. Overall, the assay is simple, uses conventional instrumentation and provides a scope to analyse all cytochrome P450 combination sets continuously. The application of the method in the cytochrome P450 liability screen of novel compounds is also presented.

Quantitation of itraconazole in rat heparinized plasma by liquid chromatography-mass spectrometry

A liquid chromatographic-mass spectrometric (LC-MS) assay was developed and validated for the determination of itraconazole (ITZ) in rat heparinized plasma using reversed-phase HPLC combined with positive atmospheric pressure ionization (API) mass spectrometry. After protein precipitation of plasma samples (0.1 ml) with acetonitrile containing nefazodone as an internal standard (I.S.), a 50-microl aliquot of the supernatant was mixed with 100 microl of 10 mM ammonium formate (pH 4.0). An aliquot of 25 microl of the mixture was injected onto a BDS Hypersil C18 column (50x2 mm; 3 microm) at a flow-rate of 0.3 ml/min. The mobile phase comprising of 10 mM ammonium formate (pH 4) and acetonitrile (60:40, v/v) was used in an isocratic condition, and ITZ was detected in single ion monitoring (SIM) mode. Standard curves were linear (r2 > or = 0.994) over the concentration range of 4-1000 ng/ml. The mean predicted concentrations of the quality control (QC) samples deviated by less than 10% from the corresponding nominal values; the intra-assay and inter-assay precision of the assay were within 8% relative standard deviation. Both ITZ and I.S. were stable in the injection solvent at room temperature for at least 24 h. The extraction recovery of ITZ was 96%. The validated assay was applied to a pharmacokinetic study of ITZ in rats following administration of a single dose of itraconazole (15 mg/kg).

In vitro protein binding studies with BMS-204352: lack of protein binding displacement interaction in human serum

BMS-204352, a maxi-K channel opener, is currently under development for the treatment of stroke. Protein binding of BMS-204352 was determined in sera from several species, namely, rat, monkey, dog, and human. Data indicated that the compound was shown to be highly protein bound in serum from all species (ca. 99.6%). In order to test for the potential for drug-drug interactions and competitive displacement of BMS-204352 by diazepam, phenytoin, propranolol, and warfarin, in vitro experiments were performed using spiked human serum and ex vivo human plasma samples. Protein binding was determined using equilibrium dialysis for 4 h at maximal therapeutic concentrations for each drug alone or in appropriate combination in spiked serum samples. Ex vivo samples from a clinical BMS-204352 study (0, 1, and 24 h) were dialyzed separately after addition of diazepam, phenytoin, propranolol, or warfarin. Drug content in biological matrices was measured for radioactivity using liquid scintillation counting. Results indicated that (1) addition of diazepam, phenytoin, propranolol, or warfarin did not alter the free fraction of BMS-204352; (2) BMS-204352 did not displace diazepam, phenytoin, propranolol, or warfarin from their protein binding sites, and (3) comparison of ex vivo plasma samples after BMS-204352 dosing indicated no impact of BMS-204352 and/or its metabolites on the free fraction of diazepam, phenytoin, propranolol, or warfarin. In conclusion, the potential for a drug-drug interaction due to alterations in protein binding with BMS-204352 is unlikely.

Simultaneous quantitation of d7-nefazodone, nefazodone, d7-hydroxynefazodone, hydroxynefazodone, m-chlorophenylpiperazine and triazole-dione in human plasma by liquid chromatographic-mass spectrometry

A rapid and sensitive LC-MS assay was developed and validated for the simultaneous determination of d7-nefazodone (d7-NEF), nefazodone (NEF), d7-hydroxynefazodone (d7-OH-NEF), hydroxynefazodone (OH-NEF), m-chlorophenylpiperazine (mCPP), and triazole-dione (Dione) in human plasma using trazodone (TRZ) as the internal standard (IS). A 0.1 mL aliquot of the plasma sample was precipitated with 0.1 mL of acetonitrile and vortexed for 2 min. After centrifugation, 50 microL of supernatant was mixed with 100 microL of 10 mM ammonium formate (pH = 4.0), and a 50 microL aliquot was injected onto a BDS Hypersil C18 column at a flow rate of 0.3 mL/min. The mobile phase consisting of 10 mM ammonium formate (pH = 4) and acetonitrile, 55:45 v/v, was used in an isocratic system. The mass spectrometer was programmed to admit the protonated molecules at m/z 477.2 (d7-NEF), 493.3 (d7-OH-NEF), 197.0 (mCPP), 372.0 (IS), 470.4 (NEF), 458.0 (Dione) and 486.2 (OH-NEF). Standard curves were linear (r(2) >/= 0.994) over the concentration range of 4-1000 ng/mL for Dione and 2-500 ng/mL for all other analytes. The lowest standard concentrations were the lower limits of quantitation for each analyte. The mean predicted quality control concentrations for all analytes deviated by less than 14.3% from the corresponding nominal values; the intra-assay and inter-assay precisions of the assay for all analytes were within 10.5% relative standard deviation. All analytes including the internal standard were stable in the injection solvent at room temperature for at least 24 h. The extraction recovery of the various analytes ranged from 79.2 to 109.1%. The validated assay was applied to the analysis of clinical samples obtained from a human subject who simultaneously received d7-NEF and NEF orally.

Single dose and multiple dose pharmacokinetics of 2'-fluoro-2',3'-dideoxyadenosine and 2'-fluoro-2',3'-dideoxyinosine, anti-HIV agents, in rats

A single and multiple dose pharmacokinetic (PK) study was conducted in rats following oral administration of 2'-fluoro-2',3'-dideoxyadenosine (FddA) and 2'-fluoro-2',3'-dideoxyinosine (FddI) at three dose levels. Six rats/gender were assigned to one of the three FddA or FddI dose levels: 40, 250, and 1000 mg/kg/day. Three rats/gender were assigned to the PK study on day 1, while the remaining 3 rats/gender were assigned to the PK study on day 14. The rats received the appropriate doses of either FddA or FddI orally by gavage once a day for 14 days. Serial blood samples up to 24 h and cumulative urine samples (0-24 h) were collected on both days 1 and 14. Plasma and urine samples were analyzed for the concentrations of intact FddA and/or FddI using a validated assay. The data were subjected to non-compartmental PK analyses. Over the dose range of 40-1000 mg/kg. both FddA and FddI exhibited dose dependent pharmacokinetics in rats. Following FddA administration, there was a rapid and extensive in vivo conversion of FddA to FddI; FddI was the major circulating moiety as reflected by Cmax and AUC values (generally 2-3-fold greater than those of FddA at each dose level) as well as the amount excreted (%UR) in the urine. In contrast, following FddI administration, Cmax, AUC, and %UR values were 2-5-fold lower as compared to the FddI generated from FddA administration at each dose level, which also suggested that FddI was not absorbed as extensively as FddA. Based on the findings of this study, FddA is an excellent prodrug of FddI.

Sensitive triple-quadrupole mass spectrometric assay for the determination of BMS-181885, a 5-HT1 agonist, in human plasma following solid phase extraction

A sensitive, selective, accurate, precise and reproducible triple-quadrupole liquid chromatographic-mass spectrometric assay was developed and validated for BMS-181885 (I), a 5HT1 agonist, in human plasma using BMS-181101 as the internal standard (IS). The method involved solid phase extraction of plasma containing I and the IS using Isoelute CN cartridges. The supernatant was then evaporated to dryness at 40 degrees C. The residue was dissolved in 100 microL of the injecting solvent. The HPLC column was ODS-3, 2 x 100 mm. The mobile phase comprised 10 mM ammonium formate (pH = 4) and acetonitrile, 55:45 v/v, used in an isocratic condition. The mass spectrometer was programmed to admit the protonated molecules at m/z 461 (I) and m/z 370 (IS) via the first quadrupole filter and to select reaction monitoring of ions at m/z 152 for I and IS for the quantification. Standard curves were fitted to a weighted quadratic function over the concentration range 0.2-200 ng/mL. The lowest standard concentration (0.2 ng/mL) was experimentally established as the lower limit of quantitation of the assay. The mean predicted quality control concentrations deviated within +/- 11% of the corresponding nominal values; the intra-assay and inter-assay precisions were within 7.0% relative standard deviation. I was stable in the injection solvent at 4 degrees C for at least 24 h and for at least three freeze-thaw cycles. Freezer stability of I in plasma was demonstrated for at least 3 months. The extraction recovery of I was established as 97%. The validated assay was applied to a pharmacokinetic study of I in humans.

Sensitive liquid chromatographic-mass spectrometric assay for the simultaneous quantitation of nefazodone and its metabolites hydroxynefazodone m-chlorophenylpiperazine and triazole-dione in human plasma using single-ion monitoring

A sensitive, selective, accurate, precise and reproducible high-performance liquid chromatographic-mass spectrometric (LC-MS) assay was developed and validated for the simultaneous determination of nefazodone (NEF), hydroxynefazodone (OH-NEF), m-chlorophenylpiperazine (mCPP), and triazole-dione (Dione) in human plasma using trazodone (TRZ) as the internal standard (I.S.). The method involved simultaneous protein precipitation with acetonitrile and liquid-liquid extraction with methylene chloride, after which the organic layer was evaporated to dryness. The residue was reconstituted in 25% acetonitrile in 10 mM ammonium formate (pH 4.0), and an aliquot was injected onto a BDS Hypersil C18 column at a flow-rate of 0.3 ml/min. The mobile phase comprising of 10 mM ammonium formate (pH 4) and acetonitrile in 55:45 (v/v) was used in an isocratic condition. The mass spectrometer was programmed to admit the protonated molecules at m/z 197.0 (mCPP), 372.0 (I.S.) 470.4 (NEF), 458.1 (Dione), and 486.2 (OH-NEF). Standard curves were linear (r2 > or = 0.995) over the concentration range of 4-1000 ng/ml for Dione and 2-500 ng/ml for other analytes. The lowest standard concentrations were the lower limit of quantitation for each analyte. The mean predicted quality control (QC) concentrations for all analytes deviated less than -12.1% from the corresponding nominal values; the intra-assay and inter-assay precision of the assay for all analytes were within 7.0% relative standard deviation. All analytes including I.S. were stable in the injection solvent at room temperature for at least 24 h. The extraction recovery of the various analytes ranged from 67.3 to 86.5%. The validated assay was applied to a pharmacokinetic study of nefazodone.

High-performance liquid chromatographic-electrochemical assay for the quantitation of BMS-181885 in monkey plasma

A high-performance liquid chromatographic-electrochemical assay was developed and validated for the quantitation of BMS-181885 (I), an anti-migraine agent, in monkey plasma. The assay involved a solid-phase extraction of I and BMY-46317 (internal standard; I.S.) on a 1-ml cyano cartridge using the automatic solid-phase extraction cartridge (ASPEC) system. Immediately following the conditioning of the cyano column (3 ml of methanol and 2 ml of 1% glacial acetic acid), plasma (0.25 ml) was loaded on to the column. The column was then washed with a 3 ml of 0.1 M ammonium acetate buffer (pH 6). The final elution of the analytes was performed using 2 ml of methanol. The eluate was then evaporated to dryness (gentle stream of nitrogen at 40 degrees C) and the residue was dissolved in the mobile phase and injected on to a YMC basic column (15 cm x 4.6 mm; 5 microm particle size) at a flow-rate of 1 ml/min. A mixture of 0.1 M ammonium acetate at pH 6-acetonitrile-methanol (70:20:10, v/v) was used as the mobile phase. Standard curves, with a lower limit of quantitation of 2 ng/ml of I were linear (r2> or =0.998; range: 2-50 ng/ml). Based on the analysis of the quality control (QC) samples, the assay was both accurate and precise. The stability of I was established following freeze-thaw cycles and storage at or below -20 degrees C. The extraction recovery of I from monkey plasma was about 82%. The validated assay method was applied to determine the pharmacokinetics of I in monkeys following a single 1 mg/kg intravenous dose.

Effects of age, gender, and diurnal variation on the steady-state pharmacokinetics of BMS-181101, an antidepressant, in healthy subjects

OBJECTIVES

To investigate the effects of age, gender, and diurnal variation on the safety, tolerability, and steady-state pharmacokinetics of BMS-181101, an antidepressant, in humans.

METHODS

This was a multiple-dose parallel-design study in 51 healthy subjects (12 young and 12 elderly men and 12 young and 15 elderly women). Each subject received a 15 mg oral dose of BMS-181101 every 12 hours on days 1 through 6 and one dose on day 7. After the evening dose on day 6 and morning dose on day 7, serial blood samples were collected at specified times after administration. Plasma was analyzed for BMS-181101 with use of an HPLC method.

RESULTS

Male subjects tolerated BMS-181101 better than female subjects. The mean values for area under the plasma concentration-time curve over the dosing interval tau (AUC tau; 58.8 to 102.4 ng.hr/ml) and elimination half-life t1/2; 5.7 to 10.4 hours) for the elderly subjects were significantly greater than those for the young subjects (39.0 to 64.3 ng.hr/ml and 3.2 to 4.5 hours). The mean values for peak plasma concentration (Cmax; 14.7 to 25.2 ng/ml) and AUC tau (52.4 to 102.4 ng.hr/ml) for the women were significantly greater than those for the men (9.08 to 15.3 ng/ml and 39.0 to 73.6 ng.hr/ml). The mean values for Cmax (14.7 to 25.2 ng/ml) and AUC tau (54.8 to 102.4 ng.hr/ml) on the morning of day 7 were significantly greater than those after the evening dose on day 6 (9.08 to 17.3 ng/ml; 39.0 to 83.4 ng.hr/ml).

CONCLUSIONS

An initial lower dose or appropriate titration of daily doses of BMS-181101 may be necessary for the treatment of elderly and female subjects, and the pharmacokinetics of BMS-181101 exhibited significant diurnal effects.

Lack of effect of food on the steady state pharmacokinetics of BMS-181101, an antidepressant, in healthy subjects

The effect of food on the pharmacokinetics of BMS-181101, a new anti-depressant under development, was investigated in 12 healthy male volunteers at steady state. Each subject received a 15 mg oral dose of BMS-181101 twice a day (q 12 h) for 11 days and a morning dose of BMS-181101 on day 12. Six subjects were randomly assigned to receive BMS-181101 under fasted conditions from days 1 to 6 and then crossed over to fed conditions from days 7 to 12. The other six subjects received the reverse conditions, fed for days 1-6 and fasted for days 7-12. Serial blood samples were collected up to 12 h on days 6 and 12 following the administration of the morning dose. In addition, trough blood samples were collected on days 4, 5, 10, and 11 prior to the morning dose. Plasma samples were analyzed for intact BMS-181101 using a validated high-performance liquid chromatography method with an electrochemical detector. BMS-181101 was well tolerated both with and without ingestion of food. The statistical evaluation of the Cmin values indicated that steady state of BMS-181101 was achieved by the fourth day of dosing regardless of whether the subject was fasted or fed. When BMS-181101 was administered with food, Cmax was reduced by about 25% and tmax was prolonged by 1 h. However, AUCtau, t1/2, and time to attain steady state of BMS-181101 were not altered by ingestion of food. In summary, BMS-181101 can be given with food without adversely impacting the safety or pharmacokinetic profiles of the drug.

Assessment of dose proportionality, absolute bioavailability, and immunogenicity response of CTLA4Ig (BMS-188667), a novel immunosuppressive agent, following subcutaneous and intravenous administration to rats

PURPOSE

The objectives of this study were: to delineate the pharmacokinetics of CTLA4Ig in rats after single and multiple intravenous (IV) and subcutaneous (SC) doses; to assess the relationship of the pharmacokinetic parameters of CTLA4Ig vs dose; to calculate the SC absolute bioavailability; and to assess the antibody response of CTLA4Ig.

METHODS

A total of 48 (24 male and 24 female) Sprague Dawley rats were divided into eight treatments with 3 rats per gender in each group: a single dose of 10, 80, or 200 mg/kg of CTLA4Ig given either IV or SC and a repeated dose of 10 mg/kg (once every other day for 7 doses over 13 days) given either SC or IV. Serial blood samples were collected up to 43 days after single dose administration and up to 50 days following the administration of the last multiple dose on day 13. The serum concentration of CTLA4Ig and anti-CTLA4Ig antibodies were measured using ELISA assays.

RESULTS

After single IV doses, Cmax and AUCinf increased in a dose proportional manner; CL appeared to be dose independent, while both Vss and T1/2 increased as the administered dose increased. Following single SC doses, Cmax and AUCinf increased in a linear manner but not proportionally; mean Tmax values were prolonged but similar among the three dose levels, while T1/2 increased as the administered dose increased. The absolute SC bioavailability of CTLA4Ig decreased as the dose increased from 10 (62.5%), 80 (55.7%), and 200 mg/kg (41.1%). Comparison of the AUCtau values between the first and last doses suggested an accumulation (3.1-4.7) of CTLA4Ig. However, regardless of the route of dosing, AUCtau after the last dose were comparable to AUCinf values following the single dose. Anti-CTLA4Ig antibodies were detected at the 10 mg/kg dose level after single or multiple doses for both routes of administration. However, regardless of single or multiple doses, antibody titers were relatively greater for the SC compared to the IV administration.

CONCLUSIONS

The key findings of this study were: (i) the elimination characteristics of CTLA4Ig were comparable between the SC and IV routes; (ii) the repeated dosing did not alter the pharmacokinetics of CTLA4Ig; (iii) the SC absolute bioavailability tended to decrease as the administered dose increased; and (iv) a greater formation of anti-CTLA4Ig antibodies was observed after SC compared to IV at a single 10 mg/kg dose level; however, after multiple dosing, the formation of antibodies from either of the two routes was relatively slower, and (v) during the study period, no antibodies were observed at either the 80 or 200 mg/kg dose levels regardless of the route of administration.

A sensitive enzyme immunoassay for the quantitation of human CTLA4Ig fusion protein in mouse serum: pharmacokinetic application to optimizing cell line selection

A sensitive, accurate, and precise enzyme immunoassay (EIA) for the quantitation of human CTLA4Ig in mouse serum was validated. The EIA method employed a technique in which a monoclonal anti-CTLA4 antibody was adsorbed onto 96-well polystyrene microtiter plates and used to capture the CTLA4Ig in mouse serum samples. The captured CTLA4Ig was then detected using a goat anti-human IgGFc antiserum conjugated to the enzyme horseradish peroxidase. The validation included assessments of method accuracy and precision, range of reliable response, lower limit of quantitation (LLQ), inter-analyst robustness, storage stability in mouse serum and assay specificity. The results indicate that this validated assay is precise, accurate, and reproducible. This EIA has a range of reliable response in 10% mouse serum of 0.14-4.58 ng ml-1 resulting in a 100% serum equivalent curve of 1.4-45.8 ng ml-1. Assessment of individual standard curve variations indicated a reproducible response with R2 values of > or = 0.995. The LLQ was established at 1.4 ng ml-1. The accuracy and precision estimates, based on the quality control values, were within 3.8% and 5.2% respectively, for CTLA4Ig. Stability of CTLA4Ig was established in mouse serum for 5 days at both 4 degrees C and room temperature, for 2 months at -70 degrees C and through five freeze-thaw cycles. This validated assay was successfully employed in the assessment of pharmacokinetic characteristics of CTLA4Ig in mice and to aid in the selection of an optimal CTLA4Ig-producing cell line.

A pharmacodynamic evaluation of hematologic toxicity observed with etoposide phosphate in the treatment of cancer patients

The pharmacodynamics of etoposide phosphate (Etopophos; Bristol-Myers Squibb Company, Princeton, NJ), a water-soluble prodrug of etoposide, was evaluated in 39 patients with solid tumors after a 30-minute intravenous infusion of escalating doses (equivalent to 50 to 175 mg/m2 of etoposide) on a day 1, 3, and 5 schedule of treatment. Serial blood samples were collected at predose and throughout the 32 hours following day 1 of treatment to determine the area under the plasma concentration-time curve (AUC) of etoposide phosphate and etoposide. Hematology profiles and serum chemistries were determined at predose and twice weekly for approximately 3 weeks after each treatment cycle. Both linear and nonlinear pharmacodynamic models were used to evaluate the relationship between hematologic toxicity and etoposide AUC and patient factors (age, gender, performance status, prior radiation therapy, prior chemotherapy, baseline albumin, bilirubin, alkaline phosphatase, creatinine, leukocyte count, granulocyte count). Etoposide phosphate was converted rapidly to etoposide in vivo. The ratio of the etoposide phosphate AUC to that of etoposide was < or = 1.2% indicating that etoposide was the main species in the systemic circulation. Myelosuppression was the dose-limiting toxicity, and significant decreases in white blood cell and granulocyte counts were noted. Hematologic toxicity was best described by a stepwise linear regression model consisting of etoposide AUC, serum albumin, and bilirubin. In summary, hematologic toxicity produced by the intravenous administration of etoposide phosphate correlates significantly with etoposide AUC and patient factors (baseline serum albumin and bilirubin) in cancer patients.

Effects of gender, age, and race on the pharmacokinetics of etoposide after intravenous administration of etoposide phosphate in cancer patients

The influence of gender, age, and race on the pharmacokinetics of etoposide and on the extent of conversion of etoposide phosphate (Etopophos; Bristol-Myers Squibb Company, Princeton, NJ) to etoposide are summarized. Included in the integrated statistical analyses were 192 patients from six phase I/II studies (102 men and 90 women, 128 aged < or = 65 years and 64 aged > 65 years; 134 were white, 18 were other races, and race was not recorded for 40). The dose of etoposide phosphate ranged from 25 to 200 mg/m2 of etoposide equivalents and was administered as 5-(bolus) to 210-minute intravenous infusions. Total body clearance of etoposide was comparable between men and women. However, significantly lower steady-state volumes of distribution and shorter half-lives were observed in women relative to men. Patients who were older than 65 years had significantly lower etoposide total body clearance and longer half-lives than younger patients. The gender- and age-related differences observed in the pharmacokinetic parameters of etoposide were significant but generally of a small magnitude (< or = 13%), indicating no need for dose adjustment in these patient populations. There were no significant race-related differences in the pharmacokinetic parameters of etoposide. All patients showed rapid conversion of etoposide phosphate to etoposide. The individual area under the plasma concentration-time curve ratio of etoposide phosphate/etoposide was < or = 0.0324, indicating that etoposide was the major circulating moiety after infusion of etoposide phosphate. Significant gender-, age-, or race-related differences in the area under the plasma concentration-time curve ratios were not observed. An evaluation of the area under the plasma concentration-time curve ratios with respect to infusion time suggested that the conversion of etoposide phosphate to etoposide was independent of infusion time.

High-performance liquid chromatographic analysis of 2'-fluoro-2',3'-dideoxyadenosine and 2'-fluoro-2',3'-dideoxyinosine in dog plasma and urine

A high-performance liquid chromatographic assay was developed and validated for a simulataneous determination of 2'-fluoro-2' 3'-dideoxyadenosine (FddA) and its metabolite, 2'-fluoro-2',3'-dideoxyinosine (Fddl) in dog plasma and urine. In vitro, FddA and Fddl exhibit activity against human immunodeficiency virus (HIV). A solid phase extraction was applied to extract FddA, Fddl, and the internal standard (IS; 3',5'-anhydrothymidine) from the biomatrices. The processed samples were chromatographed using a C8 column coupled with a mobile phase consisting of monobasic phosphate, dibasic phosphate, ethylene glycol monomethyl ether, and water. Detection was performed at 257 nm. The nominal retention times were 9, 14, and 26 min for Fddl, IS, and FddA, respectively. The lower limits of quantitation were 0.1 and 2.0 micrograms/mL in plasma and urine, respectively, for both analytes. The accuracy of the assay deviated < or = 10% from the nominal concentrations, and the precision was < or = 14% coefficient of variation. In either matrix, both analytes were stable for at least three freeze-thaw cycles and in the injection media for at least 54 h. The extraction recoveries of the analytes were greater than 80%. The application of this assay was demonstrated in a preliminary pharmacokinetic study of FddA and Fddl in dogs. Two male dogs per dose level received a 100, 250, or 500 mg/kg oral dose of FddA once daily for 14 days. The early appearance of Fddl in plasma (0.25 h; the first sampling time) and greater plasma levels of Fddl than FddA (> 50-fold of Cmax), suggested that the conversion of FddA to Fddl was rapid and extensive. Renal excretion appeared to be the major route of elimination of Fddl.

High-performance liquid chromatographic-ultraviolet assay for the simultaneous quantitation of BMS-181101 and its putative hydroxy metabolites in rat and monkey plasma

A specific, accurate, precise, and reproducible High-performance liquid chromatographic-Ultraviolet (HPLC-UV) method was developed for the simultaneous quantitation of BMS-181101 (I), a new antidepressant, and its putative metabolites, 6'-hydroxy (II) and 7'-hydroxy (III) of BMS-181101 in rat and monkey plasma. The assay procedure involved solid-phase extraction of the three analytes and the internal standard (IS; BMY-42568) on 1 mL Bond Elut CN cartridge using an automated solid phase extraction controller (ASPEC) system. The final elution of the analytes was performed using 0.25% triethylamine in methanol. The eluate mixture was evaporated to dryness, the residue was reconstituted in the mobile phase and injected onto a Zorbax Phenyl column (4.6 x 250 mm; 5 microns) at a flow-rate of 1.2 mL/min. The mobile phase consisted of 20% acetonitrile, 10% methanol, 69% water and 1% 1.0 M ammonium phosphate and 1.0 M tetramethylammonium hydroxide mixture adjusted to pH 3 by phosphoric acid. An ultraviolet absorbance detector set at 287 nm was used to detect the analytes. The nominal retention times were 5, 8, 15, and 18 min for II, III, I, and IS, respectively. The standard curves for the three analytes were linear in the concentration range of 50-1000 ng/mL. The lower limit of quantitation was 50 ng/mL for each analyte. The analyses of quality control (QC) samples indicated that the nominal values could be predicted with an accuracy of (+/-) 10.5% for all three analytes in rat and monkey plasma. The precision values of the QC samples for all three analytes were within 12.7% RSD for rat and monkey plasma. All three analytes and the IS were stable in the autosampler for at least 38 h; freeze/thaw stability of the 3 analytes was established for three cycles. Stability of BMS-181101 was established for one month at -20 degrees C. The application of the assay to a pharmacokinetic study in monkey is described.

A pharmacokinetic interaction study of didanosine coadministered with trimethoprim and/or sulphamethoxazole in HIV seropositive asymptomatic male patients

1. The pharmacokinetics of didanosine, trimethoprim, and sulphamethoxazole were evaluated in ten HIV seropositive asymptomatic patients as single agents and upon coadministration of single doses. 2. Using a randomized, balanced incomplete block crossover study with at least a 1-week washout period between successive treatments, each patient under fasting conditions received four of the following five treatments: 200 mg didanosine as a single agent; 200 mg trimethoprim + 1000 mg sulphamethoxazole; 200 mg trimethoprim + 200 mg didanosine; 1000 mg sulphamethoxazole + 200 mg of didanosine and; 200 mg trimethoprim + 1000 mg sulphamethoxazole + 200 mg didanosine. 3. Serial blood and urine samples were collected following the administration of each treatment. Plasma and urine samples were analyzed using high-pressure liquid chromatography (h.p.l.c.)/ultraviolet assays specific for unchanged didanosine, trimethoprim and/or sulphamethoxazole. 4. Percent urinary recovery (%UR) and renal clearance (CLR) emerged as consistently affected parameters, being decreased in the case of didanosine (35%, P = 0.016) and trimethoprim (32%, P = 0.019) and increased in the case of sulphamethoxazole (39%, P = 0.079), when all three agents were coadministered. The magnitude of the changes in didanosine CLR and %UR values was no greater when both trimethoprim and sulphamethoxazole were coadministered vs when each single agent was given with didanosine, suggesting that any effect was not additive. 5. Other key parameters such as Cmax, AUC, and t1/2 for didanosine (1309.9 ng ml-1, 1796.9 ng ml-1 h, and 1.61 h, respectively), trimethoprim (1.96 micrograms ml-1, 22.86 micrograms ml-1 h, and 9.03 h, respectively) or sulphamethoxazole (58.62 micrograms ml-1, 799.7 micrograms ml-1 h and 9.84 h, respectively) were not affected when didanosine was coadministered with either trimethoprim (didanosine: 1751.9 ng ml-1, 2158.0 ng ml-1 h, and 1.28 h; trimethoprim: 1.81 micrograms ml-1, 28.89 micrograms ml-1 h, and 11.4 h), sulphamethoxazole (didanosine: 1279.3 ng ml-1, 1793.2 ng ml-1 h, and 1.61 h; sulphamethoxazole: 53.57 micrograms ml-1, 732.1 micrograms ml-1 h, and 8.95 h), or the combination of trimethoprim and sulphamethoxazole (didanosine: 1283.7 ng ml-1, 1941.8 ng ml-1 h, and 1.38 h; trimethoprim: 1.59 micrograms ml-1, 26.68 micrograms ml-1 h, and 11.3 h; sulphamethoxazole: 59.48 micrograms ml-1, 760.9 micrograms ml-1 h, and 9.47 h). 6. Because the observed differences in CLR and %UR are small and not considered to be clinically relevant, it is not necessary to alter the dosing regimens of didanosine, trimethoprim or sulphamethoxazole when administered in combination to HIV seropositive patients.

A pharmacokinetic study of intravenous CTLA4Ig, a novel immunosuppressive agent, in mice

Three skin-intact mice in each group received a single 0.07-, 0.29-, or 0.57-mg dose of CTLA4Ig intravenously (i.v.). Three skin-grafted mice received a single 0.29-mg dose i.v. and another three skin-grafted mice received a 0.29-mg dose once daily for 7 days (the dose was administered via the tail vein). Serial blood samples (0.15 mL) were obtained by retro-orbital bleeds up to 240 h after all single doses and up to 360 h after the last multiple dose. Serum samples were analyzed for CTLA4Ig by a validated enzyme immunoassay method. The concentration data were subjected to noncompartmental pharmacokinetic analysis. Both Cmax and AUCinf values increased in a dose-proportional manner in skin-intact mice. The CLT values were dose independent. The MRT, t1/2, and Vdss values at the 0.07-mg dose level were significantly lower than those obtained for both the 0.29- and 0.57-mg dose levels; however, the respective values between the 0.29- and 0.57-mg dose levels were not significantly different. No significant differences were found in the pharmacokinetic parameters between the skin-intact and skin-grafted mice.