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.

Effect of piperine on antihyperglycemic activity and pharmacokinetic profile of nateglinide.

Piperine (CAS no: 94-62-2), an alkaloid obtained from Piper nigrum and P. longum is a known inhibitor of various enzymes (CYP isozymes) responsible for biotransformation of drugs. By inhibiting the metabolism of drugs, piperine improves the bioavailability of drugs. In the present study piperine (10 mg/kg) significantly increased the dose-dependent anti-hyperglycemic activity of nateglinide (CAS no: 105816-04-4) as evaluated by glucose challenged and alloxan-induced diabetic models, when it was administered with nateglinide. Nateglinide plasma concentrations were also increased, when administered with piperine. The synergistic anti-hyperglycemic activity of nateglinide when administered with piperine can be attributed to increased plasma concentration of nateglinide. The results of this study demonstrate that piperine could be used as a potential bioenhancer along with nateglinide.

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 ß450) 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.

High performance liquid chromatographic fluorescence detection method for the quantification of rivastigmine in rat plasma and brain: application to preclinical pharmacokinetic studies in rats.

A highly sensitive and selective high performance liquid chromatographic fluorescence detection method has been developed and validated for the quantification of rivastigmine in rat plasma and brain. Protein precipitation and one-step liquid-liquid extraction techniques were utilized for the extraction of RSM from brain and plasma, respectively, along with an internal standard. The chromatographic separation was achieved with a column inertsil ODS-3V and a mobile phase consisting of ammonium acetate buffer (20 mM, pH 4.5) and acetonitrile (76:24, v/v) delivered at a flow rate of 1 ml/min. The lower limit of quantitation for the developed method was 10 ng/mL for both matrices. The method was found to be accurate and reproducible and was successfully used to quantify levels of RSM in plasma and brain following intravenous administration of RSM in rats.

Altered intravenous pharmacokinetics of topotecan in rats with acute renal failure (ARF) induced by uranyl nitrate: do adenosine A1 antagonists (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.

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.

Effect of 1-aminobenzotriazole on the in vitro metabolism 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.

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.

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.