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Irving W Wainer

Publications and source records attributed to Irving W Wainer.

44 records · Page 3Linked to original sources
PubMed2002

Binding study of desethyloxybutynin using high-performance frontal analysis method.

Plasma protein binding of N-desethyloxybytynin (DEOXY), a major active metabolite of oxybutynin (OXY), was investigated quantitatively and enantioselectively using high-performance frontal analysis (HPFA). An on-line HPLC system which consists of HPFA column, extraction column and analytical column was developed to determine the unbound concentrations of DEOXY enantiomers in human plasma, in human serum albumin (HSA) solutions, and in human alpha1-acid glycoprotein (AGP) solutions. DEOXY is bound in human plasma strongly and enantioselectively. The unbound drug fraction in human plasma samples containing 5 microM (R)- or (S)-DEOXY was 1.19 +/- 0.001 and 2.33 +/- 0.044%, respectively. AGP plays the dominant role in this strong and enantioselective plasma protein binding of DEOXY. The total binding affinity (nK) of (R)-DEOXY and (S)-DEOXY to AGP was 2.97 x 10(7) and 1.31 x 10(7) M(-1), respectively, while the nK values of (R)-DEOXY and (S)-DEOXY to HSA were 7.77 x 10(3) and 8.44 x 10(3) M(-1), respectively. While the nK value of (S)-DEOXY is weaker than that of (S)-OXY (1.53 x 10(7) M(-1)), the nK value of (R)-DEOXY is 4.33 times stronger than that of (R)-OXY (6.86 x I0(6) M(-1)). This suggests that the elimination of an ethyl group weakens the binding affinity of the (S)-isomer because of the decrease in hydrophobicity, while the binding affinity of the (R)-isomer is enhanced by the decrease in steric hindrance. The total binding affinity of DEOXY to HSA is much lower than that of DEOXY-AGP binding as well as OXY-HSA binding (2.64 x 10(4) and 2.19 x 10(4) M(-1) for (R)-OXY and (S)-OXY, respectively). The study on competitive binding between OXY and DEOXY indicated that DEOXY enantiomers and OXY enantiomers are all bound competitively at the same binding site of AGP molecule.

Chromatography, High Pressure Liquid↗
PubMed2002

The enantioselective determination of chlorpheniramine and its major metabolites in human plasma using chiral chromatography on a beta-cyclodextrin chiral stationary phase and mass spectrometric detection.

A sensitive enantioselective high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of plasma concentrations of (-)(R)- and (+)(S)-chlorpheniramine (CP) and their metabolites, desmethyl-chlorpheniramine (DCP), didesmethyl-chorpheniramine (DDCP) and chlorpheniramine N-oxide (CPNO). Enantioselective separations were achieved on a beta-cyclodextrin chiral stationary phase (CYCLOBOND I 2000) with a mobile phase consisting of diethylamine acetate (0.25%, pH 4.4):methanol:acetonitrile [85:7.5:7.5, (v/v/v)]and a flow-rate of 0.5 ml/min. For CP, the enantioselectivity (alpha) of the separation was 1.12 with a resolution factor (R(s)) of 1.17. The method was validated for CP by using mass spectroscopy detection (MSD). Concentrations of each enantiomer could be measured down to 125 pg/ml from a 1-ml plasma sample. Extracted calibration curves were linear from 0.13 to 50.00 ng/ml for each enantiomer. The method was applied to samples from two clinical studies.

Adult↗
PubMed2002

On-line synthesis utilizing immobilized enzyme reactors based upon immobilized dopamine beta-hydroxylase.

Immobilized enzyme reactors (IMERs) based upon dopamine beta-hydroxylase (DBH) have been developed. Immobilized artificial membrane (IAM) and glutaraldehyde-P (Glut-P) stationary phases have been used to immobilize DBH. When DBH is immobilized on the Glut-P interphase the enzyme is outside the stationary phase whereas with the IAM interphase the enzyme is embedded within the interphase surroundings. The activity of each IMER and their ability for on-line hydroxylation has been investigated. The resulting IMERs are enzymatically active and reproducible. The IMERs can be utilized through the use of coupled chromatography to characterize the cytosolic (DBH-Glut-P-IMER) and membrane-bound (DBH-IAM-IMER) forms of the enzyme. The substrate is injected onto the individual IMERs and the reactants and products are eluted onto a phenylboronic acid column for on-line extraction. The substrates and products are then transported via a switching valve to coupled analytical columns. The results demonstrate that enzyme-substrate and enzyme-inhibitor interactions can be investigated with the on-line system. These IMERs can be utilized for the discovery and characterization of new drug candidates specific for the soluble form and membrane-bound form of DBH. The effects of flow-rate, contact time, pH and temperature have also been investigated.

Animals↗
PubMed2002

Determination of the plasma levels of metyrapone and its enantiomeric metyrapol metabolites by direct plasma injection and multidimensional achiral-chiral chromatography.

The development and validation of a direct injection high-performance liquid chromatographic (HPLC) method, with column switching, for the determination of metyrapol enantiomers and metyrapone in human plasma is described. The system used in this work was composed of a restricted access media (RAM) bovine serum albumin (BSA) octyl column coupled to an amylose tris(3,5-dimethoxyphenylcarbamate) chiral column. Water was used as eluent for the first 5 min at a flow rate of 1.0 ml/min for the elution of the plasma proteins and then acetonitrile-water (30:70 v/v) for the transfer and analysis of metyrapol enantiomers and metyrapone, which were detected by UV at lambda = 260 nm. The total analysis time was about 32 min. The calibration curves for each enantiomer and for the metyrapone were linear in the ranges 0.075-0.75 microg/ml and 0.150-1.50 microg/ml, respectively. Recoveries, intra- and interday precision and accuracy were determined using three quality controls, one low (0.18 microg/ml), one medium (0.75 microg/ml), and one high (1.35 microg/ml) plasma concentration. Quantitative recoveries and good precision and accuracy were obtained. The limit of quantitation were 0.045 microg/ml for both enantiomers and for the metyrapone.

Calibration↗
PubMed2002

The roles of CYP2D6 and stereoselectivity in the clinical pharmacokinetics of chlorpheniramine.

AIMS: To examine the stereoselective disposition of chlorpheniramine and to evaluate the role of CYP2D6 in chlorpheniramine pharmacokinetics in humans. METHODS: Eight healthy volunteers (six extensive metabolizers with respect to CYP2D6 and two poor metabolizers) received a single 8 mg oral dose of rac-chlorpheniramine either given alone or following administration of quinidine 50 mg every 6 h for 2 days prior to the study day and every 6 h thereafter until the end of the study. Plasma concentrations of (S)-(+)- and (R)-(-)-enantiomers of chlorpheniramine were determined using liquid chromatography/mass spectrometry. RESULTS: In extensive metabolizers, mean Cmax was greater (12.55+/-1.51 ng ml-1vs 5.38+/-0.44 ng ml-1) and CLoral was lower (0.49+/-0.08 l h-1 kg-1vs 1.07+/-0.15 l h-1 kg-1) for (S)-(+)- than for (R)-(-)-chlorpheniramine (P<0.005). For (S)-(+)-chlorpheniramine, administration of quinidine, an inhibitor of CYP2D6, resulted in an increase in Cmax to 13.94+/-1.51 (P<0.01), a reduction in CLoral to 0.22+/-0.03 l h-1 kg-1 (P<0.01), and a prolongation of elimination half-life from 18.0+/-2.0 h to 29.3+/-2.0 h (P<0.001). Administration of quinidine decreased CLoral for (R)-(-)-chlorpheniramine to 0.60+/-0.10 l h-1 kg-1 (P<0.005). In CYP2D6 poor metabolizers, systemic exposure was greater after chlorpheniramine alone than in extensive metabolizers, and administration of quinidine resulted in a slight increase in CLoral. CONCLUSIONS: Stereoselective elimination of chlorpheniramine occurs in humans, with the most pharmacologically active (S)-(+)-enantiomer cleared more slowly than the (R)-(-)-enantiomer. CYP2D6 plays a role in the metabolism of chlorpheniramine in humans.

Adult↗
PubMed2002

Role of chiral chromatography in therapeutic drug monitoring and in clinical and forensic toxicology.

Advances in chiral chromatographic separations have given pharmacologists and toxicologists the tools to examine unexpected clinical results involving chiral drugs. The ability to unravel complex phenomena associated with drug transport and drug metabolism is presented in this manuscript. The relation between the chirality of the drug mefloquine and the intracellular concentrations of the drug cyclosporine is illustrated by examining the effect of the enantiomers of mefloquine on the transport activity of P-glycoprotein (Pgp). These studies were conducted using a liquid chromatographic column containing immobilized Pgp. The results demonstrated that (+)-mefloquine competitively displaced the Pgp substrate cyclosporine whereas (-)-mefloquine had no effect on cyclosporine-Pgp binding. The data suggest that cyclosporine cellular and CNS concentrations can be increased through the concomitant administration of (+)-mefloquine. The use of chirality in clinical and forensic situations is also illustrated by the metabolism of the enantiomers of ketamine (KET). The plasma concentrations of (+)-KET and (-)-KET and the norketamine metabolites (+)-NK and (-)-NK were measured in rat plasma using enantioselective gas chromatography. The separations were accomplished using a gas chromatography chiral stationary phase based on beta-cyclodextrin. The pharmacokinetic profiles of (+)-, (-)-KET and (+)-, (-)-NK were determined in control and protein-calorie malnourished (PCM) rats to determine the effect of PCM on ketamine metabolism and clearance. The results indicate that PCM produced a significant and stereoselective decrease in KET and NK metabolism. The data suggest that the effects of environmental factors (smoking, alcohol use, diet) and drug interactions (coadministered agents) can be measured using the changes in stereochemical metabolic and pharmacokinetic patterns of KET and similar drugs.

Chromatography, Gas↗
PubMed2002

Genotype/phenotype comparisons: a probe for the effect of disease progression on drug metabolism.

The effect of disease state on drug metabolism has been investigated using the relationship between genotype and metabolic phenotype. The two polymorphic probes, N-acetyltransferases-2 (NAT2) and cytochrome P450 2C19 (CYP2C19), were respectively used in HIV+/AIDS patients and patients with advanced cancer. The results of the studies suggest that advanced disease produces discordances between genotype and phenotype, indicating a reduction in the metabolic capabilities of these individuals. Thus, polymorphic enzymes such as CYP2C19 and NAT2 can be used to probe changes in drug-metabolizing enzyme capacities. The development of genotype/phenotype discordances should reflect general changes in metabolic capabilities and, thus, alterations in the activities of other important enzymes such as CYP3A. The data also suggest that the genotype/phenotype probes can be used to optimize the clinical treatment of patients with advanced disease states.

Animals↗