On model selection for standard curve in assay development

This paper discusses the selection of an appropriate statistical model for representing standard curve in assay development. This is an important issue in assay validation because the accuracy and reliability of the assay result depend on the selected standard curve. In this study, we propose a selection procedure, which is based on the R2 and the mean squared error of the estimation sample, to determine the "best" model. An example concerning an assay validation study is used to illustrate the application of the proposed procedure to discriminate among the five commonly used statistical models.

Myeloperoxidase as a generator of drug free radicals

Reactive metabolites are believed to be responsible for many types of toxicity, including idiosyncratic drug reactions. Bone marrow is a frequent target of idiosyncratic reactions, and, since these reactions have characteristics that suggest involvement of the immune system, the formation of reactive metabolites by leucocytes could also play a role in the aetiology of idiosyncratic drug reactions. The major oxidation system in neutrophils and monocytes is a combination of NADPH oxidase and myeloperoxidase. This system oxidizes primary arylamines, such as sulphonamides, to reactive metabolites and these drugs are also associated with a high incidence of agranulocytosis, generalized idiosyncratic reactions and/ or drug-induced lupus. Clozapine is oxidized by this system to a relatively stable nitrenium ion; clozapine is also associated with a high incidence of agranulocytosis. Arylamines that have an oxygen or nitrogen in the para position, such as amodiaquine, vesnarinone and 5-aminosalicylic acid, are oxidized to quinone-like reactive intermediates. Aminopyrine is oxidized to a very reactive dication. Such reactive metabolites could also inhibit neutrophil function and mediate some of the therapeutic effects of these drugs: for example, the use of dapsone for dermatitis herpetiformis and the use of 5-aminosalicylic acid for inflammatory bowel disease.

Radicals from one-electron reduction of nitro compounds, aromatic N-oxides and quinones: the kinetic basis for hypoxia-selective, bioreductive drugs

Drugs based on nitroarene, aromatic N-oxide or quinone structures are frequently reduced by cellular reductases to toxic products. Reduction often involves free radicals as intermediates which react rapidly with oxygen to form superoxide radicals, inhibiting drug reduction. The elevation of cellular oxidative stress accompanying oxygen inhibition of reduction is generally less damaging than drug reduction to toxic products, so the drugs offer selective toxicity to hypoxic cells. Since such cells are resistant to radiotherapy, these bioreductive drugs offer potential in tumour therapy. The basis for the selectivity of action entails kinetic competition involving the contesting reaction pathways. The reduction potential of the drug, radical pKa and nature of radical/radical decay kinetics all influence drug activity and selectivity, including the range of oxygen tensions over which the drug offers selective toxicity. These properties may be quantified using generation of radicals by pulse radiolysis, presenting a physicochemical basis for rational drug design.

Compatibility of amifostine with selected drugs during simulated Y-site administration

The compatibility of amifostine for injection with selected other drugs during simulated Y-site injection was evaluated. Five-milliliter samples of amifostine 10 mg/mL in 5% dextrose injection were combined with 5 mL each of 100 other drugs, including antineoplastics, anti-infectives, and supportive care drugs, in 5% dextrose injection or 0.9% sodium chloride injection. The combinations were stored under fluorescent light at 23 degrees C. The combinations were evaluated initially and at one and four hours after preparation. Visual examinations were performed in fluorescent light with the unaided eye and using a high-intensity monodirectional light beam to enhance visualization of small particles and low-level turbidity. The turbidity of each sample was measured. Particle sizing and counting were performed on selected samples. Most of the test drugs were compatible with amifostine 10 mg/mL for the observation period. However, 10 drugs exhibited various incompatibilities, including turbidity, particulate formation, precipitation, and color change. These drugs were acyclovir sodium, amphotericin B, cefoperazone sodium, chlorpromazine hydrochloride, cisplatin, ganciclovir sodium, hydroxyzine hydrochloride, miconazole, minocycline hydrochloride, and prochlorperazine edisylate. Amifostine 10 mg/mL in 5% dextrose injection was compatible with most of the 100 drugs tested for four hours at 23 degrees C. However, 10 drugs exhibited incompatibility with amifostine.

Predicting drug-membrane interactions by HPLC: structural requirements of chromatographic surfaces

Drug-membrane interactions have recently been studied by immobilized artificial membrane (IAM) chromatography (Pidgeon, C.; et al. J. Med. Chem. 1995, 38, 590-595. Ong, S.; et al. Anal. Chem. 1995, 67, 755-762), and the molecular recognition properties of IAM surfaces toward drug binding/partitioning appear to be remarkably close to the molecular recognition properties of fluid membranes. The structural requirements of chromatography surfaces to emulate biological partitioning are unknown. To begin to elucidate the surface structural requirements needed to predict drug partitioning into membranes, three bonded phases were prepared. The chromatography bonded phases were prepared by immobilizing (i) a single-chain analog containing the phosphocholine (PC) headgroup (IAM.PC.DD), (ii) a long-chain alcohol containing polar OH groups protruding from the surface (12-OH-silica), and (iii) a long-chain fatty acid containing OCH3 groups protruding from the surface (12-MO-silica). The 12-OH-silica surface can be considered as an immobilized "octanol" phase with OH groups protruding from the surface and is therefore a solid phase model of octanol/water partitioning systems. As expected, improved capability of predicting solute-membrane interactions as found for the chromatographic surface containing the PC polar head-group because the PC headgroup is also found in natural cell membranes. For instance, the IAM.PC.DD column predicted drug partitioning into dimyristoylphosphatidylcholine liposomes (r = 0.864) better than 12-OH-silica (r = 0.812), and 12-MO-silica (r = 0.817). IAM. PC.DD columns also predicted intestinal drug absorption (r = 0.788) better than 12-OH-silica (r = 0.590) and 12-MO-silica (r = 0.681); reversed phase octadecylsilica (ODS) columns could not predict intestinal absorption (r = 0.10). Collectively, these results suggest that chromatographic surfaces containing interfacial polar groups, i.e., PC, OH, and OCH3, model drug-membrane interactions, but surfaces lacking interfacial polar functional groups (e.g., ODS surface) are poor models. Most interestingly, drug partitioning into octanol/water systems does not correlate with drug binding to the immobilized octanol phase. However, drug partitioning into immobilized octanol correlates with drug partitioning into liposomes (r = 0.812).

Liquid chromatographic determination of D- and L-amino acids by derivatization with o-phthaldialdehyde and N-isobutyryl-L-cysteine. Applications with reference to the analysis of peptidic antibiotics, toxins, drugs and pharmaceutically used amino acids

In order to evaluate and extend the applicability of an analytical method that enables the quantitative and simultaneous high-performance liquid chromatographic determination of D- and L-amino acids (DL-AAs) by automated precolumn derivatization with o-phthaldialdehyde together with the chiral thiol N-isobutyryl-L-cysteine [J. Chromatogr., 666 (1994) 259] selected natural and synthetic bioactive peptides, as well as pharmaceutically used formulations of AA, were investigated and the amounts of D- and L-AA determined by fluorescence detection. Peptides containing cys(e)ine were oxidized with performic acid prior to hydrolysis with 6 M HCl, and those containing Trp were hydrolyzed with 4 M methanesulfonic acid (24 h at 110 degrees C in both cases). Peptides analyzed were the peptide antibiotics bacitracin, gramicidins A and S, polymyxin B, metanicin C, the peptide toxin malformin A and the peptide drugs D-Arg-[Hyp3,Thi5,8,D-Phe7]-bradykinin, beta-casomorphin and alpha s1-exorphin. Further, the enantiomeric ratios of pharmaceutically used AA formulations containing racemic DL-Ser, DL-Asp and DL-Met were determined, and the AA drugs L-Asp and L-Trp were tested negatively for the presence of the respective D-enantiomers. In two aqueous formulations of L-AA used for parenteral nutrition, low amounts of D-AA (0.1-0.9% with respect to certain L-AA enantiomers and of totally 128 mg and 149 mg D-AAs per liter infusion solution) were determined.

Molecular mechanism of biological responses to homoeopathic medicines

Assuming that homeopathy is effective beyond the placebo effects, its biological explanation in favour of the hypothesis of the hydrate-structure formation is presented. Since cell-surface proteins are likely to be activated by the hydration-shell structure of molecules in some cases, the interaction between cell-surface proteins and the putative clathrate-like hydrate microcrystals formed during the homoeopathic dilution process is suggested as a primary molecular mechanism of biological responses to homoeopathic medicines. This paper examines the probable protein-microcrystal interaction, forcusing on the cases in which silicon dioxide (silica) microcrystals cause inflammation and in which hydrate microcrystals may be formed during general anesthesia.

Navigator: tools for informal structure-activity relationship discovery

Navigator is a molecular database visualization system, designed to support exploratory data analysis and informal structure-activity relationship studies. In addition to the operations commonly found in chemical database systems, it provides new tools that facilitate substituent analysis and help elucidate the relationships among similar molecules and between related assays. Navigator's capabilities include two ways of displaying the relationships between analogs, mouse-sensitive charts of sets of molecules, mouse-sensitive plots of assay relationships, and access to a system for three-dimensional quantitative structure-activity relationship discovery. Navigator's mouse-based user interface provides a one-object/one-window paradigm that makes data manipulation easy even for inexperienced users. Navigator runs on Silicon Graphics workstations.

Solubilisation of drugs in micellar systems studied by eluent gel permeation chromatography

PURPOSE

The purpose of the study was to investigate the potential of a chromatographic method which is based on elution gel chromatography (EGPC) in the study of solubilisation of drugs in micellar solutions.

METHODS

The EGPC method differs from conventional GPC in the use of a solution of the associating surfactant as eluent (rather than solvent) and the injection of a small volume of solution of different concentration (or alternatively injection of solvent alone) to probe the association equilibrium in the eluent. The technique was applied to a study of the solubilisation of selected drugs in aqueous micellar solutions of a triblock copolymer (Synperonic-PE F127) composed of oxyethylene [E, OCH2CH2] and oxypropylene [P, OCH2CH(CH3)] units with nominal molecular formula E98P67E98.

RESULTS

EGPC curves were obtained showing vacancy peaks at the elution volumes of the drugs, clearly demonstrating their solubilisation. In addition, the micelle-molecule equilibrium of the copolymer surfactant could be monitored at all times. Quantitative determination of the partition of solute between micelles and solvent phase was not possible due to the incomplete conversion of molecules to micelles in solutions of the selected copolymer.

CONCLUSIONS

The EGPC technique provides evidence for the solubilisation of the drugs in aqueous solutions of Synperonic F127; a more thorough assessment of its potential for quantitative measurement of solubilisation requires the use of a surfactant which is wholly (or at least mainly) in the micellar state under the conditions of use.

Liposome capillary electrophoresis for analysis of interactions between lipid bilayers and solutes

Liposomes, which mimic biomembranes, were used as a pseudostationary phase in capillary zone electrophoresis. The decrease in the mobility of an analyte owing to the presence of liposomes reflected interaction between the analyte and the liposomes. Equations were derived to calculate the specific capacity factor Ks (the capacity factor, k', normalized to the liposome concentration 1 M) from the migration times and to estimate the difference in free energy, delta(delta G0), of the weak analyte/liposome interactions. The order of Ks values for the drugs tested was aspirin < salicylic acid < warfarin << sulfasalazine. The peptide TyrGlySerThrProGlyCysCys interacted more strongly with the liposomes (Ks = 10.1 M-1) than did TyrGlySerThrProGlySerSer (Ks = 9.1 M-1). These results were similar to those obtained earlier by immobilized liposome chromatography.

Prediction of drug binding affinities by comparative binding energy analysis

A new computational method for deducing quantitative structure-activity relationships (QSARs) using structural data from ligand-macromolecule complexes is presented. First, the ligand-macromolecule interaction energy is computed for a set of ligands using molecular mechanics calculations. Then, by selecting and scaling components of the ligand-macromolecule interaction energy that show good predictive ability, a regression equation is obtained in which activity is correlated with the interaction energies of parts of the ligands and key regions of the macromolecule. Application to the interaction of the human synovial fluid phospholipase A2 with 26 inhibitors indicates that the derived QSAR has good predictive ability and provides insight into the mechanism of enzyme inhibition. The method, which we term comparative binding energy (COMBINE) analysis, is expected to be applicable to ligand-receptor interactions in a range of contexts including rational drug design, host-guest systems, and protein engineering.

Protein location in liposomes, a drug carrier: a prediction by differential scanning calorimetry

Location of protein drugs in lipid carriers often determines the stability, loading efficiency, and release rate of these drugs from the carriers following administration. On the basis of conventional differential scanning calorimetry (DSC) measurements, Papahadjopoulos et al. (Biochim. Biphys. Acta 1975, 401, 317-335) proposed that proteins can be classified into three categories depending on their effects on the thermotropic behavior of the lipids, e.g., transition temperature and enthalpy. Interactions are usually electrostatic, hydrophobic, or their combination. The nature of these interactions are reflected by changes in various thermotropic parameters. Our study aims to test the validity of Papahadjopoulos' classification. Hydrophilic ribonuclease A, cytochrome c, and superoxide dismutase (SOD), as well as hydrophobic cyclosporin A, are used as model proteins. Neutral lipids, e.g., dipalmitoylphosphatidylcholine, and/or negatively charged lipids, e.g., dipalmitoylphosphatidylglycerol (DPPG), are used to prepare liposomes. Results from conventional and high-sensitivity DSC are compared. High-sensitivity DSC gives significant, more reproducible results. We find that the classification of Papahadjopoulos et al. needs to be modified. No hydrophilic proteins bind to liposomes exclusively on the surface by electrostatic interactions, and some degree of penetration is observed in most cases. An unexpected binding between SOD and DPPG liposomes is observed. The binding of SOD to negatively charged lipids may account, at least in part, for its ability to protect lipid membranes against oxygen-mediated injury.

Pefloxacine mesilate- and ofloxacin-loaded polyethylcyanoacrylate nanoparticles: characterization of the colloidal drug carrier formulation

The entrapment of fluoroquinolones, perfloxacine mesilate (PFX) and ofloxacin (OFX), in polyalkylcyanoacrylate (PECA) nanoparticles could offer some advantages for their biological application; for examples, increasing their bioavailability, controlling the drug time-release in blood, and reducing the formation of bacterial resistance. To load these two drugs in PECA polymeric bulk, the incorporation or adsorption method was performed. These two methods were capable of influencing nanoparticle size, molecular weight, release profile, and drug-polymer association. The incorporation method, particularly for the OFX system, achieved PECA nanoparticle suspensions with a mean size value three times higher than that obtained in the absence of the drug. In contrast, negligible changes were observed for PFX systems. This preparation process also influenced the nanoparticle storage stability. The molecular weight values of the various nanoparticle preparations were also influenced; that is, the PFX-loaded systems showed an enhancement in the average molecular weight values, whereas a reduction was observed for OFX-loaded systems. The adsorption method showed no particular difference in particle size, molecular weight, and storage stability compared with nanoparticles prepared without the drugs. The nanoparticle loading capacity was higher for the colloidal systems obtained following the incorporation preparation procedure. The release of drug from the nanoparticles was biphasic for both preparation processes. The fluoro-quinolone-loaded nanoparticles showed an enhancement of the antimicrobial activity against standard bacteria strains from 2- to 50-fold compared with the free drugs.

Pharmaceutical solids: a strategic approach to regulatory considerations

PURPOSE

This review describes a conceptual approach to the characterization of pharmaceutical solids.

METHODS

Four flow charts are presented: (1) polymorphs, (2) hydrates, (3) desolvated solvates, and (4) amorphous forms.

RESULTS

These flow charts (decision trees) are suggested as tools to develop information on pharmaceutical solids for both scientific and regulatory purposes.

CONCLUSIONS

It is hoped that this review will lead to a more direct approach to the characterization of pharmaceutical solids and ultimately to faster approval of regulatory documents containing information on pharmaceutical solids.

Enantiomeric separation of basic drugs using N-benzyloxycarbonylglyclyl-L-proline as counter ion in methanol

Direct separation of enantiomeric amines using mainly N-benzyloxycarbonylglycyl-L-proline (L-ZGP) but also N-benzyloxycarbonylglyclglcyl-L-proline (L-ZGGP) as the chiral counter ion in methanol is described. The solid phase was Hypercarb porous graphitic carbon. Several amines of pharmacological interest (e.g., alprenolol, sotalol, terbutaline, promethazine and trimipramine) were separated with high enantioselectivity (alpha = 1.16-1.98) using L-ZGP and L-ZGGP as chiral selectors. In accordance with ion-pair chromatography, the retention of the enantiomeric amines was found to increase with increasing concentration of the anionic form of L-ZGP. Addition of a base (sodium hydroxide or an alkylamine) in excess of L-ZGP gave rise to a decrease in retention and enantioselectivity. The enantioselective retention was also affected by adding 2-propanol or acetonitrile to the mobile phase.

Molecular surface comparison. 2. Similarity of electrostatic vector fields in drug design

In the first article of this series a real-time graphics method was described for molecular similarity of scalar properties. This has now been extended for the comparison of molecular vector properties, most notably electrostatic field. A comparison of the various techniques of calculating fields is presented that includes a new method based on natural orbital fitted point charges. In the two examples described, namely, a series of benzodiazepine agonists and a set of serotonin 5-HT3 antagonists, the program has been shown to produce useful pharmacophoric overlaps that can be used in the design of novel therapeutic agents.

Complexes of the minor groove of DNA

An increasing number of high-resolution structures suggest that both the minor and major grooves of DNA can function as receptors for proteins and small molecules. In this review, we try to illustrate the diversity of small molecule ligands that are capable of specifically recognizing the minor groove of DNA. Complex formation results in varying degrees of conformational changes in both DNA and ligands. The discussion focuses on intermolecular interactions that contribute to binding affinity and specificity. There probably is no simple general recognition code that explains the binding specificity of minor-groove ligands. To understand DNA recognition by small molecules, characterization of the binding mode at near-atomic resolution must be combined with thermodynamic data on the energetics of ligand binding to short oligonucleotides.

Compatibility of aztreonam with selected drugs during simulated Y-site administration

The compatibility of aztreonam injection with selected other drugs during simulated Y-site injection was evaluated. A 5-mL sample of aztreonam 40 mg/mL in 5% dextrose injection was combined with 5 mL of each of 100 other drugs including antineoplastics, anti-infectives, and supportive care drugs in 5% dextrose injection or 0.9% sodium chloride injection. The combinations were stored under fluorescent light at 23 degrees C. The combinations were evaluated initially and at one and four hours after preparation by examination with the unaided eye and with a high-intensity light beam, turbidity measurement, and particle sizing and counting. Most of the test drugs were compatible with aztreonam 40 mg/mL for the observation period. However, aztreonam combinations with 12 drugs exhibited incompatibilities including turbidity, particulate formation, precipitation, and color change. These drugs were acyclovir sodium, amphotericin B, chlorpromazine hydrochloride, daunorubicin hydrochloride, ganciclovir sodium, lorazepam, metronidazole, miconazole, mitomycin, mitoxantrone hydrochloride, prochlorperazine edisylate, and streptozocin. Aztreonam 40 mg/mL in 5% dextrose injection was compatible with most of the drugs tested for up to four hours at 23 degrees C. However, 12 drugs exhibited incompatibility with aztreonam.

Electrophoretic evaluation of the mobility of drugs suitable for iontophoresis

Iontophoresis is the process of increasing the penetration of drugs for therapeutic purposes using DC electricity. The most important factor for iontophoresis is the formation of drug ions in solution. On this basis, the penetration of any drug applied by iontophoresis might be maximized at an optimal pH. Seven medications were investigated: acyclovir, methylprednisolone sodium succinate, metronidazole, dexamethasone sodium phosphate, minoxidil, lidocaine hydrochloride, and adenine arabinoside monophosphate. Using techniques of paper electrophoresis, we evaluated the influence of pH on the mobility (mu) of the drugs in phosphate buffers at pH 5, 7, and 9. The mu-values were calculated after detecting the drugs on paper with ultraviolet light. The results indicate that the seven drugs had higher mu-values usually at one, but sometimes at two, of the pH values studied. This study suggests that a variation in pH might alter the maximum ionization, and therefore, the optimal mobility for these seven drugs, as well as other drugs, suited to iontophoresis.

Separation of basic drug substances of very similar structure using micellar electrokinetic chromatography

Small molecules having very similar molecular structure--some even with the same mass over charge--are not trivial to separate by capillary electrophoresis in free solution. However, addition of surfactants to the electrophoretic buffer and thus using the principle of micellar electrokinetic chromatography may provide separation with high resolution. The use of zwitterionic and nonionic surfactants is demonstrated and an example of how a developed system may be used for drug purity testing is given.

Stereochemical determinants of the nature and consequences of drug metabolism

Enantiomeric discrimination in drug disposition depends on the mechanism of the process under consideration. Absorption, distribution and excretion are generally passive processes which do not differentiate between enantiomers, but enzymic metabolism and protein binding, to plasma or tissue proteins, can show a high degree of stereoselectivity. In terms of metabolism, chiral discrimination occurs at both substrate and product levels, giving rise to five distinct stereochemical courses for drug metabolism, namely (i) prochiral-->chiral, (ii) chiral-->chiral, (iii) chiral-->diastereoisomer, (iv) chiral-->non-chiral and (v) chiral inversion. As a result, the metabolic and pharmacokinetic profiles of enantiomers after administration of racemic drugs can be very variable, so that the exposure to the two enantiomers may be very different. There now an enormous number of examples of each of these possibilities. The net result of the interaction of the stereoselectivities of these various processes can obscure the fact that one (or more) shows a marked stereoselectivity. This is particularly the case for metabolism: while the ratios of the total plasma clearance of the enantiomers of a wide range of drugs never exceed 2, individual metabolic pathways often show much greater stereoselectivity. This is particularly evident for those high-affinity, low-capacity enzyme systems which exhibit genetic polymorphism, namely the human cytochromes P450 2C18 and 2D6. This review provides an introduction to the stereoselectivity of drug metabolism.

Optimization of the separation of enantiomers of basic drugs. Retention mechanisms and dynamic modification of the chiral bonding properties on an alpha 1-acid glycoprotein column

The chromatographic properties of 29 basic drugs were studied by varying the pH and the concentration of inorganic ions in the mobile phase. It was observed that the chromatographic performance of most hydrophobic basic drug compounds could be strongly enhanced by decreasing the pH in the mobile phase from 7 to 4-6. The enantioselectivity increased and a much faster resolution was obtained. The results indicate that ion exchange and ion-pair distribution may be involved in the retention process of cationic drug enantiomers. Increasing the concentration of acetate and phosphate increases the retention of the enantiomers of the drug compounds. The relative contribution of the two retention processes can be affected by the pH and the nature and the concentration of the ions in the mobile phase. Decreasing the pH reduces the influence of the ion-exchange process since the negative charge of the protein is decreased. The enantioselectivity is also greatly affected by increasing salt concentration.

Topological approach to drug design

In this paper we demonstrated that by an adequate combination of different topological indices it is possible to select and design new active compounds in different therapeutical scopes, with a very high efficiency level. Particularly successful in the search of new "lead drugs", the results show the surprising ability of the topological methods to describe molecular structures.

Estimation of the shelf-life of drugs with mixed effects models

This paper proposes a normal mixed effects model for stability analysis. An EM algorithm is developed to compute the maximum likelihood estimates of regression coefficients of the fixed effects and random effects, and variance components. The likelihood ratio test is used for the preliminary testing of batch-to-batch variation. An example from a marketing stability study is given to illustrate the proposed procedure.

Soft drugs. XX. Design, synthesis, and evaluation of ultra-short acting beta-blockers

A new type of ultra-short acting beta-blocker which might prove advantageous in treating acute arrhythmias was designed, synthesized and investigated. Based on the soft drug "inactive metabolite approach," the inactive phenylacetic acid metabolite of both metoprolol and atenolol was reactivated by esterification with sulfur-containing aliphatic alcohols. Since the sulfur-containing moieties are labile to the ubiquitous esterases, the new compounds should be inactivated by a one step enzymatic cleavage back to the inactive phenylacetic acid derivative. Pharmacological and pharmacokinetic profiles of the new compounds were evaluated in rats and rabbits. Isoproterenol-induced tachycardia was inhibited with short-term infusion of each compound. This tachycardia blocking effect rapidly disappeared upon termination of infusion, while beta-blocking activity was 2-4-fold longer after comparable doses of the short-acting beta-blocker, esmolol. The rapid recovery from the beta-receptor blockade is believed due to fast hydrolysis of the soft drugs in the body. This is supported from in vitro results showing the t1/2 of esmolol is about 10-fold longer than the new soft drugs in rat, rabbit, dog and human blood. Hydrolysis studies in phosphate buffered solutions indicated that the esters are labile to base-catalyzed hydrolysis. However, the relative t1/2 values measured in biological media compared to phosphate buffered solution clearly support rapid enzymatic cleavage of the soft drugs. Interestingly, one of the soft beta-blockers, the sulfonyl ester derivative, showed a unique property of exhibiting good beta-receptor blocking activity without significant hypotensive action.

Incorporation of first-order uptake rate constants from simple mammillary models into blood-flow limited physiological pharmacokinetic models via extraction efficiencies

Incorporation of First-Order Uptake Rate Constants from Simple Mammillary Models into Blood-Flow Limited Physiological Pharmacokinetic Models via Extraction Efficiencies. W. L. Roth, L. W. D. Weber, and K. Rozman (1995). Pharm. Res. 263-269. First-order rate constants obtained from classical pharmacokinetic models correspond to mammillary systems in which all of the blood (or plasma) is assumed to be located in a central compartment. In such models the rate at which chemicals are transported out of this pool and into another compartment is the product of the mass of chemical in the central compartment multiplied by a rate constant, which is not limited in magnitude by the blood flow, or the rate at which chemicals from the blood are delivered to the peripheral compartment. Most of the physiologically-based models published to date dispense with some of the information available from mammillary models by assuming that all of the chemical delivered by the flow of blood rapidly equilibrates and can be taken up by the tissue under the control of a "partition coefficient" (Rij = Cj/Ci). We show that the partition coefficient alone does not retain the uptake rate (kji) information available from a classical mammillary model, but that the uptake rate information can be incorporated via unitless extraction efficiency parameters, epsilon j.

GAME: a computer graphics method for calculating and displaying the molecular electrostatic potential

A new method for calculating and displaying the molecular electrostatic potential on the molecular surface is described. The main advantage of the method, besides some others, is its consistency. This means one only needs one data set for the surface and the MEP: a 3D field of the electron density from any source.

Effect of temperature on bleeding and drug release from a liquid droplet dispersion ointment

A liquid droplet dispersion ointment, LDDS, a formulation containing a drug solution as droplets in an oily vehicle, is excellent for percutaneous drug absorption. Bleeding of LDDS and in vitro drug release from LDDS were found to be enhanced by temperature increase. The influence of temperature on the physical properties of LDDS was studied using differential scanning calorimetry and X-ray diffraction spectroscopy. The liquid component content, possibly a hydrocarbon in the vehicle, increased with temperature; this may have been due to melting of the vehicle. In this liquid component, the drug concentration measured by HPLC increased with temperature. This change in the drug concentration may cause an increase in drug release, leading to the conclusion that, compared with conventional ointments, temperature has much greater effect on drug release from LDDS.

Recent examples of novel secondary metabolites

Modern trends in the detection, isolation and characterization of leads for novel therapeutic compounds are reviewed. Some current biological test systems (immunological, chemical, enzymic, receptor, etc.) and examples of their successful application are highlighted including the structures of selected novel and prospective metabolites.

Drug transport across nylon 610 films: influence of synthesis variables

Nylon 610 is a hydrophilic polymer with considerable potential as a membrane for drug microencapsulation. To better understand drug transport through such membrane, the influence of the solvents and monomers used in the synthesis of nylon films were examined using a full factorial study. Nylon 610 films were synthesized by an interfacial polycondensation reaction using hexamethylenediamine (HD) in the water phase and sebacoyl chloride (SC) in the organic phase, which was a solvent blend of chloroform and trichlorotrifluoroethane at ratios of 1:1, 1:4, and 4:1. Monomer concentrations studied were 0.2, 0.4, and 0.6 M with respect to their appropriate phase, while the monomer ratios were 1:1, 3:1, and 1:3. The molecular weight, porosity, thickness, and crystallinity of the films were characterized. The transport of potassium chloride, hydrocortisone, and m-cresol was studied at 25 degrees C as a function of the synthesis variables. Potassium chloride was selected to measure the porosity of the membrane. Hydrocortisone and m-cresol, a known solvent for nylon 610, were used to study pore and solution-diffusion transport, respectively. The molecular weight of the films was proportional to the chloroform concentration. As the molecular weight increased, film thickness, porosity, and hydrocortisone permeability increased. As the molecular weight decreased, film thickness and porosity decreased, while m-cresol permeability increased. These results can be explained on the basis of HD ability to readily partition into a good solvent such as chloroform permitting high molecular weight polymer to form before precipitation.

Histological study on crude drugs pai-wei, pai-chein and indigenous species of Cynanchum in Taiwan

The botanical origins of Cynanchum species (Cynanchum spp.) on the Taiwan market have been established by histological studies in the present paper. The results showed that the Chinese crude drug Pai-wei on the Taiwan market was derived from the dried roots of Cynanchum atratum Bunge; that of Pai-chein was derived from the dried roots of C. stauntonii (Decne.) Hand.-Mazz; and the Wanling-shu used locally in Taiwan was derived from the dried roots of C. taiwanianum Yamazaki.

Adsorption of charged non-albumin bound drugs by amorphous silica

We investigated the in vitro drug adsorption of PQ 10150 sodium silicate gel (AIS, Santa Clara, CA) with particle size of 230 microns and surface area of 400 m2/g. We observed 99% to 88% adsorption of gentamicin; a mean 91% of disopyramide; a mean 89% of quinidine at low concentration, falling to 75% at higher concentration. Insulin was 88% adsorbed at low concentrations but less so (65%) at higher concentrations. We observed a mean 83% adsorption of procainamide, a mean 84% of N-acetyl procainamide, 74% of lidocaine, 73% of amitriptyline, and 44% of desipramine. We found an average of 14% reduction of total digoxin concentration when serum containing digoxin (2 to 33 ng/mL) was exposed to sodium silicate, while the reduction in free digoxin concentration was 16%. Five percent ethosuximide was also removed. The adsorption of theophylline, phenobarbital, acetaminophen, phenytoin, ethylene glycol, methotrexate, salicylate, thiocyanate and diazepam was minimal and not significant. We conclude that significant amounts of charged, non-albumin bound drugs can be removed by PQ 10150 sodium silicate gel.

An in vitro study of the influence of a drug's molecular weight on its overall (Clt), diffusive (Cld) and convective (Clc) clearance through dialysers

The dialyser clearance of a drug is the sum of two components: one diffusive, arising from the concentration gradient across the membrane, and the other convective, arising from the ultrafiltration of plasma water, produced by the increases in hydraulic pressure that the membrane undergoes. To demonstrate the importance of these clearances during haemodialysis, this study analyses the influence of a drug's molecular weight on them. To this end, an experimental study of dialysis in vitro was carried out to determine the clearances, in aqueous solution, of five drugs of increasing molecular weights (theophylline, quinidine, tobramycin, digoxin, and vancomycin), using two series of dialysers with the same type of membrane (Cuprophan), differing in effective surface area and ultrafiltration coefficient. From the data obtained in this study, the importance of quantifying convective clearance during haemodialysis becomes apparent since if it is not taken into account errors of up to 20% and more may be made. This is particularly so if the drug is of high molecular weight and if a high filtration rate is being used.

NMR studies of drug-DNA complexes

The application of high-resolution, multidimensional NMR techniques to the problem of determining the structure of drug-DNA complexes in solution has led to substantial progress in understanding the effect of drugs on DNA at the molecular level. With the development of isotopic labeling methods applied in three- and four-dimensional experiments, we anticipate that more complex drug-DNA systems will become amenable to structural analysis. In addition to implementing these newer techniques, progress will also be made in terms of investigating the structure of drug complexes with more unusual forms of DNA, such as triplexes, quadruplexes, multistranded junctions, and so forth.

Thermodynamic characterization of drug binding to human serum albumin by isothermal titration microcalorimetry

Binding sites on human serum albumin (HSA) for anionic drugs and fatty acids have been thermodynamically characterized by microcalorimetry. The binding and the thermodynamic parameters were directly computed from the calorimetric titration data at 37 degrees C in a phosphate buffer (pH 7.4) using one- and two-class binding models. From compensation analyses plotting the molar enthalpy change (delta Hm,i) versus those of the molar free energy (delta Gm,i) and molar entropy (delta Sm,i) for each class of binding sites, HSA binding sites were classified into groups S1, S2, and S3. Group S1 included high-affinity binding sites for site II-bound drugs, such as ibuprofen, flufenamic acid, and ethacrynic acid, and short- or medium-length alkyl-chain fatty acids; group S2 included low-affinity binding sites of site II-bound drugs and long-length alkyl-chain fatty acids; and group S3 contained the high-affinity binding sites for site I-bound drugs, such as phenylbutazone, oxphenbutazone, and warfarin, and long-length alkyl-chain fatty acids. High- and low-affinity bindings sites for salicylic acid and acetylaslicylic acid agreed with the regions of groups S3 and S2, respectively. Groups S1 and S2 were characterized by large negative values of delta Hm,i and delta Sm,i, reflecting van der Waals interaction and hydrogen-bonding formation in low dielectric media, and the main force to stabilize the binding complex in group S3 was a hydrophobic interaction, characterized by a small negative delta Hm,i and minor or positive values of delta Sm,i (entropy-driven).

Assessment of impact of physico-chemical drug properties on monitoring drug levels by micellar electrokinetic capillary chromatography with direct serum injection

The impact of physico-chemical properties of 25 compounds, including antiepileptic, anti-inflammatory and beta-blocking drugs, on their determination by micellar electrokinetic capillary chromatography (MECC) with direct serum injection (DSI) is discussed. Having a pH 9.2 buffer containing 75 mM sodium dodecyl sulfate (SDS), elution is dependent on hydrophobicity, the order of emergence being basically according to increasing octanol/water partition coefficients (logP values). Peak shape is determined by the dissociation behavior (expressed by pKa) and plasma protein binding (PPB). Sharp peaks are produced by compounds having low PPB and, independently of PPB, by drugs with pKa values which are similar to the buffer pH. Broad or double peaks are established by drugs of low pKa values and significant (> about 40%) PPB. In order to evaluate the effective amount of a protein-bound drug measured by MECC-DSI, serum levels of drugs with different PPB, namely ethosuximide (no PPB), phenobarbital (PPB of about 50%) and naproxen (PPB > 99%) have been determined by both MECC-DSI and MECC with extract injection (MECC-EXI). In each case, with more than 40 sera, there is good agreement between the two sets of data. Thus, employing MECC-DSI, total amounts of drugs are determined, i.e. a complete release of the drugs from the proteins is effected by the impact of dodecyl sulfate on the sampled proteins.

Sub- and supercritical fluid chromatography on packed columns: a versatile tool for the enantioselective separation of basic and acidic drugs

Various chiral stationary phases were investigated in sub- and supercritical fluid chromatography for the separation, without derivatization, of basic (beta-blockers, benzodiazepines) and acidic (nonsteroidal anti-inflammatory drugs, beta-agonists) pharmaca. For all racemates, baseline separation was achieved within short analysis times. For several solutes, the high resolution obtained allowed injection of milligram amounts and semipreparative collection of the enantiomers. The parameters affecting enantioselectivity (column efficiency, influence of modifiers and basic or acidic additives, and temperature) have been studied. Enantiomerization of 3-OH-benzodiazepines could be suppressed by working at low temperatures or by using acetonitrile as a comodifier. Serial coupling of different chiral stationary phase columns resulted in a column triplet (Chiralpak AD, an amylose derivative; Chiralcel OD, a cellulose derivative; and Chirex 3022, a Brush-type with pi-donor characteristics) on which all solutes investigated could be baseline separated.

Modelling of human acute toxicity from physicochemical properties and non-vertebrate acute toxicity of the 38 organic chemicals of the MEIC priority list by PLS regression and neural network

Linear and non-linear modelling of human acute toxicity (as human lethal concentrations; HLCs) of the 38 organic chemicals from the 50 priority compounds of the Multicentre Evaluation of In Vitro Cytotoxicity (MEIC) programme was investigated. The models obtained were derived either from a set of 23 physicochemical properties of the compounds or from their acute toxicities to five aquatic non-vertebrates together with the physicochemical properties. For the linear type, modelling was performed using a partial least square projection to latent structures (PLS) regression method; for the non-linear models, both PLS regression and neural network were utilized. A neural network using a combination of backpropagation and cascade-correlation algorithms was applied in this study. The results generally reveal a slightly better predictive performance of the models obtained from PLS regression than those obtained from neural networks. However, the model composed of physicochemical properties (PC-model) from the trained neural network using a back propagation algorithm with pruning technique proved superior to that trained with a combination of backpropagation and cascade-correlation algorithms after leave-one-out cross-validation. The predictive power of the PC-models, whether linear or non-linear, was comparable with that of the corresponding models consisting of both structural descriptors and the ecotoxicological tests (ECOPC-models), except for the battery (ECOPC-model) from the neural network. The composition of the 'best' PLS and neural network models points to the importance of the combination of physicochemical properties reflecting lipophilicity, size, volume, intermolecular binding forces and electronic properties of the molecule. All the aquatic non-vertebrate tests are shown to be essential in explaining human acute toxicity. However, the degree of contribution differed, with the crustacean (Artemia salina) and the bacterial (Microtox) bioassays being more important to the linear and non-linear PLS models, whereas the crustacean (Artemia salina and Streptocephalus proboscideus) tests, and the rotifer (Brachionus calyciflorus) assay were important to the neural network models. The organochlorine (lindane) and bipyridinium (paraquat) pesticides were common outliers in all the models. Moreover, the latter two compounds and the organophosphate (malathion) pesticide were also common outliers in all ECOPC-models. Other types of pesticides, however, fit the models. The predicted HLCs of a number of non-pesticides, including some chlorinated compounds, also deviated from the observed HLCs by more than one order of magnitude.