Stereoisomers and drug toxicity. The value of single stereoisomer therapy

All drugs produce adverse effects, though the risk varies widely between different compounds. Many toxic reactions are an extension of the mechanism responsible for the therapeutic effect and can be avoided by careful dose adjustment. Other adverse events are not related to the beneficial action of the drug. Recent interest has focused on the role of the different properties of individual drug enantiomers in causing drug toxicity. For drugs with a single chiral centre, both enantiomers may be therapeutically active. However, if the main therapeutic benefit is in only 1 enantiomer, several possibilities exist for the other enantiomer--inactive, a qualitatively different effect, an antagonistic effect or greater toxicity.

[Physico-chemical compatibility of drugs with enteral nutrition]

The physical and chemical compatibility of an enteral diet (standard Precitene) with a series of liquid preparations included in the hospital's formulary was evaluated. These preparations are included in the following groups: vitamins, antibiotics and chemotherapeutic drugs, analgesics, antiepileptic drugs, neuroleptics, bronchodilators, expectorants, antihistamines, immunosuppressors and short chain triglycerides. Phase separation, particle growth pH variation, osmolality increase and viscosity increase were studied. The results obtained indicate that the majority of the drugs studied are compatible from a physical and chemical point of view with the enteral diet used, at least during a 24 hour period, with the exception of those drugs which, because of their pH, acidify the mixture, causing problems of increased viscosity and particle growth, and of those liquid preparations of continuous oleous phase where phase separation is unavoidable. Lastly, a series of recommendations are given on cases where joint administration of drugs with enteral nutrition is suitable.

Microbore liquid chromatography with electrochemical detection for the control of phenolic antioxidants in drugs and foods

Antioxidants are added to foods and drugs to inhibit their oxidation. As these additives are somewhat toxic, it is necessary to control the amount added to any food or drug. Liquid chromatography (LC) is a powerful tool for this purpose. Many antioxidants are electroactive molecules which enables the advantages of electrochemical detection or selectivity and sensitivity to be realized. The interest of analysts in microbore LC arises from the low mobile phase volumetric flow rates involved, the reduced on-column samples together with reduced chromatographic dilution and high efficiency. Coupling of microbore LC with electrochemical detection adds another advantage: the decrease of electrode ageing. The problem of extra-column band broadening with microbore column is discussed in the present communication. A micro LC-electrochemical detection system is constructed and tested using catecholamines. The limit of detection (LOD) for noradrenaline using a 0.7 mm bore column is found to be 0.1 pg injected in 0.2 microliter (0.6 femtomoles). Three phenolic antioxidants are studied: tert-butyl-p-hydroxyanisole (BHA), di-tert-butyl-hydroxytoluene (BHT) and n-propyl gallate (3,4,5-trimethoxybenzoic acid propyl ester). The dynamic range is four orders of magnitude with LODs down to 0.1 femtomoles (20 fg injected) with a 0.3 mm bore column. No electrode response change is observed after 60 injections of 3 ng BHA over 6 days. Antioxidants are determined in different pharmaceutical preparations and foodstuffs (chewing gums, dried potato flakes). The agreement between the manufacturer stated concentrations and observed results is found to be satisfactory.

CHIRBASE, a graphical molecular database on the separation of enantiomers by liquid-, supercritical fluid-, and gas chromatography

In order to cope with the increasing number of publications on the separation of enantiomers by chromatography on a chiral stationary phase, the graphical molecular database CHIRBASE was created. In the present state, the database package covers information (structural, bibliographic, and chromatographic data) on liquid-, supercritical fluid-, and gas chromatography; other methods will follow. CHIRBASE, running on the MDL software Chembase, meets the requirements of contemporary information management in the chemical and pharmaceutical industry. (Detailed information including a demo-version of each part of CHIRBASE can be obtained from the authors on request).

Drugs acting on the intracellular signalling system

Cellular response to extracellular messages is a basic process to maintain and to support cell life. Several signalling molecules important as sites of therapeutic drug action are involved in the response. Recent studies on life sciences have elucidated molecular properties of intracellular signalling factors and mechanisms of cascading. Novel drugs acting on signalling molecules and possessing new sites and mechanisms of action have been found. This article summarizes the properties (subtypes, structures, functions) of signalling factors (receptors, ion channels, GTP binding proteins, second messenger-generating enzymes, second messenger-metabolizing enzymes, second messengers protein kinases, protein phosphatases) and lists in Tables A-H drugs that act on signalling molecules and which should find clinical use.

Commonly used chiral drugs: a survey

Initial results of a comparative survey of commonly used chiral drugs are presented. The survey considered the differences between drugs used in 1982 with those in use in 1991. Two major conclusions were reached: the use of single isomer chiral drugs had increased from 31.1% in 1982 to 34.3% in 1991 and the proportion of synthetic single isomer chiral drugs available in 1991 was considerably greater than in 1982.

New algorithm for analysis of data obtained by means of circular dichroism titration method

A new method for analysis of circular dichroism titration data used for drug-protein binding investigations is proposed. A square equation between molar ellipticity change and total drug concentration is obtained which is examined analytically. A new minimization algorithm for determining the binding sites and association constants of each type of drug-protein complexes is applied.

KEY, LOCK, and LOCKSMITH: complementary hydropathic map predictions of drug structure from a known receptor-receptor structure from known drugs

Three new routines (LOCK, KEY and LOCKSMITH) for the program HINT (hydrophobic interactions) are described and demonstrated. The KEY routine uses receptor structure to model the hydropathic profile of the ideal substrate for the receptor. The LOCK routine uses substrate or drug structure to model the hydropathic character of the receptor. LOCKSMITH is an algorithm designed to highlight the significant hydropathic features from a collection of agents. Ten allosteric modifiers of hemoglobin that have been characterized biologically and with X-ray diffraction to determine their protein binding sites/conformations illustrate the KEY and LOCKSMITH routines: The LOCKSMITH composite map correctly identifies the structural features and conformation of the more active modifiers. In addition, many hydropathic features of the "ideal" drug predicted by the KEY map overlap with actual structural features of the most active hemoglobin allosteric modifiers.

Electrochemical determination of partition coefficients of drugs

An electrochemical method for the determination of partition coefficients of drugs that can exist as ions in aqueous solutions is presented. The method involves cyclic voltammetry at the polarizable interface between two immiscible electrolyte solutions. Because n-octanol is an unsuitable solvent for electrochemical purposes, 1,2-dichloroethane, which has electronic properties similar to those of n-octanol, was used in the measurements. The values obtained could be correlated with the values for n-octanol-water partition taken from the literature by an approach based on the linear solvation relationship: log P1 = a log P2 + b; in this relationship, a and b are constants and P1 and P2 correspond to the two different organic and aqueous phase partition equilibria. Furthermore, aqueous diffusion coefficients of drugs were determined from voltammograms.

Determination of ascorbic acid and isoascorbic acid by capillary zone electrophoresis: application to fruit juices and to a pharmaceutical formulation

Capillary zone electrophoresis was applied to the determination of ascorbic and isoascorbic acid, analysing the various parameters of influence such as the separation voltage, the buffer pH and concentration, the type of separation capillary or the loading conditions. Both analytes could be adequately determined within 5 min. The proposed method uses a 20 cm x 25 microns i.d. coated column, 0.1 M phosphate buffer pH 5.0, 8 kV separation voltage and light absorption detection at 265 nm. Linear calibration curves were obtained in the 0-1 mg mi-1 range, with detection limits of 0.5 micrograms ml-1. This method proved to be very rapid, simple and practical for the qualitative and quantitative determination of ascorbic acid in lemon and orange juices, as well as in a commercially available pharmaceutical formulation.

Automatic superposition of drug molecules based on their common receptor site

We have previously developed a new rational method for superposing molecules in terms of submolecular physical and chemical properties, but not in terms of atom positions or chemical structures as has been done in the conventional methods. The program was originally developed for interactive use on a three-dimensional graphic display, providing goodness-of-fit indices on molecular shape, hydrogen bonds, electrostatic interactions and others. Here, we report a new unbiased searching method for the best superposition of molecules, covering all the superposing modes and conformational freedom, as an additional function of the program. The function is based on a novel least-squares method which superposes the expected positions and orientations of hydrogen bonding partners in the receptor that are deduced from both molecules. The method not only gives reliability and reproducibility to the result of the superposition, but also allows us to save labor and time. It is demonstrated that this method is very efficient for finding the correct superposing mode in such systems where hydrogen bonds play important roles.

Drug quality control work in Daru: observations during 1983-1986

During a 4 year period (January 1983 to December 1986), 418 requests for drug analysis were received in the Drug Analysis and Research Unit, Department of Pharmacy, University of Nairobi. Of these requests, 212 were from Medical Supplies Coordination Unit, 190 from Government hospitals and health research institutions, 11 from the Ministry of Health Headquarters (Director of Medical Services and Chief Pharmacist) and 5 came from local pharmaceutical manufacturers. Of the samples analysed, 70.8% were from local manufacturers, 26.1% were imported and 3.1% were from undeclared sources. Failure to comply with test for quality, as set out in official compendia (B.P. Eur. ph. Ip, etc.) were observed at 45.8% for locally manufactured drugs and 31.4% for imported drug products.

The calculation of molecular similarity: alternative formulas, data manipulation and graphical display

The use of electrostatic potential comparisons between molecules for the elucidation of structure activity relationships is now a well-established modeling technique. The Carbo and Hodgkin similarity indices are used extensively to make quantitative comparisons of this nature; yet their roots are found in the overlap of electron density distribution, with both formulas utilizing a product-based numerator. Two new similarity indices are suggested that calculate the electrostatic potential similarity using a difference-based numerator. The form of the new indices allows the creation of additional software functions that enhance the flexibility of similarity calculations and permit the creation of similarity maps. The general properties of these software functions and all indices are discussed and applied to a series of dopamine D2 receptor agonists.

Three-dimensional view of pharmacology

The relationship between the stereochemistry of drugs and their therapeutic and toxic effects is discussed. Molecular structures that have the same chemical constituents and are related to each other as an object and its nonsuperimposable mirror image are enantiomers. A molecule that has at least one pair of enantiomers is a chiral compound, and a 50:50 mixture of enantiomers is a racemic mixture. The enantiomers of a chiral drug may vary in their interactions with chiral or asymmetric environments such as enzymes and receptors. These variations may lead to differences in pharmacology, pharmacokinetics, therapeutic effect, efficacy, and toxicity. For example, dextropropoxyphene is an analgesic, whereas its mirror image, levopropoxyphene, is an antitussive agent. Enantiomers may have identical efficacy and toxicity. They may have the same therapeutic and toxic effects but differ in the magnitude of these effects; one may possess all the pharmacologic activity and the other may be biologically inactive, or both may be pharmacologically active but have qualitatively different therapeutic and toxic effects. Continued research into the stereochemistry of drugs may lead to the development of newer, safer, and more efficacious drugs and other chemical compounds.

The study of combined action of agents using differential geometry of dose-effect surfaces

Although graphic surfaces have been used routinely in the study of combined action of agents, they are mainly used for display purposes. In this paper, it is shown that useful mechanistic information can be obtained from an analytical study of these surfaces using the tools of differential geometry. From the analysis of some simple dose-effect surfaces, it is proposed that the intrinsic curvature, referred to in differential geometry as the Gaussian curvature, of a dose-effect surface can be used as a general criterion for the classification of interaction between different agents. This is analogous to the interpretation of the line curvature of a dose-effect curve as an indication of self-interaction between doses for an agent. In this framework, the dose-effect surface would have basic uniform fabric with zero curvature in the absence of interaction, tentatively referred to as null-interaction. Pictorially speaking, this fabric is distorted locally or globally like the stretching and shrinking of a rubber sheet by the presence of interaction mechanisms between different agents. Since self-interaction with dilution dummies does not generate intrinsic curvature, this criterion of null-interaction would describe the interaction between two truly different agents. It is shown that many of the published interaction mechanisms give rise to dose-effect surfaces with characteristic curvatures. This possible correlation between the intrinsic geometric curvature of dose-effect surfaces and the biophysical mechanism of interaction presents an interesting philosophical viewpoint for the study of combined action of agents.

Determination of dissociation constants of some pharmaceutical compounds using derivative spectrophotometry

Derivative spectrophotometry is applied to the determination of the dissociation constants (pKa) of some weakly dissociating compounds. The pKa value(s) can be calculated by measuring the amplitude of derivative maxima (D) at the selected wavelengths for the dissociated, undissociated and partially dissociated forms of the compound. A graphical technique, based on plotting the derivative spectrophotometric titration curves and interpolating pKa at D1/2 is also presented. Both methods are applied to pharmaceutical compounds with single and double dissociation constants. The results are in good agreement with the reported pKa values of the investigated compounds.

What is an appropriate measure of exposure when testing drugs for carcinogenicity in rodents?

This discussion paper argues that in the carcinogenicity testing of drugs, biological measures of drug exposure may often be more relevant than the classical pharmacokinetic approaches applicable to reversible pharmacodynamic phenomena. Chemicals that produce tumors in rodents may do so (either directly or after bioactivation) by mechanisms involving inter alia a mutagenic, cytotoxic, or hormone-like effect. Such mechanisms may involve the formation of reactive metabolites of fleeting existence, and these are subject to the principles of irreversible pharmacokinetics. Examples are given of genotoxic and nongenotoxic substances for which the species and target site for tumor formation correlates not with plasma concentration, but with the amount metabolized and/or the rate of metabolism. Other compounds produce tumors in rodents, often in only one sex or species, in association with an exaggerated pharmacodynamic effect, with an increase in liver weight (by one of a diversity of mechanisms) or with hormonal or hormonal-like effects. In such cases the determinant of tumor formation is the degree of disturbance of homeostasis, not the plasma concentration of the parent substance. For drugs, the disturbance in question may have no relevance to the clinical use of the drug. Plasma concentrations of the parent substance are useful in assessing the proportion of an oral dose that is absorbed and the linearity of kinetics over the full dose range and for exploring the differences between dietary and gavage administration. They do not usually, however, provide information of direct relevance to assessment of "exposure" for the purposes of carcinogenic risk assessment.

Spectrophotometric determination of ketotifen in pharmaceutical preparations after isolation on ion-exchanger

Spectrophotometric method have been proposed for the determination of ketotifen in complex "Position" (Polfa-Poznań) samples after preliminary separation of excipients. For the determinations of the ketotifen in Pozitan a relative standard deviation of +/-2.0% was found.

Enzyme substitution in pancreatic disease: is colipase activity sufficient?

The aim of the present study was to determine colipase activity in various pancreatic enzyme tablets to ascertain whether these contained sufficient amounts of colipase to activate lipase during fat digestion. Colipase activity in all preparations tested exceeded that of lipase activity by a factor of 1.4-1.9 on a molar activity basis. Since optimal activity of lipase is obtained with colipase being present in a colipase to lipase molar activity ratio of 1.0, it is concluded that these preparations contain a sufficient amount of colipase to activate lipase.

Use of fractal geometry to determine effects of surface morphology on drug dissolution

We extend and modify the Noyes-Whitney equation and the Hixon-Crowell cube root law to include surface roughness effects on the dissolution rate of drugs. The problem is treated theoretically in terms of the fractal reaction dimension, DR, of the effective surface which undergoes dissolution. Effects of changes in DR on the dissolution rate are identified and explained.

[Our drug metabolism studies during the last four decades]

The drug metabolism studies in which we have been engaging for about 40 years since 1952 are briefly reviewed in this paper. Our main efforts were initially made to elucidate the metabolic fates of various abused drugs including barbiturates, carbamates, opioids, amphetamines and cannabinoids in mammals from pharmacological and toxicological points of view. Among the interesting findings obtained from these studies, the most remarkable one was that morphine-6-glucuronide, a minor metabolite of morphine, has much stronger analgesic activity than morphine. Recently we have also been interested in clarifying the enzyme system involved in the metabolic pathways of the above drugs. Several cytochrome P-450 isozymes were thus purified from the liver microsomes of mammals and their role in oxygenation of amphetamines and cannabinoids were elucidated. The finding that MALDO (microsomal aldehyde oxygenase), a purified P-450 isozyme, could catalyze an oxidation of lipid-soluble aldehydes to the corresponding carboxylic acids was most noticeable. Metabolic and toxicologic studies on furylfuramide (AF-2) and polychlorinated biphenyl (PCB) have also been performed using rats and other animal species, and some interesting results were obtained.

Prediction of retention indexes. III. Silylated derivatives of polar compounds

Polar compounds containing hydroxyl, amino and carboxyl groups, singly or in combination, can be chromatographed after the polar functional groups are silylated. The silylated derivatives of acids, alcohols, amines, diols, amino alcohols, amino acids are shown to behave chromatographically as hydrocarbons, and their retention indexes can be readily predicted from their base values. The column difference, namely, the difference between the retention indexes of the analyte on polar and non-polar columns is minimal for the silylated derivatives in comparison to that observed for the underivatized analytes. This minimal column difference is attributed to the hydrocarbon-like chromatographic characteristics of the silylated derivatives. The retention indexes of the silyl derivatives appear to correlate with the atom number Z of the analyte.

Prediction of retention indexes. II. Structure-retention index relationship on polar columns

A method is described for the prediction of the retention index (I) from chemical structure, using the number of atoms in the molecule (Z), the I increment for atom addition (A) and the group retention factors (GRFs) of the functional groups and substituents. This method can predict the retention indexes of a wide range of compounds, such as acids, alcohols, amines, acid esters, aldehydes, ketones, ethers, aromatic hydrocarbons, alicyclics, heterocyclics, etc. on polar as well as non-polar columns to within 3% error. Accurate A and GRF values are essential to the prediction. These values can be obtained from homologous series, but a system of arbitrarily assigned A value and adjusted GRFs are also used. The GRFs of the substituents and functional groups depend on the polarity and polarizability of the analyte and the stationary phase and also on the molecular connectivity of the atoms, namely, primary, secondary and tertiary carbon atoms or hydrogen atoms, to which these groups are attached. Highly polar and polarizable groups can alter the A value. When the functionality of a group is masked by substitution, the analyte molecule will tend to behave chromatographically like hydrocarbons. The difficulty in predicting the I values of compounds of multi-functionality by the rule of additivity is the unknown intramolecular interaction that can alter both A and GRF values.

[Photochemistry of pharmaceutical substances]

The chemistry of excited states is now well understood, and the photo-instability of pharmaceutically active molecules can be rationalized or predicted. Some relevant examples are discussed and include both reactions of the excited state of the substrate and reactions caused by active species photochemically generated from other components, as well as the effect of the physical state of the sample on the reaction.

Automatic search for maximum similarity between molecular electrostatic potential distributions

A new computer program has been developed to automatically obtain the relative position of two molecules in which the similarity between molecular electrostatic-potential distributions is greatest. These distributions are considered in a volume around the molecules, and the similarity is measured by the Spearman rank coefficient. The program has been tested using several pairs of molecules: water vs. water; phenylethylamine and phenylpropylamine vs. benzylamine; and methotrexate vs. dihydrofolic acid.

Physical characterization of pharmaceutical solids

A general review of the methods available for the physical characterization of pharmaceutical solids is presented. The techniques are classified as being on the molecular level (properties capable of being detected in an ensemble of individual molecules), the particulate level (properties which can be detected through the analysis of an ensemble of particles), and the bulk level (properties which can be measured only using a relatively large amount of material). The molecular-level properties discussed are infrared spectroscopy and nuclear magnetic resonance spectrometry, the particulate-level properties discussed are particle morphology, particle size distribution, powder X-ray diffraction, and thermal methods of analysis, and the bulk-level properties discussed are surface area, porosity and pore size distribution, and powder flow characteristics. Full physical characterization of three modifications of lactose (hydrous, anhydrous, and Fast-Flo) is presented to illustrate the type of information which can be obtained using each of the techniques discussed.

[Study of biological fluids by nuclear magnetic resonance spectroscopy]

The use of nuclear magnetic resonance (NMR) spectroscopy in the study of biofluids is rapidly developing and might soon constitute a new major medical application of this technique which benefits from technological and methodological progress such as higher magnetic fields, new probe design, solvent suppression sequences and advanced data processing routines. In this overview, the clinical and pharmacological impact of this new approach is examined, with emphasis on the NMR spectroscopy of plasma, cerebrospinal fluid and urine. Applications to pharmacokinetics and toxicology are illustrated. Interestingly, a number of biochemical components of fluids which are not usually assayed by conventional biochemical methods are readily detected by NMR spectroscopy which is clearly a new competitive entrant among the techniques used in clinical biology. Its ease-of-use, cost effectiveness and high informational content might turn it into a major diagnostic tool in the years to come.

A patent lawyer's perspective

The principles of patent law are first briefly explained. Particular patent problems which arise from the preparation of new drugs in novel chiral forms are then discussed and illustrated by reference to legal decisions.

Influence of lipophilic counter ions on the transport of ionizable hydrophilic drugs

The influence of lipophilic counter ions on the transport of the hydrophilic drugs pholedrine and bretylium across artificial lipid membranes has been studied using a permeation model system. The transport of both drugs was markedly enhanced by hexylsalicylate and by salts of fatty acids with a maximum at decanoate. The transport of pholedrine was additionally increased by bile salts such as desoxycholate.

The cosmetic ingredient review self-regulatory safety program

The CIR's 13-year history of cosmetic-ingredient safety review appears to have successfully accomplished its goal of reviewing in a scientific manner the safety of cosmetic chemical ingredients. The method of prioritization has allowed for the identification of the most frequently used and the most biologically active chemicals. To date, 310 cosmetic ingredients have been reviewed, and 33 ingredients are under current review. Although CIR does not have a safety-evaluation report available for every cosmetic ingredient in use, it has proved that CIR is a system of documentation, review, and analysis that can be used to address any safety problem that may exist with any cosmetic ingredient.

Consideration of drug load on the swelling kinetics of glassy gelatin matrices

The effect of drug load on water transport into glassy gelatin beads and on the dynamic swelling behavior of the hydrated gel was studied through microscopic measurements of moving boundaries. Isoniazid was found to alter the glassy structure of gelatin, resulting in an increase in water penetration rates with a lowering of the apparent activation energy for water front movement. Differential scanning calorimetry studies revealed a decrease in the glass transition temperature with drug load, further indicating plasticization of the gelatin glass. The presence of drug also accelerated the outer swelling gelatin front, but, in contrast to the water front, the apparent activation energy for matrix expansion rose substantially with higher drug loads for temperatures greater than 20 degrees C. This observation may be rationalized as an increasing osmotic stress on the matrix induced by greater loading with hydrophilic drug. The osmotic stress, in turn, forces the gelatin matrix to expand outward, resulting in a higher apparent activation energy (Eact). Furthermore, the enhanced expansion was especially pronounced at higher temperatures where physical bonds, which are associated with gel structure and needed to resist swelling, are presumably weaker and fewer in number.

Analysis of drugs and other toxic substances in biological samples for pharmacokinetic studies

The importance of the role of analysis of drugs and other toxic substances in biological samples (bioanalysis) in medicine, toxicology, pharmacology, forensic science, environmental research and other biomedical disciplines is self-evident. Among these disciplines, bioanalysis plays a special pivotal role in pharmacokinetics. The pharmacokinetic parameters, such as half-life, volume of distribution, clearance and bioavailability, of drugs and other compounds are derived from the concentrations of these analytes assayed in the biological samples collected at specified time points. The capability of analysts to develop sensitive and specific analytical methods for the assay of low concentrations of drugs and other toxic compounds in small amounts of biological samples has contributed significantly to the theoretical advances in pharmacokinetics and its applications in clinical pharmacology and the management of drug therapy in patients. The increased demands for pharmacokinetic applications in turn have stimulated the innovation and improvement in bioanalytical technologies. The reliability of the pharmacokinetic conclusions depends on the accuracy and precision of the analytical methods employed to assay the biological samples. Factors that affect the integrity of the bioanalytical data should therefore be controlled in analysis of biological samples for pharmacokinetics studies. The biological samples for drug concentration determination should be collected as specified in the study protocol with respect to the time and site of sampling. These samples should be processed to avoid extraneous interactions between the analytes and sampling devices or additives resulting in the redistribution of the analytes between components of the biological samples, such as displacement of drug binding and changes in the distribution of the analytes between plasma and red blood cells. The stability of the drugs and other analytes in the samples should also be evaluated to establish the conditions suitable for the transportation and storage of the samples to avoid chemical, photochemical and enzymatic degradation of the analytes. Various technologies have been utilized to assay biological samples for pharmacokinetic studies. The most frequently used are chromatography (high-performance liquid chromatography, gas chromatography and thin-layer chromatography), immunoassays and mass spectrometry.(ABSTRACT TRUNCATED AT 400 WORDS)

Application of micellar mobile phases for the assay of drugs in biological fluids

Although micellar chromatography has been used for the determination of drugs in biological fluids since 1985, relatively few researchers have applied the technique to therapeutic monitoring. The reasons for this are rather unclear. It may be that most of the present extraction/reconstitution techniques are well established or that the method development procedure is unfamiliar. Significantly lower detection limits can be obtained with micellar mobile phases and column switching than with micellar mobile phases alone. Only two groups have used micellar mobile phases in conjunction with column switching for the determination of drugs in biological fluids. Since column switching with micellar mobile phases is a relatively new and untried technique, it will take some time before the full range of its applicability and limitations are known.

Radiochromatography in pharmaceutical and biomedical analysis

Recent advances in the chromatographic analysis of radiolabelled compounds are discussed, with emphasis on the optimization of radioactivity detection in modern chromatographic techniques. Applications are mentioned only infrequently. The state-of-the-art of common radioactivity detection methods is reviewed, as well as promising new detection principles. The latter include flow-through liquid scintillation counting of reversed-phase column eluates based on post-column extraction and solvent segmentation, flow-through heterogeneous counting using a flow cell constructed from axially aligned scintillation fibres, flow cells especially constructed for the detection of beta-emitting radioisotopes in capillary zone electrophoresis, position-sensitive analysers employed in radio planar chromatography and, finally 14C atom counting (as opposed to 14C decay counting) by accelerator mass spectrometry.

Chiral high performance liquid chromatography of drug molecules

The individual enantiomers of racemic drugs frequently differ in their biological effects. For pharmacological studies of such drugs there is therefore a need for an effective means of separating and quantifying the enantiomers in biological samples. As their physicochemical properties are similar, the assay of enantiomers is generally regarded as difficult, time-consuming and error-prone. However, recent developments in high performance liquid chromatography (HPLC) chiral stationary phase technology overcome some of these problems and provide a more efficient and reliable way of assaying enantiomeric drugs.

Lactic acid oligomer microspheres containing hydrophilic drugs

A new method was developed for preparation of biodegradable lactic acid oligomer microspheres containing hydrophilic drugs. The microspheres were obtained by removal of solvent from an O/O (oil-in-oil) emulsion through evaporation. The solvent used for the dispersed phase solution was an acetonitrile: water mixture, while the continuous phase medium was cottonseed oil. Doxorubicin hydrochloride (ADR) and insulin were successfully entrapped in the microspheres with high trapping efficiencies of 80 to 90%, and their release profiles were not accompanied with the significant burst effect. The release rate of the drugs from the microspheres was greatly affected by the initial loading of the drugs and the molecular weight of the lactic acid oligomer.

Nonlinear estimation of kinetic parameters for solid-state hydrolysis of water-soluble drugs. II: Rational presentation mode below the critical moisture content

A logical presentation mode for accelerated data obtained at low relative humidities has been developed. A model is proposed leading to an equation relating the percent decomposition, x, at time t, to the temperature (T, K), and the water vapor (P, mmHg) in an open system. The data presented support the equation.

Physical and chemical factors influencing the release of drugs from acrylic resin films

An investigation was conducted to evaluate the factors influencing the release of salicylic acid and chlorpheniramine maleate from polymethacrylate amino-ester copolymer films (Eudragits RL PM and RS PM). Differential scanning calorimetry was performed on the films to study the solubility of drug in the polymer and to determine the effect of added drug on the thermal properties of the film. Incorporation of drug into the polymers decreased the glass transition temperature of the polymers. Dissolution of drug from monolithic slabs was followed as a function of temperature, drug concentration in the films, and ionic strength of the release media. In addition, adsorption studies were conducted with each drug:polymer combination to help explain release results and further characterize the drug:polymer interactions that occurred. The rate of drug release increased with increasing temperature. Adsorption of salicylic acid by the polymers was believed to influence the drug release profiles observed for different drug loadings and ionic strengths. Eudragit RL was found to adsorb salicylic acid to a greater extent than the Eudragit RS. Chlorpheniramine maleate was not found to be adsorbed by either polymer.