The Pharmaceutical Journal
Vol 269 No 7216 p414-417
21 September 2002
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The Pharmaceutical Journal |
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British Pharmaceutical Conference 2002 summary |
Science presentations
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The section on pharmaceutical analysis and analytical chemistry comprises approximately 30 papers in which a wide range of applications of analytical methods and the development of analytical techniques are eloquently described. In these, analytical techniques for the quantification of low molecular weight therapeutic agents and ions, for the analysis of the surface properties of powders, the evaluation of the stability of therapeutic agents, identification and characterisation of macromolecules and the real time analysis of interactions between macromolecules are all covered. A wide range of analytical techniques is described in these sections, including nanoelectrospray ionisation tandem mass spectrometry, high performance thin layer chromatography, high performance liquid chromatography, gas and inverse gas chromatography, voltammetry, solid phase extraction, thermal analysis, spectroscopy and different types of microscopic techniques (eg, atomic force microscopy, scanning thermal microscopy and confocal Raman microscopy).
For example, Lane et al (University of London and Applied Biosystems, Langen, Germany) describe the concurrent use of SDS-PAGE, tryptic digestion and nanoelectrospray ionisation tandem mass spectroscopy for the analysis of proteins derived from human cytochrome P450. Isoforms of these proteins are expressed in certain types of cancers and therefore these systems may have applications in drug targeting. The combination of these analytical techniques enabled a method to be developed for the analysis of these molecules.
Although the use of HPLC for the quantification of therapeutic agents is a common theme in several of the presentations, there are some interesting applications of this method to solve potentially difficult analytical problems. In the development of an HPLC method for the quantification of a novel anti-cancer drug currently in phase I trial, problems were encountered concerning the resolution of the drug and an impurity and, in addition, the linearity of another impurity. To overcome this problem, Ford et al (University of Strathclyde) apply a second order derivative to the chromatographic trace to improve the performance of the method and hence ensure progression of the drug development programme.
A further example of method development is provided by Abruz et al (Queen's University of Belfast), who describe the use of solid phase extraction to facilitate the simultaneous analysis of prednisolone and cortisol by HPLC. Suppression of urinary and plasma cortisol is the main side effect of steroid usage and, accordingly, a method to analyse these compounds simultaneously would have clinical relevance. The authors report the use of HLB cartridges for solid phase extraction before analysis by HPLC and successfully apply this method for the quantification of prednisolone and cortisol in the plasma and urine samples of asthmatic patients.
This year's conference will see a continuing theme of the application of microscopic techniques for the characterisation of pharmaceutical systems, illustrating the great potential of these methods for the improved understanding of dosage form performance. For example, Woodward et al (Molecular Profiles and the University of Nottingham) describe the concurrent use of Raman spectroscopy and scanning thermal microscopy for the identification of the polymeric components within the layers of a multilayered polymeric packaging system, whereas, atomic force microscopy was successfully used to provide information concerning the mechanical properties and adhesive interactions at the interfaces between layers. The same group (Ebbens et al, Molecular Profiles and the University of Nottingham) report the successful application of applied scanning thermal microscopy and atomic force microscopy for the identification of the components at the surface of a model paracetamol tablet.
Several themes emerge within the biopharmaceutics section, including the prediction of in vivo performance using in vitro data and the characterisation of drug transport across biological membranes. The development of a guinea pig gastric epithelial cell tissue model (that exhibited similar trans-epithelial resistance as guinea pig gastric mucosa), designed for the assessment of drug permeability across the gastrointestinal tract is described by Kawada et al (Aston University and AstraZeneca, Loughborough).
Similarly the use of a nasal epithelial cell culture for the examination of the transport and metabolism of methionine enkephalin is described by Vu Dang et al (Leuven, Belgium). They describe the enhanced transport of this therapeutic agent following co-administration with protease inhibitors (bestatin and puromycin) and absorption enhancers (dimethyl-b-cyclodextrin and sodium glycocholate). Polyethylene glycol (PEG) is a commonly used component of oral solutions and soft gelatin capsules and therefore in the development of oral products an understanding of the effects of this excipient on gastrointestinal transit is required. Therefore, Schulze et al (University of London, University College London and GlaxoSmithKline, Ware and North Carolina) examine the effects of aqueous solutions containing PEG 400 (0–5g) on gastrointestinal transit in seven male subjects using gamma scintigraphy. PEG did not affect the gastric residence time, however, the small intestinal transit time and the mean caecal arrival times were decreased as the concentration of PEG was increased. These observations are therefore relevant to the use of dosage forms containing this excipient.
As in previous years, the drug delivery sessions are well represented and several topics are addressed, including the formulation and characterisation of controlled release dosage forms for oral delivery and factors affecting the subsequent drug release, the rheology of novel gel and semi-solid drug delivery systems, bioadhesive drug delivery systems, particulate drug delivery systems, transdermal and topical drug delivery systems, dendrimers, gene delivery and responsive drug delivery. Furthermore, in many presentations drug delivery strategies are described for the improved treatment of disease states for which current treatments are sub-optimal. For example, there is a paucity of knowledge concerning drug delivery to the neonate and accordingly the availability of drug delivery systems for use in this patient population is poor. One clinical problem with neonates involves the need for local anaesthesia to facilitate routine venepuncture and heel stabs. Therefore, Long et al (Queen's University, Belfast and Royal Maternity Hospital, Belfast) describe the formulation and clinical efficacy of a novel pressure sensitive anaesthetic patch system. Following application of the patch for 30min, the authors report that an effective anaesthesia was achieved in neonates, as assessed using the neonatal facial coding score, thereby proving the validity of this formulation strategy.
A disease state that has received considerable attention in terms of drug delivery is diabetes, where research is currently ongoing to improve the delivery of insulin. At this year's conference the design and in vivo efficacy of a novel self-regulated insulin delivery system in which a complex of a polysaccharide that contains terminal glucose units, lectin and concanavalin A that acts as a rate controlling membrane for insulin is described by Taylor et al (De Montfort University, Leicester). In the absence of glucose the complex exists as a gel system due to physical cross-linking of the lectin component with the polysaccharide. However, in the presence of glucose, structural collapse occurs, thereby allowing release of insulin through the membrane. The authors report that the glucose levels in diabetic rats in which the novel insulin- containing devices had been implanted within the peritoneal cavity were constant following challenge with oral glucose. This technology may therefore offer several possibilities for the control of diabetes.
Systemic drug delivery from the vagina or the treatment of local conditions of the vagina has been examined using a number of different drug delivery platforms. However, recently an interest has developed in the use of drug-impregnated (intravaginal) silicone rings for this purpose. Traditionally, the use of these systems has been restricted to the delivery of hydrophobic drugs, due to their ability to diffuse effectively through the hydrophobic silicone matrix. To increase the spectrum of therapeutic agents that may be delivery using this drug delivery platform Tallon et al (Queen's University of Belfast) examine the effect of the inclusion of hydrophilic excipients on the mechanism and rate of release of a model hydrophilic drug, metronidazole. Using microscopic methods and thermogravimetric analysis, the authors conclude that drug release from the silicone intravaginal rings occurred through the aqueous filled channels and illustrated the ability of a hydrophilic polymer, hydroxyethylcellulose, to enhance the release of metronidazole.
A popular theme in the drug delivery category is the characterisation and application of colloidal/particulate systems for the efficient delivery of drugs, prodrugs and macromolecules. Several papers describe the pharmaceutical utility of liposomes. For example, it has been reported that liposomes may offer protection to labile drugs within the gastrointestinal tract and, in addition, may enhance the absorption of poorly soluble drugs. Accordingly Bradbury et al (Aston University and AstraZeneca, UK) examine the effect of the liposome bilayer composition on the incorporation of a model therapeutic agent and examine the liposomal retention of this agent following immersion within simulated gastric fluid and fasted intestinal fluid. The authors report that drug retention within the liposomes was dependent on bilayer rigidity. Furthermore, the liposomes were shown to have no deleterious effects on cell viability in an in vitro model. These results therefore have further illustrated the potential of liposomes for the oral delivery of therapeutic agents.
The use of liposomes and microparticulate systems for vaccine delivery is discussed by various presenters. In one approach by Wei Li et al (University of London, CRC Institute for Cancer Studies, Birmingham) complexes of DNA and polyethyleneimine were produced (due to the known ability of this complex to facilitate cellular entry of DNA) and these complexes were subsequently microencapsulated into PLGA microspheres (with the addition of PEG to stabilise the DNA complex). In vitro experiments confirmed that DNA was released from the particles as a complex and, furthermore, in vivo experiments illustrated that gene expression had occurred in the Peyer's patches, the spleen and liver. Similarly Somavarapu et al (University of London) explore the use of chitosan or polyvinyl alcohol coated polylactic acid particles for the nasal delivery of the diphtheria toxoid. The authors show that the microencapsulated antigen produced a better antigen-specific antibody titre than free antigen and, furthermore, the antigen specific antibody titres following nasal administration of the chitosan coated systems were twice those of the polyvinyl alcohol-coated counterparts. This study therefore highlighted the benefits of incorporation of antigens into particulate systems as vaccine systems and, specifically illustrated the importance of chitosan in the performance of such systems.
Further benefits of colloidal systems as delivery systems for vaccines are presented by Perrie et al (Aston University, Lipoxen Technologies Ltd and the University of London) who describe the formulation and in vivo performance of plasmids that had been entrapped within liposomes and niosomes. Following subcutaneous administration of these candidate vaccine formulations an enhanced humoral response resulted.
One of the more recent advances in colloidal drug delivery involves the use of dendrimers as platforms for drug delivery. Dendrimers are branched macromolecules that may be designed to contain reactive functional groups to which drug molecules may be attached. In a collaboration between Aston University, Oxford University and the Welsh School of Pharmacy, dendrimers, designed for use as antitumour agents, were synthesised to which antisense oligonucleotides were covalently bonded. Importantly the authors show that liberation of the free antisense oligonucleotides was not required to achieve the required biochemical activity. Accordingly dendrimers are shown to be a useful vector for the delivery of the antisense oligonucleotides.
Moreover, researchers at the Universities of Strathclyde and Glasgow describe the use of quaternary ammonium polypropylenimine dendrimers as delivery systems for DNA. Initially quaternary ammonium derivatives of third and fourth generation dendrimers were synthesised and characterised. These were then complexed with DNA and their cytotoxicity and transfection efficacy examined and compared with DNA-complexed dendrimers that were devoid of quaternary ammonium functionalities. The derivatised dendrimers exhibited lower cytotoxicity and enhanced transfection capacity in comparison with the control dendrimers.
At the conference there will be a large number of presentations on different aspects of pharmaceutics, including solid dosage form technology, rheology, the processing and stability of proteins, the production and characterisation of films as drug delivery systems and medical device biomaterials and inhalation technology. Of all the topics described above, solid dosage form technology receives the most attention.
The effect of compaction parameters on the performance of tablets is addressed by several research groups. For example, the effects of tooling geometry on the mechanical properties of tablets is discussed by Harrop et al (AstraZeneca, Charnwood and John Moore's University, Liverpool). Using punch and die sets of differing geometries and maintaining a constant fill depth, compression height and compression speed, the authors manufactured a series of tablets and characterised these in terms of the fracture force and the tensile strength. Differences in the tensile strength of the different tablets were observed and were accredited to differences in the internal structures associated with the different geometries.
In a related study by workers at Imperial College London and Merck, Sharp & Dohme (Hertfordshire), the density distribution and surface morphology of tablets that had been produced using a flat-faced punch and die are characterised, since inhomogeneity of density distribution may lead to the production of poor quality tablets. The density distribution of the exposed surfaces of tablets that had been produced using a range of compaction pressures were examined using a digital imaging system, from which, it was shown that density differences occurred within the tablet and that the magnitude of these differences increased as the compaction pressure increased. The authors conclude that the pressure distribution during compaction affects density distribution. These observations will therefore be of benefit to the optimisation of tableting processes.
One method by which the performance of solid dosage forms and particulate systems may be enhanced is by the application of a polymeric surface coating. In an interesting approach Shiu et al (Merck, Sharp & Dohme, UK, and the University of Birmingham) examine the mechanical properties of a range of polymeric coats on microcapsules that had been produced by a spray-coating process. The microcapsules were then exposed to compressive stresses using strains of up to 20 per cent and the elastic modulus of each coating determined from the initial slopes of the pseudo stress-strain relationship. The authors suggest that this technique may be useful for quality control and processing purposes.
Maintaining the theme of spray coating, Khan et al (University of Manchester, FMC Biopolymer, Belgium) have looked at the effect of processing conditions on the adhesion of HPMC films to placebo tablet cores. Using a factorial design the authors examine the effect of air flow and spray rate on the adhesive interaction of the polymer with the tablets, determined using a specially designed tablet tester. Using this method the authors conclude that spray rate (and not airflow) significantly affects the adhesive properties of the polymer coating. These results have direct implications for the spray coating of tablets.
Recently, due to the increasing significance of proteins as therapeutics agents, research has been directed at understanding the processing requirements of these systems. In one study by Vincenzi et al (University of Bradford and AstraZeneca, Charnwood) the effect of protein concentration and storage on the activity of a model protein (lactate dehydrogenase) that had been freeze-dried or freeze-thawed under defined conditions is examined. The authors show that most of the reduced enzyme activity occurred due to freezing induced stress and to a lesser extent due to drying. Increasing the protein concentration and the temperature of storage decreased the loss in activity.
In a related study Quader et al (King's College London) have used temperature modulated differential scanning calorimetry to interpret the mechanisms of stabilisation of a spray-dried model protein (catalase) by sucrose and trehalose. In addition, the authors illustrate the dependency of protein stabilisation on the spray drying temperature and the type and mass of stabiliser.
Several aspects of medicinal chemistry will be presented at the conference this year, including quantitative structure activity relationships, molecular modeling, drug (and prodrug) synthesis and the determination of the physical and structural features of therapeutic agents.
An example of innovative drug synthesis involves the synthesis of novel myoinositol tetrakisphosphate analogues designed to reduce water and chloride efflux in cystic fibrosis (Martin and Freeman, University of Manchester). In other presentations molecular modelling and drug synthesis are seamlessly combined. For example, the modeling and synthesis of NAD-dependent glycerol-3-phosphate dehydrogenase inhibitors that are specific for the treatment of leishmaniasis are described by Clark et al (University of Strathclyde). Similarly, workers at the Queens University of Belfast (Gilmore et al), recognising the contribution of seprase (surface expressed protease) to the process of metastasis, synthesise seprase specific inhibitors and illustrate the inhibitory properties of these systems using an in vitro model. The theme of the synthesis and evaluation of novel anticancer molecules is continued by Chester et al (University of Bradford), who, in an attempt to increase the selectivity of doxorubicin for the treatment of breast cancer, synthesise novel molecules in which doxorubicin and a chemically modified oestrone derivative are chemically joined via an amide linkage. The biological efficacies of these therapeutic agents were then examined in a cell culture model where it was shown that the combined doxorubicin/ modified oestrone molecule exhibited improved selectivity for the oestrogen receptor cell line. These molecules may therefore be potentially suitable for the treatment of breast tumours.
Several key themes are to be presented at the pharmacology section, including neurological, respiratory, cardiovascular and anti-inflammatory pharmacology. Within the neurological theme there are presentations on hypoxia/ischaemia, epilepsy and schizophrenia. For example, recognising hypoxia/ischaemia (resulting from strokes or head injuries) as one of the risk factors for neurological dementias, Hejmadi et al (University of Bath) examine the role of nicotinic receptors in hypoxia-induced cell death in primary cortical cultures. The authors conclude first that hypoxia-induced cell death was primarily due to apoptosis and furthermore illustrated the protective effect of (–)-nicotine against hypoxia-induced neurotoxicity. Due to the proposed relationship between a hypoglutamatergic state and increased release of dopamine in the generation of schizophrenic symptoms, Bennet and Gronier (De Montfort University, Leicester) examine the effects of glycine, an agonist for the NMDA subtype of the glutamate receptor, on the release of dopamine. The authors report that, using rat striatal preparations, the application of glycine (1mM) significantly reduced NMDA-evoked dopamine release.
The largest pharmacological theme within this section is cardiovascular pharmacology, with presentations focusing on the pharmacological effects of therapeutic agents on blood flow, hypertension and cardiovascular complications in diabetes. In a series of presentations researchers from the University of Bradford examine the effects of oestrogens on the relaxation of blood vessels in both isolated umbilical arteries and in aged rats. In light of the environmental significance of oestrogens, the same group (McCurrie et al, University of Bradford) compares actions of industrial (bisphenol-A and nonylphenol) and plant oestrogens (genistein) with that of 17b-oestradiol on the portal veins of rats. The authors observe that these agents caused blood vessel relaxation; however, the mechanisms of this effect were dependent on the type of oestrogen.
Diabetes mellitus is associated with several chronic complications, of which vascular disease is an example. Although studies have shown that cytochrome P450 metabolites of arachidonic acid and tyrosine kinase play significant roles in hypertension and related disease states, their role in the development of diabetes-related cardiovascular problems is unclear. Accordingly workers from the University of Kuwait and the Welsh School of Pharmacy examine this potential relationship using a rat model and conclude that inhibition of these metabolites of arachidonic acid improved cardiovascular reactivity. These observations have direct implications for the prevention of cardiovascular complications in diabetic patients.
The prevalence of respiratory diseases is increasing in society today and therefore better knowledge of potential causes and treatments of such diseases is required. One possible source of airway inflammation is the inhalation of chemicals from the environment, an example of which is (1Æ3)-b-D-glucan, a polyglucose that is derived from the cell wall of mould, some bacteria and plants and which has been discovered in organic dusts. The effect of this agent on airway inflammation is reported by Nicholls et al (Welsh School of Pharmacy) who aerosolised solutions of (1Æ3)-b-D-glucan to conscious guinea pigs and, following humane killing, examined the proportions of macrophages, eosinophils and neutrophils following bronchoalveolar lavage. Importantly, the authors report that there was an increase in the numbers of inflammatory cells following exposure to this agent. However, chronic exposure was required to induce neutrophilia. Conversely, the effects of novel nitro derivatives of steroids against histamine-induced bronchoconstriction are reported by Nevin et al (Welsh School of Pharmacy). Using a guinea-pig model, the authors show that, following inhalation, the nitro derivatives of prednisolone, budesonide, flumetasone and flunisolone reduced the bronchoconstriction to histamine and, furthermore, the extent of this reduction is significantly greater than with the parent molecules.
These observations indicate that these nitro derivatives may be an important therapy for the treatment of asthma.
A range of pharmacokinetic studies will be presented, including bioequivalence assessment (Tajerzadeh et al, University of Tehran, Iran), population pharmacokinetics (Smyth et al, Queen's University of Belfast), pharmacokinetic modeling (Nasseri and Rowland, University of Manchester) and the relationship between pharmacokinetic data and clinical performance. In this last category Khu et al (University of Bradford and the Leeds Teaching Hospitals NHS Trust) look at the relationship between plasma methotrexate concentration and the response to treatment in patients with rheumatoid arthritis. Pharmacokinetic parameters were generated using Bayesian analysis from one blood sample and the differences between the values of these parameters in patients who were classified as good and poor responders to drug treatment were analysed. No correlation was observed between methotrexate concentration and clinical efficacy between the good and poor responders.
The pharmacognosy section is one of the smaller sections in the conference; however, in spite of this, there will be several interesting presentations concerning the possible medicinal uses of natural products. In one study it is shown that extracts of Vernonia anthelmintica suppressed the formation of pro-inflammatory mediators (Pires et al, King's College London) whereas the same group (Bawden et al, King's College London) examine the inhibitory effects of extracts of traditional antidiabetic plants on a-amylase. Selected extracts of these plants were observed to possess significant inhibitory activity, thereby confirming a possible use of these plants in the treatment of diabetes.
In a further study, Chronnell et al (King's College London) have synthesised and examined two analogues of piperine (derived from black pepper) for their ability to stimulate melanocyte activity. The authors illustrate the stimulatory activity using a cell culture model, highlighting the potential of these substances for the treatment of vitiligo.
Several research themes will be presented at the microbiology session, including antimicrobial resistance, the antimicrobial activity of antimicrobial agents or mixtures of antimicrobial agents and factors affecting this efficacy and the mechanisms of action of antimicrobial agents. Resistance of bacteria to antimicrobial agents represents a serious clinical problem and aspects of this are addressed by Tunney and Colton (Queen's University of Belfast). In this, the ability of strains of Pseudomonas aeruginosa to acquire resistance to gentamicin following a single exposure (1h, 8 x MIC [minimum inhibitory concentration]) to this antimicrobial agent is examined. Importantly, all strains developed adaptive resistance, the extent and duration of which were strain dependent. This observation has implications for the effective treatment of infections using gentamicin.
Examination of the effects of complexation of tetracyclines (tetracycline and oxytetracycline) with aluminium and iron (Fe3+) on the activity of these antibiotics against Escherichia coli are described by workers from Liverpool John Moores University. In this experiment, the activities of the two antibiotics were dependent on the nature of the ion, the antibiotic and the ratio of ion to antibiotic in the complex. Iron synergistically enhanced the antimicrobial activity of tetracycline whereas aluminium did not influence this activity. Conversely synergy between these ions and oxytetracycline was not observed and, indeed, at low complex ratios of oxytetracycline to metal ion, the antibacterial activity of this antibiotic is inhibited.
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