Biomedical subjects

Marcus E Brewster

Publications and source records attributed to Marcus E Brewster.

16 recordsLinked to original sources

PubMed2006

Novel generic UPLC/MS/MS method for high throughput analysis applied to permeability assessment in early Drug Discovery.

A novel generic ultra performance liquid chromatography-tandem mass spectrometric (UPLC/MS/MS) method for the high throughput quantification of samples generated during permeability assessment (PAMPA) has been developed and validated. The novel UPLC/MS/MS methodology consists of two stages. Firstly, running a 1.5min isocratic method, compound-specific multiple reaction monitoring (MRM) methods were automatically prepared. In a second stage, samples were analyzed by a 1.5min generic gradient UPLC method on a BEH C18 column (50mmx2.1mm). Compounds were detected with a Waters Micromass Quattro Premier mass spectrometer operating in positive electrospray ionization using the compound-specific MRM methods. The linearity for the validation compounds (caffeine, propranolol, ampicillin, atenolol, griseofulvin and carbamazepine) typically ranges from 3.05nM to 12,500nM and the limits of detection for all generically developed methods are in the range between 0.61nM and 12nM in an aqueous buffer. The novel generic methodology was successfully introduced within early Drug Discovery and resulted in a four-fold increase of throughput as well as a significant increase in sensitivity compared to other in-house generic LC/MS methods.

Ampicillin↗

PubMed2006

Hot stage extrusion of p-amino salicylic acid with EC using CO2 as a temporary plasticizer.

The aim of the current research project was to explore the possibilities of combining pressurized carbon dioxide with hot stage extrusion during manufacturing of solid dispersions of the thermally labile p-aminosalicylic acid (p-ASA) and ethylcellulose 20cps (EC 20cps) and to evaluate the ability of the pressurized gas to act as a temporary plasticizer. The thermal stability of the p-ASA was investigated using DSC, TGA and HPLC. The compound decomposes completely upon melting. Below 110 degrees C and under atmospheric conditions, the compound is thermally stabile for 10min. Pressurized carbon dioxide was injected into a Leistritz Micro 18 intermeshing co-rotating twin-screw melt extruder using an ISCO 260D syringe pump. Carbon dioxide acted as plasticizer for p-ASA/EC 20cps, reducing the processing temperature during the hot stage extrusion process. HPLC showed that without carbon dioxide injection, approximately 17% of p-ASA degraded, while less than 5% degraded with CO(2) injection. The experiments clearly showed that injecting pressurized carbon dioxide broadens the application of hot stage extrusion to thermally labile compounds in a one step process.

Aminosalicylic Acid↗

PubMed2005

Self-assembling PEG-p(CL-co-TMC) copolymers for oral delivery of poorly water-soluble drugs: a case study with risperidone.

Diblock PEG-p(CL-co-TMC) [methoxypoly(ethylene glycol)-poly(caprolactone/trimethylene carbonate)] copolymers form micelles spontaneously and significantly increase the solubility of poorly water-soluble drugs. The aim of this work was to assess these diblock copolymers as oral drug delivery systems in both in vitro and in vivo experiments using risperidone as a model drug. The permeation of risperidone through Caco-2 cell monolayers showed that the apparent permeation coefficient (Papp) was slightly reduced when risperidone was formulated with the copolymer. Based on the higher apparent drug solubility, the copolymer increased drug flux or the total amount of drug which crossed the Caco-2 monolayers. The Papp of the micelle formulation was higher at 37 degrees C than at 4 degrees C. After oral administration to rats, the pharmacokinetic parameters and the pharmacological effect were evaluated. Time courses of receptor occupancy by risperidone after oral administration were similar when risperidone was encapsulated in PEG-p(CL-co-TMC) micelles or solubilized in an aqueous tartaric acid vehicle. The areas under the curve (AUC) were not significantly different although the maximal concentration (Cmax) was twofold lower with the copolymer. The polymeric micelles of PEG-p(CL-co-TMC) seem to be a good candidate for oral drug delivery of poorly soluble drugs.

Administration, Oral↗

PubMed2005

Preparation and physicochemical characterization of biodegradable nerve guides containing the nerve growth agent sabeluzole.

The objective of this study was to develop and characterize a biodegradable drug-loaded nerve guide for peripheral nerve regeneration. Sabeluzole, a nerve growth agent, was selected as model compound. Four biodegradable polymers were selected for this study: a copolymer of polylactic acid and polycaprolactone (PCL); a copolymer of polyglycolic acid and polycaprolactone PCL; a copolymer of PCL/polydioxanone (PDO) and PDO. Placebo and drug loaded nerve guides were obtained by melt compression and melt extrusion. It was observed that melt compression and melt extrusion are feasible techniques to prepare the nerve guides. Based on the physicochemical characterization, all samples show absence of crystalline sabeluzole, indicating the formation of an amorphous dispersion. The in vitro release measurements show that the release of sabeluzole is complete, reproducible and can be controlled by the proper selection of the polymer. The release mechanism for all samples follows Fickian release behaviour.

Absorbable Implants↗

PubMed2005

Clinical study of solid dispersions of itraconazole prepared by hot-stage extrusion.

The aim of this study was to investigate the performance of three new solid dispersion formulations of itraconazole in human volunteers in comparison with Sporanox, the marketed form. Solid dispersions made up of itraconazole (40%, w/w) and HPMC 2910, Eudragit E100 or a mixture of Eudragit E100-PVPVA64 were manufactured by hot-stage extrusion and filled in gelatin capsules. The formulations were tested in eight human volunteers in a double blind, single dose, and cross-over study. Concentrations of the drug and its metabolite hydroxyitraconazole in the plasma were determined using HPLC. The in vivo performance was evaluated by comparing the mean area under the plasma concentration-time curves (AUC), the mean maximum plasma concentration (C(max)), and the mean time to reach C(max) (T(max)). The mean bioavailability of itraconazole was comparable after administration of the HPMC solid dispersion, compared to Sporanox, while it was lower after administration of the Eudragit E100 or Eudragit E100-PVPVA64 dispersions. Due to high variability, a significant decrease in AUC and C(max) was only observed for the Eudragit E100-PVPVA formulation. Although the solid dispersions showed different in vitro dissolution behaviour, T(max) values were comparable. The same observations with respect to AUC, C(max) and T(max) could be made for hydroxyitraconazole. The present results indicate that hot-stage extrusion can be considered as a valuable alternative for manufacturing solid dispersions of itraconazole.

Administration, Oral↗

PubMed2005

The effect of pressurized carbon dioxide as a temporary plasticizer and foaming agent on the hot stage extrusion process and extrudate properties of solid dispersions of itraconazole with PVP-VA 64.

The aim of the current research project was to explore the possibilities of combining pressurized carbon dioxide with hot stage extrusion during manufacturing of solid dispersions of itraconazole and polyvinylpyrrolidone-co-vinyl acetate 64 (PVP-VA 64) and to evaluate the ability of the pressurized gas to act as a temporary plasticizer as well as to produce a foamed extrudate. Pressurized carbon dioxide was injected into a Leistritz Micro 18 intermeshing co-rotating twin-screw melt extruder using an ISCO 260D syringe pump. The physicochemical characteristics of the extrudates with and without injection of carbon dioxide were evaluated with reference to the morphology of the solid dispersion and dissolution behaviour and particle properties. Carbon dioxide acted as plasticizer for itraconazole/PVP-VA 64, reducing the processing temperature during the hot stage extrusion process. Amorphous dispersions were obtained and the solid dispersion was not influenced by the carbon dioxide. Release of itraconazole from the solid dispersion could be controlled as a function of processing temperature and pressure. The macroscopic morphology changed to a foam-like structure due to expansion of the carbon dioxide at the extrusion die. This resulted in increased specific surface area, porosity, hygroscopicity and improved milling efficiency.

Acrylates↗

PubMed2005

High-speed digital imaging method for ciliary beat frequency measurement.

The aim of this study was to develop a high-speed digital imaging system and related software for ciliary beat frequency (CFB) analysis in order to establish an automated and reliable method that is observer independent and faster compared to the conventional computerized microscope photometry method. Using primary human nasal epithelial cell cultures, the CBF was recorded with a computerized microscope photometry system and a high-speed digital imaging system. To obtain a wide range of frequencies, glycocholate (0.5%) and chlorocresol (0.005%) were used as ciliostimulatory and cilio-inhibitory reference compounds, respectively. The mean values in hertz (+/- s.d.) obtained with the photometry and high-speed digital imaging systems were: controls 8.2 +/- 0.9 and 7.9 +/- 1.1; chlorocresol 5.0 +/- 0.9 and 5.1 +/- 1.1; glycocholate 9.8 +/- 1.0 and 9.7 +/- 0.8. A similar increase (by 20 and 24%) and decrease (by 38 and 35%) in CBF was determined by the two methods after glycocholate and chlorocresol treatment, respectively. The mean difference between the photometry and high-speed digital imaging methods was 0.2 +/- 0.6 Hz, and the Bland-Altman limits of agreement were from -1.0 to +1.4 Hz, suggesting that the results obtained by these two methods could be used interchangeably. These results show the reliability of the high-speed digital imaging system and the software developed for in-vitro CBF measurements. The advantages of the system include: (i) fast data acquisition and calculation, (ii) whole field automated CBF analysis and (iii) reduction in selection bias.

Cells, Cultured↗

PubMed2004

The use of three different solid dispersion formulations--melt extrusion, film-coated beads, and a glass thermoplastic system--to improve the bioavailability of a novel microsomal triglyceride transfer protein inhibitor.

A bioavailable formulation for a water-insoluble microsomal triglyceride transfer protein inhibitor, R103757, was developed using solid dispersion technology. The need for an advanced formulation was tested in the dog by assessing the oral bioavailability of three generic concepts: a tablet (crystalline drug), a capsule (film-coated beads), and an oral solution. These screening studies steered further development in the direction of a solid dispersion. Three solid dispersion platforms were assessed: melt extrusion, film-coated beads, and a glass thermoplastic system. Thermal and spectrophotometric analysis revealed that no crystalline drug was present in any of the formulations. The dissolution profiles of the three dispersion systems showed that release was improved compared with the unmanipulated drug. In addition, stability studies confirmed the physical and chemical integrity of the formulation. A human clinical trial was performed to assess the pharmacokinetics of the three amorphous dispersions. Plasma levels were obtained after single oral administration in both the fasting and fed state. The study indicated that all three approaches improved the bioavailability of R103757 with the glass thermoplastic system providing the best performance. These studies point to the potential usefulness of solid dispersion approaches and expand the possible number of ways to implement these methodologies.

Animals↗

PubMed2004

Self-association of cyclodextrins and cyclodextrin complexes.

Cyclodextrins are useful functional excipients, which are being used in an ever-increasing way to camouflage undesirable pharmaceutical characteristics, especially poor aqueous solubility. It has generally been assumed that the mechanism whereby cyclodextrins exert their effects, especially their augmentation of solubility, is via the formation of noncovalent, dynamic inclusion complexes. This is a model, which regards drug-cyclodextrin interactions as a discrete phenomenon and ignores the possible interaction of these complexes with one another. It is becoming increasingly apparent that such assumptions may not be universally applicable or all encompassing. Specifically, there is a growing body of evidence that supports the important contribution of non-inclusion-based aspects for drug solubilization by cyclodextrins including surfactant-like effects and molecular aggregation. This short review attempts to assess the available literature for areas in which such non-inclusion mechanisms are apparent and tries to interpret these in the context of a broader working theory as to how cyclodextrins exert their beneficial effects.

Cyclodextrins↗

PubMed2004

Usefulness of a novel Caco-2 cell perfusion system. I. In vitro prediction of the absorption potential of passively diffused compounds.

A simple, reliable, and user friendly system was established to cultivate Caco-2 cell monolayer for epithelial transport studies. After an initial growth period of 1 week in a CO(2) incubator, Caco-2 cells were cultivated in an automated continuous perfusion system (Minucells and Minutissue, Germany). Medium was constantly renewed at the apical and basal side of the monolayers, which resulted in a continuous supply of nutrients as well as in a continuous removal of metabolite wastes. The monolayers obtained with the new perfusion culture system were evaluated to estimate the passive transport properties of a series of model compounds. The results produced were compared to those of monolayers obtained with the standard 21-day system. The integrity of cell monolayers was checked by measuring transepithelial electrical resistance (TEER) and by the transport of the paracellular leakage marker sodium fluorescein. The results of confocal microscopy as well as TEER measurements indicated the formation of a monolayer on various support filters. The growth and differentiation of Caco-2 cells were highly dependent upon the individual support filters and extracellular matrix proteins used for Caco-2 attachment. The permeability coefficients of several model compounds across Caco-2 cells obtained with the perfusion system were approximately two-fold higher than those obtained using the traditional 21-day Snapwell-based cultures. A good correlation was found between the transport of passively diffused drugs across Caco-2 monolayers differentiated in the perfusion system and the transport according to the standard method. The rank ordering of high permeable model compounds tested through Caco-2 monolayers, differentiated in a perfusion system, was similar to the standard 21-day culture method.

Biological Transport↗

PubMed2004

Cyclodextrin-based pharmaceutics: past, present and future.

Cyclodextrins are cyclic oligomers of glucose that can form water-soluble inclusion complexes with small molecules and portions of large compounds. These biocompatible, cyclic oligosaccharides do not elicit immune responses and have low toxicities in animals and humans. Cyclodextrins are used in pharmaceutical applications for numerous purposes, including improving the bioavailability of drugs. Current cyclodextrin-based therapeutics are described and possible future applications discussed. Cyclodextrin-containing polymers are reviewed and their use in drug delivery presented. Of specific interest is the use of cyclodextrin-containing polymers to provide unique capabilities for the delivery of nucleic acids.

Animals↗

PubMed2003

Incorporation of drugs in an amorphous state into electrospun nanofibers composed of a water-insoluble, nonbiodegradable polymer.

Electrostatic spinning was applied to the preparation of drug-laden nonbiodegradable nanofiber for potential use in topical drug administration and wound healing. The specific aim of these studies was to assess whether these systems might be of interest as delivery systems for poorly water-soluble drugs. Itraconazole and ketanserin were selected as model compounds while a segmented polyurethane (PU) was selected as the nonbiodegradable polymer. For both itraconazole and ketanserin, an amorphous nanodispersion with PU was obtained when the drug/polymer solutions were electrospun from dimethylformide (DMF) and dimethylacetamide (DMAc), respectively. The collected nonwoven fabrics were shown to release the drugs at various rates and profiles based on the nanofiber morphology and drug content. Data were generated using a specially designed release apparatus based around a rotating cylinder. At low drug loading, itraconazole was released from the nanofibers as a linear function of the square root of time suggesting Fickian kinetics. No initial drug burst was observed. A biphasic release pattern was observed for ketanserin in which two sequential linear components were noted. These release phases may be temporally correlated with (1) drug diffusion through the polymer and (2) drug diffusion through formed aqueous pores.

Calorimetry, Differential Scanning↗

PubMed2003

Characterization of solid dispersions of itraconazole and hydroxypropylmethylcellulose prepared by melt extrusion--Part I.

Solid dispersions containing different ratios of itraconazole and hydroxypropylmethylcellulose (HPMC) were prepared by solvent casting. Based on dose, differential scanning calorimetry and dissolution results, a drug/polymer ratio of 40/60 w/w was selected in order to prepare dispersions by melt extrusion. The melt extrusion process was characterized using a design of experiments (DOE) approach. All parameter settings resulted in the formation of an amorphous solid dispersion whereby HPMC 2910 5 mPas prevents re-crystallization of the drug during cooling. Dissolution measurements demonstrated that a significantly increased dissolution rate was obtained with the amorphous solid dispersion compared to the physical mixture. The outcome of DOE further indicated that melt extrusion is very robust with regard to the itraconazole/HPMC melt extrudate characteristics. Stability studies demonstrated that the itraconazole/HPMC 40/60 w/w milled melt extrudate formulation is chemically and physically stable for periods in excess of 6 months as indicated by the absence of degradation products or re-crystallization of the drug.

Hypromellose Derivatives↗

PubMed2003

Preparation and characterization of nanofibers containing amorphous drug dispersions generated by electrostatic spinning.

PURPOSE: We assessed the application of water-soluble polymer-based nanofibers prepared by electrostatic spinning as a means of altering the dissolution rate of the poorly water-soluble drug, itraconazole. METHODS: Organic solvent-based solutions of itraconazole/HPMC mixtures were electrostatically spun at 16 and 24 kV. The formed nanofibers were collected as a non-woven fabric. The samples were analyzed by scanning electron microscopy. differential scanning calorimetry, and dissolution rate. RESULTS: Scanning electron microscopy showed fiber diameters of 1-4 microm and 300-500 nm depending on the applied voltage. Differential scanning calorimetry measurements found that the melting endotherm for itraconazole was not present, suggesting the formation of an amorphous solid dispersion or solution. Dissolution studies assessed several presentations including direct addition of the non-woven fabrics to the dissolution vessels, folding weighed samples of the materials into hard gelatin capsules and placing folded material into a sinker. Controls included a physical mixture as well as solvent cast and melt extruded samples. Electrospun samples dissolved completely over time with the rate of dissolution depending on the formulation presentation and drug to polymer ratio. The physical mixture did not appreciably dissolve in these conditions. CONCLUSIONS: The application of electrostatic spinning to pharmaceutical applications resulted in dosage forms with useful and controllable dissolution properties.

Calorimetry, Differential Scanning↗

PubMed2003

A mucoadhesive, cyclodextrin-based vaginal cream formulation of itraconazole.

The development of vaginal medications, especially antifungal medications, requires that the drug is solubilized as well as retained at or near the mucosa for sufficient periods of time to ensure adequate bioavailability. Itraconazole is a broad-spectrum antifungal agent, which has been used for some time orally and intravenously but for which a vaginal formulation has not yet been developed. We present here a novel itraconazole formulation intended for vaginal use based on hydroxypropyl-beta-cyclodextrin (HPbetaCD), a functional excipient that increases drug solubility and generates a mucoadhesive system in the presence of other ingredients. An aqueous phase was prepared by solubilizing itraconazole with HCl in the presence of propylene glycol and then adding an aqueous solution of HPbetaCD. After pH adjustment, the itraconazole/HPbetaCD solution was added to the oil phase (paraffin oil, trihydroxystearate, and cetyl dimethicon copolyol) and the desired cream containing 1%, 2%, and 2.5% drug obtained by homogenization. Primary irritation studies and subchronic toxicity studies using a rabbit vaginal model indicated that the formulation was safe, well tolerated, and retained in the vaginal space. Clinical investigations indicated that application of 5 g of a 2% cream was very well tolerated and itraconazole was not systemically absorbed. Additional studies in women found that the itraconazole cream was highly effective in reducing or eliminating fungal cultures with few adverse effects. These studies suggested that an HPbetaCD-based, emulsified wax cream formulation was a useful and effective dosage form for treating vaginal candidiasis.

2-Hydroxypropyl-beta-cyclodextrin↗

PubMed2002

Characterization of the interaction of 2-hydroxypropyl-beta-cyclodextrin with itraconazole at pH 2, 4, and 7.

Phase-solubility techniques were used to assess the effect of pH on itraconazole complexation with 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD). In addition, molecular modeling using beta-cyclodextrin as a surrogate for HPbetaCD was completed. Data suggested A(p)-type solubility relationships, indicating higher order complexation at higher HPbetaCD concentrations. Stability constants were derived from the solubility isotherms using a simplex optimization procedure. At pH 2 (2 units below the pK(a4)), a 1:2 complex formation was observed, whereas at pH 4 (i.e., the pK(a4) for itraconazole) and at pH 7, 1:3 complexation occurred. The lower order of complexation observed at lower pH may be related to substructure protonation which reduced HPbetaCD interaction. Molecular mechanics also suggest 1:3 complex formation for the neutral species, indicating that possible interaction sites may include (in order of binding) triazole > 1,4-diaminophenyl > 2-butyl approximate, equals piperazine.

2-Hydroxypropyl-beta-cyclodextrin↗