Chitosan-poly(acrylic) acid polyionic complex: in vivo study to demonstrate prolonged gastric retention

The aim of this study was to develop a chitosan-poly(acrylic) acid based controlled drug release system for gastric antibiotic delivery. Different mixtures of amoxicillin (A), chitosan (CS), and poly(acrylic) acid (PAA) were employed to obtain these polyionic complexes. A non-invasive method was employed for determining the gastric residence time of the formulations. It was studied the swelling behavior and drug release from these complexes. Gastric emptying rate study was performed by means of the [13C]octanoic acid breath test. The gastric emptying rates of two different formulations (conventional and gastric retentive system) were studied. Swelling studies indicated that the extent of swelling was greater in the polyionic complexes than in the single chitosan formulations. The amoxicillin diffusion from the hydrogels was controlled by the polymer/drug interaction. The property of these complexes to control the solute diffusion depends on the network mesh size, which is a significant factor in the overall behavior of the hydrogels. The gastric half-emptying time of the polyionic complex was significantly delayed compared to the reference formulation, showing mean values of 164.32+/-26.72 and 65.06+/-11.50min, respectively (P<0.01). The results of this study suggest that, these polyionic complexes are good systems for specific gastric drug delivery.

Controlled drug release from hydrogel nanoparticle networks

Monodisperse nanoparticles of poly-N-isopropylacrylamide-co-allylamine (PNIPAM-co-allylamine) and PNIPAM-co-acrylic acid (PNIPAM-co-AA) were synthesized. The close-packed PNIPAM-co-allylamine and PNIPAM-co-AA nanoparticles were converted to three-dimensional gel networks by covalently crosslinking neighboring particles at room temperature and neutral pH using glutaric dialdehyde and adipic acid dihydrazide, respectively. Controlled release studies were conducted using dextran markers of various molecular weights as model macromolecular drugs. Release was quantified under various physical conditions, including a range of temperatures and dextran molecular weights. Dextran, entrapped in cavities in the nanoparticle network, was released with a rate regulated by their molecular weights and cavity size. No release from a conventional bulk PNIPAM gel, with high crosslinking density, was observed. The rate of release from the PNIPAM-co-allylamine network was temperature-dependent, being much faster at room temperature than that at human body temperature. In contrast, release of low molecular weight dextrans from the PNIPAM-co-AA network showed a temperature-independent release profile. These nanoparticle networks have several advantages over conventional bulk gels for controlling the release of high molecular weight biomolecules.

[Effect in vitro of environmental parameters on the release of fluoride ions from some materials used in dentistry]

The aim of this in vitro study was to evaluate the influence of calcium ions and pH on fluoride release from selected dental materials. The materials studied included a resin composite (Te-Econom), fissure sealant (Conseal F) and compomer (Freedom). Samples were placed for 7 days in artificial saliva with or without calcium ions and pH ranging from 4.5 to 7.5. Fluoride release from the studied materials was measured with an ion-selective electrode (Orion). The results demonstrate differing effects of calcium concentration and pH on fluoride release. The highest cumulative fluoride release was observed from Freedom and the lowest from Te-Econom. Addition of calcium ions to the medium reduced the release of fluoride.

Carbopols as factors buffering triethanolamine interacting with artificial skin sebum

Triethanolamine is an ethanolamine applied as counter-ion for fatty acid soaps. Interaction between triethanolamine and free fatty acids is suggested to be useful for cleansing sebaceous follicles in acne prevention. Considering relatively high pH of aqueous triethanolamine solutions we investigated influence of different concentrations of anionic polymers--Carbopol 934P, Carbopol 974P and Carbopol 980 on pH, rheological behavior and, most of them, intensity of triethanolamine interaction with artificial skin sebum components. Triethanolamine buffered using Carbopols influenced artificial skin sebum. Intensity of this interaction was measured applying specific optical method. Penetration of triethanolamine into artificial sebum and its uplift induced by above mentioned interaction were measured. Respective penetration rates and uplift rates were calculated. We found significant differences between Carbopols. The values of the penetration rates amounted 2.94 x 10(-04) h(-1) to 4.12 x 10(-03) h(-1), whereas rates for the uplift process were from 1.97 x 10(-04) h(-1) to 3.28 x 10(-03) h(-1). The value of pH is reduced from 10.06 for pure 0.1 M aqueous triethanolamine solution to 7.67 with the increase of polymer to triethanolamine molar ratio in the preparations. It is considered that triethanolamin buffered with acrylic acid polymers--Carbopols could influence cleansing of pilosebaceous unit follicles and contribute to acne prevention.

Preparation and in vitro characterization of poly(acrylic acid)–cysteine microparticles

The purpose of the present study was to prepare and characterize a novel mucoadhesive microparticulate drug delivery system. Microparticles were prepared by the solvent evaporation emulsion technique using a poly(acrylic acid)-cysteine conjugate of an average molecular mass of 450 kDa with an amount of 308 micromol thiol groups per gram polymer. The cross-linking of thiol groups via the formation of disulfide bonds during this preparation process was pH-controlled. The resulting microparticles were characterized with regard to the degree of cross-linking and the amount of remaining free thiol groups, shape, size distribution and stability. Furthermore, the drug release behaviour using bromelain as model drug and the mucoadhesive properties were evaluated.Results demonstrated that the higher the pH of the aqueous phase was during the preparation process, the higher was the degree of cross-linking within the particles. However, even at pH 9, 8.9+/-2.2% of free thiol groups remained on the microparticles. Particles were of spherical and partially porous structure and had a main size in the range of 20-60 microm with a center at 35 microm. Because of the formation of disulfide bonds within the particles, they did not disintegrate under physiological conditions within 48 h. In addition, a controlled drug release of bromelain was achieved. Due to the immobilization of thiol groups on poly(acrylic acid), the mucoadhesive properties of the corresponding microparticles were improved threefold. These features should render poly(acrylic acid)-cysteine conjugate microparticles useful as drug delivery system providing a prolonged residence time on mucosal epithelia.

Influence of an enteric polymer on drug release rates of theophylline from pellets coated with Eudragit RS 30D

The purpose of this research study was to investigate the influence of an enteric polymer on the drug release properties of theophylline pellets coated with Eudragit RS 30D. Theophylline pellets were coated with aqueous colloidal dispersions of Eudragit RS 30D containing various amounts of Eudragit L 100-55. The effect of storage conditions on the release of drug from coated pellets was determined as a function of the pH of the dissolution medium. The results from the dissolution study showed significant changes in the dissolution rate of theophylline from pellets coated with Eudragit RS 30D when cured at 40 degrees C for 4 days. No change in the drug release rate was observed when Eudragit L100-55 was present in the Eudragit RS 30D dispersion. Increasing the ratio of Eudragit L100-55 to Eudragit RS 30D resulted in faster drug release rates from the coated pellets. An increase in the pH of the dissolution medium was found to enhance drug release from the pellets coated with Eudragit RS 30D containing Eudragit L 100-55. Theophylline pellets when coated with Eudragit RS 30D containing the enteric polymer Eudragit L100-55 demonstrated no aging effects when stored at elevated temperatures. The overcoating of the pellets with Eudragit RD 100 did not affect the drug release profiles and prevented the particles from agglomerating during curing and storage.

Effect of Curing Conditions and Plasticizer Level on the Release of Highly Lipophilic Drug from Coated Multiparticulate Drug Delivery System

The study aimed to investigate the effect of triethyl citrate (TEC) plasticizer level (10, 15, and 20%), curing temperature (40, 50, and 60 degrees C) and time (0 to 168 h) on the release of a highly lipophilic drug bumetanide from pellets coated with methacrylate ester copolymer (Eudragit RS). Bumetanide was layered onto sugar pellets followed by coating with 6% Eudragit RS with and without hydroxypropyl methyl cellulose (HPMC) seal coat using Wurster Fluid Bed equipment. Coated pellets were stored for 3 months at room temperature and the release was tested in USP purified water. At 10% TEC level, increasing curing time and temperature lead to slower drug release. At 15 and 20% TEC levels, curing initially decreased drug release followed by increase in the release at longer curing time and higher temperature. Drug release from coated pellets plasticized with 15% TEC and completely cured followed zero order kinetic models. At plasticizer level of 20%, bumetanide release from the completely cured pellets was better modeled using the Higuchi's equation reflecting possible drug migration during curing. Storage led to an increase in drug release. The use of HPMC seal coat stabilized drug release after storage. It was concluded that bumetanide migration into Eudragit RS film coat was the main cause of the accelerated release after curing and storage. The drug migration during storage at room temperature was prevented by seal coating the pellets with HPMC.

Composite film-coated tablets intended for colon-specific delivery of 5-aminosalicylic acid: using deesterified pectin

Combinations of Eudragit RS and deesterified pectin, polygalacturonic acid (PGA), or its potassium and sodium salts, when applied as a film coat, has a potential value as a colon-specific delivery system. Dispersions of PGA in Eudragit RS were used as the film former for coating of 5-aminosalicylic acid (5-ASA) tablet cores. Drug release behavior was assessed, in vitro, under simulating conditions in term of pH and time to in vivo during their transit to the colon. Negligible drug release occurred during first 5 hr where the coated tablets were in the stomach and small intestine. After that, the pectinolytic enzymes were added into the pH 6.8 medium to simulate the in vivo condition where there is the digestion of bacteria in the colon. The release of 5-ASA from the coated tablets occurred linearly as a function of time. Drug release depended on the composition of the mixed film, as well as the ratio of Eudragit RS to PGA or its salts. The highest drug release from the coated tablets of about 40% was obtained when the ratio of Eudragit RS to potassium salt of PGA was 2.5 to 1. Drug release profiles seemed to conform to the mechanism involving the osmotically driven release and formation of channels in the film caused by dissolution of PGA salts. Channel formation was, in most cases, activated by the presence of pectinolytic enzymes, showing that the PGA in the mixed film was subjected to enzymic breakdown. In conclusion, PGA could be used as an additive in Eudragit RS films to control the release of colonic delivery system.

Mucoadhesive ocular insert based on thiolated poly(acrylic acid): development and in vivo evaluation in humans

The aim of the study was to develop a mucoadhesive ocular insert for the controlled delivery of ophthalmic drugs and to evaluate its efficacy in vivo. The inserts tested were based either on unmodified or thiolated poly(acrylic acid). Water uptake and swelling behavior of the inserts as well as the drug release rates of the model drugs fluorescein and two diclofenac salts with different solubility properties were evaluated in vitro. Fluorescein was used as fluorescent tracer to study the drug release from the insert in humans. The mean fluorescein concentration in the cornea/tearfilm compartment as a function of time was determined after application of aqueous eye drops and inserts composed of unmodified and of thiolated poly(acrylic acid). The acceptability of the inserts by the volunteers was also evaluated. Inserts based on thiolated poly(acrylic acid) were not soluble and had good cohesive properties. A controlled release was achieved for the incorporated model drugs. The in vivo study showed that inserts based on thiolated poly(acrylic acid) provide a fluorescein concentration on the eye surface for more than 8 h, whereas the fluorescein concentration rapidly decreased after application of aqueous eye drops or inserts based on unmodified poly(acrylic acid). Moreover, these inserts were well accepted by the volunteers. The present study indicates that ocular inserts based on thiolated poly(acrylic acid) are promising new solid devices for ocular drug delivery.

The influence of chitosan on in vitro properties of Eudragit RS microspheres

Eudragit RS microspheres containing chitosan hydrochloride were prepared by the solvent evaporation method using acetone/liquid paraffin solvent system and their properties were compared with Eudragit RS microspheres without chitosan, prepared in our previous study. Different stirring rates were applied (400-1200 rpm) and drug content, Higuchi dissolution rate constant, surface and structure characteristics of the microspheres were determined for each size fraction. An increase in average particle size with a reduction of stirring rate appeared in limited interval in both series. The average particle size of microspheres without chitosan, prepared at the same stirring rate, was smaller. Pipemidic acid content increased with increasing fraction particle size, but not with increasing stirring rate as it was observed for microspheres without chitosan. We presume that high pipemidic acid content in larger microspheres is a consequence of cumulation of undissolved pipemidic acid particles in larger droplets during microspheres preparation procedure. Pipemidic acid release was faster from microspheres with chitosan and no correlation between Higuchi dissolution rate constant and stirring rate or fraction particle size was found, though it existed in the system without chitosan. Structure and surface characteristics of microspheres observed by scanning electron microscope (SEM) were not changed significantly by incorporation of chitosan. But in contrast with microspheres without chitosan, the surface of chitosan microspheres was more porous after three hours of dissolution. It is supposed that the influence of particle size fraction and stirring rate on release characteristics is expressed to a great extent through porosity and indirectly through total effective surface area, but the incorporation of highly soluble component i.e. chitosan salt hides these effects on drug release. In conclusion, changes in biopharmaceutical properties due to varying stirring rate and fraction particle size exhibited the same direction as those reported for the microspheres without chitosan, although they are less expressed because of increased experimental variability, likely caused by chitosan.

Preparation and in vitro evaluation of modified release ketoprofen microsponges

Microsponges containing ketoprofen and Eudragit RS 100 were prepared by quasi-emulsion solvent diffusion method. The effects of different mixing speeds, drug-polymer ratios, solvent-polymer ratios on the physical characteristics of the microsponges as well as the in vitro release rate of the drug from the microsponges were investigated. All the factors studied had an influence on the physical characteristics of the microsponges. In vitro dissolution results showed that the release rate of ketoprofen was modified in all formulations.

In vitro evaluation of the permeation enhancing effect of polycarbophil-cysteine conjugates on the cornea of rabbits

It was the aim of this study to investigate the permeation enhancing effect of thiolated polycarbophil on the cornea of rabbits in vitro. The proposed reaction mechanism involves the opening of the tight junctions in the corneal epithelium. The modification of polycarbophil was achieved via covalent attachment of L-cysteine mediated by a carbodiimide. Transcorneal permeation studies were performed in Ussing-type diffusion chambers. As model compounds, sodium fluorescein, as a marker for paracellular transport, and dexamethasone phosphate were used. To evaluate potential corneal damage the corneal hydration level of each cornea was determined. Polycarbophil-cysteine was found to increase the permeation of sodium fluorescein 2.2-fold and that of dexamethasone phosphate 2.4-fold in comparison to the unmodified polymer. The concentration of dexamethasone in the acceptor medium was 1.5-fold increased. As evidenced by the corneal hydration level, polycarbophil-cysteine did not damage the corneal tissues. Therefore, polycarbophil-cysteine conjugates seem to be promising excipients for ocular drug delivery systems where they might be used as safe permeation enhancers.

Toxicokinetic of HEMA in guinea pigs

OBJECTIVE

Unconverted 2-hydroxyethylmethacrylate (HEMA) can be released from dental resin materials and can enter the body in humans. In the present study the uptake, distribution and excretion of 14C-HEMA applied via different routes were examined in vivo in guinea pigs.

METHODS

HEMA (0.02 mmol/kg bw labelled with a tracer dose 14C-HEMA 0.3 Bq/g bw) was administered by gastric tube or by subcutaneous injection. Urine, feces, and exhaled carbon dioxide were collected for 24 h after administration. Guinea pigs were killed 24 h after the beginning of the experiment and various organs removed and 14C radioactivity measured.

RESULTS

Low fecal 14C levels (about 2% of the dose) and urinary levels of about 15% after 24 h were noted with either route of administration. Direct measurement of exhaled CO(2) showed that about 70% of the dose left the body via the lungs. Two pathways for the metabolism of 14C-HEMA can be described. It is likely that 14C-pyruvate is formed in vivo resulting in the formation of toxic 14C-HEMA intermediates. 14C-HEMA was taken up rapidly from the stomach and small intestine after gastric administration and was widely distributed in the body following administration by each of the routes.

CONCLUSIONS

Clearance from most tissues following gastric and intradermal administration was essentially complete within one day. The peak HEMA levels in all tissues examined after 24 h were at least onemillion-fold less than known toxic levels.

[The investigation of bioadhesive property of carbomer 934 by gamma camera in vivo]

To study bioadhesive property of carbomer 934 in dog alimentary tract, carbomer 934 and ethylcellulose were radiolabelled with technetium-99 m. The gastrointestinal emptying rate of these materials was measured by the technique of gamma scintiscan. The results showed that the empty rate of adhesive material (carbomer 934) was remarkably slower in dog alimentary tract compared to nonadhesive material (ethylcellulose). It is concluded that, in dog, the interaction between gastrointestinal mucus layer and adhesive material or nonadhesive material was significantly different. Carbomer 934 had stronger bioadhesive property in vivo than that of ethylcellulose.

Hepatocyte attachment onto thermosensitive poly(N-isopropylacrylamide-co-N-p-vinylbenzyl-O-beta-D-galactopyranosyl-(1 --> 4)-D-gluconamide)

Temperature sensitive poly(N-isopropylacrylamide) (PIPAAM) was incorporated into hepatocyte-recognizable poly[N-p-vinylbenzyl-O-beta-D-galactopyranosyl-(1 --> 4)-D-gluconamide] (PVLA) for thermal modulating of hepatocyte attachment. The copolymer, poly(N-isopropylacrylamide-co-N-p-vinylbenzyl-O-beta-D-galactopyranosyl-(1 --> 4)-D-gluconamide) (abbreviated as [P(IPAAM-co-VLA)] (PIPAAM/PVLA = 9/1 in mol%) exhibited lower critical solution temperature (LCST) at 34 degrees C and also showed very good hepatocytes-recognizablility through the specific interaction between asialoglycoprotein receptors on the cell surfaces and galactose moiety of the copolymer. The cells attached on this copolymer were easily detached by lowering the temperature below the LCST of the copolymer. Morphological damage of the detached cell was not observed.

Time-programmed pulsatile release of dextran from calcium-alginate gel beads coated with carboxy-n-propylacrylamide copolymers

Time-programmed release of macromolecular drugs was achieved by utilization of calcium-alginate gel beads modified with coated copolymer layers. Modified calcium-alginate gel beads coated with poly(carboxy-n-propylacrylamide-co-dimethylacrylamide) [poly(CNPAAm-co-DMAAm)] (22.7 mol% of CNPAAm) of varying coating thickness from 25 to 125 microm were developed as drug carriers. Model macromolecular drugs used were fluorescein isothiocyanate (FITC)-labeled dextrans with different molecular weights ranging from 9400 to 145000. FITC-dextran release was strongly dependent on both copolymer coating thicknesses and the dextran molecular weights. Release of FITC-dextran (MW 9400) followed Fickian diffusion according to t(1/2) dependence, indicating that the drug diffusion is the main driving force for release of dextran MW 9400. Release of higher molecular weight FITC-dextrans (71,00 and 145,00) exhibited a burst-effect preceded by a preset lag time. These release profiles were governed by the dissociation of calcium ions from polyguluronate sequences in alginate molecules along with the diffusion of sodium ions into the gel bead core. This created osmotic pressure inside the gel, inducing breakage of the coated copolymer layer and accelerated drug release. Burst release of macromolecular drugs thus occurred after a certain lag period. The lag time was regulated by the copolymer coat thickness. A pulsatile release of FITC-dextran was demonstrated by combining a series of modified alginate gel beads in a single batch.

An in vitro model for investigating the gastric mucosal retention of 14C-labelled poly(acrylic acid) dispersions

Polymers that bind from solution onto gastric mucosae can be used as a means of facilitating localised drug delivery, or act as therapeutic agents in their own right (e.g. by forming a protective layer or by inhibiting enzymes). Previous workers have used semi-quantitative methods to identify the ability of commercially available poly(acrylic acid)s to bind to gastric mucosa. In this study, the binding and retention of labelled poly(acrylic acid)s to sections of gastric mucosa from the pyloric region of pigs stomach were evaluated using 'static' and 'dynamic flow' test systems. Dispersions (3%) of 'low', 'high' and 'ultra high' (cross-linked) polymers were seen to adhere to porcine pyloric mucosa after exposure and rinsing in the 'static' system. The high molecular weight polymer showed the greatest retention in the 'dynamic' test system when washing continuously with simulated gastric acid. Changing the pH of the dispersions from 4.3 to 6.2 had little effect on polymer retention. It was concluded that polymers that were sufficiently mobile in solution to spread on, and interact with, the mucosal surface, but had a sufficiently high molecular weight to form viscous solutions and/or bioadhere to the mucosa, may be retained on the mucosal surface for the longest periods.

[Physicochemical and pharmacological characteristic and clinical efficacy of an anti-irritable bowel syndrome agent, polycarbophil calcium (Polyful)]

Irritable bowel syndrome (IBS) is a functional bowel disorder characterized by abdominal pain or discomfort and abnormal defecation. Polycarbophil calcium, a water-absorbing polymer, is expected to improve stool consistency. Polycarbophil calcium decalcified under the acidic condition and then absorbed 70 times its weight of water under the neutral condition. In in situ experiments using rat jejunum and colon, polycarbophil decreased water absorption by the intestine without affecting water secretion. Polycarbophil inhibited prostaglandin E2-, 5-hydroxy-L-tryptophan- and castor oil-induced diarrhea in mice or rats. Polycarbophil calcium also inhibited sennoside-induced diarrhea in dogs. Polycarbophil increased the weight of feces in naive or low-fiber diet feeding rats. In naive dogs, polycarbophil calcium increased stool frequency, stool weight and moisture. Polycarbophil was not absorbed from the gastrointestine, not metabolized and eliminated into feces in rats and dogs. Polycarbophil calcium did not affect the absorption of coadministered drugs in dogs. In the dose-finding clinical study for IBS, polycarbophil calcium was effective both in diarrhea and constipation. In the Phase III study, polycarbophil calcium was superior to trimebutine maleate in efficacy and equal in safety. Emesis/vomiting and thirst were observed, but episodes of diarrhea or constipation by excessive action were few. Polycarbophil calcium seems promising as an anti-IBS agent.

Study on of bioadhesive property of carbomer934 by a gamma camera in vivo

AIM: To study the bioadhesive property of carbomer934 in dog alimentary tract.

METHODS: Carbomer934 and ethylcellulose were radiolabelled with technetium-99 m; and Gastrointestinal emptying rate of materials was measured using the technique of gamma scintigraphy.

RESULTS: After oral administration, the maximum intestinal radioactivity of non-bioadhesive granules and bioadhesive granules were observed in the second hour and the sixth hour respectively. Constants of stomach emptying rate of nonadhesive granules, bioadhesive granulesI and bioadhesive granulesII were 0.774 h^-1,0.265 h^-1 and 0.321 h^-1 respectively on the base of gastric residual amount. Compared to nonadhesive material (ethylcellulose), the migration rate of adhesive material(carbomer934) was remarkably slower in dog alimentary canal.

CONCLUSION: It is concluded that, in the dog, interactions between gastrointestinal mucus layer and adhesive material or nonadhesive material were significantly different. Carbomer934 had stronger in vivo bioadhesive property than ethylcellulose.

Mechanism of lidocaine release from carbomer-lidocaine hydrogels

Rheology, acid-base behavior, and kinetics of lidocaine release of carbomer-lidocaine (C-L) hydrogels are reported. A series of (C-L)(x) (x = mol% of L = 25, 50, 75, 100) that covers a pH range between 5.33 and 7.96 was used. Concentrations of ion pair ([R-COO(-)LH(+)]) and free species (L) and (LH(+)) were determined by the selective extraction of (L) with cyclohexane (CH) together with pH measurements, i.e., CH in a ratio CH/hydrogel 2:1 extracted 48% of the whole concentration of lidocaine [L(T)] of a (C-L)(100), [[L(T)] = ([R-COO(-)LH(+)]) + (L) + (LH(+))]. The remaining species in the aqueous phase were distributed as: (L) 3.82%, (LH(+)) 14.5%, and [R-COO(-) LH(+)] 81.7%. Rheology and pH as a function of (C-L) concentration are also reported. Delivery rates of free base L were measured in a Franz-type bicompartmental device using water and NaCl 0.9% solution as receptor media. (C-L) hydrogels behave as a reservoir that releases the drug at a slow rate. pH effects on rate suggest that, under the main conditions assayed, dissociation of [R-COO(-)LH(+)] is the slow step that controls releasing rates. Accordingly, release rate was increased upon addition of a second counterion (i.e., Na(+)), or through the diffusion of neutral salts such as NaCl, into the matrix of the gel.

Water transport and drug release study from cross-linked polyacrylamide grafted guar gum hydrogel microspheres for the controlled release application

The graft copolymer (pAAm-g-GG) of guar gum with acrylamide was prepared and cross-linked with glutaraldehyde to form the hydrogel microspheres by the water-in-oil (w/o) emulsification method. The microspheres were loaded with two antihypertensive drugs, verapamil hydrochloride (water-soluble) and nifedipine (water-insoluble) to investigate their controlled release characteristics. The drugs were incorporated either during cross-linking by dissolving it in the reaction medium or after cross-linking by the soaking technique. The microspheres were characterized by Fourier transform infrared spectroscopy, thermogravimetry, differential scanning calorimetry, equilibrium water uptake and dynamic swelling. The microspheres are spherical with smooth surfaces. Dynamic swelling experiments indicated that with an increase in cross-linking, water transport deviates from Fickian to non-Fickian mechanism. The in vitro drug release showed a dependence on the extent of cross-linking, amount of drug loading, nature of drug molecule and method of drug loading. Even though the release of drugs is swelling controlled in the initial stages, in the later stage diffusion of the solute is dominating. Various transport parameters have been calculated and the results are discussed in terms of the nature of the drug and the polymer.

Long-circulating PEGylated polycyanoacrylate nanoparticles as new drug carrier for brain delivery

PURPOSE

The aim of this study was to evaluate the ability of long-circulating PEGylated cyanoacrylate nanoparticles to diffuse into the brain tissue.

METHODS

Biodistribution profiles and brain concentrations of [14C]-radiolabeled PEG-PHDCA, polysorbate 80 or poloxamine 908-coated PHDCA nanoparticles, and uncoated PHDCA nanoparticles were determined by radioactivity counting after intravenous administration in mice and rats. In addition, the integrity of the blood-brain barrier (BBB) after nanoparticles administration was evaluated by in vivo quantification of the diffusion of [14C]-sucrose into the brain. The location of fluorescent nanoparticles in the brain was also investigated by epi-fluorescent microscopy.

RESULTS

Based on their long-circulating characteristics, PEGylated PHDCA nanoparticles penetrated into the brain to a larger extent than all the other tested formulations. Particles were localized in the ependymal cells of the choroid plexuses, in the epithelial cells of pia mater and ventricles, and to a lower extent in the capillary endothelial cells of BBB. These phenomena occurred without any modification of BBB permeability whereas polysorbate 80-coated nanoparticles owed, in part, their efficacy to BBB permeabilization induced by the surfactant. Poloxamine 908-coated nanoparticles failed to increase brain concentration probably because of their inability to interact with cells.

CONCLUSIONS

This study proposes PEGylated poly (cyanoacrylate) nanoparticles as a new brain delivery system and highlights two requirements to design adequate delivery systems for such a purpose: a) long-circulating properties of the carrier, and b) appropriate surface characteristics to allow interactions with BBB endothelial cells.

The gastrointestinal transit profile of 14C-labelled poly(acrylic acids): an in vivo study

The gastrointestinal distribution profiles for three 14C-labelled poly(acrylic acid)s of different average molecular weights and degrees of cross-linking have been established using the rat model. Despite initial differences in transit times and retention characteristics, these structural features were found to be of little influence to the overall gastrointestinal transit of the materials under consideration. No evidence for the systemic absorption of any of the polymers could be identified.

Pulmonary reduction of an intravascular redox polymer

Pulmonary endothelial cells in culture reduce external electron acceptors via transplasma membrane electron transport (TPMET). In studying endothelial TPMET in intact lungs, it is difficult to exclude intracellular reduction and reducing agents released by the lung. Therefore, we evaluated the role of endothelial TPMET in the reduction of a cell-impermeant redox polymer, toluidine blue O polyacrylamide (TBOP(+)), in intact rat lungs. When added to the perfusate recirculating through the lungs, the venous effluent TBOP(+) concentration decreased to an equilibrium level reflecting TBOP(+) reduction and autooxidation of its reduced (TBOPH) form. Adding superoxide dismutase (SOD) to the perfusate increased the equilibrium TBOP(+) concentration. Kinetic analysis indicated that the SOD effect could be attributed to elimination of the superoxide product of TBOPH autooxidation rather than of superoxide released by the lungs, and experiments with lung-conditioned perfusate excluded release of other TBOP(+) reductants in sufficient quantities to cause significant TBOP(+) reduction. Thus the results indicate that TBOP(+) reduction is via TPMET and support the utility of TBOP(+) and the kinetic model for investigating TPMET mechanisms and their adaptations to physiological and pathophysiological stresses in the intact lung.

Preparation and in vivo evaluation of mucoadhesive microparticles containing amoxycillin-resin complexes for drug delivery to the gastric mucosa

In this work, microparticles consisting of amoxycillin-loaded ion-exchange resin encapsulated in mucoadhesive polymers (polycarbophil and Carbopol 934) were prepared with the aim of increasing the efficacy of amoxycillin in the treatment of peptic ulcers by achieving targeted delivery to the gastric mucosa and prolonged drug release. An oil-in-oil solvent evaporation technique was conveniently modified in order to obtain polymer microparticles containing multiple amoxycillin-resin cores. Polycarbophil microparticles were spherical, Carbopol 934 microparticles irregular. In vitro release of amoxycillin was rapid with or without a polymer coating. Gastrointestinal transit in rats was investigated by fluorescence microscopy using particles loaded with fluorescein instead of amoxycillin: gastric residence time was longer, and the distribution of the particles on the mucosa apparently better, without any polymer coating.