G. Coppi

AIR COMPARTMENT MULTIPLE – UNIT SYSTEM FOR PROLONGED GASTRIC RESIDENCE (PART I. FORMULATION STUDY)

Abstract A pre-formulation study was directed to optimize the in vitro floating ability of an air compartment multiple-unit system. Each unit was formed by a coated bead composed of a calcium alginate core separated by an air compartment from a calcium alginate or calcium alginate/polyvinylalcohol (PVA) membrane. The floating ability depended on the presence of the air compartment and on membrane porosity. The porous structure generated by the leaching of PVA, employed as a water-soluble additive in the coating composition, increased the membrane permeability preventing air compartment shrinkage. In this way, units were produced which were able to float immediately upon contact with artificial gastric juice and for a long period of time. The floating ability increased with the increase in PVA concentration and molecular weight and it was found to be excellent when using PVA 100 000 at a concentration of at least 5%.

Chitosan-Alginate Microparticles as a Protein Carrier

The oral administration of peptidic drugs requires their protection from degradation in the gastric environment and the improvement of their absorption in the intestinal tract. For these requirements, a microsystem based on cross-linked alginate as the carrier of bovine serum albumin (BSA), used as a model protein, was proposed. A spray-drying technique was applied to BSA/sodium alginate solutions to obtain spherical particles having a mean diameter less than 10 μm. The microparticles were hardened using first a solution of calcium chloride and then a solution of chitosan (CS) to obtain stable microsystems. The cross-linking process was carried out at different CS concentrations and pH values of the cross-linking medium. The CS concentration affected the BSA loading in the microparticles prepared at a pH value less than the protein isoelectric point (pI). Moreover, the BSA loading at a pH value less than the pI was higher than that at a pH similar to the pI regardless of the CS concentration. This finding could be attributable to the formation of a BSA/alginate complex. The evaluation of the interaction between BSA and alginate at different pH values by means rheological measurements confirmed this hypothesis. This approach may represent a promising way to devise a microcarrier system with appropriate size for targeting the Peyers patches, with appropriate immobilization capacity, and suitable for the oral administration of peptidic drugs.

Air compartment multiple-unit system for prolonged gastric residence. Part II. In vivo evaluation

Abstract The intragastric behaviour of a floating multiple-unit system was assayed in humans. The floating units used in this study, composed of a calcium alginate core separated by an air compartment from a calcium alginate/polyvinylalcohol membrane, had shown an excellent buoyancy ability in the previous in vitro investigation. The present in vivo study was conducted in three different sessions (fasted state, fed state after a meal and fed state after a succession of meals) by administering to each subject at the same time both floating and control systems, loaded with barium sulfate, and monitoring them in the gastric region at determined time intervals using X-ray apparatus. Unlike the control, the floating system remained buoyant on the gastric content under both fasted and fed states. In the fasted state, the intragastric buoyancy of the system did not influence its gastric residence time (GRT). In the fed state after a meal, all the floating units showed a floating time (FT) of about 5 h and a GRT prolonged by about 2 h over the control. In the fed state after a succession of meals, most of the floating units showed a FT of about 6 h and a GRT prolonged by about 9 h over the control, though a certain variability of the data owing to mixing with heavy solid food ingested after the dosing was observed.

Protein immobilization in crosslinked alginate microparticles

Oral administration of peptide and protein drugs requires their protection from the acidic and enzymatic degradation in the gastro-intestinal environment and their targeting to the absorption zone. For this purpose, an alginate microsystem, as a carrier of bovine serum albumin (BSA), as a model protein, was developed using a spray-drying technique. A hardening process with Ca 2+ and chitosan (CS) provided a system with resistance to the gastro-intestinal barriers and of appropriate size for targeting to the Peyers patches. The present work aims to evaluate the effects of the ratio of sodium alginate (Na-A) and BSA as well as the pH of the crosslinking medium on the microsystem properties. Microparticle morphological and dimensional characteristics did not change significantly with the formulation variables. BSA loading at a pH value less than the protein isoelectric point (pI) was higher than that at a pH similar to the pI owing to an electrostatic interaction between the charged protein and the polyanionic alginate. The maximum encapsulation efficiency was obtained at the highest Na-A/BSA ratio. Protein release in a simulated gastro-intestinal fluid was not affected by the preparative variables, but was controlled by the pH-dependent nature of the polymer material. Polyacrylamide gel electrophoresis (PAGE) demonstrated the stability of the protein to both the preparative conditions and the gastro-intestinal pH values.

Alginate/chitosan microparticles for tamoxifen delivery to the lymphatic system.

Oral administration of the nonsteroidal anti-estrogen tamoxifen (TMX) is the treatment of choice for metastatic estrogen receptor-positive breast cancer. With the aim to improve TMX oral bioavailability and decrease its side effects, crosslinked alginate microparticles for the targeting to the lymphatic system by Peyers patch (PP) uptake were developed and in vitro characterized. TMX was molecularly dispersed inside the microparticles and an electrostatic interaction involving the TMX tertiary amine was detected by rheological and FT-IR assays. Microparticles showed a size less than 3mum, then suitability to be taken up by M cells in PP and a positive surface charge. Moreover, TMX loading level as well as in vitro release behaviour was affected by the polymer network connected with the mannuronic/guluronic ratio of the alginate chains.

PVP Solid Dispersions for the Controlled Release of Furosemide from a Floating Multiple-Unit System

The poor bioavailability of orally dosed furosemide (FUR) is due to the presence of a biological window in the upper gastrointestinal tract. The purpose of the present study was to develop and optimize in vitro a multiple-unit floating system with increased gastric residence time for FUR. The incomplete release of FUR from the units, related to its low water solubility, led to the preparation and evaluation of different FUR samples to be incorporated into the units. The complete dose release over the actual intragastric residence time of the system (about 8 hr) was achieved by loading both the core and the membrane forming the units with a 1:5 FUR/polyvinylpyrrolidone (FUR/PVP) solid dispersion. Physicochemical analyses suggested the predominant role of the amorphous state of FUR in producing enhanced drug solubility and dissolution rate, which led to the desired release profile from the floating units.

Alginate microparticles for enzyme peroral administration

In order to protect protein and peptide drugs against inactivation by different barriers in the gastro-intestinal tract and to improve their absorption, alginate microparticles as a carrier of L-lactate dehydrogenase, were developed by spray-drying technique. However, alginate complexation and spray-drying conditions led to enzyme activity loss. Such a drawback was overcome by using protectant additives (carboxymethylcellulose sodium salt, polyacrylic acid sodium salt, lactose) preventing the enzyme inactivation by both interaction with alginate and experimental conditions, lactose having the most protective effect. Nevertheless, only polyacrylic acid sodium salt provided a microparticulate structure required for the target of the Peyers patches.

Alginate microparticles for Polymyxin B Peyer's patches uptake: microparticles for antibiotic oral administration.

Microparticles with size less than 3 µm, able to be taken up by M cell of Peyers patches for the drug delivery to the Gut Associated Limphoid Tissue (GALT), were developed in order to improve oral bioavailability of Polymyxin B (PMB). Less than 3 µm alginate microparticles resistant to gastro-intestinal media were prepared by spray-drying technique and cross-linking by calcium ions and chitosan. The cross-linked microparticles were evaluated for PMB content by spectrophotometric method, alginate/PMB interaction by rheological study, cross-linking degree by EDS analysis and PMB activity by microbiological assay. By modulating the polymer cross-linking degree, cationic PMB interacted on alginate chains leading to a proper PMB loading as well as antibiotic retention in gastric environment and sustained delivery in intestinal fluid. Moreover, the procedure resulted suitable for PMB biological activity preservation.

Biodegradable intraoperative system for bone infection treatment. II. In vivo evaluation

Abstract A biodegradable implant containing gentamicin sulphate for the prevention or the treatment of bone infections was designed by using, as the polymer material, sodium alginate containing a high proportion of mannuronic sequences capable of forming a complex with the drug. By a crosslinking procedure with calcium ions, insoluble but biodegradable calcium alginate spheres were obtained and formed into a chain by means a surgical wire. To evaluate the implant effectiveness, the implant was inserted at the femur level of Wistar rats and gentamicin levels in plasma, bone and soft tissues were detected by microbiological assay. The gentamicin concentrations were found to be sufficiently high to control pathogens for at least 30 and 7 days in the bone and soft tissue, respectively, whereas plasma levels were low and detectable for only 1 day. The complete implant bioabsorption occurred within 8–10 days after implantation and no signs of rejection or inflammatory reactions were observed at the level of the surrounding tissues.

Biodegradable intraoperative system for bone infection treatment. I. The drug/polymer interaction

In order to design and evaluate an implantable device of calcium alginate spheres releasing gentamicin sulphate to prevent or treat bone infections, the interaction between the cationic gentamicin and the polyanionic alginate was examined. Such an interaction took place, both in sodium alginate solution—as shown by theological study, and during the Ca-induced polymer gelation which led to the formation of the calcium alginate spheres. Gentamicin sulphate was found to interact selectively on the mannuronic residues of alginate without competition with calcium ions involved in the polymer gelation. In contrast, calcium ions were found to interact preferentially at the level of the polyguluronic sequences, though polymannuronic sequences can also play a role. This prevented the saturation of the polymannuronic sequences by the drug. Therefore, the alginate having a higher mannuronic acid content, i.e. capable of associating a greater amount of drug, could be considered the more suitable material for the implant design.