Rheological evaluation of deacetylated gellan gum (Gelrite) for pharmaceutical use

Design of in-situ implant for the brain-targeted drug delivery using cross-linked gellan gum polymer through response surface methodology

The analysis aimed to prepare an in-situ implant (ISFI) formulation holding dimethyl fumarate as (a model drug) using cross-linked gellan gum by homogenization method. Cross-linking of gellan gum was done with L-cysteine to improve its gelation properties. Fourier transform infrared spectroscopy (FTIR) and (DSC) Differential scanning calorimetry were used to test the compatibility of the drug-polymer. The diverse formulations were prepared and tested using Design Expert® ver 8.0.1 software to optimize the experiment technique and employ the response surface. The tissue compatibility of the test verified the existence of non-irritants in the established formulation. All preparations contained the drug content from approximately 97.98 to 99.88%. Viscosities are ideal for injection in the optimized formulation (1,55 percent w/w in water). The optimized formula was monitored, and up to 156hours, it was found to be 95.7%. The result was that ISFI can effectively monitor and control the delivery of several powerful drug products.

Comparative Study of In Situ Gel Formulation Based on the Physico-Chemical Aspect: Systematic Review

In recent years, in situ gel delivery systems have received a great deal of attention among pharmacists. The in situ gelation mechanism has several advantages over ointments, the most notable being the ability to provide regular and continuous drug delivery with no impact on visual clarity. Bioavailability, penetration, duration, and maximum medication efficacy are all improved by this mechanism. Our review systematically synthesizes and discusses comparisons between three types of in situ gelling system according to their phase change performance based on the physicochemical aspect from publications indexed in the Pubmed, ResearchGate, Scopus, Elsevier, and Google Scholar databases. An optimal temperature-sensitive in situ gelling solution must have a phase change temperature greater than ambient temperature (25 °C) to be able to be readily delivered to the eye; hence, it was fabricated at 35 °C, which is the precorneal temperature. In a pH-sensitive gelling system, a gel develops immediately when the bio-stimuli come into contact with it. An in situ gelling system with ionic strength-triggered medication can also perhaps be used in optical drug-delivery mechanisms. In studies about the release behavior of drugs from in situ gels, different models have been used such as zero-order kinetics, first-order kinetics, the Higuchi model, and the Korsmeyer-Peppas, Peppas-Sahlin and Weibull models. In conclusion, the optimum triggering approach for forming gels in situ is determined by a certain therapeutic delivery application combined with the physico-chemical qualities sought.

Ion-Triggered In Situ Gelling Nanoemulgel as a Platform for Nose-to-Brain Delivery of Small Lipophilic Molecules

Background: Intranasal route offers a direct nose-to-brain delivery via olfactory and trigeminal nerves and minimizes the systemic exposure of the drug. Although reliable and non-invasive, intranasal administration of lipophilic neuroprotective agents for brain targeting is still challenging. Literature focuses on naturally-derived compounds as a promising therapeutics for chronic brain diseases. Naringin, a natural flavonoid obtained from citrus fruits possesses neuroprotective effects. By regulating multiple crucial cellular signaling pathways, naringin acts on several therapeutic targets that make it suitable for the treatment of neurodegenerative diseases like Alzheimer’s disease and making it a suitable candidate for nasal administration. However, the hydrophobicity of naringin is the primary challenge to formulate it in an aqueous system for nasal administration. Method: We designed a lipid-based nanoemulsifying drug delivery system of naringin using Acrysol K140 as an oil, Tween 80 as a surfactant and Transcutol HP as a cosolvent, to improve solubility and harness the benefits of nanosizing like improved cellular penetration. Intranasal instillations of therapeutic agents have limited efficacy due to drug washout and inadequate adherence to the nasal mucosa. Therefore, we reconstituted the naringin self-emulsifying system in a smart, biodegradable, ion-triggered in situ gelling hydrogel and optimized for desirable gel characteristics. The naringin-loaded composition was optimized and characterized for various physicochemical and rheological properties. Results: The formulation showed a mean droplet size 152.03 ± 4.6 nm with a polydispersity index <0.23. Ex vivo transmucosal permeation kinetics of the developed formulation through sheep nasal mucosa showed sustained diffusion and enhanced steady-state flux and permeability coefficient. Scanning and transmission electron microscopy revealed the spherical shape of emulsion droplets and entrapment of droplets in a gel structure. The formulation showed excellent biocompatibility as analyzed from the viability of L929 fibroblast cells and nasal mucosa histopathology after treatment. In vivo biodistribution studies revealed significantly higher drug transport and brain targeting efficiency. Conclusion: In situ gelling system with nanoemulsified naringin demonstrated a safe nasal delivery providing a new dimension to the treatment of chronic neurodegenerative diseases using small hydrophobic phytoconstituents with minimization of dose and related systemic adverse effects.

Contact-free determination of viscosity in multiple parallel samples

Viscosity is an inherent characteristic of fluids and is therefore an important parameter in many different processes. Current methods to measure viscosity involve direct contact with the liquid sample, which is often undesirable. Here we present a simple, precise and robust contact-free method to determine viscosity, using a single drive motor, inexpensive components and disposable sample vessels. The measurement principle involves the detection of viscosity-dependent angular positions in a rotating liquid relative to the direction of centrifugal acceleration in an orbitally shaken vessel. The signal can be detected using different optical methods, as shown here using fluorescence and transmitted light. The sensitivity of the system can be adjusted over a wide range by varying the sample volume or the shaking diameter, and multiple samples can be analysed in parallel. This novel viscometer is also applicable to characterize non-Newtonian shear rate-dependent fluids.

Polysaccharide matrices used in 3D in vitro cell culture systems

Polysaccharides comprise a diverse class of polymeric materials with a history of proven biocompatibility and continual use as biomaterials. Recent focus on new matrices appropriate for three-dimensional (3D) cell culture offers new opportunities to apply polysaccharides as extracellular matrix mimics. However, chemical and structural bases for specific cell-polysaccharide interactions essential for their utility as 3-D cell matrices are not well defined. This review describes how these naturally sourced biomaterials satisfy several key properties for current 3D cell culture needs and can also be synthetically modified or blended with additional components to tailor their cell engagement properties. Beyond their benign interactions with many cell types in cultures, their economical and high quality sourcing, optical clarity for ex situ analytical interrogation and in situ gelation represent important properties of these polymers for 3D cell culture applications. Continued diversification of their versatile glycan chemistry, new bio-synthetic sourcing strategies and elucidation of new cell-specific properties are attractive to expand the polysaccharide polymer utility for cell culture needs. Many 3D cell culture priorities are addressed with the portfolio of polysaccharide materials available and under development. This review provides a critical analysis of their properties, capabilities and challenges in 3D cell culture applications.

Engineered Gellan Polysaccharides in the Design of Controlled Drug Delivery Systems

Natural polysaccharides are getting increasing attention in the development of pharmaceutical dosage forms due to their encouraging reports on nontoxicity and biodegradability. Natural gums can also be engineered to have better materials for drug delivery system design. Gellan gum originates from microbial fermentation and has been declared as safe by US FDA for human consumption. It possesses gelling ability in presence of multivalent earth metal cations and thus enabled the design of mutiparticulate drug delivery systems in completely aqueous environment avoiding the use of organic solvents. Due to faster drug release profiles of divalent cation-induced gellan gum particles, nowadays chemically modified forms of gellan polysaccharide are currently being investigated for the controlled release of drugs. This chapter discusses the factors contributing to the varying gelling characteristics of gellan gum and the recent developments in its chemical modification towards the fabrication of novel controlled drug delivery devices.

Thiomers and their potential applications in drug delivery

INTRODUCTION

Thiomers are the product of the immobilization of sulfhydryl-bearing ligands onto the polymer backbone of a conventional polymer, which results in a significant improvement in mucoadhesion; in situ gelation and efflux inhibition compare with unchanged polymers. Because of thiol groups, thiomers have more reactivity and enhanced protection against oxidation. Since the late 1990s, extensive work has been conducted on these promising polymeric excipients in the pharmaceutical field. Areas covered: This review covers thiomers, their classification and their different properties. Various techniques for the synthesis, purification and characterization of thiomers are described in detail. This review also encompasses their various properties such as mucoadhesion, permeation enhancement, in situ gelation and efflux inhibition, as well as different formulations based on thiomers. In addition to the use of thiomers as multifunctional excipients, this review also encompasses their use as drugs. Expert opinion: The synthesis is realized by linkage of sulfhydryl-bearing ligands but reported methods give low yields. Higher degrees of modification are not necessary and would probably lead to extreme changes in properties. Nevertheless, an accurate characterization of the final product is important. The scale-up procedure for industrial manufacturing has been adapted to produce GMP materials; Lacrimera® eye drops have already entered the European market.

Liposome incorporated ion sensitive in situ gels for opthalmic delivery of timolol maleate

This study was aimed to design a liposomal based ion-sensitive in situ ophthalmic delivery system of timolol maleate (TM). The TM liposome was produced by the reverse evaporation technique coupled with pH-gradients method (REVPR), and then was incorporated into deacetylated gellan gum gels. The TM liposome was demonstrated to be a round and uniform shape in TEM pictures. Compared with the TM eye drops, the TM liposome produced a 1.93 folds increase in apparent permeability coefficients (Papp), resulting in a significant increase of the corneal penetration. The TM-loaded liposome incorporated ion sensitive in situ gels (TM L-ISG) showed longer retention time on corneal surface compared with the eye drops using gamma scintigraphy technology. Draize testing showed that TM L-ISG was non-irritant for ocular tissues. The biggest efficacy of TM L-ISG occurred 30 min after eye drops administration, and efficacy disappeared after 240min. Then, compared with the eye drops, the optimal TM L-ISG could quickly reduce the intraocular pressure and the effective time was significantly longer (P≤0.05). These results indicate that liposome incorporated ion sensitive in situ gels have a potential ability for the opthalmic delivery.

Preactivated thiomers: their role in drug delivery

INTRODUCTION

Since thiolated polymers - known as thiomers - have entered the pharmaceutical arena in the late 1990 s, more and more academic and industrial research groups have started to work with these promising polymeric excipients. Meanwhile, various thiomers are the subject of clinical trials and the first product based on thiolated chitosan will reach the market in 2015. Due to the formation of disulfide bonds with mercaptopyridine substructures, thiol groups of thiomers are on the one hand more reactive and on the other hand are protected toward oxidation. These so-called preactivated thiomers representing the second generation of thiomers are subject of this review.

AREAS COVERED

Within this review, preactivated thiomers are classified and their mode of action is described. Furthermore, different synthetic pathways, purification and chemical characterization methods of preactivated thiomers are explained. Their properties including mucoadhesive, permeation-enhancing, efflux pump inhibitory and in situ gelling properties are described. In addition, various formulations based on preactivated thiomers are introduced.

EXPERT OPINION

The first-generation thiomers have already shown great potential resulting in various product developments. Preactivated thiomers - representing the second generation of thiomers - offer the additional advantage of even comparatively more reactive sulfhydryl ligands and of stability toward oxidation. According to this, they are promising novel polymeric excipients for various applications.

Rheological and mechanical properties of poloxamer mixtures as a mucoadhesive gel base

This study described the thermosensitive formulations composed of poloxamer mixtures for use as drug delivery platform via mucosal route. It also characterized the poloxamer mixtures' rheological, mechanical and mucoadhesive properties. Poloxamer (Plx) 407 and Plx 188 were used alone and together for preparing the mucosal drug delivery platform. The mixtures of Plx 407 and Plx 188 in ratio of 15:15 (F5); 15:20 (F6); 20:10 (F7) existed liquid at room temperature, but gelled at physiological temperature. Flow rheometry studies and oscillatory analysis of each formulation were performed at 20 ± 0.1°C and 37 ± 0.1°C. F5 and F7 formulations exhibited typical gel-type mechanical spectra (G' > G″) after the determined frequency value at 37°C whereas F6 behaved as weakly cross-linked gel. Texture profile analysis presented that F5 and F7 showed similar mechanical properties and can be used as base for mucosal dosage form. Mucoadhesion studies indicated the difference among the formulations and the effect of the mucosal surface on mucoadhesive properties. Mucin disc, bovine vaginal and buccal mucosa were used as mucosal platform for mucoadhesion studies. It is suggested that these investigations may be usefully combined to provide a more rational basis for selecting the ratio of Plx to prepare a topical thermosensitive drug delivery system for mucosal administration.

In situ gelling gelrite/alginate formulations as vehicles for ophthalmic drug delivery

The objective of this study was to develop an ion-activated in situ gelling vehicle for ophthalmic delivery of matrine. The rheological properties of polymer solutions, including Gelrite, alginate, and Gelrite/alginate solution, were evaluated. In addition, the effect of formulation characteristics on in vitro release and in vivo precorneal drug kinetic of matrine was investigated. It was found that the optimum concentration of Gelrite solution for the in situ gel-forming delivery systems was 0.3% (w/w) and that for alginate solution was 1.4% (w/w). The mixture of 0.2% Gelrite and 0.6% alginate solutions showed a significant enhancement in gel strength at physiological condition. On the basis of the in vitro results, the Gelrite formulations of matrine-containing alginate released the drug most slowly. For each tested polymer solution, the concentration of matrine in the precorneal area was higher than that of matrine-containing simulated tear fluid (STF) almost at each time point (p < 0.05). The area under the curve of formulation 16 (0.2%Gelrite/0.6%alginate) was 4.65 times greater than that of containing matrine STF. Both the in vitro release and in vivo pharmacological studies indicated that the Gelrite/alginate solution had the better ability to retain drug than the Gelrite or alginate solutions alone. The tested formulation was found to be almost non-irritant in the ocular irritancy test. The overall results of this study revealed that the Gelrite/alginate mixture can be used as an in situ gelling vehicle to enhance ocular retention.

Study of Formulation Variables on Properties of Drug-Gellan Beads by Factorial Design

The aim of the present study was to obtain cross-linked calcium-gellan beads containing diclofenac sodium as model drug, using full 3(3) factorial design. Drug quantity, pH of cross-linking solution, and speed of agitation were selected as variables for factorial design. The resultant beads were evaluated by scanning electron microscopy (SEM), percent yield, entrapment efficiency, micromeritic properties, swelling and drug release studies. The drug-loaded beads were spherical with size range of 0.85-1.8 mm. Percent yield and entrapment efficiency of various batches were in the range of 86.48-98.28% w/w and 72.52-92.74% w/w, respectively. Calcium-gellan beads containing diclofenac sodium showed pH-dependent swelling and drug release properties. Swelling and drug release were significantly higher in pH 7.4 phosphate buffer than 0.1N HCl. The swelling ratio for beads was up to 22 and 3 for phosphate buffer and 0.1N HCl, respectively. Cumulative diclofenac sodium release from calcium-gellan beads was 12-35% in 0.1N HCl within 2 h, whereas complete drug release was observed within 3-4 h in pH 7.4 phosphate buffer.

In situ-forming hydrogels for sustained ophthalmic drug delivery

Ophthalmic drug delivery is one of the most interesting and challenging endeavors facing the pharmaceutical scientist. The conventional ocular drug delivery systems like solutions, suspensions, and ointments show drawbacks such as increased precorneal elimination, high variability in efficiency, and blurred vision respectively. In situ-forming hydrogels are liquid upon instillation and undergo phase transition in the ocular cul-de-sac to form visco-elastic gel and this provides a response to environmental changes. In the past few years, an impressive number of novel temperature, pH, and ion induced in situ-forming systems have been reported for sustain ophthalmic drug delivery. Each system has its own advantages and drawbacks. The choice of a particular hydrogel depends on its intrinsic properties and envisaged therapeutic use. This review includes various temperature, pH, and ion induced in situ-forming polymeric systems used to achieve prolonged contact time of drugs with the cornea and increase their bioavailability.

Thiolated chitosans

The derivatization of the primary amino groups of chitosan with coupling reagents bearing thiol functions leads to the formation of thiolated chitosans. So far, three types of thiolated chitosans have been generated: chitosan-cysteine conjugates, chitosan-thioglycolic acid conjugates and chitosan-4-thio-butyl-amidine conjugates. Various properties of chitosan are improved by this immobilization of thiol groups. Due to the formation of disulfide bonds with mucus glycoproteins, the mucoadhesiveness is 6--100-fold augmented (I). The permeation of paracellular markers through intestinal mucosa can be enhanced 1.6--3-fold utilizing thiolated instead of unmodified chitosan (II). Moreover, thiolated chitosans display in situ-gelling features, due to the pH-dependent formation of inter- as well as intra-molecular disulfide bonds (III). This latter process provides a strong cohesion and stability of carrier matrices being based on thiolated chitosans (IV). Consequently, thiolated chitosans can guarantee a prolonged controlled release of embedded therapeutic ingredients (V). The potential of thiolated chitosans has meanwhile also been demonstrated in vivo. A significant pharmacological efficacy of 1.3% of orally given salmon calcitonin, for instance, could be achieved utilizing thiolated chitosan as polymeric drug carrier matrix, while no effect was reached using unmodified chitosan. According to these results thiolated chitosans represent a promising new category of polymeric excipients in particular for the non-invasive administration of hydrophilic macromolecules. Further applications such as their use as scaffold materials in tissue engineering or as coating material for stents seem feasible.

Effect of pH on the conformation of gellan chains in aqueous systems

The optical rotation and fluorescence anisotropy for gellan aqueous systems were measured at pH 4, 7, and 10 to elucidate the effect of pH on the conformation of gellan chains. The optical rotation study suggests that pH affects the conformation of helical gellan chains and their aggregation behavior but the coil-helix transition temperature. By comparing the chain mobility estimated from the fluorescence anisotropy between different pH conditions, it has been revealed that the degree of expansion of random-coiled gellan chains varies with pH. These results indicate that the effect of pH is explained by the change in the anionic nature of gellan chains rather than in the shielding effect of hydrogen ions surrounding gellan chains as a cation species.

Biodegradation Behavior of Gellan Gum in Simulated Colonic Media

The objective of this investigation was to test the biodegradability of gellan gum in the presence of galactomannanase in order to explore its suitability for the development of colon-specific controlled delivery systems. Gellan beads containing azathioprine (AZA) were prepared by ionotropic gelation in the presence of Ca2+ ions and were coated with an enteric polymer, Eudragit S-100. The effects of the simulated colonic fluid (SCF, pH 7.4 phosphate buffer) containing 15 mg/mL of galactomannanase on the in vitro release profiles of uncoated and enteric-coated beads were investigated, and the morphological changes in the structure of uncoated beads were assessed by scanning electron microscopy (SEM). In addition, 1% solution of deacetylated gellan gum was prepared and several aliquots of the resulting solution were evaluated rheologically to determine the concentration- and time-dependent effects of galactomannanase. Based on the percent drug released at 2 h, approximately 10% greater amount of drug was released in the SCF containing galactomannanase when compared with the enzyme-free dissolution medium. Results of rheological studies demonstrated that effects of galactomannanase on the viscosity of gellan gum solution are concentration-dependent rather than time-dependent. A significant decrease in the viscosity was noted in the presence of galactomannanase at a concentration of 15 mg/ mL, indicating that the polysaccharide degraded in an enzymatic reaction. SEM micrographs showed a distinct disruption of the polymeric network in the SCF. Overall, the results suggest that gellan gum undergoes significant degradation in the presence of galactomannanase which in turn facilitates the drug release from beads in the SCF in a controlled manner, thus approving the suitability of gellan gum as a carrier for controlled colonic delivery.

Ocular preparations: the formulation approach

The main aim of pharmacotherapeutics is the attainment of an effective drug concentration at the intended site of action for a sufficient period of time to elicit the response. A major problem being faced in ocular therapeutics is the attainment of an optimal concentration at the site of action. Poor bioavailability of drugs from ocular dosage forms is mainly due to the tear production, non-productive absorption, transient residence time, and impermeability of corneal epithelium. This article reviews: (1) the barriers that decrease the bioavailability of an ophthalmic drug; (2) the objectives to be considered in producing optimal formulations; and (3) the approaches being used to improve the corneal penetration of a drug molecule and delay its elimination from the eye. The focus of this review is on the recent developments in topical ocular drug delivery systems, the rationale for their use, their drug release mechanism, and the characteristic advantages and limitations of each system. In addition, the review attempts to give various analytical procedures including the animal models and other models required for bioavailability and pharmacokinetic studies. The latter can aid in the design and predictive evaluation of newer delivery systems. The dosage forms are divided into the ones which affect the precorneal parameters, and those that provide a controlled and continuous delivery to the pre- and intraocular tissues. The systems discussed include: (a) the commonly used dosage forms such as gels, viscosity imparting agents, ointments, and aqueous suspensions; (b) the newer concept of penetration enhancers, phase transition systems, use of cyclodextrins to increase solubility of various drugs, vesicular systems, and chemical delivery systems such as the prodrugs; (c) the developed and under-development controlled/continuous drug delivery systems including ocular inserts, collagen shields, ocular films, disposable contact lenses, and other new ophthalmic drug delivery systems; and (d) the newer trends directed towards a combination of drug delivery technologies for improving the therapeutic response of a non-efficacious drug. The fruitful resolution of the above-mentioned technological suggestions can result in a superior dosage form for both topical and intraocular ophthalmic application.

Natural gums and modified natural gums as sustained-release carriers

Although natural gums and their derivatives are used widely in pharmaceutical dosage forms, their use as biodegradable polymeric materials to deliver bioactive agents has been hampered by the synthetic materials. These natural polysaccharides do hold advantages over the synthetic polymers, generally because they are nontoxic, less expensive, and freely available. Natural gums can also be modified to have tailor-made materials for drug delivery systems and thus can compete with the synthetic biodegradable excipients available in the market. In this review, recent developments in the area of natural gums and their derivatives as carriers in the sustained release of drugs are explored.

Evaluation of mucoadhesion for two polyelectrolyte gels in simulated physiological conditions using a rheological method

A rheological method to measure mucoadhesion was evaluated for two ion-sensitive polymers, Carbopol 934 and Gelrite((R)) (deacetylated gellan gum), in a simulated physiological environment using two commercially available mucins. The method simulates the interpenetration layer in the mucoadhesion process. The elastic modulus for a polymer/mucin mixture is compared with the elastic modulus for the polymer alone, and an increase in the elastic modulus for the mixture compared to the polymer is interpreted as a positive interaction caused by mucoadhesion. In this study the influence of polymer concentration, type of mucin and experimental rheological factors, such as gap width, were examined. The choice of polymer concentration was crucial, especially with the porcine gastric mucin. We found that one is more likely to obtain positive interactions with weak gels. It was also shown that the choice of mucin has a large influence on the results obtained. Carbopol 934 interacted more strongly with the bovine submaxillary gland mucin than with the porcine gastric mucin, whereas the gel structure of Gelrite((R)) was destroyed when mixed with the bovine mucin. Furthermore, it was concluded that with hydrogels consisting of gel particles (such as Carbopol 934), rheological measurements can give highly varying results, depending on, for example, the concentration and ion-sensitivity of the polymer, the quantity of ions present, as well as the gap width of the measuring system.

In situ-gelling gellan formulations as vehicles for oral drug delivery

Gels formed in situ following oral administration of 1% (w/v) aqueous solutions of gellan to rats and rabbits were evaluated as sustained-release vehicles. The formulation contained calcium ions in complexed form, the release of which in the acidic environment of the stomach caused gelation of the gellan gum. The in vitro release of theophylline from the rigid gellan gels followed root-time kinetics over a period of 6 h. Plasma levels of theophylline after oral administration of gellan solutions and a commercial oral sustained-release liquid dosage form containing an identical drug concentration were compared in both rats and rabbits. Bioavailability of theophylline from gellan gels formed by in situ gelation in the animal stomach was increased by four-fivefold in rats and threefold in rabbits compared with that from the commercial oral formulation. There was no significant difference in the mean residence times of theophylline when administered by these two vehicles.

Effect of the formulation on the in-vitro release of propranolol from gellan beads

Gellan gum beads of propranolol hydrochloride, a hydrophilic model drug, were prepared by solubilising the drug in a dispersion of gellan gum and then dropping the dispersion into calcium chloride solution. The droplets formed gelled beads instantaneously by ionotropic gelation. Major formulation and process variables which might influence the preparation of the beads and the drug release from gellan gum beads were studied. Very high entrapment efficiencies were obtained (92%) after modifying the pH of both the gellan gum dispersion and the calcium chloride solution. The beads could be stored for 3 weeks in a wet or dried state without modification of the drug release. Oven-dried beads released the drug somewhat more slowly than the wet or freeze-dried beads. The drug release from oven-dried beads was slightly affected by the pH of the dissolution medium. Gellan gum could be a useful carrier for the encapsulation of fragile drugs and provides new opportunities in the field of bioencapsulation.

A novel co-crosslinked polysaccharide: studies for a controlled delivery matrix

The formulation of a new controlled delivery system, based on a novel type of matrix obtained by the chemical reaction carried out in an aqueous medium on a mixed physical gel of gellan and scleroglucan, is described in this paper. The preparation yielded a new co-crosslinked polysaccharide (CCP) hydrogel, bearing carboxylic groups, that showed a sustained release behaviour that can be modulated by means of calcium ions. For the characterization of CCP, diffusion experiments through the swelled hydrogel were carried out in different environmental conditions and the release from tablets prepared with CCP and a model drug was evaluated. The addition of CaCl2 in the formulation of the dosage forms allowed a further marked reduction in delivery rate to be obtained; this effect is to be related to the free ionized carboxylic groups still present in the gellan moiety of CCP. The different behaviour of Ca+2 and Na+ ions is discussed.

Physical characteristics and release behavior of salbutamol sulfate beads prepared with different ionic polysaccharides

Salbutamol sulfate beads were prepared using anionic and cationic polysaccharides, Gelrite and chitosan, respectively. Alginate beads were also prepared for comparison. The mean diameter, porosity, and drug content of the beads were determined. The beads were examined by scanning electron microscopy (SEM), DSC, and x-ray diffraction. The drug release from the beads was studied in 0.1 N HCl (pH 1.2), distilled water, and phosphate buffer (pH 7.4). The physical examination of the beads indicated the presence of drug crystals with no interaction between the drug and polymers. The drug release was dependent on the ionic properties of the polymers and the pH of the release media. In acidic pH, chitosan beads showed a rapid drug release, whereas a sustained drug release was obtained from Gelrite beads. In contrast, the drug release in phosphate buffer was rapid from Gelrite, and chitosan showed a sustained drug release. The results of drug release from Gelrite were comparable to that from alginate beads. Gelrite is recommended as an anionic polysaccharide for sustained-release preparations.

Rheological evaluation of Gelrite in situ gels for ophthalmic use

One of the reasons for the relatively low bioavailability of conventional eye drops is their short precorneal contact times. In situ gels are promising ocular drug delivery systems since they are conveniently dropped into the eye as a liquid whereafter they undergo a transition into a gel. Due to their elastic properties hydrogels resist ocular drainage leading to longer contact times. In this paper the rheology of Gelrite in situ gels was studied. A complementary in vivo study for determining precorneal contact times in humans and in rabbits was performed. The elastic moduli of the gels increased with increasing concentration of electrolytes. At physiological concentration of the electrolytes, the elasticity of the gels was independent of Gelrite concentration. The human contact times increased up to 20 h with decreasing osmolality of the formulations. The results indicate that a high rate of the sol/gel transition results in long contact times.

Rheological evaluation of poloxamer as an in situ gel for ophthalmic use

The contact time of a vehicle on the cornea is of utmost importance for ocular drug delivery. In the present study rheological measurements were performed to study the gel and the sol-gel transition of an in situ gel, Poloxamer 407. The rheological measurements and a small in vivo study of ocular residence times in humans were used to evaluate poloxamer as an ocular vehicle. An increasing concentration of poloxamer resulted in a slightly increasing elasticity of the gels and a decreasing sol-gel transition temperature. The contact time increased with increasing concentration of poloxamer which could be explained and correlated with the rheology of poloxamer solutions/gels mixed with simulated tear fluid. The maximum contact time for the preparations studied was about 1 h. The poloxamer system did not seem to be promising as an ophthalmic in situ gel due to the strong concentration dependence of the sol-gel transition temperature combined with the dilution that occurs in the eye.

Gellan in sustained release formulations: preparation of gel capsules and release studies

The ability of gellan to form gels in the presence of calcium ions enabled us to prepare capsules by gelation of this polysaccharide around a core containing starch, calcium chloride and a model drug. Release from the dried capsules was studied in vitro by means of the rotating basket technique (USP) in different environmental conditions (distilled water, pH = 2.0, pH = 6.8) and the effects of the presence of increasing amounts of drug in the formulation were also investigated. The behaviour of the gellan capsules was compared with that of beads prepared with the same polysaccharide but containing different additives. Results obtained indicate that gellan is suitable for the formulation of sustained release capsules and that solvent uptake by the dried capsules is most likely the main factor capable of affecting the rate of delivery from the tested preparations.