Preactivated thiomers for vaginal drug delivery vehicles

Repurposing Disulfiram as an Antifungal Agent: Development of a New Disulfiram Vaginal Mucoadhesive Gel

Alternative formulations need to be developed to improve the efficacy of treatments administered via the vaginal route. Mucoadhesive gels with disulfiram, a molecule that was originally approved as an antialcoholism drug, offer an attractive alternative to treat vaginal candidiasis. The aim of the current study was to develop and optimize a mucoadhesive drug delivery system for the local administration of disulfiram. Such formulations were composed of polyethylene glycol and carrageenan to improve the mucoadhesive and mechanical properties and to prolong the residence time in the vaginal cavity. Microdilution susceptibility testing showed that these gels had antifungal activity against Candida albicans, Candida parapsilosis, and Nakaseomyces glabratus. The physicochemical properties of the gels were characterized, and the in vitro release and permeation profiles were investigated with vertical diffusion Franz cells. After quantification, it was determined that the amount of the drug retained in the pig vaginal epithelium was sufficient to treat candidiasis infection. Together, our findings suggest that mucoadhesive disulfiram gels have the potential to be an effective alternative treatment for vaginal candidiasis.

In situ gelation of thiolated poly(aspartic acid) derivatives through oxidant-free disulfide formation for ophthalmic drug delivery

Efficient topical treatment of ocular diseases requires a prolonged residence time of drug formulations. An in situ gelling, mucoadhesive system can provide improved residence time while keeps the installation of the formulation easy and accurate due to its low initial viscosity. We synthesized a two-component, biocompatible water-based liquid formulation showing in situ gelation upon mixing. S-protected, preactivated derivatives of thiolated poly(aspartic acid) (PASP-SS-MNA) were synthesized by coupling the free thiol groups of thiolated poly(aspartic acid) (PASP-SH) with 6-mercaptonicotinic acid (MNA). The amount of protecting groups was 242, 341, and 530 µmol/g depending on the degree of thiolation of PASP. The chemical interaction between PASP-SS-MNA and mucin was proven, indicating the mucoadhesive properties. Disulfide cross-linked hydrogels were formed in situ without an oxidizing agent by mixing the aqueous solutions of PASP-SS-MNA and PASP-SH. The gelation time was controlled between 1 and 6 min, while the storage modulus was as high as 4-16 kPa depending on the composition. Swelling experiments showed that hydrogels with no residual thiol groups are stable in phosphate-buffered saline at pH = 7.4. In contrast, the presence of free thiol groups leads to the dissolution of the hydrogel with a rate depending on the excess of thiol groups. The biological safety of the polymers and MNA was confirmed on Madin-Darby Canine Kidney cell line. Furthermore, a prolonged release of ofloxacin was observed at pH = 7.4 compared to a conventional liquid formulation, supporting the potential of the developed biopolymers in ophthalmic drug delivery.

Thiolated Polymeric Hydrogels for Biomedical Applications: A Review

Hydrogels are a three-dimensional (3D) network of hydrophilic polymers. The physical and chemical crosslinking of polymeric chains maintains the structure of the hydrogels even when they are swollen in water. They can be modified with thiol by thiol epoxy, thiol-ene, thiol-disulfide, or thiol-one reactions. Their application as a matrix for protein and drug delivery, cellular immobilization, regenerative medicine, and scaffolds for tissue engineering was initiated in the early 21st century. This review focuses on the ingredients, classification techniques, and applications of hydrogels, types of thiolation by different thiol-reducing agents, along with their mechanisms. In this study, different applications for polymers used in thiolated hydrogels, including dextran, gelatin, polyethylene glycol (PEG), cyclodextrins, chitosan, hyaluronic acid, alginate, poloxamer, polygalacturonic acid, pectin, carrageenan gum, arabinoxylan, carboxymethyl cellulose (CMC), gellan gum, and polyvinyl alcohol (PVA) are reviewed.

Surface Modification of Lipid-Based Nanoparticles

There is a growing interest in the development of lipid-based nanocarriers for multiple purposes, including the recent increase of these nanocarriers as vaccine components during the COVID-19 pandemic. The number of studies that involve the surface modification of nanocarriers to improve their performance (increase the delivery of a therapeutic to its target site with less off-site accumulation) is enormous. The present review aims to provide an overview of various methods associated with lipid nanoparticle grafting, including techniques used to separate grafted nanoparticles from unbound ligands or to characterize grafted nanoparticles. We also provide a critical perspective on the usefulness and true impact of these modifications on overcoming different biological barriers, with our prediction on what to expect in the near future in this field.

Recent Advances in Polymer-Based Vaginal Drug Delivery Systems

The vagina has been considered a potential drug administration route for centuries. Most of the currently marketed and investigated vaginal formulations are composed with the use of natural or synthetic polymers having different functions in the product. The vaginal route is usually investigated as an administration site for topically acting active ingredients; however, the anatomical and physiological features of the vagina make it suitable also for drug systemic absorption. In this review, the most important natural and synthetic polymers used in vaginal products are summarized and described, with special attention paid to the properties important in terms of vaginal application. Moreover, the current knowledge on the commonly applied and innovative dosage forms designed for vaginal administration was presented. The aim of this work was to highlight the most recent research directions and indicate challenges related to vaginal drug administrations. As revealed in the literature overview, intravaginal products still gain enormous scientific attention, and novel polymers and formulations are still explored. However, there are research areas that require more extensive studies in order to provide the safety of novel vaginal products.

The progress on sulfhydryl modified polymers with regard to synthesis, characterization and mucoadhesion

The concepts of mucoadhesion and mucoadhesive polymers were introduced in the 20th century, leading to several advantages. These included enhanced drug absorption and extended residence at specific site of action. Polymeric excipients underwent chemical modification with sulfhydryl groups on the polymeric backbone so as to improve mucoadhesive features as well as potential. This modification resulted in compounds mimicking the nature of secreted mucus glycoproteins. Thus, these thiol group-bearing excipients presented the ability to attach covalently to the mucosa by the disulfide bonding. Nevertheless, the first generation of these thiol-modified polymers, named thiomers, presented disadvantages such as low stability in aqueous media and/or the high susceptibility towards oxidation along with the drawback of low sufficient reactive functional moieties on the polymeric backbone at lower pH. Therefore, in the 21st century, a second generation of preactivated or S-protected polymers with protected thiol moieties were developed, as well as a third generation of thiomers, solving some of the previously described problems. This review article aimed to highlight the progess on a potent sulfhydryl modification during the last decades and the posterior characterization and in vitro/ex vivo/in vivo mucoadhesiveness.

Biocompatibility of Biomaterials for Nanoencapsulation: Current Approaches

Nanoencapsulation is an approach to circumvent shortcomings such as reduced bioavailability, undesirable side effects, frequent dosing and unpleasant organoleptic properties of conventional drug delivery systems. The process of nanoencapsulation involves the use of biomaterials such as surfactants and/or polymers, often in combination with charge inducers and/or ligands for targeting. The biomaterials selected for nanoencapsulation processes must be as biocompatible as possible. The type(s) of biomaterials used for different nanoencapsulation approaches are highlighted and their use and applicability with regard to haemo- and, histocompatibility, cytotoxicity, genotoxicity and carcinogenesis are discussed.

The application of nanomaterial science in the formulation a novel antibiotic: Assessment of the antifungal properties of mucoadhesive clotrimazole loaded nanofiber versus vaginal films

Candidiasis is the origin of several chronic diseases and causes a wide range of symptoms from mucosal to systemic and deadly infections. Vaginal patches are one of the best drug delivery systems for the treatment of fungal infections in the vaginal environment, so a mucoadhesive film containing drugs such as clotrimazole and metronidazole is commercially available for patients. In the present study, a physicochemical comparison is made between clotrimazole loaded film and nanofiber fabricated with the new hybrid mucoadhesive formulation of dextran and alginate. Toxicity testing was performed using the MTT assay. Bioadhesion and antifungal effects were investigated for fibers and films. The release behavior of clotrimazole from two systems was evaluated by Franz cell in each case. The most important difference between nanofibrous and film mats were obtained in antifungal, mucoadhesive, Young's modulus and morphology. The nanofiber has a higher antifungal effect and two-fold adhesive to the mouse tissue, than film. The inherent flexibility of nanofiber obviated the need for a plasticizer, which may have cytotoxic side effects. The Clotrimazole loaded nanofibrous of Alginate/Dextran mats were successfully electrospun. They exhibited more bioadhesive with higher and faster antifungal properties versus similar formulation film. Further in vivo investigation is required for their application in vaginal candidiasis.

Solid Lipid Nanoparticles Based on L-Cysteine for Progesterone Intravaginal Delivery

The present work has as its purpose the synthesis and characterization of a novel lipid material to be used in the preparation of solid lipid nanoparticles (SLNs) for the potential sustained release of progesterone in the vagina. For this reason, a material capable of ensuring the permanence of the formulation in the administration site for the time needed to guarantee the transmucosal absorption of the steroid was synthetized in order to reduce the number of administrations and to ensure an effective concentration of drug at the site of action. To this end, an ester, 2,3-dihydroxypropanoate of octadecyl (stearyl glycerine), containing two hydroxyl groups was initially synthesized. In particular, the hydroxyl group less sterically encumbered was functionalized with a thiol group, in a coupling reaction, with the amino acid L-cysteine. The obtained compound was characterized by FT-IR spectrometry and 1H-NMR. The functionalized lipid with L-cysteine was then used for the preparation of solid lipid nanoparticles that were loaded with progesterone. Finally, the release of progesterone from the lipid matrix based on newly synthesized ester, under conditions that simulate the vaginal physiological environment, was evaluated. All the obtained results suggest that the prepared nanoparticles could be used for the administration of progesterone, when its integration is essential, for example, in cases of threats of abortion or to increase fertility.

In situ gelling and mucoadhesive polymers: why do they need each other?

INTRODUCTION

Mucosal drug delivery is an attractive route of administration, particularly in overcoming deficits of conventional dosage forms including high first-pass metabolism and poor bioavailability. Fast drainage from the target mucosa, however, represents a major limitation as it prevents sufficient drug absorption. In order to address these problems, mucoadhesive in situ gelling drug delivery systems have been investigated as they facilitate easy application in combination with a longer residence time at the administration site resulting in more desirable therapeutic effects.

AREAS COVERED

The present review evaluates the importance of the combination of mucoadhesive and in situ gelling polymers along with mechanisms of in situ gelation and mucoadhesion. In addition, an overview about recent applications in mucosal drug delivery is provided.

EXPERT OPINION

In situ gelling and mucoadhesive polymers proved to be essential excipients in order to prolong the mucosal residence time of drug delivery systems. Due to this prolonged residence time both local and systemic therapeutic efficacy of numerous drugs can be substantially improved. Depending on the site of administration and the incorporated drug, combinations of different polymers with in situ gelling and mucoadhesive properties are needed to keep the delivery system as long as feasible at the target site.

Thiolated Hyaluronic Acid as Versatile Mucoadhesive Polymer: From the Chemistry Behind to Product Developments-What Are the Capabilities?

Within the last decade, intensive research work has been conducted on thiolated hyaluronic acids (HA-SH). By attaching sulfhydryl ligands onto naturally occurring hyaluronic acid various types of HA-SH can be designed. Due the ability of disulfide bond formation within the polymer itself as well as with biological materials, certain properties such as mucoadhesive, gelling, enzyme inhibitory, permeation enhancing and release controlling properties are improved. Besides the application in the field of drug delivery, HA-SH has been investigated as auxiliary material for wound healing. Within this review, the characteristics of novel drug delivery systems based on HA-SH are summarized and the versatility of this polymer for further applications is described by introducing numerous relevant studies in this field.

Entirely S-protected chitosan: A promising mucoadhesive excipient for metronidazole vaginal tablets

AIM

Synthesis and evaluation of an entirely S-protected chitosan as mucoadhesive excipient for vaginal drug delivery.

METHODS

N-acetyl-cysteine was linked to 6-mercaptonicotinamide via disulphide exchange reaction. The obtained ligand, NAC-6-MNA, was subsequently attached to chitosan by carbodiimide mediated amide bond formation in two concentrations. The synthesized S-protected chitosan was chemically characterized and mucoadhesive properties and stability against oxidation were investigated. Moreover, metronidazole tablets comprising the S-protected chitosan were evaluated regarding water uptake capacity, disintegration behaviour, residence time on vaginal mucosa, release of the encapsulated drug and antimicrobial activity.

RESULTS

S-protected chitosan displayed 160±19 (CS-MNA-160) and 320±38 (CS-MNA-320)µmol of ligand per gram of polymer. At pH 4.2, CS-MNA-160 and CS-MNA-320 showed 5.2-fold and 6.2-fold increase in mucus viscosity in comparison to unmodified chitosan (One-way ANOVA, p<.001), whereas, 9.9-fold (CS-MNA-160) and 15.6-fold (CS-MNA-320) (One-way ANOVA, p<.001) increase in viscosity was measured at pH 6. The S-protected chitosan remained stable against oxidation in presence of 0.5%v/v hydrogen peroxide. Metronidazole tablets consisting in S-protected chitosan showed prolonged residence time on vaginal mucosa and improved water uptake capacity and disintegration time in comparison to tablets consisting of unmodified chitosan. Moreover, CS-MNA-320 metronidazole tablets displayed prolonged drug release and antimicrobial activity.

CONCLUSIONS

On the basis of the achieved results, entirely S-protected chitosan represents a promising excipient for the development of metronidazole vaginal tablets.

STATEMENT OF SIGNIFICANCE

S-protected thiomers are polymers modified with thiol groups protected by aromatic ligands and characterized by strong mucoadhesive properties and high stability against oxidation. Up to date, the entirely S-protection of thiol groups was achieved via the synthesis of the ligand 2-((2-amino-2-carboxyethyl)disulfanyl)nicotinic acid) which can be directly bound to the backbone of polymers bearing carboxylic moieties as pectin. However, this ligand is not suitable for positively charged polymers due to the negative charge. In this paper, the synthesis of a suitable ligand for the entirely S-protection of positively charged polymers is presented. The first entirely S-protected chitosan was synthesized, characterized and its mucoadhesive properties were assessed. Moreover, metronidazole tablets comprising the entirely S-protected chitosan were developed and evaluated as vaginal drug delivery system.

Self-emulsifying drug delivery systems: Design of a novel vaginal delivery system for curcumin

AIM

The aim of this study was to develop a vaginal self-emulsifying delivery system for curcumin being capable of spreading, of permeating the mucus gel layer and of protecting the drug being incorporated in oily nanodroplets towards mucus interactions and immobilization.

METHODS

The emulsifying properties of curcumin loaded SEDDS containing 30% Cremophor RH40, 20% Capmul PG-8, 30% Captex 300, 10% DMSO and 10% tetraglycol (SEDD formulation A) as well as 25% PEG 200, 35% Cremophor RH40, 20% Captex 355, 10% Caprylic acid and 10% Tween 80 (SEDD formulation B) after diluting 1+2 with artificial vaginal fluid were characterized regarding droplet size and zeta potential. Collagen swelling test was used to examine the irritation potential of SEDDS. Additionally to mucus binding studies, permeation studies in the mucus were performed. Furthermore, spreading potential of the novel developed formulations was compared with a commercial available o/w cream (non-ionic hydrophilic cream) on vaginal mucosa.

RESULTS

SEDDS displayed a mean droplet size between 38 and 141nm and a zeta potential of -0.3 to -1.6mV. The collagen swelling test indicated no significant irritation potential of both formulations over 24h. An immediate interaction of unformulated curcumin with the mucus was determined, whereas both SEDDS facilitated drug permeation through the mucus layer. Formulation B showed a 2.2-fold improved transport ratio of curcumin compared to SEDD formulation A. In comparison to the vaginal cream, SEDD formulation A and B were able to spread over the vaginal mucosa and cover the tissue to a 17.8- and 14.8-fold higher extent, respectively.

CONCLUSION

According to these results, SEDDS seems to be a promising tool for vaginal application.

Combination of SEDDS and Preactivated Thiomer Technology: Incorporation of a Preactivated Thiolated Amphiphilic Polymer into Self-Emulsifying Delivery Systems

PURPOSE

The aim of the study was to create novel mucoadhesive drug delivery systems by incorporating amphiphilic hydrophobically modified, thiolated and preactivated polymers (preactivated thiomers) into self-emulsifying drug delivery systems (SEDDS).

METHODS

L-Cysteine methyl ester was covalently attached to the polymeric backbone of Pemulen TR-2 and preactivated using 2-mercaptonicotinic acid (2-MNA). These thiomers were incorporated in a concentration of 0.3% (w/v) into SEDDS. The size distribution and the zeta potential of the emulsions were evaluated by dynamic light scattering. Mucoadhesive properties of thiomers-SEDDS spiked with FDA (fluorescein diacetate) were examined utilizing rheological measurement, permeation studies and in vitro residence time study on porcine mucosa. Cell viability tests were additionally performed.

RESULTS

734 ± 58 μmol L-Cysteine methyl ester and 562 ± 71 μmol 2-MNA could be attached per gram polymer of Pemulen TR-2. Emulsions exhibited a droplet size range between 180 and 270 nm. Blank SEDDS possessed a zeta potential value between -5.7 and -8.6 mV, whereas thiomers-SEDDS between -14.6 and -17.2 mV. Viscous modulus of thiomer and preactivated thiomer containing SEDDS-mucus mixture was 8-fold and 11-fold increased in comparison to reference. The amount of FDA permeated the mucus layer was 2-fold lower in case of thiomers-SEDDS compared to blank SEDDS. A prolonged residence time was observed for thiomers-SEDDS over 45 min. During cell viability studies no severe toxic effects were detected.

CONCLUSION

The novel developed SEDDS with incorporated thiomers might be a promising tool for mucoadhesive oral drug delivery.

Thiolated polymers as mucoadhesive drug delivery systems

Mucoadhesion is the process of binding a material to the mucosal layer of the body. Utilising both natural and synthetic polymers, mucoadhesive drug delivery is a method of controlled drug release which allows for intimate contact between the polymer and a target tissue. It has the potential to increase bioavailability, decrease potential side effects and offer protection to more sensitive drugs such as proteins and peptide based drugs. The thiolation of polymers has, in the last number of years, come to the fore of mucoadhesive drug delivery, markedly improving mucoadhesion due to the introduction of free thiol groups onto the polymer backbone while also offering a more cohesive polymeric matrix for the slower and more controlled release of drug. This review explores the concept of mucoadhesion and the recent advances in both the polymers and the methods of thiolation used in the synthesis of mucoadhesive 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.

PEGDA hydrogels as a replacement for animal tissues in mucoadhesion testing

Utilization of animal parts in ex-vivo mucoadhesion assays is a common approach that presents many difficulties due to animal rights issues and large variance between animals. This study examines the suitability of two PEGDA (poly(ethylene glycol) diacrylate) based hydrogels to serve as tissue mimetics for mucoadhesion evaluation. One hydrogel, termed PEGDA-QT, was composed of pentaerythritol tetrakis (3-mercaptopropionate) and PEG and contained free thiol groups mimicking those found in natural mucosa. The other hydrogel was formed by UV (ultraviolet) curing of PEGDA and mimicked the mechanical property of mucosa but not its chemical constitute. When ranking different first generation mucoadhesive polymers using a tensile assay, both hydrogels showed good agreement with the ranking achieved for porcine small intestine. However, only PEGDA-QT and porcine small intestine shared a similar displacement curve. The same ranking for PEGDA-QT and porcine small intestine was also observed when comparing a second-generation mucoadhesive polymer, thiolated alginate, to native alginate. Our findings suggest that PEGDA-QT could serve as a replacement for porcine small intestine in both mucoadhesion evaluations using a tensile machine and the flow-through method for first and second-generation mucoadhesive polymers.

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.

Mucin-controlled drug release from mucoadhesive phenylboronic acid-rich nanoparticles

Phenylboronic acid-rich nanoparticles (PBNPs) were designed as a novel mucoadhesive vaginal drug delivery system. PBNPs effectively adsorbed mucin in vitro and could be easily loaded with the model drug interferon (IFN). Drug release from PBNPs was controlled by the presence of mucin. Neither obvious cytotoxicity nor vaginal histological changes in mice caused by PBNPs or IFN-loaded PBNPs were observed.

Acrylate-tethering drug carrier: covalently linking carrier to biological surface and application in the treatment of Helicobacter pylori infection

The development of carriers to sustain drugs at stomach surface is an attractive strategy to increase drug bioavailability locally and systematically. So far, the only reported carrier that can form a covalent bond with mucus, the thiolated carrier, relies on a reversible disulfide exchange reaction between thiols on the carrier and disulfide bridges on the mucus. Here we show the design and fabrication of a cellulose carrier with tethering acrylate groups (denoted here as clickable carrier) that, under a nontoxic condition, can efficiently react with thiols on biomaterials in situ through the thermodynamically driven and kinetically probable Michael thiol-ene click reaction. Here we show the attachments of the clickable carriers to a mucin protein, a surface of human laryngeal carcinoma cells, and a surface of a fresh porcine stomach. We also show that the required thiol moieties can be generated in situ by reducing existing cystine disulfide bridges with either the edible vitamin C or the relatively nontoxic tris(2-carboxyethyl) phosphine. Comparing to a control carrier, the clickable carrier can increase some drug concentrations in an ex vivo stomach tissue, and improve the Helicobacter pylori treatment in infected C57BL/6 mice.

Thiomers--from bench to market

Thiolated polymers or designated thiomers are obtained by immobilization of sulhydryl bearing ligands on the polymeric backbone of well-established polymers such as poly(acrylates) or chitosans. This functionalization leads to significantly improved mucoadhesive properties compared to the corresponding unmodified polymers, as disulfide bonds between thiol groups of thiomers and cysteine-rich glycoproteins of the mucus gel layer are formed. Furthermore, enzyme- and efflux-pump inhibiting as well as improved permeation-enhancing properties are advantages of thiolization. By the covalent attachment of mercaptonicotinamide substructures via disulfide bonds to thiolated polymers these properties are even substantially further improved and stability towards oxidation even in aqueous media can be provided. Meanwhile, more than 50 research groups worldwide are working on thiolated polymers. For certain thiomers the scale up process for industrial production has already been done and GMP material is available. Furthermore, safety of thiolated poly(acrylic acid), thiolated chitosan and thiolated hyaluronic acid could be demonstrated via orientating studies in human volunteers and via various clinical trials. The first product (Lacrimera® eye drops, Croma-Pharma) containing a chitosan-N-acetylcysteine conjugate for treatment of dry eye syndrome will enter the European market this year. It is the only product providing a sustained protective effect on the ocular surface due to its comparatively much more prolonged residence time worldwide. Various further products utilizing, for instance, thiolated hyaluronic acid in ocular surgery are in the pipeline.

Development of a dosage form for accelerated release

PURPOSE

It was the aim of this study to develop an oral capsule delivery system capable of rapidly ejecting the incorporated payload in the small intestine.

METHODS

The capsule consists of four parts: a reaction mixture comprising of a basic and a corresponding acidic component, a plunger necessary to separate the reaction mixture from the inserted ingredients, capsule cap and body (made out of ethylcellulose (EC)), where at the bottom of the body a semipermeable filter membrane is mounted. As soon as water permeates through the membrane, the reaction mixture dissolves and carbon dioxide (CO2) is released resulting in a high speed liberation of inserted compounds onto the intestinal mucosa. Several filter membranes were investigated regarding water influx, capillary force and water retention capacity. CO2 release of sodium hydrogen carbonate (NaHCO3) was examined in presence of several acidic components in different morphological forms (powder, lyophilisate and granule) and the amount of CO2 liberation out of prepared capsules was determined. Furthermore, release of enteric coated capsules was tested within 0.1M HCl and 100mM phosphate buffer pH 6.8.

RESULTS

The rank order regarding membrane permeability was determined to be: cellulose acetate with a pore diameter of 12-15 μm>4-12 μm cellulose acetate>8 μm cellulose nitrate>8-12 μm cellulose acetate. NaHCO3 in combination with tartaric acid in form of a granule could be identified as the most promising reaction mixture with the highest amount of released CO2 compared to all other reaction mixture combinations. Stability of enteric coated capsules in HCl and a spontaneous release in phosphate puffer could be demonstrated within in vitro release studies.

CONCLUSION

In light of these results, the developed releasing system seems to be a promising tool for an accelerated delivery of several incorporated excipients.