Development of a Sustained Release Solid Dispersion Using Swellable Polymer by Melting Method.

PURPOSE: This study is to design a sustained release solid dispersion using swellable polymer by melting method. METHODS: Polyethylene glycol 6000 (PEG 6000) and hydroxypropyl methylcellulose 4000 (HPMC 4000) were used in solid dispersion for not only enhancing drug dissolution rate but also sustaining drug release. HPMC 4000 is a common swellable polymer in matrix sustained release dosage form, but could not be used in preparation of solid dispersion by melting method. However, the current study utilized the swelling capability of HPMC 4000 accompanied by the common carrier PEG 6000 in solid dispersion to accomplish the goal. RESULTS: While PEG 6000 acted as a releasing stimulant carrier and provided an environment to facilitate the swelling of HPMC 4000, this swellable polymer could act as a rate-controlling agent. This greatly assisted the dissolution enhancement by changing the crystalline structure of drug to more amorphous form and creating a molecular interaction. CONCLUSIONS: These results suggested that this useful technique can be applied in designing a sustained release solid dispersion with many advantages.

Polymer conjugate-based nanomaterials for drug delivery.

The structure of polymeric amphiphiles with both hydrophilic and hydrophobic groups forming self-assembled nanoparticles have attracted increasing attention in studies of delivery systems of therapeutic agents. An amphiphilic carrier for self-assembly in an aqueous solution is preferable because of its structure with a hydrophobic core and hydrophilic outer shell, which can be applied to many biotechnological and pharmaceutical fields with numerous types of drugs. An amphiphilic carrier for self-assembly also represents the most appealing delivery system owing to its exceptional advantages in selectively delivering drugs to tumor cells and thus, reduction of side effects. This paper reviews two types of self-assembled nanoparticles/micelles of conjugated polymeric amphiphiles: (1) self-assembled micelles/nanoparticles of amphiphilic conjugates followed by drug loading and (2) self-assembled micelles/nanoparticles of polymer-drug conjugates where a conjugation reaction occurs between the polymer and drug. The development of the research has been addressed in this review with up-to-date references. In conclusion, the challenges and remaining difficulties for the future development are discussed.

Dissolution-enhancing mechanism of alkalizers in poloxamer-based solid dispersions and physical mixtures containing poorly water-soluble valsartan.

The purpose of this study was to investigate the effects of alkalizers in dissolution rate and crystal structure of valsartan (VAL) in Poloxamer 407 (POX)-based solid dispersions (SD). VAL, a poorly-water soluble drug was selected as a model drug because of its low solubility at low pH. The POX-based SDs containing alkalizers (Na2CO3, MgO, meglumine and arginine) were prepared by melting method. The dissolution tests were performed using the United States Pharmacopeia (USP) paddle II method in enzyme-free simulated gastric fluid (pH 1.2) for 2 h. Microenvironmental pH (pH(M)) was examined potentiometrically by using a surface pH electrode. Dissolution rate of SD incorporating Na2CO3 was drastically increased. The differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) data indicated that crystalline structure of VAL in SD was transformed to amorphous form by the addition of alkalizers but could not explain the differences in the dissolution rates. The molecular interaction between VAL and Na2CO3 was observed in the Fourier transform infrared spectroscopy (FT-IR) spectra by the shift of C=O band from 1732 to 1719 cm⁻¹ and the disappearance of carbonyl group at 1598 cm⁻¹. Furthermore, Na2CO3 efficiently modulated pH(M) by providing a favorable microenvironment for drug dissolution. A combination of SD method and use of alkalizer is a promising approach to modulate release rate of poorly water-soluble and ionizable drug with an aid of changes of drug crystallinity, molecular interaction and pH(M).

Design and mechanism of on-off pulsed drug release using nonenteric polymeric systems via pH modulation.

The aim was to design a pH-sensitive pulsatile drug delivery system that allows for an on-off pulsed release of a drug using polyacrylic acid (PAA) blended with ethyl cellulose (EC) in different ratios. PAA, a polyelectrolyte polymer, exhibits a highly coiled conformation at low pH but a highly extended structure at high pH. Fumaric acid, which is an internal acidifying agent, was incorporated into the hydroxypropyl methylcellulose-based core tablets to create an acidic microenvironmental pH (pH(M)). The concentration of fumaric acid inside the core tablet and the ratio of PAA/EC in the coating layer were very crucial in modulating drug release behaviors. When the fumaric acid was retained in the core tablet, it gave a more acidic pH(M), so that the PAA was kept in a highly coiled state in the coated film, which hindered drug release ("off" release pattern). Interestingly, the release profiles of the drug and fumaric acid from coated tablets showed the on-off pulsed pattern upon dissolution. Imaging analyses using scanning electron microscopy, near-infrared imaging, confocal laser scanning microscopy, and Fourier transform infrared spectroscopy confirmed this on-off release behavior of the drug and fumaric acid from coated tablets.

Fattigation-platform theranostic nanoparticles for cancer therapy.

A new conceptual nanoparticle consisting of a silica-coated iron oxide magnetic core and a fattigation-based biocompatible shell with oleic acid and hydrophilic protein (gelatin). The prepared particle can be a useful theranostics platform material for diagnostic imaging and as a drug delivery system. Oleic acid and gelatin were conjugated on the silica-coated magnetic nanoparticle surface to provide three primary functionalities: 1) enhancing biocompatibility and solubility in aqueous solution and providing the ability to incorporate hydrophobic chemical drugs into the shell for delivery, 2) improving treatment-response magnetic monitoring as a diagnostic agent with low nanotoxicity, and 3) increasing anticancer efficacy owing to the controlled release of the incorporated drug in cells and in an animal model. We prepared magnetic-silica nanoparticles with super-paramagnetic properties, which are utilized as a T2-weighted magnetic resonance imaging agent. After formation of an oleic acid-gelatin shell, the prepared materials exhibited high loading capacity for a hydrophobic anticancer drug (paclitaxel). Our particle platform system exhibited higher therapeutic efficacy and lower toxicological effects in vitro and in an in vivo cancer model than a clinically available chemo-drug (Taxol®). Our findings strongly suggest that this nanoparticle system can serve as a platform for cancer therapy by the incorporation of chemical drugs.

Transforming doxorubicin into a cancer stem cell killer via EpCAM aptamer-mediated delivery.

Chemotherapy-resistant cancer stem cells (CSCs) are a major obstacle to the effective treatment of many forms of cancer. To overcome CSC chemo-resistance, we developed a novel system by conjugating a CSC-targeting EpCAM aptamer with doxorubicin (Apt-DOX) to eliminate CSCs. Incubation of Apt-DOX with colorectal cancer cells resulted in high concentration and prolonged retention of DOX in the nuclei. Treatment of tumour-bearing xenograft mice with Apt-DOX resulted in at least 3-fold more inhibition of tumour growth and longer survival as well as a 30-fold lower frequency of CSC and a prolonged longer tumourigenic latency compared with those receiving the same dose of free DOX. Our data demonstrate that a CSC-targeting aptamer is able to transform a conventional chemotherapeutic agent into a CSC-killer to overcome drug resistance in solid tumours.

Nanoparticulate Drug Delivery to Colorectal Cancer: Formulation Strategies and Surface Engineering.

The evolution of polymer-based nanoparticle as a drug delivery carrier has greatly contributed to the development of advanced nano and micro-medicine in the past few decades. The polymer-based nanoparticles of biodegradable and biocompatible polymers such as poly (lactide-co-glycolide) and chitosan which have been approved by Food & Drug Administration and/or European Medicine Agency can particularly facilitate the maintaining of specific properties for a real transition from laboratory to the clinical oral and parental administration. This review presents an overview of the strategies of preparing polymeric nanoparticles and using them for targeting colorectal cancer. Theranostics and surface engineering aspects of nanoparticle design in colonic cancer delivery are also highlighted.

Perspectives of Engineered Marine Derived Polymers for Biomedical Nanoparticles.

Marine environment exhibits an enormous diversity of organisms which contains an abundant source of polysaccharides. As polymer matrix carriers, marine-based polymers possess several valuable properties including high stability, non-toxicity, hydrophilicity, biodegradability, with low production cost. Despite notable biological activities of these natural polymers, there are certain limitations in exploring their functions in applications of nano-sized drug delivery systems. The review aims to demonstrate exceptional characteristics of marine-based polymers including fucoidan, alginate, carrageenan, hyaluronic acid, chondroitin sulfate, and chitosan as well as provide perspectives of current publications on their nanoparticle formulations for biomedical applications.

Hydrophilic-hydrophobic polymer blend for modulation of crystalline changes and molecular interactions in solid dispersion.

This research study aimed to develop a new strategy for using a polymer blend in solid dispersion (SD) for dissolution enhancement of poorly water-soluble drugs. SDs with different blends of hydrophilic-hydrophobic polymers (zein/hydroxypropyl methylcellulose - zein/HPMC) were prepared using spray drying to modulate the drug crystal and polymer-drug interactions in SDs. Physicochemical characterizations, including power X-ray diffraction and Fourier transform infrared spectroscopy, were performed to elucidate the roles of the blends in SDs. Although hydrophobic polymers played a key role in changing the model drug from a crystal to an amorphous state, the dissolution rate was limited due to the wetting property. Fortunately, the hydrophilic-hydrophobic blend not only reduced the drug crystallinity but also resulted in a hydrogen bonding interaction between the drugs and the polymer for a dissolution rate improvement. This work may contribute to a new generation of solid dispersion using a blend of hydrophilic-hydrophobic polymers for an effective dissolution enhancement of poorly water-soluble drugs.

Design of sustained release tablet containing fucoidan.

The study introduced a new therapeutic agent, fucoidan, which can offer potential medical treatments including anti-inflammatory and anti-coagulant activities, as well as anti-proliferative effects on cancer cells. Fucoidan was included in sustained release formulations expected for an effective plasma drug concentration for approximately 24 h. The matrices based on the two polymers hydroxypropyl methycellulose (HPMC) and polyethylene oxide (PEO) were prepared with various ratios between the polymers and fucoidan. The dissolution profiles of various matrix tablets performed in enzyme-free simulated intestinal fluid (pH 6.8) for 24 h indicated a higher potential of PEO-based matrix tablets in sustaining release of fucoidan. The swelling and erosion of the tablets were also characterized to elucidate the difference among those dissolution profiles.

Development of a modified - solid dispersion in an uncommon approach of melting method facilitating properties of a swellable polymer to enhance drug dissolution.

The study aimed to develop a modified-solid dispersion method using a swellable hydrophilic polymers accompanied by a conventional carrier to enhance the dissolution of a drug that possesses poor water solubility. Two swellable polymers (hydroxypropyl methylcellulose and polyethylene oxide) were swelled in melted polyethylene glycol 6000 (PEG 6000) in different ratios and under different conditions. The type, amount, and, especially, incorporation method of the swellable polymers were crucial factors affecting the dissolution rate, crystallinity, and molecular interaction of the drug. Interestingly, the method in which the swellable polymer was thoroughly mixed with the melted PEG 6000 as the first step was more effective in increasing drug dissolution than the method in which the drug was introduced to the melted PEG 6000 followed by the addition of the swellable polymer. This system has potential for controlling drug release due to high swelling capabilities of these polymers. Therefore, the current study can be considered to be a promising model for formulations of controlled release systems containing solid dispersions.

Novel multifunctional biocompatible gelatin-oleic acid conjugate: self-assembled nanoparticles for drug delivery.

In this work, a novel, biocompatible conjugates of gelatin and oleic acid (GOC) were synthesized by a novel aqueous solvent-based method that overcame challenges of completely contrary solubility between gelatin and oleic acid (OA). The GO nanoparticles (GONs) and Paclitaxel encapsulated nanoparticles (PTX-GON) were prepared by self-assembly in water. These nanoparticles (NPs) were then conjugated with folic acid (FA) for targeting cervical cancer cells (Hela cells) and were characterized for their various physicochemical and pharmaceutical properties. Fourier transform infrared spectroscopy (FT-IR) and 1H NMR studies indicated the successful synthesis of GOC which showed low critical aggregation concentration in water (0.015 mg/ml). All NPs were stable in human blood serum and their mean diameters were below 300 nm suitable for passive targeting. Powder X-ray diffraction (PXRD) diffractograms showed the reduction in drug crystallinity and hence, leading to the solubility enhancement of PTX. The release of PTX from both PTX-GON and FA conjugated PTX-GON (PTX-FA-GON) was controlled for a long time. The cytotoxicity results demonstrated great advantages of PTX-FA-GON and PTX-GON over the conventional dosage form of pacliaxel (Taxol). These results, therefore, indicate that GOC is a promising material to prepare drug encapsulated NP as a controlled delivery system and PTX-FA-GON is a potential targeted delivery system for cancer therapy.

Physical properties and in vivo bioavailability in human volunteers of isradipine using controlled release matrix tablet containing self-emulsifying solid dispersion.

Poorly water-soluble drug with a short half-life such as isradipine (IDP) offer challenges in the controlled release formulation because of low dissolution rate and poor bioavailability. Self-emulsifying solid dispersions (SESD) of IDP consisted of surfactant and fatty acid in poloxamer 407 (POX 407) as a carrier and were manufactured by the melting method. Then, controlled release HPMC matrix tablet containing SESD were prepared via direct compression. The dissolution behaviors and in vivo bioavailability of controlled release matrix tablet in healthy human volunteers were investigated. The physical properties of solid dispersion were also examined using differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). It was shown that structure of IDP was amorphous in the solid dispersion. The dissolution rate of IDP from SESD was markedly enhanced because of increased solubility and wetting effect. Controlled release HPMC matrix tablets containing SESD released drug in a controlled manner and were stable during storage over 3 months at 40 °C/75% RH. Furthermore, the tablet containing 5mg IDP SESD showed significantly increased oral bioavailability and extended plasma concentration compared with the marketed 5 mg Dynacirc(®) capsule. A combined method of solid dispersion and controlled release technology could provide versatile dosage formulations containing IDP with poor water solubility and short half-life.

Roles of MgO release from polyethylene glycol 6000-based solid dispersions on microenvironmental pH, enhanced dissolution and reduced gastrointestinal damage of telmisartan.

The roles of magnesium oxide (MgO) release from solid dispersions (SDs) in simulated gastric fluid (SGF), simulated intestinal fluid (SIF) and water were investigated to elucidate the enhanced dissolution and reduced intestinal damages of telmisartan as a model drug. The polyethylene glycol 6000 (PEG 6000) was used to prepare the SDs. Three SDs were prepared: SD1 (PEG, MgO, TEL), SD2 (PEG 6000, TEL), SD3 (MgO, TEL). The physical mixture (PM) consisting of SD2 and MgO was also prepared. A binary SD without MgO (SD2) was also prepared for comparison in microenvironmental pH (pH(M)) modulation. The faster MgO released, the less control of pH(M) and the less enhanced dissolution of TEL were in consequences. SD3 increased dissolution in SIF and water (about 67%). Interestingly, ternary SD1 showed almost complete dissolution in all three media but dissolution of PM was the lowest due to the fast release of MgO and poor modulation of pH(M). MgO did not change the drug crystallinity but did have a strong molecular interaction with the drug. Additionally, the SD3-bearing tablet quickly increased pH(M) but then gradually decreased due to faster release of MgO while the SD1-bearing tablet gradually increased pH(M) at all fractional dimensions of the tablet by the MgO slowly released. The pH(M) of PM-bearing tablets was not varied as a function of time. Thus, the MgO-bearing SD1 also minimized gastrointestinal tissue damage caused by the model drug.

Investigation of physicochemical factors affecting the stability of a pH-modulated solid dispersion and a tablet during storage.

The stability of solid dispersions (SD) during storage is of concern. We prepared the pH-modulated SD (pSD) and compressed tablets consisting of polyethylene glycol (PEG) 6000 as a carrier, drug and MgO (alkalizer). Telmisartan (TEL), an ionizable poorly water-soluble drug, was chosen as a model drug. The changes in physicochemical factors such as the dissolution rate, drug crystallinity, microenvironmental pH (pH(M)) and intermolecular interactions of the pSD and the tablets were investigated over 3 months under different temperature and relative humidity (RH) conditions: refrigerator (5-8 °C), 25 °C/32% RH, 25 °C/55% RH, 25 °C/75% RH, 40°C/32% RH, 40 °C/55% RH, and 40 °C/75% RH. Differential scanning calorimetry (DSC) analysis of all samples revealed no distinct changes in the drug melting point. In contrast, powder X-ray diffraction (PXRD) diffractograms revealed that samples stored at 40 °C/75% RH for 1 month, 25 °C/75% RH for 3 months and 40 °C at all humidity conditions for 3 months showed gradual recrystallization of the drug. Fourier transform infrared (FTIR) spectra indicated a reduced intensity of intermolecular interactions between TEL and MgO in the pSD and tablet. The pH(M) also gradually decreased. These altered physicochemical factors under the stressed conditions resulted in decreased dissolution profiles in intestinal fluid (pH 6.8). In contrast, the dissolution rate in gastric fluid (pH 1.2) was almost unchanged because of the high intrinsic solubility of TEL at this pH.

Physicochemical principles of controlled release solid dispersion containing a poorly water-soluble drug.

BACKGROUND: The aim of this study was to investigate the physicochemical properties of polyethylene oxide (PEO)-based controlled release solid dispersions (CR-SDs) containing aceclofenac, Gelucire 44/14, poloxamer 407 and pH modifier (Na2CO3). RESULTS: The immediate release solid dispersions containing the pH modifier greatly enhanced the drug dissolution rate to approximately 100%, while the CR-SDs with PEO showed controlled release. A bigger droplet size and a higher surface charge for the CR-SDs were observed compared with the immediate release solid dispersions. The pH modifier played an important role in modulating the release rate of the drug through changes in the drug crystallinity and the hydrogen-bonding interaction, as well as the microenvironmental pH. Near-infrared images revealed a modulation of the PEO concentration to preserve the pH modifier within the system for controlled release of the drug. CONCLUSION: The dissolution process of PEO-based solid dispersions containing a water-insoluble drug was governed by the changing net effect of the microenvironmental pH, the surface charge, the particle size and the release rate of the pH modifier, as well as the function of PEO in controlling drug release.

Dissolution-modulating mechanism of alkalizers and polymers in a nanoemulsifying solid dispersion containing ionizable and poorly water-soluble drug.

We investigated the dissolution-modulating mechanism of alkalizers and polymers in nanoemulsifying Gelucire 44/14 (GUC)-based solid dispersions (SDs) for controlled release. Aceclofenac (AFC), an ionizable and poorly water-soluble drug, was chosen because of its extremely low solubility at low pH. Nanoemulsifying SD systems containing alkalizers and/or polymers were prepared by the melting method. Drug crystallinity, microenvironmental pH (pH(M)), dissolution rate, and droplet size in the media from nanoemulsifying SD were then characterized. Ternary SD containing alkalizers, mainly Na(2)CO(3) and NaHCO(3), enhanced the initial release rate of AFC in simulated gastric fluid (pH 1.2), but resulted in spring-like precipitation. However, adding a secondary polymer, Poloxamer 407, prevented precipitation in the quaternary SD system. Poloxamer 407 and alkalizer (Na(2)CO(3)) facilitated nanoemulsion formation (80-140 nm) with a smaller droplet size in a medium of pH 1.2 as visualized by TEM. The surface and inner pH(M) were also modulated by the alkalizers, but not by the polymers. The drug's crystalline structure was further changed to partially or almost amorphous form by the alkalizers and polymers in SD as characterized by instrumental analysis. The synergistic effects of alkalizers and secondary polymers in SD on reduction of drug crystallinity and modulation of pH(M) via molecular interactions could modulate dissolution rates of ionizable and poorly water-soluble model drug without spring-like precipitation by providing more favorable nanoemulsion-forming environment.

Modulation of microenvironmental pH and crystallinity of ionizable telmisartan using alkalizers in solid dispersions for controlled release.

The present work is an original evaluation of the microenvironmental pH (pH(M)) and crystallinity of an ionizable drug in order to enhance its dissolution using alkalizers in polyethylene glycol 6000 (PEG 6000) based solid dispersions (SDs). Telmisartan (TEL) was chosen as a model drug due to its poor and pH-dependent water solubility. The nine alkalizers used to modify the pH of TEL were MgO, NaOH, KOH, Na2CO3, NaHCO, bentonite, Na2HPO4, K2HPO4 and arginine. MgO, NaOH, KOH and Na2CO3 in the SD system significantly increased the drug dissolution rate in intestinal fluid (pH 6.8) and water. Modulation of pH(M) was clearly observed as a function of time at different fractional dimensions of tablet. Structural change in drug crystallinity to an amorphous form was also a contributing factor based on differential scanning calorimetry (DSC) thermograms and powder X-ray diffraction (PXRD) patterns. The drug frequency of the CO band decreased and the O-H broad band in the Fourier transform infrared (FTIR) spectra disappeared when these alkalizers were added. It was evident that the alkalizers in PEG 6000 based SDs synergistically enhanced dissolution of TEL not only by modulating pH(M) but also by changing drug crystallinity to an amorphous form via molecular interactions.