The role of the carrier in the formulation of pharmaceutical solid dispersions. Part II: amorphous carriers

Preformulation Studies and Enabling Formulation Selection for an Insoluble Compound at Preclinical Stage-From In Vitro, In Silico to In Vivo

The objective of this work was to identify an enabling formulation for an insoluble compound ZL006 with potency of boosting leukocytes after chemotherapy. The low oral bioavailability (<1%) of its conventional suspension was the hurdle for the preclinical evaluation via oral administration. Preformulation studies including physical form screening and physicochemical properties determination were performed. Polymorphism was observed, and the more thermodynamically stable form was selected for further studies. ZL006 showed certain supersaturation solubility, although the thermodynamic solubility in FaSSIF was low, which indicated the supersaturating formulation might work. Parameter sensitivity analysis by in silico simulation predicted that in vivo exposure was sensitive to solubility, while particle size reduction would have limited impact on exposure. Based on in silico prediction and the understanding of the molecule from preformulation studies, solid dispersion approach was selected. A preliminary dose escalation pharmacokinetic study in rats demonstrated that in vivo exposure increased in dose-proportional manner from 12.5 mg/kg to 50 mg/kg with around 50% oral bioavailability after oral dosing of the solid dispersion. This work showed that combination of preformulation studies and in silico simulation could efficiently guide the selection of enabling formulation, which could save resources at preclinical stage.

Spray Congealing: An Emerging Technology to Prepare Solid Dispersions with Enhanced Oral Bioavailability of Poorly Water Soluble Drugs

The low and variable oral bioavailability of poorly water soluble drugs remains a major concern for the pharmaceutical industry. Spray congealing is an emerging technology for the production of solid dispersion to enhance the bioavailability of poorly soluble drugs by using low-melting hydrophilic excipients. The main advantages are the absence of solvents and the possibility to obtain spherical free-flowing microparticles (MPs) by a relatively inexpensive, simple, and one-step process. This review aims to fully describe the composition, structure, physico-chemical properties, and characterization techniques of spray congealed-formulations. Moreover, the influence of these properties on the MPs performance in terms of solubility and dissolution enhancement are examined. Following, an overview of the different spray congealed systems developed to increase the oral drug bioavailability is provided, with a focus on the mechanisms underpinning the bioavailability enhancement. Finally, this work gives specific insights on the main factors to be considered for the rational formulation, manufacturing, and characterization of spray congealed solid dispersions.

A comprehensive understanding of lowly-hydrolyzed polyvinyl alcohol-based ternary solid dispersions with the use of a combined mixture-process design

We recently reported lowly hydrolyzed polyvinyl alcohol (L-PVA, 70-74% hydrolyzed, about 580 polymerized, JR-05) as a promising matrix for hot-melt extrusion (HME) due to its unique micelle formation ability compared to the most commonly used PVA (87-89% hydrolyzed, about 580 polymerized). In the present study, we focused on the effect of composition [indomethacin (IND), L-PVA, sorbitol] and process parameters (temperature and screw speed) on each response, i.e. processing torque, and physicochemical properties such as residual crystallinity, residual ratio, and area under the dissolution curve (AUDC) in supersaturated solution using a HME by applying the design of experiment (DoE) approach. To overcome the poor processability of L-PVA, given its semicrystalline nature, we applied sorbitol as a plasticizer and systematically and simultaneously evaluated its influence on the outputs based on the mixture design combined with process factors. Few studies have focused on comprehensive evaluation of the composition and HME process conditions because obtaining a design space requires numerous experiments. We found that incorporating sorbitol into the L-PVA greatly improved the processing torque. However, sorbitol negatively influenced the degree of residual crystallinity and the AUDC of IND. Lastly, we established a laboratory-scale design space that could achieve high supersaturation and ensure adequate miscibility between each component, using an acceptable processing torque for HME, by applying the minimum amount of sorbitol. These fundamental results suggest that sorbitol maximizes the potency of L-PVA as a carrier in HME.

Impact of phase separation morphology on release mechanism of amorphous solid dispersions

Amorphous solid dispersions (ASDs) can phase separate in the gel phase during dissolution, lowering the chemical potential and thus the driving force for drug release. The purpose of this study is to explore the connection between amorphous phase separation in the hydrated ASD and its resulting release rate. Poorly soluble model compounds - indomethacin (IND) and ritonavir (RTV) - were formulated as ASDs using PVP as carrier. Rotating disk dissolution studies with varying drug loading levels of IND-PVP and RTV-PVP showed that the drug release was fastest at an intermediate drug loading level. This was in part due to faster erosion of the ASD at lower drug loading levels. More interestingly, at low drug loading levels, PVP and the drug co-eroded, while at high drug loading levels, PVP was released preferentially. In the case of RTV-PVP, the loading level corresponding to this transition was correlated with the change in phase separation morphology as probed by confocal fluorescence imaging studies. At low drug loading levels, the hydrophobic domains were discrete domains while at high drug loading levels, hydrophobic domains were continuous. Our results suggest that at low drug loadings, release is mediated by erosion of the polymer along with embedded drug rich droplets, whereas at high drug loadings, formation of a drug-rich domain continuous morphology leads to preferential release of the polymer-rich domains. The transition from hydrophobic discrete to hydrophobic continuous morphology occurs at the percolation threshold. We discuss the two mechanisms of phase separation and its impact on the drug release from ASDs in the context of the ternary phase diagram.

Solid dispersion technology as a strategy to improve the bioavailability of poorly soluble drugs

Over the last half-century, solid dispersions (SDs) have been intensively investigated as a strategy to improve drugs solubility and dissolution rate, enhancing oral bioavailability. In this review, an overview of the state of the art of SDs technology is presented, focusing on their classification, the main preparation methods, the limitations associated with their instability, and the marketed products. To fully take advantage of SDs potential, an improvement in their physical stability and the ability to prolong the supersaturation of the drug in gastrointestinal fluids is required, as well as a better scientific understanding of scale-up for defining a robust manufacturing process. Taking these limitations into account will contribute to increase the number of marketed pharmaceutical products based on SD technology.

Effect of preparation method on the surface properties and UV imaging of indomethacin solid dispersions

This work explores the use of UV imaging in solid dispersion systems. Solid dispersions are one of the common strategies used in improving the dissolution of poorly soluble drugs. Three manufacturing techniques (spray drying (SD), freeze drying (FD) and homogenising (HG)) are investigated. Differential Scanning Calorimetry (DSC) and X-Ray Powder Diffraction (XRPD) was used in characterising the solid dispersions. Advanced imaging was implemented to give an insight into how these solid dispersions performed. The DSC and XRPD results showed that all three methods and the various ratios studied produced amorphous solid dispersions. Ultra-Violet (UV) imaging of the pseudo Intrinsic Dissolution Rate (IDR) deduced only two samples to have superior pseudo IDR values to the IDR of the parent drug indomethacin (INDO). The whole dose imaging of the capsule formulation however showed all the samples (SD, FD and HG) to have superior dissolution to that of INDO which was in contrast to the IDR results. The UV images obtained from the determination of the pseudo IDR also showed a phenomenon the authors are reporting for the first time where increased polymer (Soluplus) content produced "web-like" strands that migrated to the top of the quartz cell which may have been responsible for the low pseudo IDR values. The authors also report for the first time using this UV imaging technique, the tip of a capsule coming off for drug to go into solution. The area under the curve suggested the best five samples dissolution wise to be 1:3 SD > 1:1 HG > 1:1 SD > 1:3 FD > 1:3 HG meaning a ratio of INDO to SOL in these dispersion of up to 1:3 being sufficient to produce significant dissolution increases. The developed interfacial (surface) area ratio (Sdr) highlighted how the surface area of the IDR compacts varied between the batches, in particular highlighting larger surface area gains for the FD and HG compacts. A choice of instrumentation/techniques to use in making solid dispersions may well come down to cost or instrument availability for a formulator as all three techniques were successful in improving the dissolution of indomethacin. This work thus highlights the importance of having both complimentary IDR and whole dosage imaging techniques in giving a better understanding of solid dispersion systems.

Molecular modelling and simulation of fusion-based amorphous drug dispersions in polymer/plasticizer blends

A realistic molecular description of amorphous drug-polymer-plasticizer matrices, suitable for the preparation of amorphous solid dispersions (ASDs) with the aid of fusion-based techniques, was evaluated. Specifically, the incorporation of two model drugs (i.e. ibuprofen, IBU, and carbamazepine, CBZ) having substantially different thermal properties and glass forming ability, on the molecular representation of polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer (SOL)/polyethylene glycol (PEG, working as a plasticizer) molecular and thermal properties were evaluated with the aid of classical molecular dynamics (MD) and docking simulations. Results showed good agreement between molecular modelling estimations and experimentally determined properties. Specifically, the computed T_g values that resulted from MD simulations for IBU-SOL/PEG and CBZ-SOL/PEG (53.8 and 54.2 °C, respectively) were in reasonable agreement with the corresponding values resulting from differential scanning calorimetry (DSC) measurements (49.8 and 50.1 °C), while both molecular modelling and experimental obtained results suggested miscibility among system components. Additionally, interactions between CBZ and SOL observed during MD simulations were verified by FTIR analysis, while MD simulations of the hydration process suggested strong molecular interactions between IBU-SOL and CBZ-SOL.

Effect of Polymer Hydrophobicity on the Stability of Amorphous Solid Dispersions and Supersaturated Solutions of a Hydrophobic Pharmaceutical

Amorphous solid dispersions of pharmaceuticals often show improved solubility over crystalline forms. However, the crystallization of amorphous solid dispersions during storage, or from elevated supersaturation once dissolved, compromise the solubility advantage of delivery in the amorphous phase. To combat this phenomenon, polymer additives are often included in solid dispersions to inhibit crystallization; however, the optimal properties for polymer to stabilize against crystallization are not fully understood, and furthermore, it is not known how inhibition of precipitation from solution is related to the propensity of a polymer to inhibit crystallization from the amorphous phase. Here, polymers of varied hydrophobicity are employed as crystallization inhibitors in supersaturated solutions and amorphous solid dispersions of the BCS Class II pharmaceutical ethenzamide to investigate the chemical features of polymer that lead to long-term stability for a hydrophobic pharmaceutical. A postpolymerization functionalization strategy was employed to alter the hydrophobicity of poly( N-hydroxyethyl acrylamide) without changing physical properties such as number-average chain length. It was found that supersaturation maintenance for ethenzamide is improved by increasing the hydrophobicity of dissolved polymer in aqueous solution. Furthermore, amorphous solid dispersions of ethenzamide containing a more hydrophobic polymer showed superior stability compared to those containing a less hydrophobic polymer. This trend of increasing polymer hydrophobicity leading to improved amorphous stability is interpreted by parsing the effects of water absorption in amorphous solid dispersions using intermolecular interaction strengths derived from global structural analysis. By comparing the structure-function relationships, which dictate stability in solution and amorphous solid dispersions, the effect of hydrophobicity can be broadly understood for the design of polymers to impart stability throughout the application of amorphous solid dispersions.

The Influence of Cellulosic Polymer's Variables on Dissolution/Solubility of Amorphous Felodipine and Crystallization Inhibition from a Supersaturated State

The collective impact of cellulosic polymers on the dissolution, solubility, and crystallization inhibition of amorphous active pharmaceutical ingredients (APIs) is still far from being adequately understood. The goal of this research was to explore the influence of cellulosic polymers and incubation conditions on enhancement of solubility and dissolution of amorphous felodipine, while inhibiting crystallization of the drug from a supersaturated state. Variables, including cellulosic polymer type, amount, ionic strength, and viscosity, were evaluated for effects on API dissolution/solubility and crystallization processes. Water-soluble cellulosic polymers, including HPMC E15, HPMC E5, HPMC K100-LV, L-HPC, and MC, were studied. All cellulosic polymers could extend API dissolution and solubility to various extents by delaying crystallization and prolonging supersaturation duration, with their effectiveness ranked from greatest to least as HPMC E15 > HPMC E5 > HPMC K100-LV > L-HPC > MC. Decreased polymer amount, lower ionic strength, or higher polymer viscosity tended to decrease dissolution/solubility and promote crystal growth to accelerate crystallization. HPMC E15 achieved greatest extended API dissolution and maintenance of supersaturation from a supersaturated state; this polymer thus had the greatest potential for maintaining sustainable API absorption within biologically relevant time frames.

Fast Dissolving of Ferulic Acid via Electrospun Ternary Amorphous Composites Produced by a Coaxial Process

Enhancing the dissolution of insoluble active ingredients comprises one of the most important issues in the pharmaceutical and biomaterial fields. Here, a third generation solid dispersion (3rd SD) of ferulic acid was designed and fabricated by a modified coaxial electrospinning process. A traditional second generation SD (2nd SD) was also prepared by common one-fluid blending electrospinning and was used as a control. With poly(vinyl alcohol) as the fiber matrix and polyvinylpyrrolidone K10 as an additive in the 3rd SDs, the two electrospinning processes were investigated. The prepared 2nd and 3rd SDs were subjected to a series of characterizations, including X-ray diffraction (XRD), scanning electron microscope (SEM), hydrophilicity and in vitro drug dissolving experiments. The results demonstrate that both SDs were monolithic nanocomposites and that the drugs were amorphously distributed within the matrix. However, the 3rd SDs had better morphology with smaller size, narrower size distribution, and smaller water contact angles than the 2nd SDs. Dissolution tests verified that the 3rd SDs could release their loaded cargoes within 60 s, which was over three times faster than the 2nd SDs. Therefore, a combined strategy based on the modified coaxial electrospinning and the logical selections of drug carriers is demonstrated for creating advanced biomaterials.

Amorphous solid dispersions of darunavir: Comparison between spray drying and electrospraying

The interest in using electrospraying as a manufacturing method for amorphous solid dispersions has grown remarkably. However, the impact of formulation and process parameters needs further clarification. In this study, amorphous solid dispersions of darunavir and hydroxypropyl methylcellulose (HPMC), hydroxypropyl methylcellulose acetate succinate (HPMC AS) and polyvinylpyrrolidone K-30 (PVP) were prepared with electrospraying and spray drying, in order to compare both solvent based manufacturing techniques. Our results revealed that electrospraying was as successful as spray drying. The formulations prepared with the two methods were amorphous and had similar characteristics concerning the residual solvent and drug release. Although differences in the morphology and the particle size distributions were observed, this was not reflected in the pharmaceutical performance of the formulations. Electrosprayed amorphous solid dispersions made up of darunavir and PVP were studied in more detail by means of a full factorial experimental design. The impact of two process and two formulation parameters on the properties of the amorphous solid dispersions was determined. The feed flow rate had a significant effect on the diameter and morphology of the particles whereas the tip-to-collector distance had no significant impact within the tested range. The drug loading influenced the homogeneity and the residual solvent, and the total solids concentration had an impact on the homogeneity and the morphology.

Preparation, characterizations and anti-pollutant activity of 7,3',4'-trihydroxyisoflavone nanoparticles in particulate matter-induced HaCaT keratinocytes

Background

7,3',4'-Trihydroxyisoflavone (734THI), a secondary metabolite derived from daidzein in soybean, possesses several biological activities, including antioxidant, skin whitening and anti-atopic dermatitis properties, but the poor aqueous solubility of 734THI has limited its application in medicine and cosmetic industry.

Methods

The aim of the present study was to improve the physicochemical properties of 734THI using planetary ball mill preparation under a solvent-free process to improve its solubility and anti-pollutant activity.

Results

734THI nanoparticle powder (734THIN) was successfully prepared by the planetary ball mill technique using polyvinylpyrrolidone K30 as the excipient. 734THIN effectively increased the aqueous solubility and cellular uptake of 734THI by improving its physicochemical properties, including particle size reduction, crystalline-amorphous transformation and intermolecular hydrogen bonding with polyvinylpyrrolidone K30. In addition, 734THIN inhibited the overexpression of COX-2 and MMP-9 by downregulating MAPK pathway signaling in particulate matter-exposed HaCaT keratinocytes, while raw 734THI in PBS with low aqueous solubility did not show any anti-inflammatory or antiaging activity.

Conclusion

734THIN may be used as an additive in anti-pollutant skin care products for preventing particulate matter-induced inflammation and aging in skin.

Physical Stability of Amorphous Solid Dispersions: a Physicochemical Perspective with Thermodynamic, Kinetic and Environmental Aspects

PURPOSE

Amorphous solid dispersions (ASDs) have been widely used in the pharmaceutical industry for solubility enhancementof poorly water-soluble drugs. The physical stability, however, remainsone of the most challenging issues for the formulation development.Many factors can affect the physical stability via different mechanisms, and therefore an in-depth understanding on these factors isrequired.

METHODS

In this review, we intend to summarize the physical stability of ASDsfrom a physicochemical perspective whereby factors that can influence the physical stability areclassified into thermodynamic, kinetic and environmental aspects.

RESULTS

The drug-polymer miscibility and solubility are consideredas the main thermodynamicfactors which may determine the spontaneity of the occurrence of the physical instabilityof ASDs. Glass-transition temperature,molecular mobility, manufacturing process,physical stabilityof amorphous drugs, and drug-polymerinteractionsareconsideredas the kinetic factors which areassociated with the kinetic stability of ASDs on aging. Storage conditions including temperature and humidity could significantly affect the thermodynamicand kineticstabilityof ASDs.

CONCLUSION

When designing amorphous solid dispersions, it isrecommended that these thermodynamic, kinetic and environmental aspects should be completely investigatedand compared to establish rationale formulations for amorphous solid dispersions with high physical stability.

Enhanced delivery of fixed-dose combination of synergistic antichagasic agents posaconazole-benznidazole based on amorphous solid dispersions

Posaconazole (PCZ) and benznidazole (BNZ) are known to show synergetic effect in treating the acute and chronic phases of Chagas disease, a neglected parasitic disease. However, as both compounds are poorly water soluble, the development of amorphous solid dispersions (ASDs) of a PCZ/BNZ fixed-dose combination in a water-soluble polymer becomes an attractive option to increase their apparent solubility and dissolution rate, potentially improving their oral bioavailability. The initial approach was to explore solvent evaporated solid dispertion (SD) systems for a PCZ/BNZ 50:50 (wt%) combination at several total drug loading levels (from SD with 10% to 50% drug loading) in water-soluble carriers, including polyvinylpyrrolidone (PVP K-30) and vinylpyrrolidone-vinyl acetate copolymer (PVPVA 64). Based on comparison of non-sink in vitro dissolution performance, ASD systems based on PVPVA was identified as the most effective carrier for a 50:50 (w/w %) fixed-dose combination of PCZ/BNZ to increase their apparent solubility and dissolution rate, mainly at 10% drug loading, which shows more expressive values of area under the curve (AUC) (7336.04 ± 3.77 min.μL/mL for PCZ and 15,795.02 ± 7.29 min.μL/mL for BNZ). Further characterization with polarized microscopy, powder X-ray diffraction, and thermal analysis reveals that there exists a threshold drug loading level at about 30% PCZ/BNZ, below which ASDs are obtained and above which a certain degree of crystallinity tends to result. Moreover, infrared spectroscopic analysis reveals the lack of hydrogen bonding interactions between the drugs (PCZ and BNZ) and the polymer (PVPVA) in the ASD, this is also confirmed through molecular dynamics simulations. The molecular modeling results further show that even in the absence of meaningful hydrogen bonding interactions, there is a greater tendency for PVPVA to interact preferentially with PCZ and BNZ through electrostatic interactions thereby contributing to the stability of the system. Thus, the present SD system has the advantage of presenting a fixed-dese combination of two synergistic antichagasic agents PCZ and BNZ together in amorphous form stabilized in the PVPVA matrix with enhanced dissolution, potentially improving their bioavailability and therapeutic activity in treating Chagas disease.

New Strategies for Improving the Development and Performance of Amorphous Solid Dispersions

The understanding of amorphous solid dispersions has grown significantly in the past decade. This is evident from the number of approved commercial amorphous solid dispersion products. While amorphous formulation is considered an enabling technology, it has become the norm for formulating poorly soluble compounds. Despite this success, improvements can still be made that enable early development formulation decisions, to develop a rationale for selecting a manufacturing process, to overcome degradation and phase separation during processing, to help achieve physical stability during storage, and to optimize dissolution behavior. The purpose of this literature review is to present recently reported strategies for improving the development and performance of ASDs. The benefits and limitations of each strategy as well as recent relevant case studies will be presented in this review. The strategies are presented from three different aspects: (a) prediction techniques that enable formulation decisions, (b) manufacturing considerations that help produce physically and chemically stable ASDs, and

Microstructure of Pharmaceutical Semicrystalline Dispersions: The Significance of Polymer Conformation

The microstructure of pharmaceutical semicrystalline solid dispersions has attracted extensive attention due to its complexity that might result in the diversity in physical stability, dissolution behavior, and pharmaceutical performance of the systems. Numerous factors have been reported that dictate the microstructure of semicrystalline dispersions. Nevertheless, the importance of the complicated conformation of the polymer has never been elucidated. In this study, we investigate the microstructure of dispersions of polyethylene glycol and active pharmaceutical ingredients by small-angle X-ray scattering and high performance differential scanning calorimetry. Polyethylene glycol with molecular weight of 2000 g/mol (PEG2000) and 6000 g/mol (PEG6000) exhibited remarkable discrepancy in the lamellar periodicity in dispersions with APIs which was attributed to the differences in their folding behavior. The long period of PEG2000 always decreased upon aging-induced exclusion of APIs from the interlamellar region of extended chain crystals whereas the periodicity of PEG6000 may decrease or increase during storage as a consequence of the competition between the drug segregation and the lamellar thickening from nonintegral-folded into integral-folded chain crystals. These processes were in turn significantly influenced by the crystallization tendency of the pharmaceutical compounds, drug-polymer interactions, as well as the dispersion composition and crystallization temperature. This study highlights the significance of the polymer conformation on the microstructure of semicrystalline systems that is critical for the preparation of solid dispersions with consistent and reproducible quality.

Understanding the generation and maintenance of supersaturation during the dissolution of amorphous solid dispersions using modulated DSC and 1H NMR

In this study, the dissolution behaviour of dipyridamole (DPM) and cinnarizine (CNZ) spray-dried amorphous solid dispersions (ASDs) using polyvinyl pyrrolidone (PVP) and polyacrylic acid (PAA) as a carrier matrix were evaluated and compared. The drug concentrations achieved from the dissolution of PVP and PAA solid dispersions were significantly greater than the equilibrium solubility of crystalline DPM and CNZ in phosphate buffer pH 6.8 (PBS 6.8). The maximum drug concentration achieved by dissolution of PVP and PAA solid dispersions did not exceed the theoretically calculated apparent solubility of amorphous DPM and CNZ. However, the degree of supersaturation of DPM and CNZ increased considerably as the polymer weight fraction within the solid dispersion increased. In addition, the supersaturation profile of DPM and CNZ were studied in the presence and absence of the polymers. PAA was found to maintain a higher level of supersaturation compared to PVP. The enhanced drug solution concentration following dissolution of ASDs can be attributed to the reduced crystal growth rates of DPM and CNZ at an equivalent supersaturation. We have also shown that, for drugs having high crystallization tendency and weak drug-polymer interaction, the feasible way to increase dissolution might be increase the polymer weight fraction in the ASD. Solution ¹H NMR spectra were used to understand dissolution mechanism and to identify drug-polymer interaction. The change in electron densities of proton attached to different groups in DPM and CNZ suggested drug-polymer interaction in solution. The relative intensities of peak shift and nature of interaction between drug and polymer in different systems are different. These different effects suggest that DPM and CNZ interacts in a different way with PVP and PAA in solution which goes some way towards explaining the different polymeric effect, particularly in terms of inhibition of drug recrystallization and dissolution of DPM and CNZ ASDs. These results established that the different drug/polymer interactions in the solid state and in solution give rise to the variation in dissolution profile observed for different systems.

Influence of PVP molecular weight on the microwave assisted in situ amorphization of indomethacin

In situ amorphization is an approach that enables a phase transition of a crystalline drug to its amorphous form immediately prior to administration. In this study, three different polyvinylpyrrolidones (PVP K12, K17 and K25) were selected to investigate the influence of the molecular weight of the polymer on the degree of amorphization of the model drug indomethacin (IND) upon microwaving. Powder mixtures of crystalline IND and the respective PVP were compacted at 1:2 (w/w) IND:PVP ratios, stored at 54% RH and subsequently microwaved with a total energy input of 90 or 180kJ. After storage, all compacts had a similar moisture content (∼10% (w/w)). Upon microwaving with an energy input of 180kJ, 58±4% of IND in IND:PVP K12 compacts was amorphized, whereas 31±8% of IND was amorphized by an energy input of 90kJ. The drug stayed fully crystalline in all IND:PVP K17 and IND:PVP K25 compacts. After plasticization by moisture, PVP K12 reached a T_g below ambient temperature (16±2°C) indicating that the T_g of the plasticized polymer is a key factor for the success of in situ amorphization. DSC analysis showed that the amorphized drug was part of a ternary glass solution consisting of IND, PVP K12 and water. In dissolution tests, IND:PVP K12 compacts showed a delayed initial drug release due to a lack of compact disintegration, but reached a higher total drug release eventually. In summary, this study showed that the microwave assisted in situ amorphization was highly dependent on the T_g of the plasticized polymer.

Controlling the Release of Indomethacin from Glass Solutions Layered with a Rate Controlling Membrane Using Fluid-Bed Processing. Part 2: The Influence of Formulation Parameters on Drug Release

This study aimed to investigate the pharmaceutical performance of an indomethacin-polyvinylpyrrolidone (PVP) glass solution applied using fluid bed processing as a layer on inert sucrose spheres and subsequently top-coated with a release rate controlling membrane consisting of either ethyl cellulose or Eudragit RL. The implications of the addition of a pore former (PVP) and the coating medium (ethanol or water) on the diffusion and release behavior were also considered. In addition, the role of a charge interaction between drug and controlled release polymer on the release was investigated. Diffusion experiments pointed to the influence of pore former concentration, rate controlling polymer type, and coating solvent on the permeability of the controlled release membranes. This can be translated to drug release tests, which show the potential of diffusion tests as a preliminary screening test and that diffusion is the main factor influencing release. Drug release tests also showed the effect of coating layer thickness. A charge interaction between INDO and ERL was demonstrated, but this had no negative effect on drug release. The higher diffusion and release observed in ERL-based rate controlling membranes was explained by a higher hydrophilicity, compared to EC.