Characterization of amorphous solid dispersions

Pharmaceutical approaches for enhancing solubility and oral bioavailability of poorly soluble drugs

High solubility in water and physiological fluids is an indispensable requirement for the pharmacological efficacy of an active pharmaceutical ingredient. Indeed, it is well established that pharmaceutical substances exhibiting limited solubility in water are inclined towards diminished and inconsistent absorption following oral administration, consequently resulting in variability in therapeutic outcomes. The current advancements in combinatorial chemistry and pharmaceutical design have facilitated the creation of drug candidates characterized by increased lipophilicity, elevated molecular size, and reduced aqueous solubility. Undoubtedly, the issue of poorly water-soluble medications has been progressively escalating over recent years. Indeed, 40% of the top 200 oral medications marketed in the United States, 33% of drugs listed in the US pharmacopoeia, 75% of compounds under development and 90% of new chemical entities are insufficiently water-soluble compounds. In order to address this obstacle, formulation scientists employ a variety of approaches, encompassing both physical and chemical methods such as prodrug synthesis, salt formation, solid dispersions formation, hydrotropic substances utilization, solubilizing agents incorporation, cosolvent addition, polymorphism exploration, cocrystal creation, cyclodextrins complexation, lipid formulations, particle size reduction and nanoformulation techniques. Despite the utilization of these diverse approaches, the primary reason for the failure in new drug development persists as the poor aqueous solubility of pharmaceutical compounds. This paper, therefore, delves into the foundational principles that underpin the implementation of various formulation strategies, along with a discussion on the respective advantages and drawbacks associated with each approach. Additionally, a discourse is provided regarding methodological frameworks for making informed decisions on selecting an appropriate formulation strategy to effectively tackle the key challenges posed during the development of a poorly water-soluble drug candidate.

Application of Atomic Force Microscopy in the Development of Amorphous Solid Dispersion

Development of Amorphous Solid Dispersion (ASD) requires an in-depth characterization at different stages due to its structural and functional complexity. Various tools are conventionally used to investigate the processing, stability, and functionality of ASDs. However, many subtle features remain poorly understood due to lack of nano-scale characterization tools in routine practice. Atomic force microscopy (AFM) is a type of scanning probe microscopy, used for high resolution imaging and measuring features at the nano-scale. In recent years AFM has been used increasingly as a characterization tool in different areas of the development of ASD, including drug-polymer miscibility, localized characterization of the phase separated domains, lateral molecular diffusivity on ASD surface, crystallinity and crystallization kinetics in ASD, phase behavior of ASD during dissolution, and conformation of polymer during dissolution. In this review, we have highlighted the current applications of AFM in capturing critical aspects of stability and dissolution behavior of ASD. Potential areas of future development in this domain have been discussed.

Microfluidics-on-a-chip for designing celecoxib-based amorphous solid dispersions: when the process shapes the product

The fundamental idea underlying the use of amorphous solid dispersions (ASDs) is to make the most of the solubility advantage of the amorphous form of a drug. However, the drug stability becomes compromised due to the higher free energy and disorder of molecular packing in the amorphous phase, leading to crystallization. Polymers are used as a matrix to form a stable homogeneous amorphous system to overcome the stability concern. The present work aims to design ASD-based formulations under the umbrella of quality by design principles for improving oral drug bioavailability, using celecoxib (CXB) as a model drug. ASDs were prepared from selected polymers and tested both individually and in combinations, using various manufacturing techniques: high-shear homogenization, high-pressure homogenization, microfluidics-on-a-chip, and spray drying. The resulting dispersions were further optimized, resorting to a 32 full-factorial design, considering the drug:polymers ratio and the total solid content as variables. The formulated products were evaluated regarding analytical centrifugation and the influence of the different polymers on the intrinsic dissolution rate of the CXB-ASDs. Microfluidics-on-a-chip led to the amorphous status of the formulation. The in vitro evaluation demonstrated a remarkable 26-fold enhancement in the intrinsic dissolution rate, and the translation of this formulation into tablets as the final dosage form is consistent with the observed performance enhancement. These findings are supported by ex vivo assays, which exhibited a two-fold increase in permeability compared to pure CXB. This study tackles the bioavailability hurdles encountered with diverse active compounds, offering insights into the development of more effective drug delivery platforms.

Electromagnetic drop-on-demand (DoD) technology as an innovative platform for amorphous solid dispersion production

Production of amorphous solid dispersions (ASDs) is an effective strategy to promote the solubility and bioavailability of poorly water soluble medicinal substances. In general, ASD is manufactured using a variety of classic and modern techniques, most of which rely on either melting or solvent evaporation. This proof-of-concept study is the first ever to introduce electromagnetic drop-on-demand (DoD) technique as an alternative solvent evaporation-based method for producing ASDs. Herein 3D printing of ASDs for three drug-polymer combinations (efavirenz-Eudragit L100-55, lumefantrine-hydroxypropyl methylcellulose acetate succinate, and favipiravir-polyacrylic acid) was investigated to ascertain the reliability of this technique. Polarized light microscopy, differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), and Fourier Transform  Infrared (FTIR) spectroscopy results supported the formation of ASDs for the three drugs by means of DoD 3D printing, which significantly increases the equilibrium solubility of efavirenz from 0.03 ± 0.04 µg/ml to 21.18 ± 4.20 µg/ml, and the equilibrium solubility of lumefantrine from 1.26 ± 1.60 µg/ml to 20.21 ± 6.91 µg/ml. Overall, the reported findings show how this new electromagnetic DoD technology can have a potential to become a cutting-edge 3D printing solvent-evaporation technique for on-demand and continuous manufacturing of ASDs for a variety of drugs.

Advancing Drug Delivery Paradigms: Polyvinyl Pyrolidone (PVP)-Based Amorphous Solid Dispersion for Enhanced Physicochemical Properties and Therapeutic Efficacy

BACKGROUND

The current challenge in drug development lies in addressing the physicochemical issues that lead to low drug effectiveness. Solubility, a crucial physicochemical parameter, greatly influences various biopharmaceutical aspects of a drug, including dissolution rate, absorption, and bioavailability. Amorphous solid dispersion (ASD) has emerged as a widely explored approach to enhance drug solubility.

OBJECTIVE

The objective of this review is to discuss and summarize the development of polyvinylpyrrolidone (PVP)-based amorphous solid dispersion in improving the physicochemical properties of drugs, with a focus on the use of PVP as a novel approach.

METHODOLOGY

This review was conducted by examining relevant journals obtained from databases such as Scopus, PubMed, and Google Scholar, since 2018. The inclusion and exclusion criteria were applied to select suitable articles.

RESULTS

This study demonstrated the versatility and efficacy of PVP in enhancing the solubility and bioavailability of poorly soluble drugs. Diverse preparation methods, including solvent evaporation, melt quenching, electrospinning, coprecipitation, and ball milling are discussed for the production of ASDs with tailored characteristics.

CONCLUSION

PVP-based ASDs could offer significant advantages in the formulation strategies, stability, and performance of poorly soluble drugs to enhance their overall bioavailability. The diverse methodologies and findings presented in this review will pave the way for further advancements in the development of effective and tailored amorphous solid dispersions.

Molecular Dynamics Simulations of Selected Amorphous Stilbenoids and Their Amorphous Solid Dispersions with Poly(Vinylpyrrolidone)

Amorphous solid dispersions (ASDs) are one of the promising strategies to improve the solubility and dissolution rate of poorly soluble compounds. In this study, Molecular Dynamics simulations were used to investigate the interactions between three selected stilbenoids with important biological activity (resveratrol, pinostilbene and pterostilbene) and poly(vinylpyrrolidone). The analysis of the pair distribution functions and hydrogen bond distributions reveals a significant weakening of the hydrogen bond network of the stilbenoids in ASDs compared to the pure (no polymer) amorphous systems. This is accompanied by an increase in the mobility of the stilbenoid molecules in the ASDs, both in the translational dynamics determined from the molecular mean square displacements, and in the molecular reorientations followed by analysing several torsional distributions.

Preformulation study for the selection of a suitable polymer for the development of ellagic acid-based solid dispersion using hot-melt extrusion

Ellagic acid is one of the most studied polyphenolic compounds due to its numerous promising therapeutic properties. However, this therapeutic potential remains difficult to exploit owing to its low solubility and low permeability, resulting in low oral bioavailability. In order to allow an effective therapeutic application of EA, it is therefore necessary to develop strategies that sufficiently enhance its solubility, dissolution rate and bioavailability. For this purpose, solid dispersions based on pre-selected polymers such as Eudragit® EPO, Soluplus® and Kollidon® VA 64, with 5% w/w ellagic acid loading were prepared by hot extrusion and characterized by X-ray diffraction, FTIR spectroscopy and in vitro dissolution tests in order to select the most suitable polymer for future investigations. The results showed that Eudragit® EPO was the most promising polymer for ellagic acid solid dispersions development because its extrudates allowed to obtain a solution supersaturated in ellagic acid that was stable for at least 90 min. Moreover, the resulting apparent solubility was 20 times higher than the actual solubility of ellagic acid. The extrudates also showed a high dissolution rate of ellagic acid (96.25% in 15 min), compared to the corresponding physical mixture (6.52% in 15 min) or the pure drug (1.56% in 15 min). Furthermore, increasing the loading rate of ellagic acid up to 12% in extrudates based on this polymer did not negatively influence its release profile through dissolution tests.

Downstream processing of amorphous solid dispersions into orodispersible tablets

The formulation development of amorphous solid dispersions (ASDs) towards a patient-friendly oral solid dosage form is proving to be still challenging. To increase patient's compliance orodispersible tablets (ODTs) can be seen as promising alternative. Two different ASDs were prepared via hot melt extrusion (HME), using PVPVA as polymer for ritonavir (RTV) and HPMCAS for lopinavir (LPV). The extrudates were milled, sieved, and blended with Hisorad® (HRD) or Ludiflash® (LF), two established co-processed excipients (CPE) prior to tableting. Interestingly, the selected ASD particle size was pointed out to be a key parameter for a fast disintegration and high mechanical strength. In terms of PVPVA based ASDs, larger particle sizes > 500 µm enabled a rapid disintegration even under 30 s for 50 % ASD loaded ODTs, whereas the use of smaller particles went along with significant higher disintegration times. However, the influence of the CPE was immense for PVPVA based ASDs, since it was only possible to prepare well performing ODTs, when Hisorad® was chosen. In contrast for HPMCAS based ASDs the selection of smaller particle sizes 180-500 µm was beneficial for overcoming the poor compressibility of the ASD matrix polymer. ODTs with LPV could be produced using both CPEs even with higher ASD loads up to 75 %, while still showing remarkably fast disintegration.

Recent Advances in Amorphous Solid Dispersions: Preformulation, Formulation Strategies, Technological Advancements and Characterization

Amorphous solid dispersions (ASDs) are among the most popular and widely studied solubility enhancement techniques. Since their inception in the early 1960s, the formulation development of ASDs has undergone tremendous progress. For instance, the method of preparing ASDs evolved from solvent-based approaches to solvent-free methods such as hot melt extrusion and Kinetisol^®. The formulation approaches have advanced from employing a single polymeric carrier to multiple carriers with plasticizers to improve the stability and performance of ASDs. Major excipient manufacturers recognized the potential of ASDs and began introducing specialty excipients ideal for formulating ASDs. In addition to traditional techniques such as differential scanning calorimeter (DSC) and X-ray crystallography, recent innovations such as nano-tomography, transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray microscopy support a better understanding of the microstructure of ASDs. The purpose of this review is to highlight the recent advancements in the field of ASDs with respect to formulation approaches, methods of preparation, and advanced characterization techniques.

Downstream Processing of Itraconazole:HPMCAS Amorphous Solid Dispersion: From Hot-Melt Extrudate to Tablet Using a Quality by Design Approach

The downstream processing of hot-melt extruded amorphous solid dispersions (ASDs) into tablets is challenging due to the low tabletability of milled ASDs. Typically, the extrudate strand is sized before milling, as the strand cannot be fed directly into the milling system. At the lab scale, the strand can be sized by hand-cutting before milling. For scaling up, pelletizers or chill roll and flaker systems can be used to break strands. Due to the different techniques used, differences in milling and tablet compaction are to be expected. We present a systematic study of the milling and tableting of an extruded ASD of itraconazole with hypromellose acetate succinate (HPMCAS) as a carrier polymer. The strand was sized using different techniques at the end of the extruder barrel (hand-cutting, pelletizer, or chill roll and flaker) before being milled at varying milling speeds with varying screen sizes. The effects of these variables (sizing technology, milling speed, and screen size) on the critical quality attributes (CQAs) of the milled ASD, such as yield, mean particle size (D50), tablet compaction characteristics, and tablet dissolution, were established using response surface methodology. It was found that the CQAs varied according to sizing technology, with chill roll flakes showing the highest percentage yield, the lowest D50, and the highest tabletability and dissolution rate for itraconazole. Pearson correlation coefficient tests indicated D50 as the most important CQA related to tabletability and dissolution. For certain milling conditions, the milling of hand-cut filaments results in similar particle size distributions (PSDs) to the milling of pellets or chill roll flakes.

Investigation of tadalafil molecular arrangement in solid dispersions using inverse gas chromatography and Raman mapping

The aim of this study was to investigate the molecular structures of tadalafil solid dispersions prepared by different techniques and further to relate them to surface free energy information indicating the final amorphousness of the product. Thus, we tried to complement the existing knowledge of solid dispersion formation. Poorly water-soluble tadalafil was combined with different polymers, i.e. Kollidon® 12 PF, Kollidon® VA 64 and Soluplus®, to form model systems. To assess the extent of drug-polymer miscibility, we studied model solid dispersion surface energy using inverse gas chromatography and phase micro-structure using confocal Raman microscopy. The selection of the preparation method was found to play a crucial role in the molecular arrangement of the incorporated drug and the polymer in resulting solid dispersion. Our results showed that a lower surface free energy indicated the formation of a more homogeneous solid dispersion. Conversely, a higher surface free energy corresponded to the heterogeneous systems containing tadalafil amorphous clusters that were captured by Raman mapping. Thus, we successfully introduced a novel evaluation approach of the drug molecular arrangement in solid dispersions that is especially useful for examining the miscibility of the components when the conventional characterizing techniques are inconclusive or yield variable results.

A systematic and robust assessment of hot-melt extrusion-based amorphous solid dispersions: Theoretical prediction to practical implementation

Amorphous solid dispersions (ASDs) have gained attention as a formulation strategy in recent years, with the potential to improve the apparent solubility and, hence, the oral bioavailability of poorly soluble drugs. The process of formulating ASDs is commonly faced with challenges owing to the intrinsic physical and chemical instability of the initial amorphous form and the long-term physical stability of drug formulations. Numerous research publications on hot-melt extrusion (HME) technology have demonstrated that it is the most efficient approach for manufacturing reasonably stable ASDs. The HME technique has been established as a faster scale-up production strategy for formulation evaluation and has the potential to minimize the time to market. Thermodynamic evaluation and theoretical predictions of drug-polymer solubility and miscibility may assist to reduce the product development cost by HME. This review article highlights robust and established prediction theories and experimental approaches for the selection of polymeric carriers for the development of hot melt extrusion based stable amorphous solid dispersions (ASDs). In addition, this review makes a significant contribution to the literature as a pilot guide for ASD assessment, as well as to confirm the drug-polymer compatibility and physical stability of HME-based formulations.

Active coating of immediate-release evogliptin tartrate to prepare fixed dose combination tablet with sustained-release metformin HCl

This study was aimed to develop a fixed dose combination (FDC) tablet containing a low dose of evogliptin tartrate (6.87 mg) for immediate release combined with a high dose (1000 mg) of sustained-release (SR) metformin HCl appropriate for once daily dosing the treatment of type 2 diabetes. To prepare the FDC tablets, an active coating was used in this study, whereby evogliptin tartrate film was layered on a matrix core tablet containing metformin HCl. To overcome the problem caused by a low-dose drug in combination with a relatively large matrix tablet containing high-dose drug, it was also aimed to confirm the formulation and coating operation for satisfactory content uniformity, and to describe the chemical stability during storage of the amorphous active coating layer formulation in relation to molecular mobility. Furthermore, the in vitro release and in vivo pharmacokinetic profiles of metformin HCl and evogliptin tartrate in the FDC active coating tablet were compared to those of the commercially marketed reference drugs, Diabex XR® (Daewoong, Seoul, Korea) containing metformin HCl and Suganon® (Donga ST, Seoul, Korea) containing evogliptin tartrate. In conclusion, the newly developed FDC active coating tablet in this study was confirmed to be bioequivalent to the reference marketed products in beagle dogs, with satisfactory content uniformity and stability.

Long-term stability of clopidogrel solid dispersions-Importance of in vitro dissolution test

Formulation of solid dispersions (SDs), in which the drug substance is dissolved or dispersed inside a polymer matrix, is one of the modern approaches to increase the solubility and dissolution rate of poorly soluble active pharmaceutical ingredients (APIs), such as clopidogrel. In the form of a free base, clopidogrel is unstable under increased both high moisture and temperature, so it is most often used as its salt form, clopidogrel hydrogen sulfate (CHS).The aim of this study was the formulation, characterization, and long-term stability investigation of CHS solid dispersions, prepared with four different hydrophilic polymers (poloxamer 407, macrogol 6000, povidone, copovidone) in five API/polymer ratios (1:1, 1:2, 1:3, 1:5, 1:9). SDs were prepared by the solvent evaporation method, employing ethanol (96% v/v) as a solvent. Initial results of the in vitro dissolution test showed an increase in the amount of dissolved CHS from all prepared SD samples compared to pure CHS, corresponding physical mixtures (PMs), and commercial tablets. SDs, prepared with poloxamer 407, macrogol 6000, and copovidone, at CHS/polymer ratios 1:5 and 1:9, notably increased the amount of dissolved CHS (> 80%, after 60 min), thus they were selected for further characterization. To assess the SDs long-term stability, in vitro dissolution studies, clopidogrel content determination, differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FT-IR) were performed initially and after 12 months of long-term stability studies under controlled conditions (25°C, 60% RH) meeting the ICH guideline Q1A (R2) requirements. The clopidogrel content in the selected samples was very similar at the beginning (96.13% to 99.93%) and at the end (95.98% to 99.86%) of the conducted test. DSC curves and FT-IR spectra of all SD samples after 12 months of stability study, showed the absence of CHS crystallization, which is an indication of good stability. However, the in vitro dissolution test showed a considerable reduction in CHS released from SDs with macrogol 6000. The amount of dissolved CHS from SDs with macrogol 6000 was initially 94.02% and 92.01%, and after 12 months of stability study, only 65.13% and 49.62%. In contrast, the amount of dissolved CHS from SDs prepared with poloxamer 407 and copovidone was very similar after 12 months of the stability study compared to the initial values. Results obtained indicated the great importance of the in vitro dissolution test in determining the long-term stability and quality of SDs.

Atomic Force Microscopy for Tumor Research at Cell and Molecule Levels

Tumors have posed a serious threat to human life and health. Researchers can determine whether or not cells are cancerous, whether the cancer cells are invasive or metastatic, and what the effects of drugs are on cancer cells by the physical properties such as hardness, adhesion, and Young's modulus. The atomic force microscope (AFM) has emerged as a key important tool for biomechanics research on tumor cells due to its ability to image and collect force spectroscopy information of biological samples with nano-level spatial resolution and under near-physiological conditions. This article reviews the existing results of the study of cancer cells with AFM. The main foci are the operating principle of AFM and research advances in mechanical property measurement, ultra-microtopography, and molecular recognition of tumor cells, which allows us to outline what we do know it in a systematic way and to summarize and to discuss future directions.

Optimization of Spray-Drying Parameters for Formulation Development at Preclinical Scale

Spray-drying dispersion (SDD) is a well-established manufacturing technique used to prepare amorphous solid dispersions (ASDs), allowing for poorly soluble drugs to have improved bioavailability. However, the process of spray-drying with multiple factors and numerous variables can lead to a lengthy development timeline with intense resource requirements, which becomes the main obstacle limiting spray-drying development at the preclinical stage. The purpose of this work was to identify optimized preset parameters for spray-drying to support the early development of ASDs suitable for most circumstances rather than individual optimization. First, a mini-DoE (Design of Experiment) study was designed to evaluate the critical interplay of two key variables for spray-drying using a BUCHI B-290 mini spray dryer: solid load and atomizing spray gas flow. The critical quality attributes (CQAs) of the ASDs, including yield, particle size, morphology, and in vitro release profile, were taken into account to identify the impact of the key variables. The mini-DoE results indicated that a 5% solid load (w/v %) and 35 mm height atomizing spray gas flow were the most optimized parameters. These predefined values were further verified using different formulation compositions, including various polymers (Eudragit L100-55, HPMCAS-MF, PVAP, and PVP-VA64) and drugs (G-F, GEN-A, Indomethacin, and Griseofulvin), a range of drug loading (10 to 40%), and scale (200 mg to 200 g). Using these predefined parameters, all ASD formulations resulted in good yields as well as consistent particle size distribution. This was despite the differences in the formulations, making this a valuable and rapid approach ideal for early development. This strategy of leveraging the preset spray-drying parameters was able to successfully translate into a reproducible and efficient spray-drying platform while also saving material and reducing developmental timelines in early-stage formulation development.

Amorphous Solid Dispersions: Utilization and Challenges in Preclinical Drug Development within AstraZeneca

The poor aqueous solubility of many active pharmaceutical ingredients (APIs) dominates much of the early drug development portfolio and poses a major challenge in pharmaceutical development. Polymer-based amorphous solid dispersions (ASDs) are becoming increasingly common and offer a promising formulation strategy to tackle the solubility and oral absorption issues of these APIs. This review discusses the design, manufacture, and utilisation of ASD formulations in preclinical drug development, with a key focus on the pre-formulation assessments and workflows employed at AstraZeneca.

Benzoic acid complexes with Eudragit E100®: New alternative antimicrobial preservatives

Given that the use of some preservatives in cosmetics has been restricted, novel alternative preservatives are needed. The aim of this study was to characterize the physicochemical and antimicrobial properties of two polyelectrolyte complexes (EuB₁₀₀ and EuB₇₅Cl₂₅), which were developed through hot melt extrusion (HME) using benzoic acid (BA) and Eudragit E100. Based on phase diagrams and an experimental statistical design, the solubility of the acid in the polymer and the HME conditions were established. Intermolecular interactions were evaluated through Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRPD). Release behavior was determined for the systems. Antibacterial activity and ζ-potential were determined on Escherichia coli. FTIR revealed acid-base interaction, and XPS showed that the percentages of protonated nitrogen N1s were 13.5% for EuB₁₀₀ and 20.3% for EuB₇₅Cl₂₅. The BA released showed a non-Fickian behavior, and a satisfactory antibacterial activity against E. coli was demonstrated at pH 6.9. The complexes modified ζ-potential, destabilizing the membrane functionality of E. coli. These complexes are potential antimicrobial preservatives with a greater spectrum of action, with bactericidal activity against E. coli in a wider pH range than uncomplexed BA, even at pH 6.9.

Amorphous Salts Solid Dispersions of Celecoxib: Enhanced Biopharmaceutical Performance and Physical Stability

Numerous amorphous solid dispersion (ASD) formulations of celecoxib (CEL) have been attempted for enhancing the solubility, dissolution rate, and in vivo pharmacokinetics via high drug loading, polymer combination, or by surfactant addition. However, physical stability for long-term shelf life and desired in vivo pharmacokinetics remains elusive. Therefore, newer formulation strategies are always warranted to address poor aqueous solubility and oral bioavailability with extended shelf life. The present investigation elaborates a combined strategy of amorphization and salt formation for CEL, providing the benefits of enhanced solubility, dissolution rate, in vivo pharmacokinetics, and physical stability. We generated amorphous salts solid dispersion (ASSD) formulations of CEL via an in situ acid-base reaction involving counterions (Na⁺ and K⁺) and a polymer (Soluplus) using the spray-drying technique. The generated CEL-Na and CEL-K salts were homogeneously and molecularly dispersed in the matrix of Soluplus polymer. The characterization of generated ASSDs by differential scanning calorimetry revealed a much higher glass-transition temperature (T_g) than the pure amorphous CEL, confirming the salt formation of CEL in solid dispersions. The micro-Raman and proton nuclear magnetic resonance spectroscopy further confirmed the formation of salt at the -S═O position in the CEL molecules. CEL-Na-Soluplus ASSD exhibited a synergistic enhancement in the aqueous solubility (332.82-fold) and in vivo pharmacokinetics (9.83-fold enhancement in the blood plasma concentration) than the crystalline CEL. Furthermore, ASSD formulations were physically stable for nearly 1 year (352 days) in long-term stability studies at ambient conditions. Hence, we concluded that the ASSD is a promising strategy for CEL in improving the physicochemical properties and biopharmaceutical performance.

Role of Surfactant Micellization for Enhanced Dissolution of Poorly Water-Soluble Cilostazol Using Poloxamer 407-Based Solid Dispersion via the Anti-Solvent Method

This study aimed to investigate the role of micellization of sodium lauryl sulfate (SLS) in poloxamer 407 (POX)-based solid dispersions (POX-based SDs) using the anti-solvent method in enhancing the dissolution rate of practically water-insoluble cilostazol (CLT). Herein, SLS was incorporated into CLT-loaded SDs, at a weight ratio of 50:50:10 of CLT, POX, and SLS by three different methods: anti-solvent, fusion (60 °C), and solvent (ethanol) evaporation. The SDs containing micellar SLS in the anti-solvent method were superior in the transformation of the crystalline form of the drug into a partial amorphous state. It was notable that there was an existence of a hydrophobic interaction between the surfactant and the hydrophobic regions of polymer chain via non-covalent bonding and the adsorption of micellar SLS to the POX-based SDs matrix. Moreover, SLS micellization via the anti-solvent method was effectively interleaved in SDs and adhered by the dissolved CLT, which precluded drug particles from aggregation and recrystallization, resulting in improved SD wettability (lower contact angle) and reduced particle size and dissolution rate. In contrast, SDs without micellar SLS prepared by the solvent method exerted drug recrystallization and an increase of particle size, resulting in decreased dissolution. Incorporation of surfactant below or above critical micellar concentration (CMC) in SDs using the anti-solvent method should be considered in advance. Dissolution results showed that the pre-added incorporation of micellar SLS into POX-based SDs using the anti-solvent method could provide a way of a solubilization mechanism to enhance the dissolution rate of poorly water-soluble drugs.

Formulation of solid dispersion to improve dissolution and oral bioavailability of poorly soluble dexibuprofen

Dexibuprofen (DEXI) belongs to BCS class II drug with poor aqueous solubility resulting in poor bioavailability. To enhance solubility and bioavailability of DEXI, DEXI-loaded solid dispersion (SD) was formulated. DEXI-SDs were prepared by melting method and solvent evaporation method. Amphipathic polymer poloxamer 407 (pol 407) was selected based on solubility and dissolution tests. The ratio of DEXI:pol 407 was optimized as 1:2. The physicochemical properties, dissolution, and oral bioavailability of SD3 and SD6 were evaluated to compare preparation methods. The dissolution rate of DEXI from SD formulations was higher at pH 6.8 and pH 7.2 than at pH 1.2. Following oral administration in rats, the C_max and AUC_last of SD3 and SD6 formulations were significantly higher compared with raw DEXI. In addition, the SD6 formulation showed increased C_max and AUC_last by 1.34- and 1.33-fold, compared with those of SD3 formulation, respectively. These results demonstrated that SD formulation has excellent potential as a formulation for poorly soluble drug DEXI.

Preparation of Hot-Melt Extruded Dosage Form for Enhancing Drugs Absorption Based on Computational Simulation

The aim of this study was to control the dissolution rate and permeability of cilostazol. To enhance the dissolution rate of the active pharmaceutical ingredient (API), hot-melt extrusion (HME) technology was applied to prepare a solid dispersion (SD). To control permeability in the gastrointestinal tract regardless of food intake, the HME process was optimized based on physiologically based pharmacokinetic (PBPK) simulation. The extrudates were produced using a laboratory-scale twin-screw hot-melt extruder with co-rotatory screws and a constant feeding rate. Next, for PBPK simulation, parameter-sensitive analysis (PSA) was conducted to determine the optimization approach direction. As demonstrated by the dissolution test, the solubility of extrudate was enhanced comparing cilostazol alone. Based on the PSA analysis, the surfactant induction was a crucial factor in cilostazol absorption; thus, an extrudate with an even distribution of lipids was produced using hot-melt extrusion technology, for inducing the bile salts in the gastrointestinal tract. In vivo experiments with rats demonstrated that the optimized hot-melt extruded formulation was absorbed more rapidly with lower deviation and regardless of the meal consumed when compared to marketed cilostazol formulations.

Unraveling Particle Formation: From Single Droplet Drying to Spray Drying and Electrospraying

Spray drying and electrospraying are well-established drying processes that already have proven their value in the pharmaceutical field. However, there is currently still a lack of knowledge on the fundamentals of the particle formation process, thereby hampering fast and cost-effective particle engineering. To get a better understanding of how functional particles are formed with respect to process and formulation parameters, it is indispensable to offer a comprehensive overview of critical aspects of the droplet drying and particle formation process. This review therefore closely relates single droplet drying to pharmaceutical applications. Although excellent reviews exist of the different aspects, there is, to the best of our knowledge, no single review that describes all steps that one should consider when trying to engineer a certain type of particle morphology. The findings presented in this article have strengthened the predictive value of single droplet drying for pharmaceutical drying applications like spray drying and electrospraying. Continuous follow-up of the particle formation process in single droplet drying experiments hence allows optimization of manufacturing processes and particle engineering approaches and acceleration of process development.

In Vitro-In Vivo Correlation for Solid Dispersion of a Poorly Water-Soluble Drug Efonidipine Hydrochloride

The aim of this present study was to investigate the ability of different dissolution methods to predict the in vivo performance of efonidipine hydrochloride (EFH). The solid dispersions of EFH were prepared by solvent evaporation method with HPMC-AS as matrix and urea as a pH adjusting agent. The paddle method, the open-loop, and the closed-loop flow-through cell methods were studied. In the study, Weibull's model was the best fit to explain release profiles. The pharmacokinetics behaviors of two kinds of solid dispersions with different release rate were investigated in comparison to the EFH after oral administration in rats. In vivo absorption was calculated by a numerical deconvolution method. In the study, the level A in vivo and in vitro correlation (IVIVC) was utilized. The correlation coefficient was calculated and interpreted by means of linear regression analysis (Origin.Pro.8.5 software). As a result, excellent IVIVC for solid dispersions and crude drug (r² = 0.9352-0.9916) was obtained for the dissolution rate determined with flow-through cell open-loop system in phosphate buffer solution with 0.1% (w/v) polysorbate 80 at pH 6.5, the flow-rate of 4 mL/min. In addition, the self-assembled flow cell system had good repeatability and accuracy. The dissolution rate of the solid dispersion could be slowed down by the flow-through method, and the difference caused by preparation was significantly distinguished. The study demonstrated that flow-through cell method of the open-loop, compared with paddle method, was suitable for predicting in vivo performance of EFH solid dispersions.

Pure Trans-Resveratrol Nanoparticles Prepared by A Supercritical Antisolvent Process Using Alcohol and Dichloromethane Mixtures: Effect of Particle Size on Dissolution and Bioavailability in Rats

The aim of this study was to prepare pure trans-resveratrol nanoparticles without additives (surfactants, polymers, and sugars) using a supercritical antisolvent (SAS) process with alcohol (methanol or ethanol) and dichloromethane mixtures. In addition, in order to investigate the effect of particle size on the dissolution and oral bioavailability of the trans-resveratrol, two microparticles with different sizes (1.94 μm and 18.75 μm) were prepared using two different milling processes, and compared to trans-resveratrol nanoparticles prepared by the SAS process. The solid-state properties of pure trans-resveratrol particles were characterized. By increasing the percentage of dichloromethane in the solvent mixtures, the mean particle size of trans-resveratrol was decreased, whereas its specific surface area was increased. The particle size could thus be controlled by solvent composition. Trans-resveratrol nanoparticle with a mean particle size of 0.17 μm was prepared by the SAS process using the ethanol/dichloromethane mixture at a ratio of 25/75 (w/w). The in vitro dissolution rate of trans-resveratrol in fasted state-simulated gastric fluid was significantly improved by the reduction of particle size, resulting in enhanced oral bioavailability in rats. The absolute bioavailability of trans-resveratrol nanoparticles was 25.2%. The maximum plasma concentration values were well correlated with the in vitro dissolution rate. These findings clearly indicate that the oral bioavailability of trans-resveratrol can be enhanced by preparing pure trans-resveratrol nanoparticles without additives (surfactants, polymers, and sugars) by the SAS process. These pure trans-resveratrol nanoparticles can be applied as an active ingredient for the development of health supplements, pharmaceutical products, and cosmetic products.

Melt Amorphisation of Orlistat with Mesoporous Silica Using a Supercritical Carbon Dioxide: Effects of Pressure, Temperature, and Drug Loading Ratio and Comparison with Other Conventional Amorphisation Methods

The aim of this work was to develop an amorphous orlistat-loaded mesoporus silica formulation using the melt-amorphisation by supercritical fluid (MA-SCF) and to investigate the effects of pressure and temperature on the pharmaceutical properties of the developed formulation. In addition, the effect of orlistat mass ratio to the mesoporus silica was also evaluated. The carbon dioxide was used as a supercritical fluid, and Neusilin^®UFL2 was selected as the mesoporous silica. For comparison with conventional amorphisation methods, orlistat formulations were also prepared by solvent evaporation and hot melt methods. Various pharmaceutical evaluations including differential scanning calorimetry, powder X-ray diffraction, scanning electron microscopy, specific surface area, total pore volume, and content uniformity were performed to characterise the prepared orlistat formulation. The melting point depression and the solubility of orlistat in supercritical carbon dioxide (SC-CO₂) were selected for the interpretation of evaluated results in relation to temperature and pressure. The total pore volume of the prepared orlistat-loaded mesoporus silica decreased with an increasing density of SC-CO₂ to about 500 g/L at a constant temperature or pressure. From these results, it was suggested that increasing the density of SC-CO₂ to about 500 g/L could result in the easier penetration of CO₂ into molten orlistat and lower viscosity, hence facilitating the introduction and loading of orlistat into the pores of Neusilin^®UFL2. However, when the density of SC-CO₂ increased to more than 500 g/L, the total pore volume increased, and this may be due to the release out of orlistat from the pores of Neusilin^®UFL2 by the increased orlistat solubility in SC-CO₂. Interestingly, as the total pore volume decreased by the filling of the drug, the drug crystallinity decreased; hence, the dissolution rate increased. Furthermore, it was shown that the most desirable mass ratio of Neusilin^®UFL2:orlistat for the amorphisation was 1:0.8 at an optimised supercritical condition of 318 K and 10 MPa. Compared with other amorphisation methods, only the sample prepared by the MA-SCF method was in pure amorphous state with the fastest dissolution rate. Therefore, it was concluded that the amorphous orlistat-loaded mesoporus silica prepared using MA-SCF under optimised conditions was more advantageous for enhancing the dissolution rate of orlistat than other conventional amorphisation methods.

Current Status of Supersaturable Self-Emulsifying Drug Delivery Systems

Self-emulsifying drug delivery systems (SEDDSs) are a vital strategy to enhance the bioavailability (BA) of formulations of poorly water-soluble compounds. However, these formulations have certain limitations, including in vivo drug precipitation, poor in vitro in vivo correlation due to a lack of predictive in vitro tests, issues in handling of liquid formulation, and physico-chemical instability of drug and/or vehicle components. To overcome these limitations, which restrict the potential usage of such systems, the supersaturable SEDDSs (su-SEDDSs) have gained attention based on the fact that the inclusion of precipitation inhibitors (PIs) within SEDDSs helps maintain drug supersaturation after dispersion and digestion in the gastrointestinal tract. This improves the BA of drugs and reduces the variability of exposure. In addition, the formulation of solid su-SEDDSs has helped to overcome disadvantages of liquid or capsule dosage form. This review article discusses, in detail, the current status of su-SEDDSs that overcome the limitations of conventional SEDDSs. It discusses the definition and range of su-SEDDSs, the principle mechanisms underlying precipitation inhibition and enhanced in vivo absorption, drug application cases, biorelevance in vitro digestion models, and the development of liquid su-SEDDSs to solid dosage forms. This review also describes the effects of various physiological factors and the potential interactions between PIs and lipid, lipase or lipid digested products on the in vivo performance of su-SEDDSs. In particular, several considerations relating to the properties of PIs are discussed from various perspectives.

Pharmaceutical Characterization and In Vivo Evaluation of Orlistat Formulations Prepared by the Supercritical Melt-Adsorption Method Using Carbon Dioxide: Effects of Mesoporous Silica Type

Orlistat, an anti-obesity drug, has two critical issues—the first is its low efficacy due to low water solubility and the second is side effects such as oily spotting due to its lipase inhibition. The present study was designed to propose a solution using a formulation with mesoporous silica to simultaneously overcome two issues. Orlistat was loaded onto mesoporous silica by the supercritical melt-adsorption (SCMA) method, using carbon dioxide (CO₂). Various types of mesoporous silica were used as adsorbents, and the effects of the pore volume, diameter and particle size of mesoporous silica on the pharmaceutical characteristics were evaluated by various solid-state characterization methods and in vitro and in vivo studies in relation to pharmacological efficacy and the improvement of side effects. The results showed that the pore volume and diameter determine loadable drug amount inside pores and crystallinity. The dissolution was significantly influenced by crystallinity, pore diameter and particle size, and the inhibition of lipase activity was in proportion to the dissolution rate. In vivo studies revealed that the serum triglyceride (TG) concentration was significantly decreased in the group administered amorphous orlistat-loaded Neuisilin^®UFL2 with the highest in vitro dissolution rate and lipase activity inhibition in comparison to the commercial product. Furthermore, oily spotting tests in rats revealed that undigested oil was adsorbed onto mesoporous silica after orlistat was released in the gastro-intestinal tract, and it correlated with in vitro result that oil adsorption capacity was dependent on the surface area of empty mesoporous silica. Therefore, it was concluded that mesoporous silica type plays a major role in determining the pharmaceutical characteristics of orlistat formulation prepared using SCMA with CO₂ for improving the low solubility and overcoming the side effects.

Characterization and therapeutic efficacy evaluation of glimepiride and L-arginine co-amorphous formulation prepared by supercritical antisolvent process: Influence of molar ratio and preparation methods

The glimepiride/L-arginine (GA) binary systems were prepared at various molar ratios by using a supercritical antisolvent (SAS) process. For comparison, the GA system was also prepared by physical mixing (PM), melt quenching (MQ), and solvent evaporation (SE) methods. Analyses by DSC and PXRD showed that only the GA binary mixture at 1:1 M ratio prepared by the SAS process was a pure co-amorphous mixture with an excellent content uniformity. On the other hand, GA mixture prepared by PM and SE were not pure co-amorphous systems and contained crystalline eutectic mixture, and MQ method at 170 °C induced the decrease in drug content due to decomposition of glimepiride. The positive deviation of experimentally measured glass transition temperature (T_g) compared to predicted T_g by the Gordon Taylor equation suggests specific molecular interactions between glimepiride and L-arginine in solid-state GA co-amorphous (GACA) mixture. The intermolecular interactions between glimepiride and L-arginine in GACA system were characterized by FT-IR and solid-state NMR analyses. Improved glimepiride dissolution rate of GACA formulation were confirmed using the solubility test, contact angle measurement, and dissolution test. Furthermore, the evaluation of pharmacodynamic hypoglycemic effect demonstrated that GACA prepared by the SAS process significantly improved the therapeutic efficacy of glimepiride.

Development of a Resveratrol Nanosuspension Using the Antisolvent Precipitation Method without Solvent Removal, Based on a Quality by Design (QbD) Approach

The purpose of this study was to develop a resveratrol nanosuspension with enhanced oral bioavailability, based on an understanding of the formulation and process parameters of nanosuspensions and using a quality by design (QbD) approach. Particularly, the antisolvent method, which requires no solvent removal and no heating, is newly applied to prepare resveratrol nanosuspension. To ensure the quality of the resveratrol nanosuspensions, a quality target product profile (QTPP) was defined. The particle size (z-average, d90), zeta potential, and drug content parameters affecting the QTPP were selected as critical quality attributes (CQAs). The optimum composition obtained using a 3-factor, 3-level Box-Behnken design was as follows: polyvinylpyrrolidone vinyl acetate (10 mg/mL), polyvinylpyrrolidone K12 (5 mg/mL), sodium lauryl sulfate (1 mg/mL), and diethylene glycol monoethyl ether (DEGEE, 5% v/v) at a resveratrol concentration of 5 mg/mL. The initial particle size (z-average) was 46.3 nm and the zeta potential was -38.02 mV. The robustness of the antisolvent process using the optimized composition conditions was ensured by a full factorial design. The dissolution rate of the optimized resveratrol nanosuspension was significantly greater than that of the resveratrol raw material. An in vivo pharmacokinetic study in rats showed that the area under the plasma concentration versus time curve (AUC0-12h) and the maximum plasma concentration (Cmax) respectively, than those of the resveratrol raw material. Therefore, the prepara values of the resveratrol nanosuspension were approximately 1.6- and 5.7-fold higher,tion of a resveratrol nanosuspension using the QbD approach may be an effective strategy for the development of a new dosage form of resveratrol, with enhanced oral bioavailability.

Utilization of a fattigation platform gelatin-oleic acid sodium salt conjugate as a novel solubilizing adjuvant for poorly water-soluble drugs via self-assembly and nanonization

Solubilizing adjuvants are commonly used to dissolve insoluble drugs by simply adding in a formulation. In this study, gelatin and oleic acid sodium salt (OAS), a generally recognized as safe-listed material were chosen and conjugated to develop a natural solubilizing adjuvant using the fattigation platform technology to enhance solubility and dissolution rate of poorly water-soluble drugs according to self-assembly and nanonization principle when simply mixed with poorly water-soluble drugs. We synthesized the gelatin and OAS conjugates (GOC) at three different ratios (1:1, 1:3, 1:5; GOC 1, GOC 2, and GOC 3, respectively) via the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide reaction using a spray dryer. This amphiphilic micronized GOC was self-assembled into nanoparticles. The synthesis of new amphiphilic conjugates was identified through Fourier transform-infrared (FT-IR) spectroscopy. The powder properties of the GOCs, such as angle of repose, bulk density, and tapped density were varied with the oleic acid bonding ratio. Then, GOCs were utilized to investigate the enhanced solubility and release rate of various poorly water-soluble drugs such as cilostazol (CSZ), coenzyme Q10, ticagrelor, telmisartan, aprepitant and itraconazole as model drugs. Based on the solubility studies by concentration and type of GOCs, 3% GOC 2 was selected. When this GOC was mixed with these model drugs by the physical mixing, wetting and hot melting methoods, the solubility was highly enhanced compared to the pure control drug, ranging from 20 to 150,000 times. In case of CSZ, all formulations were significantly improved release rate compared to the of CSZ alone and the reference tablet, cilostan® (Korea United Pharm) in simulated intestinal fluid containing 0.2% sodium lauryl sulfate. Differential scanning calorimetry and powder X-ray diffraction were conducted to confirm the crystal polymorphic structure of CSZ, and as a result they changed to diminutive peak intensity compared to CSZ alone. Field-emission scanning electron microscopy indicated that GOC was round with a reduced size of about 100 nm. The reduction of drug particles via nanonization and self-assembly of amphiphilic GOC in an aqueous media could be a key factor to improve poor water solubility by providing a favorable dispersion of drug molecules in an amphiphilic network.

Preparation and Evaluation of Resveratrol-Loaded Composite Nanoparticles Using a Supercritical Fluid Technology for Enhanced Oral and Skin Delivery

We created composite nanoparticles containing hydrophilic additives using a supercritical antisolvent (SAS) process to increase the solubility and dissolution properties of trans-resveratrol for application in oral and skin delivery. Physicochemical properties of trans-resveratrol-loaded composite nanoparticles were characterized. In addition, an in vitro dissolution-permeation study, an in vivo pharmacokinetic study in rats, and an ex vivo skin permeation study in rats were performed. The mean particle size of all the composite nanoparticles produced was less than 300 nm. Compared to micronized trans-resveratrol, the trans-resveratrol/hydroxylpropylmethyl cellulose (HPMC)/poloxamer 407 (1:4:1) nanoparticles with the highest flux (0.792 μg/min/cm²) exhibited rapid absorption and showed significantly higher exposure 4 h after oral administration. Good correlations were observed between in vitro flux and in vivo pharmacokinetic data. The increased solubility and flux of trans-resveratrol generated by the HPMC/surfactant nanoparticles increased the driving force on the gastrointestinal epithelial membrane and rat skin, resulting in enhanced oral and skin delivery of trans-resveratrol. HPMC/surfactant nanoparticles produced by an SAS process are, thus, a promising formulation method for trans-resveratrol for healthcare products (owing to their enhanced absorption via oral administration) and for skin application with cosmetic products.

Solid-state analysis of amorphous solid dispersions: Why DSC and XRPD may not be regarded as stand-alone techniques

Amorphous solid dispersions (ASDs) are single-phase amorphous systems, where drug molecules are molecularly dispersed (dissolved) in a polymer matrix. The molecular dispersion of the drug molecules is responsible for their improved dissolution properties. Unambiguously establishing the phase behavior of the ASDs is of utmost importance. In this paper, we focused on the complementary nature of (modulated) differential scanning calorimetry ((m)DSC) and X-ray powder diffraction (XRPD) to elucidate the phase behavior of ASDs as demonstrated by a critical discussion of practical real-life examples observed in our research group. The ASDs were manufactured by either applying a solvent-based technique (spray drying), a heat-based technique (hot melt extrusion) or mechanochemical activation (cryo-milling). The encountered limiting factors of XRPD were the lack of sensitivity for small traces of crystallinity, the impossibility to differentiate between distinct amorphous phases and its impossibility to detect nanocrystals in a polymer matrix. In addition, the limiting factors of (m)DSC were defined as the well-described heat-induced sample alteration upon heating, the interfering of residual solvent evaporation with other thermal events and the coinciding of enthalpy recovery with melting events. In all of these cases, the application of a single analytical technique would have led to erroneous conclusions, whilst the combination of (m)DSC and XRPD elucidated the true phases of the ASD.

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.

Spray-Dried Amorphous Solid Dispersions of Atorvastatin Calcium for Improved Supersaturation and Oral Bioavailability

Over the past few decades, the amorphous solid dispersions (ASDs) technique has emerged as a promising strategy to enhance the in vitro/in vivo characteristic of hydrophobic drugs. The low aqueous solubility and poor bioavailability of atorvastatin calcium (ATO), a lipid-lowering drug, present challenges for effective drug delivery. The objective of this work was to improve the aqueous solubility, in vitro dissolution, and oral absorption of ATO with amorphous solid dispersion technique prepared by spray-drying method. The optimized ternary formulation comprising of ATO; hydroxypropyl methylcellulose (HPMC), as a hydrophilic polymer; and sodium lauryl sulfate (SLS), as a surfactant, at a weight ratio of 1/1/0.1, showed significant improvement in aqueous solubility by ~18-fold compared to that of the free drug, and a cumulative release of 94.09% compared to a release of 59.32% of the free drug. Further, physicochemical studies via scanning electron microscopy, differential scanning calorimetry, and powder X-ray diffraction revealed a change from the crystalline state of the free drug to its amorphous state in the ASD. Pharmacokinetic analysis in rats demonstrated 1.68- and 2.39-fold increments in AUC and Cmax, respectively, in the ASD over the free drug. Altogether, hydrophilic carrier-based ASDs prepared by the spray-drying technique represent a promising strategy to improve the biopharmaceutical performance of poorly soluble drugs.

Modelling phase separation in amorphous solid dispersions

Much work has been devoted to analysing thermodynamic models for solid dispersions with a view to identifying regions in the phase diagram where amorphous phase separation or drug recrystallization can occur. However, detailed partial differential equation non-equilibrium models that track the evolution of solid dispersions in time and space are lacking. Hence theoretical predictions for the timescale over which phase separation occurs in a solid dispersion are not available. In this paper, we address some of these deficiencies by (i) constructing a general multicomponent diffusion model for a dissolving solid dispersion; (ii) specializing the model to a binary drug/polymer system in storage; (iii) deriving an effective concentration dependent drug diffusion coefficient for the binary system, thereby obtaining a theoretical prediction for the timescale over which phase separation occurs; (iv) calculating the phase diagram for the Felodipine/HPMCAS system; and (iv) presenting a detailed numerical investigation of the Felodipine/HPMCAS system assuming a Flory-Huggins activity coefficient. The numerical simulations exhibit numerous interesting phenomena, such as the formation of polymer droplets and strings, Ostwald ripening/coarsening, phase inversion, and droplet-to-string transitions. A numerical simulation of the fabrication process for a solid dispersion in a hot melt extruder was also presented. STATEMENT OF SIGNIFICANCE: Solid dispersions are products that contain mixtures of drug and other materials e.g. polymer. These are liable to separate-out over time - a phenomenon known as phase separation. This means that it is possible the product differs both compositionally and structurally between the time of manufacture and the time it is taken by the patient, leading to poor bioavailability and so ultimately the shelf-life of the product has to be reduced. Theoretical predictions for the timescale over which phase separation occurs are not currently available. Also lacking are detailed partial differential equation non-equilibrium models that track the evolution of solid dispersions in time and space. This study addresses these issues, before presenting a detailed investigation of a particular drug-polymer system.

Twin-screw extrusion of sustained-release oral dosage forms and medical implants

Most of published reviews of twin-screw extrusion focused on its application for enhancing the bioavailability of amorphous solid dispersions while few of them focused on its use for manufacturing sustained-release oral dosage forms and medical implants, despite the considerable interest and success this process has garnered both in academia and in the pharmaceutical industry. Compared to conventional batch processing, twin-screw extrusion offers the advantages of continuous processing and the ability to prepare oral dosage forms and medical implants that have unique physicochemical and drug release attributes. This review provides an in-depth analysis of the formulation composition and processing conditions of twin-screw extrusion and how these factors affect the drug release properties of sustained-release dosage forms. This review also illustrates the unique advantages of this process by presenting case studies of a wide variety of commercial sustained-release products manufactured using twin-screw extrusion.