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

Investigation of a Palbociclib and Naringin Co-Amorphous System to Ameliorate Anticancer Potential: Insights on In Silico Modeling, Physicochemical Characterization, Ex Vivo Permeation, and In Vitro Efficacy

Palbociclib (PCB), categorized as a BCS class II drug, is characterized by low aqueous solubility. The drug's limited aqueous solubility and poor dissolution rate pose significant challenges, potentially affecting its absorption and overall therapeutic efficacy. Co-amorphous (CAM) systems have been extensively investigated as a potential solution to overcome the issue of poor water solubility in numerous active pharmaceutical ingredients. This research study hypothesized that the coamorphization process involving the compounds PCB and naringin (NG) would lead to an increase in the aqueous solubility of PCB. Additionally, it was proposed that this process would also enhance the anticancer impact of PCB since NG is recognized for its pharmacological impact on breast cancer cells. In silico studies, it was revealed that PCB could interact with NG via hydrogen bonding. Furthermore, the prepared CAM (PCB-NG-CAM) system using PCB and NG was characterized by PXRD, DSC, FTIR, Raman spectroscopy, solid-state 13C nuclear magnetic resonance, and SEM. PCB-NG-CAM exhibited a significant increase in solubility, dissolution rate, and intestinal permeation compared to crystalline PCB. Furthermore, PCB-NG-CAM exhibited excellent physical stability at 40 °C/75% RH for up to 3 months. In addition, PCB-NG-CAM showed superior in vitro efficacy on MDA-MB-231 triple-negative breast cancer cell lines. PCB-NG-CAM resulted in a 2.24 times higher apoptosis rate and a 1.6 times greater ROS production than free PCB. Additionally, the inhibitory effect on cell migration and alterations in MMP was more pronounced in cells treated with PCB-NG-CAM. Therefore, this study indicated that PCB-NG-CAM has the potential to significantly improve the oral administration, solubility, and therapeutic efficacy of PCB.

A review on design rules for formulating amorphous solid dispersions based on drug-polymer interactions in aqueous environment

Amorphous solid dispersions (ASDs) are multi-component formulations in which a drug is molecularly dispersed in a carrier. ASDs undergo complex dissolution mechanisms to generate and sustain a supersaturated state of poorly soluble drugs. The link between enhanced solubility, supersaturation stability and drug-polymer interaction (DPI) is critical for the rational design of ASDs. The key mechanism responsible for a high bioavailability is the evolution of supersaturation during the dissolution of ASDs which is also the driving force for drug precipitation. A critical determinant of robust supersaturation generation and stability during dissolution is the molecular interaction between the drug and polymer. Characterization of DPI in a solution state is, however, challenging because of the poor hydrodynamic resolution of the techniques, traditionally used in solid-state analysis. Further, the dissolution conditions, such as the choice of buffer, pH and ionic strength may complicate the analyses and predictions. The role of DPI is a poorly understood aspect of ASD dissolution and therefore is an active area of research. DPI is critical for understanding the design rules for formulating an optimal ASD formulation. The review focuses on different aspects of DPI to stabilize the supersaturated state of a drug during the dissolution of ASDs.

Calorimetric Monitoring of the Sub-Tg Crystal Growth in Molecular Glasses: The Case of Amorphous Nifedipine

Non-isothermal differential scanning calorimetry (DSC) and Raman microscopy were used to study the crystallization behavior of the 20-50 μm amorphous nifedipine (NIF) powder. In particular, the study was focused on the diffusionless glass-crystal (GC) growth mode occurring below the glass transition temperature (Tg). The exothermic signal associated with the GC growth was indeed directly and reproducibly recorded at heating rates q+ ≤ 0.5 °C·min-1. During the GC growth, the αp polymorphic phase was exclusively formed, as confirmed via Raman microscopy. In addition to the freshly prepared NIF samples, the crystallization of the powders annealed for 7 h at 20 °C was also monitored-approx. 50-60% crystallinity was achieved. For the annealed NIF powders, the confocal Raman microscopy verified a proportional absence of the crystalline phase on the sample surface (indicating its dominant formation along the internal micro-cracks, which is characteristic of the GC growth). All DSC data were modeled in terms of the solid-state kinetic equation paired with the autocatalytic model; the kinetic complexity was described via reaction mechanism based on the overlap of 3-4 independent processes. The kinetic trends associated with decreasing q+ were identified, confirming the temperature-dependent kinetic behavior, and used to calculate a theoretical kinetic prediction conformable to the experimentally performed 7 h annealing at 20 °C. The theoretical model slightly underestimated the true extent of the GC growth, predicting the crystallinity to be 35-40% after 7 h (such accuracy is still extremely good in comparison with the standard kinetic approaches nowadays). Further research in the field of kinetic analysis should thus focus on the methodological ways of increasing the accuracy of considerably extrapolated kinetic predictions.

Reversibly Charge-Switching Polyzwitterionic/Polycationic Coatings for Biomedical Applications: Optimizing the Molecular Structure for Improved Stability

Materials that can be switched between a polycationic/antimicrobial and a polyzwitterionic/protein-repellent state have important applications, e.g., as biofilm-reducing coatings in medical devices. However, the lack of stability under storage and application conditions so far restricts the lifetime and efficiency of such materials. In this work, a polynorbornene-based polycarboxybetaine with an optimized molecular structure for improved hydrolytic stability is presented. The polymer is fully characterized on the molecular level. Surface-attached polymer networks are obtained by spin-coating and UV cross-linking. These coatings are highly uniform and demonstrate charge-switching in zeta-potential studies. Storage stability in the dry state, as well as in aqueous systems at pH 4.5 and 7.4 for 28 days, is demonstrated. At pH 8, hydrolytic degradation is observed. Overall, the materials are substantially more stable than the corresponding ester-based systems.

A Facile Way to Enhance the Therapeutic Efficacy of Hydrophobic Drugs via Amorphous Solid Dispersions

Approximately 40% of marketed drugs and 75% of invested drugs in the pharmaceutical field are poorly soluble hydrophobic drugs with minimal solubility in water which make them difficult to be absorbed by the body and significantly limiting their applications. Among chemotherapeutic agents, numerous antitumor drugs such as platinum compounds, camptothecin, paclitaxel and others are also restricted in processing and preparation due to solubility issues. Therefore, improving the solubility and enhancing the therapeutic efficacy of drugs have always been significant research topics in current pharmaceutics. Herein, we propose an amorphous solid dispersion system PRTA-DOX, involving the protein drug protamine sulphate and hydrophobic doxorubicin as the model hydrophobic drug. In previous studies, ASD (Amorphous Solid Dispersion) has been demonstrated to enhance the solubility of hydrophobic drugs and result in a storage-stable system. Protamine sulphate as a marketed drug is reliable in safety and conveniently obtained. Doxorubicin, an antitumor drug with a broad antitumor spectrum, is commonly used in the treatment of breast cancer. Typically, doxorubicin is prepared in the form of a hydrochloride salt to increase its solubility. However, the utilization of doxorubicin hydrochloride is reduced due to drug resistance issues in biological cells and it exhibits higher toxicity to the body. In this system, protamine sulphate which is rich in arginine guanidino hydrophobic planes physically mixes with doxorubicin which is a hydrophobic molecule with aromatic rings and they are connected through weak interactions: π-π conjugation. They constitute an amorphous solid dispersion system which increases the solubility of hydrophobic doxorubicin, enhances cellular uptake, mitigate some cellular drug resistance and thereby achieves the purpose of improving therapeutic efficacy.

Synergistic effect of polymers in stabilizing amorphous pretomanid through high drug loaded amorphous solid dispersion

Pretomanid (PTM), an oral antibiotic used in the treatment of adults with pulmonary extensively drug-resistant, nonresponsive multidrug-resistant tuberculosis (MDR-TB). It is a poor glass former, that shows high recrystallization tendency from the amorphous and supersaturated state, resulting in low aqueous solubility and suboptimal absorption through the gastrointestinal tract. The present investigation aimed to develop high drug loaded ternary amorphous solid dispersions (ASDs) of PTM with improved stability and enhanced biopharmaceutical performance by utilizing a combination of polymers. The polymers were comprehensively screened based on drug-polymer miscibility and saturation solubility analysis. A combination of Hydroxypropyl Methylcellulose Acetate Succinate (HPMCAS-HF) and Polyvinylpyrrolidone K-30 (PVP K-30) showed synergism in drug-polymer miscibility as evidenced through pronounced depression in the melting endotherm of PTM. The Powder X-ray Diffraction (P-XRD) diffractograms of 30% w/w PTM loaded ternary ASDs displayed the halo pattern, contrary to the binary ASDs. Drug-polymer interactions (hydrophobic forces) involved between PTM and polymers were detected through Fourier Transform Infrared Spectroscopy (FT-IR) and Nuclear Magnetic Resonance Spectroscopy (13C-NMR) which contributed to the synergistic enhancement in solubility and dissolution of ternary ASDs with sustained release over 12 h. Ternary ASDs demonstrated better in-vivo performance compared to the binary ASDs, showing a 4.63-fold increase in maximum plasma concentration. All ASDs remained stable and resisted phase separation during short-term stability studies for 3 months at ambient conditions. It was concluded that the hydrophobic and hydrophilic polymeric combination (HPMCAS-HF and PVP K-30, respectively) effectively prevented the crystallization and ensured sustained drug release with improved in-vivo absorption of PTM.

Creation of Long-Term Physical Stability of Amorphous Solid Dispersions N-Butyl-N-methyl-1-phenylpyrrolo[1,2-a]pyrazine-3-carboxamide, Resistant to Recrystallization Caused by Exposure to Moisture

Amorphous solid dispersion (ASD) technology is often used as a promising strategy to improve the solubility of active pharmaceutical ingredients (APIs). ASDs allow APIs to be dispersed at the molecular level in a polymer carrier, destroying the crystalline structure of the APIs and, thanks to the polymer, providing long-term supersaturation in solution. However, stability issues are an obstacle to the development of new medications with ASD. In addition to the molecular mobility at elevated temperatures leading to the crystallization of APIs, moisture affects the physical stability of ASD, leading to fractional separation and recrystallization. N-butyl-N-methyl-1-phenylpyrrolo[1,2-a]pyrazine-3-carboxamide (GML-3) is an original API with both anxiolytic and antidepressant activity, but its insolubility in water can negatively affect (influence) bioavailability. Our study aims to create ASD GML-3 with moisture-resistant polymers (Soluplus®, HPC) and assess the stability of the amorphous state of ASD after storage in high humidity conditions. As a result, HPC KlucelTM FX was revealed to be more stable than the brand, providing a high level of API release into the purified water environment and stability after 21 days (3 weeks) of storage in high humidity conditions.

Correlation of surface properties with dissolution behavior of amorphous solid dispersion of Riluzole and its pharmacodynamic evaluation

Formulation of amorphous solid dispersion (ASD) of any poorly water-soluble drug is among the most promising techniques to increase the dissolution profile of drug and hence its bioavailability. Various literatures give evidences of the role of drug-polymer interactions in the ASD systems, very little information is available about the surface properties of the drug molecule and their ASDs which contributes to a higher dissolution profile. Current work focuses on exploring the surface behavior of a poorly water-soluble drug Riluzole (RLZ) and its ASDs prepared with two highly hydrophilic polymers, polyacrylic acid (PAA), and polyvinylpyrrolidone vinyl acetate (PVP VA). Initial characterization using X-ray diffraction (XRD) revealed about the weight fraction of drug required to prepare a single-phase homogenous system with both the polymers. The saturation solubility and the dissolution studies showed an increase in RLZ solubility as well as the dissolution profile due to the presence of polymers. The role of polymers in changing the surface properties in terms of wettability and polarity were explored using contact angle method and X-ray photon spectroscopy (XPS). Additionally, the neuroprotective efficacy and dose dependent hepatotoxicity were also evaluated in male wistar rats. These studies confirmed the increase in the surface polarity and hence the enhanced ability of ASD formulations to interact with water. The in vivo studies indicated that at the current recommended dose the efficacy as well as toxicity is increased for the ASD formulation. Hence, this formulation can be given at a lower dose to achieve same therapeutic effect with lower toxicity.

A Miscibility Study of p(MMA-co-HEMA)-Based Polymer Blends by Thermal Analysis and Solid-State NMR Relaxometry

Ternary amorphous solid dispersions (ASDs) consist of a multicomponent carrier with the aim of improving physical stability or dissolution performance. A polymer blend as a carrier that combines a water-insoluble and a water-soluble polymer may delay the drug release rate, minimizing the risk of precipitation from the supersaturated state. Different microstructures of the ternary ASD may result in different drug release performances; hence, understanding the phase morphology of the polymer blend is crucial prior to drug incorporation. The objective of this study is to investigate the miscibility of the water-insoluble p(MMA-co-HEMA) and water-soluble polymers such as HPC, HPMC, HPMC-AS, and Soluplus. To prepare the polymer blends, p(MMA-co-HEMA) was spray dried in 80/20 and 90/10 (w/w) ratios with one of the water-soluble polymers. Thermal analysis (mDSC and DMA) and solid-state (ss)NMR relaxometry were applied to study the miscibility of these blends. No conclusions regarding miscibility could be drawn from the Tg measurements by thermal analysis. However, phase-separation could be demonstrated in all blends by ssNMR relaxometry. Moreover, by measuring both the T1ρH and T1H relaxation times, domain sizes between 5 and 50 nm could be estimated. This work shows the importance of using complementary analytical techniques to investigate polymer miscibility.

Poly(vinylpyridine-co-vinylpyridine N-oxide) Excipients Mediate Rapid Dissolution and Sustained Supersaturation of Posaconazole Amorphous Solid Dispersions

The chemical structure of excipients molecularly mixed in an amorphous solid dispersion (ASD) has a significant impact on properties of the ASD including dissolution behavior, physical stability, and bioavailability. Polymers used in ASDs require a balance between hydrophobic and hydrophilic functionalities to ensure rapid dissolution of the amorphous dispersion as well as sustained supersaturation of the drug in solution. This work demonstrates the use of postpolymerization functionalization of poly(vinylpyridine) excipients to elucidate the impact of polymer properties on the dissolution behavior of amorphous dispersions containing posaconazole. It was found that N-oxidation of pyridine functionalities increased the solubility of poly(vinylpyridine) derivatives in neutral aqueous conditions and allowed for nanoparticle formation which supplied posaconazole into solution at concentrations exceeding those achieved by more conventional excipients such as hydroxypropyl methylcellulose acetate succinate (HPMCAS) or Eudragit E PO. By leveraging these functional modifications of the parent poly(vinylpyridine) excipient to increase polymer hydrophilicity and minimize the effect of polymer on pH, a new polymeric excipient was optimized for rapid dissolution and supersaturation maintenance for a model compound.

Navigating the Solution to Drug Formulation Problems at Research and Development Stages by Amorphous Solid Dispersion Technology

Amorphous Solid Dispersions (ASDs) have indeed revolutionized the pharmaceutical industry, particularly in drug solubility enhancement. The amorphous state of a drug, which is a highenergy metastable state, can lead to an increase in the apparent solubility of the drug. This is due to the absence of a long-range molecular order, which results in higher molecular mobility and free volume, and consequently, higher solubility. The success of ASD preparation depends on the selection of appropriate excipients, particularly polymers that play a crucial role in drug solubility and physical stability. However, ASDs face challenges due to their thermodynamic instability or tendency to recrystallize. Measuring the crystallinity of the active pharmaceutical ingredient (API) and drug solubility is a complex process that requires a thorough understanding of drug-polymer miscibility and molecular interactions. Therefore, it is important to monitor drug solids closely during preparation, storage, and application. Techniques such as solid-state nuclear magnetic resonance (ssNMR), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, and dielectric spectroscopy have been successful in understanding the mechanism of drug crystallization. In addition, the continuous downstream processing of drug-loaded ASDs has introduced new automated methods for consistent ASD production. Advanced techniques such as hot melt extrusion, KinetiSol, electro spraying, and electrospinning have gained popularity. This review provides a comprehensive overview of Amorphous Solid Dispersions (ASDs) for oral drug delivery. It highlights the critical challenges faced during formulation, the impact of manufacturing variables, theoretical aspects of drug-polymer interaction, and factors related to drug-polymer miscibility. ASDs have been recognized as a promising strategy to improve the oral bioavailability of poorly water-soluble drugs. However, the successful development of an ASD-based drug product is not straightforward due to the complexity of the ASD systems. The formulation and process parameters can significantly influence the performance of the final product. Understanding the interactions between the drug and polymer in ASDs is crucial for predicting their stability and performance.

The Implications of Drug-Polymer Interactions on the Physical Stability of Amorphous Solid Dispersions

Amorphous solid dispersions (ASDs) are a formulation and development strategy that can be used to increase the apparent aqueous solubility of poorly water-soluble drugs. Their implementation, however, can be hindered by destabilization of the amorphous form, as the drug recrystallizes from its metastable state. Factors such as the drug-polymer solubility, miscibility, mobility, and nucleation/crystal growth rates are all known to impact the physical stability of an ASD. Non-covalent interactions (NCI) between the drug and polymer have also been widely reported to influence product shelf-life. In this review, the relationship between thermodynamic/kinetic factors and adhesive NCI is assessed. Various types of NCIs reported to stabilize ASDs are described, and their role in affecting physical stability is examined. Finally, NCIs that have not yet been widely explored in ASD formulations, but may potentially impact their physical stability are also briefly described. This review aims to stimulate further theoretical and practical exploration of various NCIs and their applications in ASD formulations in the future.

Solid Form Screenings in Pharmaceutical Development: a Perspective on Current Practices

Solid form screening is a crucial step in new drug development because solid forms of a drug substance significantly affect stability, dissolution and manufacturing processes of its drug products. This perspective introduces solid-state science from a practical standpoint, aiming to reduce knowledge gaps and promote communications among scientists with diverse background. This perspective starts with a concise overview that followed by discussion on timeline and goals of solid form screening. Techniques for solid from identification and characterization are then discussed. Subsequently, the perspective presents commonly used methods in solid form screening and introduces criteria and strategies to effectively select a favorable solid form based on screening results. The last section summarizes current practices in pharmaceutical industries and suggests potential opportunities for future research and development.

Advances in the development of amorphous solid dispersions: The role of polymeric carriers

Amorphous solid dispersion (ASD) is one of the most effective approaches for delivering poorly soluble drugs. In ASDs, polymeric materials serve as the carriers in which the drugs are dispersed at the molecular level. To prepare the solid dispersions, there are many polymers with various physicochemical and thermochemical characteristics available for use in ASD formulations. Polymer selection is of great importance because it influences the stability, solubility and dissolution rates, manufacturing process, and bioavailability of the ASD. This review article provides a comprehensive overview of ASDs from the perspectives of physicochemical characteristics of polymers, formulation designs and preparation methods. Furthermore, considerations of safety and regulatory requirements along with the studies recommended for characterizing and evaluating polymeric carriers are briefly discussed.

Preparation of Polylactic Acid/Calcium Peroxide Composite Filaments for Fused Deposition Modelling

Fused Deposition Modelling (FDM) 3D printers have gained significant popularity in the pharmaceutical and biomedical industries. In this study, a new biomaterial filament was developed by preparing a polylactic acid (PLA)/calcium peroxide (CPO) composite using wet solution mixing and extrusion. The content of CPO varied from 3% to 24% wt., and hot-melt extruder parameters were optimised to fabricate 3D printable composite filaments. The filaments were characterised using an X-ray diffraction analysis, surface morphology assessment, evaluation of filament extrudability, microstructural analysis, and examination of their rheological and mechanical properties. Our findings indicate that increasing the CPO content resulted in increased viscosity at 200 °C, while the PLA/CPO samples showed microstructural changes from crystalline to amorphous. The mechanical strength and ductility of the composite filaments decreased except for in the 6% CPO filament. Due to its acceptable surface morphology and strength, the PLA/CPO filament with 6% CPO was selected for printability testing. The 3D-printed sample of a bone scaffold exhibited good printing quality, demonstrating the potential of the PLA/CPO filament as an improved biocompatible filament for FDM 3D printing.

Structural Modifications of Polyethylenimine to Control Drug Loading and Release Characteristics of Amorphous Solid Dispersions

Crystalline drugs with low solubility have the potential to benefit from delivery in the amorphous form. The polymers used in amorphous solid dispersions (ASDs) influence their maximum drug loading, solubility, dissolution rate, and physical stability. Herein, the influence of hydrophobicity of crosslinked polyethylenimine (PEI) is investigated for the delivery of the BCS class II nonsteroidal anti-inflammatory drug flufenamic acid (ffa). Several synthetic variables for crosslinking PEI with terephthaloyl chloride were manipulated: solvent, crosslinking density, reactant concentration, solution viscosity, reaction temperature, and molecular weight of the hyperbranched polymer. Benzoyl chloride was employed to cap amine groups to increase the hydrophobicity of the crosslinked materials. Amorphous deprotonated ffa was present in all ASDs; however, the increased hydrophobicity and reduced basicity from benzoyl functionalization led to a combination of amorphous deprotonated ffa and amorphous neutral ffa in the materials at high drug loadings (50 and 60 wt %). All ASDs demonstrated enhanced drug delivery in acidic media compared to crystalline ffa. Physical stability testing showed no evidence of crystallization after 29 weeks under various relative humidity conditions. These findings motivate the broadening of polymer classes employed in ASD formation to include polymers with very high functional group concentrations to enable loadings not readily achieved with existing polymers.

Synthesis of Microwave Functionalized, Nanostructured Polylactic Co-Glycolic Acid (nfPLGA) for Incorporation into Hydrophobic Dexamethasone to Enhance Dissolution

The low solubility and slow dissolution of hydrophobic drugs is a major challenge for the pharmaceutical industry. In this paper, we present the synthesis of surface-functionalized poly(lactic-co-glycolic acid) (PLGA) nanoparticles for incorporation into corticosteroid dexamethasone to improve its in vitro dissolution profile. The PLGA crystals were mixed with a strong acid mixture, and their microwave-assisted reaction led to a high degree of oxidation. The resulting nanostructured, functionalized PLGA (nfPLGA), was quite water-dispersible compared to the original PLGA, which was non-dispersible. SEM-EDS analysis showed 53% surface oxygen concentration in the nfPLGA compared to the original PLGA, which had only 25%. The nfPLGA was incorporated into dexamethasone (DXM) crystals via antisolvent precipitation. Based on SEM, RAMAN, XRD, TGA and DSC measurements, the nfPLGA-incorporated composites retained their original crystal structures and polymorphs. The solubility of DXM after nfPLGA incorporation (DXM-nfPLGA) increased from 6.21 mg/L to as high as 87.1 mg/L and formed a relatively stable suspension with a zeta potential of -44.3 mV. Octanol-water partitioning also showed a similar trend as the logP reduced from 1.96 for pure DXM to 0.24 for DXM-nfPLGA. In vitro dissolution testing showed 14.0 times higher aqueous dissolution of DXM-nfPLGA compared to pure DXM. The time for 50% (T₅₀) and 80% (T₈₀) of gastro medium dissolution decreased significantly for the nfPLGA composites; T₅₀ reduced from 57.0 to 18.0 min and T₈₀ reduced from unachievable to 35.0 min. Overall, the PLGA, which is an FDA-approved, bioabsorbable polymer, can be used to enhance the dissolution of hydrophobic pharmaceuticals and this can lead to higher efficacy and lower required dosage.

Supersaturation and phase behavior during dissolution of amorphous solid dispersions

Amorphous solid dispersion (ASD) is a promising strategy to enhance solubility and bioavailability of poorly water-soluble drugs. Due to higher free energy of ASD, supersaturated drug solution could be generated during dissolution. When amorphous solubility of a drug is exceeded, drug-rich nanodroplets could form and act as a reservoir to maintain the maximum free drug concentration in solution, facilitating the absorption of the drug in vivo. Dissolution behavior of ASD has received increasing interests. This review will focus on the recent advances in ASD dissolution, including the generation and maintenance of supersaturated drug solution in absence or presence of liquid-liquid phase separation. Mechanism of drug release from ASD including polymer-controlled dissolution and drug-controlled dissolution will be introduced. Formation of amorphous drug-rich nanodroplets during dissolution and the underlying mechanism will be discussed. Phase separation morphology of hydrated ASD plays a critical role in dissolution behavior of ASD, which will be highlighted. Supersaturated drug solution shows poor physical stability and tends to crystallize. The effect of polymer and surfactant on supersaturated drug solution will be demonstrated and some unexpected results will be shown. Physicochemical properties of drug and polymer could impact ASD dissolution and some of them even show opposite effect on dissolution and physical stability of ASD in solid state, respectively. This review will contribute to a better understanding of ASD dissolution and facilitate a rational design of ASD formulation.

Preparation and Characterization of Stable Amorphous Glassy Solution of BCS II and IV Drugs

The focus of the present investigation was to develop amorphous glassy solutions (AGSs) of BCS Class II and IV drugs using sucrose acetate isobutyrate (SAIB). The drugs studied were rifaximin (RFX), dasatinib (DST), aripiprazole (APZ), dolutegravir (DLT), cyclosporine (CYS), itraconazole (ITZ), tacrolimus (TAC), sirolimus (SRL), aprepitant (APT), and carbamazepine (CBZ). AGSs were prepared by dissolving known quantity of the drug in the SAIB at 120 (TAC and APZ), 140 (CYS) or 150 ^oC (RFX, DST, DLT, ITZ, SRL, APT, and CBZ). They were characterized visually and by NIR, NIR hyperspectroscopy (NIR-H), and XRPD. Stability were determined by exposing open vials to 40 ^oC/75% RH for a week. AGSs behave like a glassy solid at room temperature and liquified above 60 ^oC. The solubility of APT, DLT, SRL, APZ, RFX, CBZ, TAC and CYS in SAIB was 0.4±0.0, 1.7±0.4, 1.9±0.0, 21.6±2.6, 36.4±0.9, 76.5±4.0, 115.1±2.3, and 239.0±12.6 mg/g, respectively. NIR, NIR-H, and XRPD data indicated the amorphous nature of the AGSs. Furthermore, AGSs were stable against devitrification on exposure to high temperature and humidity. In summary, SAIB can be employed to develop stable AGSs of poorly soluble drugs to increase dissolution, and oral bioavailability with the addition of hydrophilic excipients.

Role of polymers in the physical and chemical stability of amorphous solid dispersion: A case study of carbamazepine

Incorporating the amorphous drug in polymeric components has been demonstrated as a feasible approach to enhance the bioavailability of poorly water-soluble drugs. The objective of this study was to investigate the role of polymers in the stability of amorphous solid dispersion (ASD) by evaluating the drug-polymer interaction, microenvironmental pH, and stability of ASD. Carbamazepine (CBZ), a Biopharmaceutics Classification System Class II compound, was utilized as a model drug. Polyvinylpyrrolidone (PVP), poly(1-vinylpyrrolidone-co-vinyl acetate) (PVPVA), polyacrylic acid (PAA), and hydroxypropyl methylcellulose (HPMCAS) were selected as model polymers. CBZ ASDs were characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and dissolution studies. Molecular modeling was conducted to understand the strength of interaction between CBZ and each polymer. FTIR spectroscopy and molecular modeling results show that the interaction between CBZ and PAA is the strongest among all the ASDs, as PAA is an acidic polymer with the potential to form strong hydrogen bonding with CBZ. Besides, hydrophobic interaction is detected between CBZ and HPMCAS. CBZ-PAA and CBZ-HPMCAS ASDs reveal better physical stability than CBZ-PVP and CBZ-PVPVA ASDs under 40 °C/75% RH for 8 weeks. However, CBZ-PAA ASD shows chemical degradation after stability testing due to its acidic microenvironmental pH. This paper shows that strong intermolecular interactions between CBZ and polymers contribute to the physical stability of the ASDs. Additionally, acidic polymers yield an acidic microenvironment pH of the ASDs that causes chemical degradation during storage. Hence, a balance between the ability of a given polymer to promote physical stability and chemical stability may need to be considered.

Optimizing Solvent Selection and Processing Conditions to Generate High Bulk-Density, Co-Precipitated Amorphous Dispersions of Posaconazole

Co-precipitation is an emerging method to generate amorphous solid dispersions (ASDs), notable for its ability to enable the production of ASDs containing pharmaceuticals with thermal instability and limited solubility. As is true for spray drying and other unit operations to generate amorphous materials, changes in processing conditions during co-precipitation, such as solvent selection, can have a significant impact on the molecular and bulk powder properties of co-precipitated amorphous dispersions (cPAD). Using posaconazole as a model API, this work investigates how solvent selection can be leveraged to mitigate crystallization and maximize bulk density for precipitated amorphous dispersions. A precipitation process is developed to generate high-bulk-density amorphous dispersions. Insights from this system provide a mechanistic rationale to control the solid-state and bulk powder properties of amorphous dispersions.

Supersaturation and Solubilization upon In Vitro Digestion of Fenofibrate Type I Lipid Formulations: Effect of Droplet Size, Surfactant Concentration and Lipid Type

Lipid-based formulations (LBF) enhance oral drug absorption by promoting drug solubilization and supersaturation. The aim of the study was to determine the effect of the lipid carrier type, drop size and surfactant concentration on the rate of fenofibrate release in a bicarbonate-based in vitro digestion model. The effect of the lipid carrier was studied by preparing type I LBF with drop size ≈ 2 µm, based on medium-chain triglycerides (MCT), sunflower oil (SFO), coconut oil (CNO) and cocoa butter (CB). The drop size and surfactant concentration effects were assessed by studying MCT and SFO-based formulations with a drop size between 400 nm and 14 µm and surfactant concentrations of 1 or 10%. A filtration through a 200 nm filter followed by HPLC analysis was used to determine the aqueous fenofibrate, whereas lipid digestion was followed by gas chromatography. Shorter-chain triglycerides were key in promoting a faster drug release. The fenofibrate release from long-chain triglyceride formulations (SFO, CNO and CB) was governed by solubilization and was enhanced at a smaller droplet size and higher surfactant concentration. In contrast, supersaturation was observed after the digestion of MCT emulsions. In this case, a smaller drop size and higher surfactant had negative effects: lower peak fenofibrate concentrations and a faster onset of precipitation were observed. The study provides new mechanistic insights on drug solubilization and supersaturation after LBF digestion, and may support the development of new in silico prediction models.

Application of Polymers as a Tool in Crystallization-A Review

The application of polymers as a tool in the crystallization process is gaining more and more interest among the scientific community. According to Web of Science statistics the number of papers dealing with “Polymer induced crystallization” increased from 2 in 1990 to 436 in 2020, and for “Polymer controlled crystallization”—from 4 in 1990 to 344 in 2020. This is clear evidence that both topics are vivid, attractive and intensively investigated nowadays. Efficient control of crystallization and crystal properties still represents a bottleneck in the manufacturing of crystalline materials ranging from pigments, antiscalants, nanoporous materials and pharmaceuticals to semiconductor particles. However, a rapid development in precise and reliable measuring methods and techniques would enable one to better describe phenomena involved, to formulate theoretical models, and probably most importantly, to develop practical indications for how to appropriately lead many important processes in the industry. It is clearly visible at the first glance through a number of representative papers in the area, that many of them are preoccupied with the testing and production of pharmaceuticals, while the rest are addressed to new crystalline materials, renewable energy, water and wastewater technology and other branches of industry where the crystallization process takes place. In this work, authors gathered and briefly discuss over 100 papers, published in leading scientific periodicals, devoted to the influence of polymers on crystallizing solutions.

The effect of some acrylic polymers on dissolution of celecoxib solid dispersion formulations

OBJECTIVE

The purpose of the present study was firstly to identify the effectiveness of Eudragit® polymers (Eudragit^® RL, RS, L100-55, L100, S100 and E100) in inhibition of celecoxib precipitation from buffer solutions (pH = 6.8). Furthermore, the influence of Eudragit^® polymers on non-sink dissolution behavior of celecoxib from solid dispersions was investigated.

METHODS

Solid dispersions were prepared by the rotary evaporation method. In vitro dissolution studies, FT-IR and differential scanning calorimetry were employed to characterize the formulations.

RESULTS

The results revealed that Eudragit^® E100, L100 and S100 inhibited precipitation of celecoxib efficiently. It is understood that crystallization during the dissolution of solid dispersions could happen through crystallization from solid matrix following contact with the dissolution medium or from the supersaturated solution produced following dissolution. The supersaturated drug concentrations attained from the dissolution of Eudragit^®-celecoxib solid dispersions were almost similar, suggesting that crystallization from solid matrix did not occur readily. However, only solid dispersions containing efficient crystallization inhibitor polymers were able to maintain the supersaturated solution up to the end of the dissolution run.

CONCLUSION

Results revealed that the principal mechanism of attaining supersaturated solution of celecoxib from solid dispersions was related to crystallization inhibition from solution not from solid matrix.

Facile preparation of solid dispersions by dissolving drugs in N-vinyl-2-pyrrolidone and photopolymerization

Drug solid dispersions improve the dissolution of drugs in aqueous media for enhancement of oral bioavailability. The current preparation methods of drug solid dispersions mainly involve the evaporation of solvents or the melting of drugs and matrix. Here, we create a new and simple method for the preparation of drug solid dispersions by dissolving drugs in N-vinyl-2-pyrrolidone (NVP) and then NVP photopolymerization. A variety of drugs were explored to find whether they were suitable for this method and only some of them were soluble in NVP and formed transparent and hard solid dispersions, including fluconazole, ketoconazole, bifonazole, miconazole nitrate, sulfamethoxazole, aspirin, ibuprofen and artesunate. The formation of photocuring solid dispersions was highly related to the free radical scavenging function of drugs. Those drugs with strong free radical scavenging capability, including curcumin, resveratrol, quercetin, genistein, puerarin, nicergoline, olanzapine, indomethacin, did not form solid dispersions. They scavenged 2,2-diphenyl-1-picrylhydrazyl free radicals, which was demonstrated by ultraviolet spectrometry and electron spin resonance. The scavenging of free radicals stopped the chain polymerization of NVP. The Fourier transform infrared spectra, X-ray diffraction and differential scanning calorimetry of ibuprofen solid dispersions and artesunate solid dispersions showed the molecularly miscible state of the drugs and the hydrogen bonding between the drugs and polyvinyl pyrrolidone. The NVP-based solid dispersions of the two drugs had faster and more complete dissolution than their traditional solid dispersions. The NVP photopolymerization-based solid dispersion method provides a new choice for the production of solid dispersions in the research and industrial fields.

Prediction of the physical stability of amorphous solid dispersions: relationship of aging and phase separation with the thermodynamic and kinetic models along with characterization techniques

Introduction: Solid dispersion has been considered to be one of the most promising methods for improving the solubility and bioavailability of insoluble drugs. However, the physical stability of solid dispersions (SDs), including its aging and recrystallization, or phase separation, has always been one of the most challenging problems in the process of formulation development and storage.Areas covered: The high energy state of SDs is one of the primary reasons for the poor physical stability. The factors affecting the physical stability of SDs have been described from the perspective of thermodynamics and kinetics, and the corresponding theoretical model is put forward. We briefly summarize several commonly used techniques to characterize the thermodynamic and kinetic properties of SDs. Specific measures to improve the physical stability of SDs have been proposed from the perspective of prescription screening, process parameters, and storage conditions.Expert opinion: The separation of the drug from the polymer, the formation, and migration of drug crystals will cause the SDs to shift toward the direction of energy reduction, which is the intrinsic cause of instability. Furthermore, computational simulation can be used for efficient and rapid screening suitable for the excipients to improve the physical stability of SDs.

Overview of Extensively Employed Polymeric Carriers in Solid Dispersion Technology

Solid dispersion is the preferred technology to prepare efficacious forms of BCS class-II/IV APIs. To prepare solid dispersions, there exist a wide variety of polymeric carriers with interesting physicochemical and thermochemical characteristics available at the disposal of a formulation scientist. Since the advent of the solid dispersion technology in the early 1960s, there have been more than 5000 scientific papers published in the subject area. This review discusses the polymeric carrier properties of most extensively used polymers PVP, Copovidone, PEG, HPMC, HPMCAS, and Soluplus® in the solid dispersion technology. The literature trends about preparation techniques, dissolution, and stability improvement are analyzed from the Scopus® database to enable a formulator to make an informed choice of polymeric carrier. The stability and extent of dissolution improvement are largely dependent upon the type of polymeric carrier employed to formulate solid dispersions. With the increasing acceptance of transfer dissolution setup in the research community, it is required to evaluate the crystallization/precipitation inhibition potential of polymers under dynamic pH shift conditions. Further, there is a need to develop a regulatory framework which provides definition and complete classification along with necessarily recommended studies to characterize and evaluate solid dispersions.

A novel amorphous solid dispersion based on drug-polymer complexation

Rafoxanide (RAF) is a poorly water-soluble drug that forms a complex with povidone K25 (PVP) in a cosolvent system containing acetone and an alkaline aqueous medium. This study aims to investigate the impact of RAF-PVP complexation on in vitro and in vivo release of RAF. We prepared two RAF amorphous solid dispersions (ASDs) spray-dried from these two cosolvents. The first is a complexation-based spray-drying using a 70% 0.1 N NaOH solution with 30% acetone. The second is a traditional spray-dried formulation containing 80% acetone and 20% ethanol. Evidence from multiple solid-state characterization techniques indicated that ASDs spray-dried using both methods were amorphous. However, RAF ASDs based on drug-polymer complexation in the feed solution demonstrated not only faster drug release during dissolution testing but also higher in vivo absorption in an animal model. The improved RAF release in the complexation-based ASD is due to (1) high energy state of RAF owing to the amorphous form, (2) high pH in the microenvironment due to the ionized state of RAF and residual sodium hydroxide, (3) increased apparent solubility of RAF results from RAF-PVP complexation in dissolution media and biological media, and (4) improved wettability.

Characterizing and Exploring the Differences in Dissolution and Stability Between Crystalline Solid Dispersion and Amorphous Solid Dispersion

Solid dispersion is one of the most effective ways to improve the dissolution of insoluble drugs. When the carrier can highly disperse the drug, it will increase the wettability of the drug and reduce the surface tension, thus improving the solubility, dissolution, and bioavailability. However, amorphous solid dispersions usually have low drug loading and poor stability. Therefore, the goal of this work is to study the increased dissolution and high stability of high drug-loading crystalline solid dispersion (CSD), and the difference in dissolution and stability of high-loading and low-loading amorphous solid dispersion (ASD). A CSD of nimodipine with a drug loading of 90% was prepared by wet milling, with hydroxypropyl cellulose (model: HPC-SL) and sodium dodecyl sulfate as stabilizers and spray drying. At the same time, the gradient drug-loaded ASD was prepared by hot melt extrusion with HPC-SL as the carrier. Each preparation was characterized by DSC, PXRD, FT-IR, SEM, and in vitro dissolution testing. The results indicated that the drug in CSD existed in a crystalline state. The amorphous drug molecules in the low drug-loading ASD were uniformly dispersed in the carrier, while the drug state in the high drug-loading ASD was aggregates of the amorphous drug. At the end of the dissolution assay, the 90% drug-loading CSD increased cumulative dissolution to 60%, and the 10% drug-loading ASD achieved a cumulative dissolution rate of 90%.

Degrees of order: A comparison of nanocrystal and amorphous solids for poorly soluble drugs

Poor aqueous solubility is currently a prevalent issue in the development of small molecule pharmaceuticals. Several methods are possible for improving the solubility, dissolution rate and bioavailability of Biopharmaceutics Classification System (BCS) class II and class IV drugs. Two solid state approaches, which rely on reductions in order, and can theoretically be applied to all molecules without any specific chemical prerequisites (compared with e.g. ionizable or co-former groups, or sufficient lipophilicity), are the use of the amorphous form and nanocrystals. Research involving these two approaches is relatively extensive and commercial products are now available based on these technologies. Nevertheless, their formulation remains more challenging than with conventional dosage forms. This article describes these two technologies from both theoretical and practical perspectives by briefly discussing the physicochemical backgrounds behind these approaches, as well as the resulting practical implications, both positive and negative. Case studies demonstrating the benefits and challenges of these two techniques are presented.

Inhibiting or Accelerating Crystallization of Pharmaceuticals by Manipulating Polymer Solubility

Polymers play a central role in controlling the crystallization of pharmaceuticals with effects as divergent as amorphous form stabilization and the acceleration of crystallization. Here, using pyrazinamide and hydrochlorothiazide as model pharmaceuticals, it is demonstrated that the same functional group interactions are responsible for these opposing behaviors and that whether a polymer speeds or slows a crystallization can be controlled by polymer solubility. This concept is applied for the discovery of polymers to maintain drug supersaturation in solution: the strength of functional group interactions between drug and polymer is assessed through polymer-induced heteronucleation, and soluble polymers containing the strongest-interacting functional groups with drug are shown to succeed as precipitation inhibitors.