Assessing the performance of amorphous solid dispersions

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

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

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

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

Probing the molecular interactions between pharmaceutical polymeric carriers and bile salts in simulated gastrointestinal fluids using NMR spectroscopy

The number of poorly soluble new drugs is increasing and one of the effective ways to deliver such pharmaceutically active molecules is using hydrophilic polymers to form a solid dispersion. Bile salts play an important role in the solubilisation of poorly soluble compounds in the gastrointestinal tract (gut) prior to absorption. When a poorly water-soluble drug is delivered using a hydrophilic polymer based solid dispersion oral formulation, it is still unclear whether there are any polymer-bile salt interactions, which may influence the drug dissolution and solubilisation. This study, using two widely used hydrophilic model polymers, Hydroxypropyl methylcellulose (HPMC) and polyvynilpirrolidone (PVP), and sodium taurocholate (NaTC) as the model bile salt, aims to investigate the interactions between the polymers and bile salts in simulated fed state (FeSSIF) and fasted state (FaSSIF) gut fluids. The nature of the interactions was characterised using a range of NMR techniques. The results revealed that the aggregation behaviour of NaTC in FaSSIF and FeSSIF is much more complex than in water. The addition of hydrophilic polymers led to the occurrences of NaTC-HPMC and NaTC-PVP aggregation. For both systems, pH and ionic strength strongly influenced the aggregation behavior, while the ion type played a less significant role. The outcome of this study enriched the understanding of the aggregation behaviour of bile salts and typical hydrophilic pharmaceutical polymers in bio-relevant media. Due to the high surface-activity of the bile salts and their ability to interact with polymers, such aggregation behaviour is expected to play a role in drug solubilisation in the gut when the drug is delivered by hydrophilic polymer based dispersions.

Insights into the Dissolution Mechanism of Ritonavir-Copovidone Amorphous Solid Dispersions: Importance of Congruent Release for Enhanced Performance

The aim of this study was to probe the dissolution mechanisms of amorphous solid dispersions (ASDs) of a poorly water-soluble drug formulated with a hydrophilic polymer. Ritonavir (RTV) and polyvinylpyrrolidone/vinyl acetate (PVPVA) were used as the model drug and polymer, respectively. ASDs with drug loadings (DLs) from 10 to 50 wt % were prepared by solvent evaporation. Surface-normalized dissolution experiments were carried out using Wood's intrinsic dissolution apparatus, and both drug and polymer release were quantified. ASDs at or below 25% DL showed rapid, complete, and congruent (i.e., simultaneous) release of the drug and polymer with dissolution rates similar to that of the polymer alone. The highest drug loading at which congruent release was observed is termed the limit of congruency (LoC) and occurred at 25% DL for RTV-PVPVA. The ASD with 30% DL showed an initial lag time, followed by a period of congruent release. At later times, the release of drug and polymer became incongruent with polymer releasing faster than drug. Higher DL ASDs (40 and 50%) showed slow release of both drug and polymer, whereby the drug release rate was similar to that of the neat amorphous drug. In cases where the release of the ASD components was congruent or close to congruent, the drug concentration exceeded the amorphous solubility, and liquid-liquid phase separation (LLPS) occurred with the formation of colloidal, drug-rich species. Solid state analyses of the ASD tablet surface by infrared spectroscopy and scanning electron microscopy revealed that the partially dissolved tablet surface remains smooth, and drug-polymer miscibility is retained at low DLs; whereas, at a very high DL, the surface is porous and enriched with amorphous drug. In concert, these observations suggest that ASD dissolution and drug release at low DLs is governed primarily by hydrophilic polymer; whereas, at high DLs, amorphous drug controls dissolution. Fluorescence microscopy images of thin ASD films suggested that ASDs at or below the LoC remain homogeneous even after exposure to water. In contrast ASDs with DL above LoC undergo, to various extents, water-induced amorphous-amorphous phase separation (AAPS) leading to demixing of the drug and polymer. Correlating the observations of the dissolution study with the solid state data suggest that the ASDs with DLs higher than the LoC undergo AAPS in the hydrating matrix on the surface of the dissolving solid during dissolution, leading to separation of drug and polymer, the formation of a drug-rich interface, and hence, incongruent and/or slow release of the components. In contrast, low DL ASDs dissolve before AAPS occurs. The competition between these two parallel and competing processes on the surface of ASD solids, i.e., dissolution and AAPS, thus dictates the overall release characteristics of the ASD formulations, which is one of the most important considerations in designing formulations with superior dissolution and absorption.

Drug Carrier-Oriented Polygeline for Preparing Novel Polygeline-Bound Paclitaxel Nanoparticles

Polygeline is a highly promising drug carrier-oriented material for important applications in pharmacy field due to its low-cost and unique properties similar to albumin. In this study, polygeline-bound paclitaxel nanoparticles (Npb-PTXS) were fabricated through a combination of low-pressure emulsification and high-pressure homogenization. The effects of a series of production parameters on mean particle size, particle size distribution and drug loading of Npb-PTXS were systematically evaluated. The characteristics of Npb-PTXS, such as surface morphology, physical status of paclitaxel (PTX) in Npb-PTXS, redispersibility of Npb-PTXS in purified water and bioavailability in vivo were also investigated. It is revealed that the optimal preparation conditions included an aqueous phase pH value of about 6.5, protein mass concentration of 0.33%, with mass ratio of PTX to protein of 30%, high pressure of 1200 bar, high-pressure passes of 25 times and low-pressure emulsifying passes of 20 times. Obtained Npb-PTXS shows good resolubility compared to commercially available Abraxane^®, containing round or oval shaped particles with mean particle size of around 188.3 nm, polydispersity index of 0.163 and zeta potential of -31.1 mV. PTX in Npb-PTX is amorphous, and its content is approximately 12.04%. Encapsulation efficiency of Npb-PTXS reaches 81.2%. Moreover, in vivo pharmacokinetic studies showed that the intravenous relative bioavailability of Npb-PTXS to Abraxane was 83.89%.

Building a better particle: Leveraging physicochemical understanding of amorphous solid dispersions and a hierarchical particle approach for improved delivery at high drug loadings

Amorphous solid dispersions are a promising option for managing compounds with poor aqueous solubility. However, for compounds with high melting points, thermal stability limitations, or poor solubility in volatile solvents, conventional routes of hot melt extrusion or spray drying may not be viable. Co-precipitated amorphous dispersions (cPAD) can provide a solution. For the material studied in this paper, the cPAD material that was seemingly identical to spray dried material in terms of being single phase amorphous (as measured by DSC and XRD ) but showed slower dissolution behavior. It was identified that physical properties of the cPAD material could be improved to enhance wettability and improve dissolution performance. This was achieved by incorporating the cPAD material into a matrix of water soluble excipients generated via evaporative isolation routes. Importantly, this approach appears to offer another route to further increase the drug load in final dosage units and is significant as increased drug loading generally results in slower or incomplete release. Results showed successful proof of concept via in vitro biorelevant dissolution and confirmatory canine pharmacokinetic studies yielding comparable exposure for capsules comprised of conventional spray dried material as well as capsules with elevated drug load comprised of cPAD hierarchical particles.

Designing an ADME liquid formulation with matching exposures to an amorphous dosage form

Amorphous Solid Dispersion (ASD) based formulations have been frequently used to improve the bioavailability of poorly water soluble drugs, however, common processes to produce ASDs are not feasible for Absorption, Distribution, Metabolism and Excretion (ADME) studies with radio-labeled Active Pharmaceutical Ingredients (API) due to the complications associated with radioactive material handling. Liquid formulations are routinely used to support the ADME studies, though bridging the bioperformance between a liquid formulation to the amorphous dosage form for poorly soluble compounds has not been well studied, and can be challenging due to the potentially rapid in vitro and in vivo recrystallization and precipitation. Here we report the development of a fit for purpose liquid formulation that could accommodate the radioactive API and provide comparable bioavailability relative to the amorphous formulation without the need for dose adjustment. A number of formulation approaches were explored and the prototype formulations were evaluated by dissolution and preclinical pharmacokinetic studies. A PolyEthylene Glycol 400 (PEG 400) based solution formulation impregnated with a polymer, HydroxyPropyl MethylCellulose Acetate Succinate-L (HPMCAS-L), was identified as the lead formulation. It was found that the bioavailability of the formulation can be compromised by the presence of undissolved crystalline seeds, and the inclusion of HPMCAS-L can mitigate this effect, as well as potentially facilitate the nanoparticle formation. During the study, it is also noted that although dissolution test is instrumental in the formulation development, the in vitro study over predicted the extent of in vivo precipitation for PEG 400 formulation containing no crystalline seeds.

Insight into Amorphous Solid Dispersion Performance by Coupled Dissolution and Membrane Mass Transfer Measurements

The tendency of highly supersaturated solutions of poorly water-soluble drugs to undergo liquid-liquid phase separation (LLPS) into drug-rich and water-rich phases when the concentration exceeds the amorphous solubility, for example, during dissolution of some amorphous solid dispersions, is thought to be advantageous from a bioavailability enhancement perspective. Recently, we have developed a high surface area, flow-through absorptive dissolution testing apparatus that enables fast mass transfer providing more in vivo relevant conditions and time frames for formulation testing. Using this apparatus, the absorption behaviors of solutions with different extents of supersaturation below and above the amorphous solubility were evaluated. In addition, simultaneous dissolution-absorption testing of amorphous solid dispersions (ASDs) with varying drug loadings and polymer types was carried out to study and distinguish the absorption behavior of ASDs that do or do not undergo LLPS. When compared with closed-compartment dissolution testing, a significant influence of the absorptive compartment on the dissolution rate of ASDs, particularly at high drug loadings, was observed. The formation of drug-rich nanodroplets, generated by both solvent-addition and ASD dissolution, resulted in a higher amount of drug transferred across the membrane. Moreover, the mass transfer was further enhanced with increasing concentration above the amorphous solubility, thereby showing correlation with an increase in the number of drug-rich particles. The importance of including an absorptive compartment in dissolution testing is highlighted in this study, enabling coupling of dissolution to membrane transport, and providing a more meaningful comparison between different formulations.

Impact of a Single Hydrogen Substitution by Fluorine on the Molecular Interaction and Miscibility between Sorafenib and Polymers

We aim to understand the potential impact of a modest chemical modification of a drug molecule on the downstream design of its amorphous solid dispersion (ASD) formulation. To this end, we used sorafenib (SOR) and its fluorinated form, regorafenib (REG), as model drugs, to assess the impact of a single hydrogen substitution by fluorine on the molecular interaction and miscibility between drug and PVP or PVP-VA, two commonly used polymers for ASDs. In this study, we observed that the T_g values of PVP or PVP-VA based ASDs of SOR deviated positively from the Gordon-Taylor prediction, which assumes ideal mixing, yet the T_g of REG ASDs deviated negatively from or matched well with the ideal mixing model, suggesting much stronger drug-polymer interactions in SOR ASDs compared with the REG ASDs. Using solution NMR and computational methods, we proved that a six-member-ring formed between the carbonyl groups on the polymers and the uramido hydrogen of SOR or REG, through intermolecular hydrogen bonding. However, steric hindrance resulting from fluorination in REG caused weaker interaction between REG-polymer than SOR-polymer. To further confirm this mechanism, we investigated the molecular interactions of other two uramido-containing model compounds, triclocarban (TCC) and gliclazide (GCZ), with PVP. We found that TCC but not GCZ formed a hexatomic ring with PVP. We concluded that PVP based polymers can easily interact with N, N'-disubstituted urea compounds with a trans-trans structure in the form of hexatomic rings, and the interaction strength of the hexatomic ring largely depended on the chemistry of drug molecules. This study illustrated that even a slight chemical modification on drug molecules could result in substantial difference in drug-polymer interactions, thus significantly impacting polymer selection and pharmaceutical performance of their ASD formulations.

Early stages of drug crystallization from amorphous solid dispersion via fractal analysis based on chemical imaging

Early stages of crystallization from amorphous solid dispersion (ASD) are typically not detected by means of standard methods like powder X-ray diffraction (XRPD). The aim of this study is therefore to evaluate if fractal analysis based on energy dispersive X-ray imaging can provide the means to identify early signs of physical instability. ASDs of the poorly water-soluble compound, felodipine (FEL) were prepared by solvent evaporation using different grades of HPMCAS, at 50 wt% drug loading. Samples were stored at accelerated conditions of 40 °C. Scanning electron microscopy equipped with an energy-dispersive X-ray spectroscopy (SEM-EDS) was used for elemental mapping of tablet surfaces. Comparative data were generated with a standard XRPD and with more sensitive methods for detection of early instability, i.e. laser scanning confocal microscopy (LSM) and atomic force microscopy (AFM). The SEM-EDS identified changes of drug-rich domains that were confirmed by LSM and AFM. Early changes in drug clusters were also revealed by a multifractal analysis that indicated a beginning phase separation and drug crystallization. Therefore, the presented fractal cluster analysis based on chemical imaging bears much promise as a new method to detect early signs of physical instability in ASD, which is of great relevance for pharmaceutical development.

Cooperative effect of polyvinylpyrrolidone and HPMC E5 on dissolution and bioavailability of nimodipine solid dispersions and tablets

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HPMC was used to inhibit crystallization both in solid dispersions and tablets.

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Fluid-bed technique was employed to realize the scaling-up of solid dispersions.

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Dissolution results became reliable with the usage of discriminatory media.

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The results of the bioavailability showed a higher AUC_{0–12 h} value for fluid-bed tablets, compared to Nimotop™.

Solid dispersion (SD) systems have been extensively used to increase the dissolution and bioavailability of poorly water-soluble drugs. To circumvent the limitations of polyvinylpyrrolidone (PVP) dispersions, HPMC E5 was applied in the formulation process and scaling-up techniques, simultaneously. In this study, SD of nimodipine (NMP) and corresponding tablets were prepared through solvent method and fluid bed granulating one step technique, respectively. Discriminatory dissolution media were used to obtain reliable dissolution results. Meanwhile, the stability study of SDs was investigated with storage under high temperature and humidity conditions. Moreover, the solubility of SDs was measured to explore the effect of carriers. The preparations were characterized by DSC, PXRD, and FTIR. Dramatical improvements in the dissolution rate of NMP were achieved by the ingenious combination of the two polymers. Binary NMP/PVP/HPMC-SDs released steadily, while the dissolution of single NMP/PVP-SDs decreased rapidly in water. The fluid-bed tablets (FB-T) possessed a similar dissolution behavior to the commercial Nimotop™ tablets. The characterization patterns implied that NMP existed in an amorphous state in our SDs. Furthermore, the results of stability tests suggested a better stability of the binary SDs. A special cooperative effect of PVP and HPMC was discovered on dissolution characteristics of NMP SDs and tablets, which could be extended to other drugs henceforth. Finally, the bioavailability of FB-T was evaluated in beagle dogs with Nimotop™ as the reference, and the results showed a higher AUC_0–12hvalue for FB-T.

Effects of Dendrimer-Like Biopolymers on Physical Stability of Amorphous Solid Dispersions and Drug Permeability Across Caco-2 Cell Monolayers

The potential applications of dendrimer-like biopolymers (DLB) as stabilizing excipients for amorphous solid dispersion (ASD) of niclosamide, celecoxib, and resveratrol were evaluated based on (1) the formation and physical stability of the ASD and (2) the permeability and flux of the agents across Caco-2 cell monolayers. The evaluation was made by comparing the performance of prototype phytoglycogen derivatives (DLB1, DLB2, and DLB3) with commonly used polymers such as HPMCAS, PVPVA, and Soluplus®. PXRD was used to confirm the formation of the dispersions and detect crystallinity peaks formed during 2- and 4-week storage at 40°C/75% RH. At concentrations below 2 g/mL, the viability of Caco-2 cells remained above 80% for all DLB samples compared to untreated cells in the MTT assay. Permeability studies revealed a repeating pattern in which an increase in the initial concentration (C₀) was associated with a concomitant decrease in the apparent permeability (P_app) which we theorize is due to differences in drug-polymer interactions. Niclosamide-DLB1 dispersion had the lowest flux due to a significant reduction in P_app. The high increase in the C₀ of celecoxib-DLB2, however, made up for the reduction in the P_app and produced the highest flux values compared to other polymers. Resveratrol-DLB3 had a 5× reduction in P_app, but C₀ increased from 25.8 to 176 μg/mL led to a higher flux compared to the crystalline drug without polymer. Collectively, these results provide a "proof-of-concept" basis to demonstrate that DLB excipients have the ability to increase apparent solubility (Sol_app), most likely due to drug-binding capacity.

Effect of amorphous phase separation and crystallization on the in vitro and in vivo performance of an amorphous solid dispersion

In this study, the performance of phase separated and crystallized amorphous solid dispersions (ASDs) was evaluated by non-sink in vitro dissolution testing in fasted-state simulated intestinal fluid (FaSSIF) and in vivo in rats. The amorphous phase-separated or crystallized ASDs were prepared by mixing an ASD of the model drug celecoxib (CCX) in polyvinylpyrrolidone (PVP) with pure amorphous or micronized crystalline CCX at 20, 40, 60 or 100% of the total drug load (25:75 w/w CCX:PVP), respectively. As expected, crystallization of CCX in the ASDs generally had a negative influence on both the area under the curve of the dissolution curve (in vitro AUC) and the plasma concentration-time profile (in vivo AUC) in rats compared to the pure ASD. However, the difference between the in vivo AUC of the pure ASD and the 20% and 40% crystallized ASDs was not statistically significant, which could indicate that a low fraction of crystallization of a drug in an ASD may only have limited impact on in vivo performance and hence bioavailability. In comparison, amorphous phase separation of CCX in the ASDs did not negatively influence the in vitro AUC and in vivo AUC to the same degree as crystallization and the dissolution profiles of all the amorphous phase-separated ASDs were similar to that of the pure ASD. In fact, even though a slight decrease of in vivo AUC with increasing fraction of amorphous phase separation was observed, the 20% and 40% amorphous phase-separated ASDs were bioequivalent with the pure ASD.

DNP-enhanced solid-state NMR spectroscopy of active pharmaceutical ingredients

Solid-state NMR spectroscopy has become a valuable tool for the characterization of both pure and formulated active pharmaceutical ingredients (APIs). However, NMR generally suffers from poor sensitivity that often restricts NMR experiments to nuclei with favorable properties, concentrated samples, and acquisition of one-dimensional (1D) NMR spectra. Here, we review how dynamic nuclear polarization (DNP) can be applied to routinely enhance the sensitivity of solid-state NMR experiments by one to two orders of magnitude for both pure and formulated APIs. Sample preparation protocols for relayed DNP experiments and experiments on directly doped APIs are detailed. Numerical spin diffusion models illustrate the dependence of relayed DNP enhancements on the relaxation properties and particle size of the solids and can be used for particle size determination when the other factors are known. We then describe the advanced solid-state NMR experiments that have been enabled by DNP and how they provide unique insight into the molecular and macroscopic structure of APIs. For example, with large sensitivity gains provided by DNP, natural isotopic abundance, ¹³ C-¹³ C double-quantum single-quantum homonuclear correlation NMR spectra of pure APIs can be routinely acquired. DNP also enables solid-state NMR experiments with unreceptive quadrupolar nuclei such as ² H, ¹⁴ N, and ³⁵ Cl that are commonly found in APIs. Applications of DNP-enhanced solid-state NMR spectroscopy for the molecular level characterization of low API load formulations such as commercial tablets and amorphous solid dispersions are described. Future perspectives for DNP-enhanced solid-state NMR experiments on APIs are briefly discussed.

Expanding the Application and Formulation Space of Amorphous Solid Dispersions with KinetiSol®: a Review

Due to the high number of poorly soluble drugs in the development pipeline, novel processes for delivery of these challenging molecules are increasingly in demand. One such emerging method is KinetiSol, which utilizes high shear to produce amorphous solid dispersions. The process has been shown to be amenable to difficult to process active pharmaceutical ingredients with high melting points, poor organic solubility, or sensitivity to heat degradation. Additionally, the process enables classes of polymers not conventionally processable due to their high molecular weight and/or poor organic solubility. Beyond these advantages, the KinetiSol process shows promise with other applications, such as the production of amorphous mucoadhesive dispersions for delivery of compounds that would also benefit from permeability enhancement.

Effects of the Preparation Process on the Properties of Amorphous Solid Dispersions

The use of amorphous solid dispersions to improve the bioavailability of active ingredients from the BCS II and IV classifications continues to gain interest in the pharmaceutical industry. Over the last decade, methods for generating amorphous solid dispersions have been well established in commercially available products and in the literature. However, the amorphous solid dispersions manufactured by different technologies differ in many aspects, primarily chemical stability, physical stability, and performance, both in vitro and in vivo. This review analyzes the impact of manufacturing methods on those properties of amorphous solid dispersions. For example, the chemical stability of drugs and polymers can be influenced by differences in the level of thermal exposure during fusion-based and solvent-based processes. The physical stability of amorphous content varies according to the thermal history, particle morphology, and nucleation process of amorphous solid dispersions produced by different methods. The in vitro and in vivo performance of amorphous formulations are also affected by differences in particle morphology and in the molecular interactions caused by the manufacturing method. Additionally, we describe the mechanism of manufacturing methods and the thermodynamic theories that relate to amorphous formulations.

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

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

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

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

In vitro characterization of ritonavir formulations and correlation to in vivo performance in dogs

Ritonavir (RTV) is a weakly basic drug with a pH-dependent solubility. In vitro characterization of dissolution and supersaturation behaviors of three PEG-8000 based amorphous solid dispersions (ASD) and a physical blend (PB) with crystalline drug were performed in the biomimetic media (e.g., FaSSGF, FaSSIF, FaSSIF-V2). A two-stage dissolution test and a biphasic dissolution-partition test at the small scale (referred as to biphasic test) were employed with intention to examine the in vitro and in vivo relationship (IVIVR) with retrospective PK data in dog model. The two-stage dissolution test revealed a high degree of supersaturation of RTV from these ASDs accompanied by the occurrence of liquid-liquid phase separation (LLPS) in the biomimetic media. A rapid decrease of apparent RTV concentrations of these ASDs was associated with significant precipitation upon the pH shift of the dissolution medium, revealing the important role of "the gastric stage". In comparison, the biphasic test revealed a lower degree of supersaturation of RTV that is attributed to removal of RTV through partition into octanol, acting as "the absorption compartment". These two dissolution tests provide characterization of the supersaturation state with a complex, dynamic interplay among dissolution, precipitation and partition processes. Results of both in vitro dissolution tests are in good agreement with in vivo results in dogs. In addition, three commercial generic RTV drug products were examined by the biphasic test. Agreement was also obtained between the RTV concentrations in octanol at 3 h from these generic drug products and their corresponding relative bioavailability in dogs.

Influence of Polymer and Drug Loading on the Release Profile and Membrane Transport of Telaprevir

During the dissolution of amorphous solid dispersions (ASDs), various phase transformations can occur, which will ultimately impact the degree of supersaturation. This study employed dissolution and diffusion measurements to compare the performance of various ASD formulations based on the maximum amount of free drug in the solution that was able to permeate through a cellulose-based membrane. Telaprevir (TPV) was used as the model drug compound, and ASDs were prepared with different drug loadings and with four different polymers. Four possible scenarios that can influence TPV mass flow rates upon ASD dissolution were described and supported with experimental data: (1) a system dissolves readily and completely undergoes phase separation via glass-liquid phase separation (GLPS), forming drug-rich aggregates, and reaches the maximum anticipated mass flow rate; (2) where the maximum mass flow rate decreases due to substantial mixing of the polymer into the drug-rich phase, and/or due to the formation of soluble polymer-drug complexes; (3) a system does not undergo GLPS due to slow drug release and/or matrix crystallization; and (4) a system does not undergo GLPS due to rapid crystallization from the supersaturated solution generated during dissolution. The results described herein support the importance of the combined use of the dissolution-diffusion measurements to determine the maximum level of supersaturation achievable for diverse drug formulations.

Mechanistic understanding of the phase behavior of supersaturated solutions of poorly water-soluble drugs

Amorphous solid dispersions (ASDs) are a promising formulation strategy to increase both the apparent aqueous solubility and bioavailability of poorly water-soluble drugs. Upon dissolution under nonsink conditions, ASDs can generate highly supersaturated drug solutions which can undergo liquid-liquid phase separation (LLPS) and/or crystallization. In this study, the phase behavior of supersaturated solutions generated by antisolvent addition and upon the dissolution of ASDs was evaluated using fluorescence lifetime measurements and several other orthogonal techniques, including steady-state fluorescence spectroscopy, ultraviolet (UV) extinction and concentration profiles, ultracentrifuge measurements and nanoparticle tracking analysis. Ritonavir and lopinavir were chosen as poorly water-soluble model drugs, and the polymer, Kollidon VA64, was selected to form the dispersions. The fluorescence lifetime of the environment-sensitive fluoroprobe, PRODAN, was monitored to determine the occurrence of LLPS and crystallization. It was found that only the 10% w/w drug loading ASDs dissolved to a concentration in solution higher than the LLPS concentration and this led to an increase in the lifetime of PRODAN due to partitioning of the fluoroprobe into the drug-rich phase. In contrast, the 50% w/w drug loading ASDs did not reach the amorphous solubility, pointing to a dissolution behavior controlled by the low water solubility and high hydrophobicity of the drug. Fluorescence lifetime measurements were demonstrated to be extremely useful for the characterization of the phase behavior of supersaturated solutions of poorly water-soluble drugs.

Numerical simulation of hot-melt extrusion processes for amorphous solid dispersions using model-based melt viscosity

Simulation of HME processes is a valuable tool for increased process understanding and ease of scale-up. However, the experimental determination of all required input parameters is tedious, namely the melt rheology of the amorphous solid dispersion (ASD) in question. Hence, a procedure to simplify the application of hot-melt extrusion (HME) simulation for forming amorphous solid dispersions (ASD) is presented. The commercial 1D simulation software Ludovic^® was used to conduct (i) simulations using a full experimental data set of all input variables including melt rheology and (ii) simulations using model-based melt viscosity data based on the ASDs glass transition and the physical properties of polymeric matrix only. Both types of HME computation were further compared to experimental HME results. Variation in physical properties (e.g. heat capacity, density) and several process characteristics of HME (residence time distribution, energy consumption) among the simulations and experiments were evaluated. The model-based melt viscosity was calculated by using the glass transition temperature (T_g) of the investigated blend and the melt viscosity of the polymeric matrix by means of a T_g-viscosity correlation. The results of measured melt viscosity and model-based melt viscosity were similar with only few exceptions, leading to similar HME simulation outcomes. At the end, the experimental effort prior to HME simulation could be minimized and the procedure enables a good starting point for rational development of ASDs by means of HME. As model excipients, Vinylpyrrolidone-vinyl acetate copolymer (COP) in combination with various APIs (carbamazepine, dipyridamole, indomethacin, and ibuprofen) or polyethylene glycol (PEG 1500) as plasticizer were used to form the ASDs.

Factors Affecting the Dissolution of Indomethacin Solid Dispersions

The aim of this study was to investigate the influence of factors such as carrier type, drug/carrier ratio, binary carriers, and preparation method on the dissolution of an insoluble drug, indomethacin (IM), under supersaturation conditions. Using a solvent evaporation (SE) method, poloxamer 188 and PVP K30 showed better dissolution among the selected carriers. Furthermore, as the ratio of carriers increased (drug/carrier ratio from 1:0.5 to 1:2), the dissolution rate increased especially in almost two times poloxamer 188 solid dispersions (SDs), while the reverse results were observed for PVP K30 SDs. For the binary carrier SD, a lower dissolution was found. Under hot melt extrusion (HME), the dissolution of poloxamer 188 SD and PVP K30 SD was 0.83- and 0.94-folds lower than that using SE, respectively, while the binary carrier SD showed the best dissolution. For poloxamer 188 SDs, the drug's crystal form changed when using SE, while no crystal form change was observed using HME. IM was amorphous in PVP K30 SDs prepared by both methods. For binary carrier systems, amorphous and crystalline drugs coexisted in SD using SE, and negligible amorphous IM was in SD using HME. This study indicated that a higher amorphous proportion in SD did not correlate with higher dissolution rate, and other factors, such as carrier type, particle size, and density, were also critical.

Mechanistic Physiologically Based Pharmacokinetic Modeling of the Dissolution and Food Effect of a Biopharmaceutics Classification System IV Compound-The Venetoclax Story

Venetoclax, a selective B-cell lymphoma-2 inhibitor, is a biopharmaceutics classification system class IV compound. The aim of this study was to develop a physiologically based pharmacokinetic (PBPK) model to mechanistically describe absorption and disposition of an amorphous solid dispersion formulation of venetoclax in humans. A mechanistic PBPK model was developed incorporating measured amorphous solubility, dissolution, metabolism, and plasma protein binding. A middle-out approach was used to define permeability. Model predictions of oral venetoclax pharmacokinetics were verified against clinical studies of fed and fasted healthy volunteers, and clinical drug interaction studies with strong CYP3A inhibitor (ketoconazole) and inducer (rifampicin). Model verification demonstrated accurate prediction of the observed food effect following a low-fat diet. Ratios of predicted versus observed C_max and area under the curve of venetoclax were within 0.8- to 1.25-fold of observed ratios for strong CYP3A inhibitor and inducer interactions, indicating that the venetoclax elimination pathway was correctly specified. The verified venetoclax PBPK model is one of the first examples mechanistically capturing absorption, food effect, and exposure of an amorphous solid dispersion formulated compound. This model allows evaluation of untested drug-drug interactions, especially those primarily occurring in the intestine, and paves the way for future modeling of biopharmaceutics classification system IV compounds.

Coamorphous Active Pharmaceutical Ingredient-Small Molecule Mixtures: Considerations in the Choice of Coformers for Enhancing Dissolution and Oral Bioavailability

In the recent years, coamorphous systems, containing an active pharmaceutical ingredient (API) and a small molecule coformer have appeared as alternatives to the use of either amorphous solid dispersions containing polymer or cocrystals of API and small molecule coformers, to improve the dissolution and oral bioavailability of poorly soluble crystalline API. This Commentary article considers the relative properties of amorphous solid dispersions and coamorphous systems in terms of methods of preparation; miscibility; glass transition temperature; physical stability; hygroscopicity; and aqueous dissolution. It also considers important questions concerning the fundamental criteria to be used for the proper selection of a small molecule coformer regarding its ability to form either coamorphous or cocrystal systems. Finally, we consider various aspects of product development that are specifically associated with the formulation of commercial coamorphous systems as solid oral dosage forms. These include coformer selection; screening; methods of preparation; preformulation; physical stability; bioavailability; and final formulation. Through such an analysis of coamorphous API-small molecule coformer systems, against the more widely studied API-polymer dispersions and cocrystals, it is believed that the strengths and weaknesses of coamorphous systems can be better understood, leading to more efficient formulation and manufacture of such systems for enhancing oral bioavailability.

Crystal packing and crystallization tendency from the melt of 2-((2-ethylphenyl)amino)nicotinic acid

2-((2-ethylphenyl)amino)nicotinic acid (2EPNA) was synthesized and its crystal structure was determined. It was observed that alkylation of the phenyl ring with ethyl group disrupts the planar conformation of the molecule by steric repulsion, resulting in formation of an acid-pyridine heterosynthon (instead of acid-acid homosynthon) in the crystal. Crystallization tendency from the melt state of the polymorph was studied by differential scanning calorimetry (DSC). It was revealed that this compound could form a very stable amorphous phase on melt quenching and not crystallize even on re-heating. The formation of acid-pyridine hydrogen bonding in the amorphous state is believed to be responsible for its good glass forming ability.

Producing Amorphous Solid Dispersions via Co-Precipitation and Spray Drying: Impact to Physicochemical and Biopharmaceutical Properties

Many small-molecule active pharmaceutical ingredients (APIs) exhibit low aqueous solubility and benefit from generation of amorphous dispersions of the API and polymer to improve their dissolution properties. Spray drying and hot-melt extrusion are 2 common methods to produce these dispersions; however, for some systems, these approaches may not be optimal, and it would be beneficial to have an alternative route. Herein, amorphous solid dispersions of compound A, a low-solubility weak acid, and copovidone were made by conventional spray drying and co-precipitation. The physicochemical properties of the 2 materials were assessed via X-ray diffraction, differential scanning calorimetry, thermal gravimetric analysis, and scanning electron microscopy. The amorphous dispersions were then formulated and tableted, and the performance was assessed in vivo and in vitro. In human dissolution studies, the co-precipitation tablets had slightly slower dissolution than the spray-dried dispersion, but both reached full release of compound A. In canine in vitro dissolution studies, the tablets showed comparable dissolution profiles. Finally, canine pharmacokinetic studies showed that the materials had comparable values for the area under the curve, bioavailability, and C_max. Based on the summarized data, we conclude that for some APIs, co-precipitation is a viable alternative to spray drying to make solid amorphous dispersions while maintaining desirable physicochemical and biopharmaceutical characteristics.

Water-induced phase separation of miconazole-poly (vinylpyrrolidone-co-vinyl acetate) amorphous solid dispersions: Insights with confocal fluorescence microscopy

The aim of this study was to evaluate the utility of confocal fluorescence microscopy (CFM) to study the water-induced phase separation of miconazole-poly (vinylpyrrolidone-co-vinyl acetate) (mico-PVPVA) amorphous solid dispersions (ASDs), induced during preparation, upon storage at high relative humidity (RH) and during dissolution. Different fluorescent dyes were added to drug-polymer films and the location of the dyes was evaluated using CFM. Orthogonal techniques, in particular atomic force microscopy (AFM) coupled with nanoscale infrared spectroscopy (AFM-nanoIR), were used to provide additional analysis of the drug-polymer blends. The initial miscibility of mico-PVPVA ASDs prepared under low humidity conditions was confirmed by AFM-nanoIR. CFM enabled rapid identification of drug-rich and polymer-rich phases in phase separated films prepared under high humidity conditions. The identity of drug- and polymer-rich domains was confirmed using AFM-nanoIR imaging and localized IR spectroscopy, together with Lorentz contact resonance (LCR) measurements. The CFM technique was then utilized successfully to further investigate phase separation in mico-PVPVA films exposed to high RH storage and to visualize phase separation dynamics following film immersion in buffer. CFM is thus a promising new approach to study the phase behavior of ASDs, utilizing drug and polymer specific dyes to visualize the evolution of heterogeneity in films exposed to water.

Improving the solubility of nilotinib through novel spray-dried solid dispersions

The tyrosine kinase inhibitor nilotinib has a very low aqueous solubility and a low and variable oral bioavailability. A pharmaceutical formulation with an improved solubility may enhance the bioavailability and reduce the variability thereof and of the pharmacokinetics. The aim of this study was to enhance the solubility of nilotinib by developing a spray dried solid dispersion. A broad selection of polymer excipients were tested for solubilizing properties. The spray drying technique was used to produce solid dispersions of nilotinib hydrochloride (NH) in matrices of the best performing polymers. Both the dissolution and physicochemical characteristics of the formulations were studied using a pH-switch dissolution model and conventional microscopic, thermal and spectrometric techniques. Of the tested spray dried solid dispersions, the ones containing the co-block polymer Soluplus^® performed best in terms of in vitro dissolution properties. Further testing led to an optimized weight ratio of 1:7 (NH:Soluplus^®) that improved the solubility up to 630-fold compared to crystalline NH (1.5μg/mL) in simulated intestinal fluid. This effect can be attributed to the amorphization of NH and the solubilization of the drug due to micelle formation. A spray dried solid dispersion formulation of NH with Soluplus^® in a ratio of 1:7 was developed that showed a significant increase in solubility.

Enhanced dissolution of poorly soluble antiviral drugs from nanoparticles of cellulose acetate based solid dispersion matrices

Polysaccharide-based polymers were used to produce nanoparticles of poorly soluble antiviral drugs using a rapid precipitation process. The structure-property relationships of four novel cellulose acetate-based polymers were studied for their solubility enhancement of poorly soluble drugs. Particles were purified by dialysis, and dried powders were recovered after freeze-drying. The particle diameters were 150–200 nm. The target drug loading in the particles was 25 wt%, and the drug loading efficiencies were 80–96%. The effects of the formulation process and nanoparticle properties on drug solubility were investigated. All nanoparticles afforded increased solubility and faster release compared to pure drugs. Drug release was a function of the relative hydrophobicity (or solubility parameters) of the polymers.

Amorphous-based controlled-release gliclazide matrix system

The aim of this study was to develop a hydrophilic oral controlled release system (CRS) using the amorphous form of gliclazide, a BCS class II compound, listed on the WHO list of essential medicines. For this purpose, spray-dried dispersions (SDDs) of gliclazide were produced using various grades of hydroxypropyl methylcellulose acetate succinate (HPMCAS) or copovidone as carrier under fully automated conditions. The solid-state properties of prepared SDDs were characterized using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), modulated differential scanning calorimetry (MDSC), and Fourier transform infrared spectroscopy (FTIR). Supersaturated micro-dissolution testing of SDDs in fasted state-simulated intestinal fluid showed prolonged supersaturation state, with solubility increases of 1.5- to 4.0-fold. Solubility and stability characteristics of the most desirable SDDs in terms of relative dissolution area under the curves (AUCs) (AUC_(SDD)/AUC_{(crystalline)}) and stable supersaturated state concentration ratio up to 180 min (C₁₈₀/C_max) were determined. The optimized gliclazide-SDD amorphous forms were included into matrix tablets with HPMC blends using compaction simulator. Developed matrix systems were subjected to standard USP dissolution testing. Dissolution profiles obtained were linear with different slopes indicating varying rates of dissolution. Six-month storage stability testing was performed, and dissolution profiles remained stable with "similarity factor" (f ₂ = 85). Results show that the use of various HPMCAS as a drug carrier in the spray-drying process produces homogeneous single-phase SDDs which are stable and promising for inclusion into HPMC-based hydrophilic matrix systems.

Impact of Supramolecular Aggregation on the Crystallization Kinetics of Organic Compounds from the Supercooled Liquid State

Despite numerous challenges in their theoretical description and practical implementation, amorphous drugs are of growing importance to the pharmaceutical industry. One such challenge is to gain molecular level understanding of the propensity of a molecule to form and remain as a glassy solid. In this study, a series of structurally similar diarylamine compounds was examined to elucidate the role of supramolecular aggregation on crystallization kinetics from supercooled liquid state. The structural similarity of the compounds makes it easier to isolate the molecular features that affect crystallization kinetics and glass forming ability of these compounds. To examine the role of hydrogen-bonded aggregation and motifs on crystallization kinetics, a combination of thermal and spectroscopic techniques was employed. Using variable temperature FTIR, Raman, and solid-state NMR spectroscopies, the presence of hydrogen bonding in the melt and glassy state was examined and correlated with observed phase transition behaviors. Spectroscopic results revealed that the formation of hydrogen-bonded aggregates involving carboxylic acid and pyridine nitrogen (acid-pyridine aggregates) between neighboring molecules in the melt state impedes crystallization, while the presence of carboxylic acid dimers (acid-acid dimers) in the melt favors crystallization. This study suggests that glass formation of small molecules is influenced by the type of intermolecular interactions present in the melt state and the kinetics associated with the molecules to assemble into a crystalline lattice. For the compounds that form acid-pyridine aggregates, the formation of energy degenerate chains, produced due to conformational flexibility of the molecules, presents a kinetic barrier to crystallization. The poor crystallization tendency of these aggregates stems from the highly directional hydrogen-bonding interactions needed to form the acid-pyridine chains. Conversely, for the compounds that form acid-acid dimers, the nondirectional van der Waals forces needed to construct a nucleus promote rapid assembly and crystallization.

Insights into Nano- and Micron-Scale Phase Separation in Amorphous Solid Dispersions Using Fluorescence-Based Techniques in Combination with Solid State Nuclear Magnetic Resonance Spectroscopy

PURPOSE

Miscibility between the drug and the polymer in an amorphous solid dispersion (ASD) is considered to be one of the most important factors impacting the solid state stability and dissolution performance of the active pharmaceutical ingredient (API). The research described herein utilizes emerging fluorescence-based methodologies to probe (im)miscibility of itraconazole (ITZ)-hydroxypropyl methylcellulose (HPMC) ASDs.

METHODS

The ASDs were prepared by solvent evaporation with varying evaporation rates and were characterized by steady-state fluorescence spectroscopy, confocal imaging, differential scanning calorimetry (DSC), and solid state nuclear magnetic resonance (ssNMR) spectroscopy.

RESULTS

The size of the phase separated domains for the ITZ-HPMC ASDs was affected by the solvent evaporation rate. Smaller domains (<10 nm) were observed in spray-dried ASDs, whereas larger domains (>30 nm) were found in ASDs prepared using slower evaporation rates. Confocal imaging provided visual confirmation of phase separation along with chemical specificity, achieved by selectively staining drug-rich and polymer-rich phases. ssNMR confirmed the results of fluorescence-based techniques and provided information on the size of phase separated domains.

CONCLUSIONS

The fluorescence-based methodologies proved to be sensitive and rapid in detecting phase separation, even at the nanoscale, in the ITZ-HPMC ASDs. Fluorescence-based methods thus show promise for miscibility evaluation of spray-dried ASDs.

Understanding the Impact of Water on the Miscibility and Microstructure of Amorphous Solid Dispersions: An AFM-LCR and TEM-EDX Study

Miscibility is critical for amorphous solid dispersions (ASDs). Phase-separated ASDs are more prone to crystallization, and thus can lose their solubility advantage leading to product failure. Additionally, dissolution performance can be diminished as a result of phase separation in the ASD matrix. Water is known to induce phase separation during storage for some ASDs. However, the impact of water introduced during preparation has not been as thoroughly investigated to date. The purpose of this study was to develop a mechanistic understanding of the effect of water on the phase behavior and microstructure of ASDs. Evacetrapib and two polymers were selected as the model system. Atomic force microscopy coupled with Lorentz contact resonance, and transmission electron microscopy with energy dispersive X-ray spectroscopy were employed to evaluate the microstructure and composition of phase-separated ASDs. It was found that phase separation could be induced via two routes: solution-state phase separation during ASD formation caused by water absorption during film formation by a hydrophilic solvent, or solid-phase separation following exposure to high RH during storage. Water contents of as low as 2% in the organic solvent system used to dissolve the drug and polymer were found to result in phase separation in the resultant ASD film. These findings have profound implications on lab-scale ASD preparation and potentially also for industrial production. Additionally, these high-resolution imaging techniques combined with orthogonal analyses are powerful tools to visualize structural changes in ASDs, which in turn will enable better links to be made between ASD structure and performance.