Impact of Polymer Enrichment at the Crystal–Liquid Interface on Crystallization Kinetics of Amorphous Solid Dispersions

Strategies and challenges of cytosolic delivery of proteins

The cytosolic delivery of therapeutic proteins represents a promising strategy for addressing diseases caused by protein dysfunction. Despite significant advances, efficient delivery remains challenging due to barriers such as cell membrane impermeability, endosomal sequestration and protein instability. This review summarises recent progress in protein delivery systems, including physical, chemical and biological approaches, with a particular focus on strategies that enhance endosomal escape and targeting specificity. We further discuss the clinical translatability of these approaches and propose future directions for improving delivery efficiency and safety, ultimately unlocking the therapeutic potential of intracellular proteins.

Design, Development, and Characterization of High Drug-Loaded Drug-Drug-Polymer Ternary Amorphous Solid Dispersions

Ternary amorphous solid dispersions (TASD) are a three-component system that incorporates at least one drug in an amorphous form, offering potential advantages over conventional binary amorphous solid dispersions (ASD). This study aimed to design, characterize, and evaluate a stable and soluble high drug-loaded TASD combining two poorly water-soluble drugs, curcumin (CUR) and resveratrol (RES), with a hydrophilic polymer. Polymer screening studies, including miscibility, crystallization tendency, Flory-Huggins interaction parameter, and solubility parameter, were complemented by advanced techniques such as crystallization kinetics and molecular interaction analysis to assess drug-polymer interactions and amorphous stability. After selecting the optimal polymer, TASDs were prepared by rotary evaporation. Pure drugs, physical mixtures, binary, and ternary ASDs were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, and Raman spectroscopy. In-vitro dissolution under non-sink conditions was performed using a USP-II apparatus, and centrifuged samples were analyzed by UV-Vis spectroscopy. Long-term physical stability was assessed over 12 months at room temperature. Eudragit EPO was identified as the optimal polymer among EPO, HPMCAS, and S100. The resulting high drug-loaded (50% w/w) TASD was amorphous, exhibiting a single glass transition temperature (Tg) with strong drug-polymer interactions. In dissolution studies, the 50% drug-loaded TASD showed a ~ 197-fold and ~ fourfold increase in dissolved CUR and RES, respectively, compared to the crystalline drugs in the physical mixture after 1 h in acidic condition. Despite a lower RES release, it was still twice the release from binary ASDs. The TASD formulation remained physically amorphous for 12 months at room temperature storage.

In Situ Raman Spectroscopy as a Valuable Tool for Monitoring Crystallization Kinetics in Molecular Glasses

The performance of in situ Raman microscopy (IRM) in monitoring the crystallization kinetics of amorphous drugs (griseofulvin and indomethacin) was evaluated using a comparison with the data obtained via differential scanning calorimetry (DSC). IRM was found to accurately and sensitively detect the initial stages of the crystal growth processes, including the rapid glass-crystal surface growth or recrystallization between polymorphic phases, with the reliable localized identification of the particular polymorphs being the main advantage of IRM over DSC. However, from the quantitative point of view, the reproducibility of the IRM measurements was found to be potentially significantly hindered due to inaccurate temperature recording and calibration, variability in the Raman spectra corresponding to the fully amorphous and crystalline phases, and an overly limited number of spectra possible to collect during acceptable experimental timescales because of the applied heating rates. Since theoretical simulations showed that, from the kinetics point of view, the constant density of collected data points per kinetic effect results in the smallest distortions, only the employment of the fast Raman mapping functions could advance the performance of IRM above that of calorimetric measurements.

Effects of Polymers on Cocrystal Growth in a Drug-Drug Coamorphous System: Relations between Glass-to-Crystal Growth and Surface-Enhanced Crystal Growth

Coamorphous and cocrystal drug delivery systems provide attractive crystal engineering strategies for improving the solubilities, dissolution rates, and oral bioavailabilities of poorly water-soluble drugs. Polymeric additives have often been used to inhibit the unwanted crystallization of amorphous drugs. However, the transformation of a coamorphous phase to a cocrystal phase in the presence of polymers has not been fully elucidated. Herein, we investigated the effects of low concentrations of the polymeric excipients poly(ethylene oxide) (PEO) and poly(vinylpyrrolidone) (PVP) on the growth of carbamazepine-celecoxib (CBZ-CEL) cocrystals from the corresponding coamorphous phase. PEO accelerated the growth rate of the cocrystals by increasing the molecular mobility of the coamorphous system, while PVP had the opposite effect. The coamorphous CBZ-CEL system exhibited two anomalously fast crystal growth modes: glass-to-crystal (GC) growth in the bulk and accelerated crystal growth at the free surface. These two fast growth modes both disappeared after doping with PEO (1-3% w/w) but were retained in the presence of PVP, indicating a potential correlation between the two fast crystal growth modes. We propose that the different effects of PEO and PVP on the crystal growth modes arose from weaker effects of the polymers on cocrystallization at the surface than in the bulk. This work provides a deep understanding of the mechanisms by which polymers influence the cocrystallization kinetics of a multicomponent amorphous phase and highlights the importance of polymer selection in stabilizing coamorphous systems or preparing cocrystals via solid-based methods.

Implications of Low-concentration Polymer on the Physical Stability of Glassy Griseofulvin: Role of the Segmental Mobility

Crystallization of amorphous pharmaceutical solids are widely reported to be affected by the addition of polymer, while the underlying mechanism require deep study. Herein, crystal growth behaviors of glassy griseofulvin (GSF) doped with various 1% w/w polymer were systematically studied. From the molecular structure, GSF cannot form the hydrogen bonding interactions with the selected polymer poly(vinyl acetate), polyvinyl pyrrolidone (PVP), 60:40 vinyl pyrrolidone-vinyl acetate copolymer (PVP/VA 64), and poly(ethylene oxide) (PEO). 1% w/w polymer exhibited weak or no detectable effects on the glass transition temperature (Tg) of GSF. However, crystal growth rates of GSF was altered from 4.27-fold increase to 2.57-fold decrease at 8 ℃ below Tg of GSF. Interestingly, the ability to accelerate and inhibit the growth rates of GSF crystals correlated well with Tg of polymer, indicating the controlling role of segmental mobility of polymer. Moreover, ring-banded growth of GSF was observed in the polymer-doped systems. Normal compact bulk and ring-banded crystals of GSF were both characterized as the thermodynamically stable form I. More importantly, formation of ring-banded crystals of GSF can significantly weaken the inhibitory effects of polymer on the crystallization of glassy GSF.

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.

Crystallinity: A Complex Critical Quality Attribute of Amorphous Solid Dispersions

Does the performance of an amorphous solid dispersion rely on having 100% amorphous content? What specifications are appropriate for crystalline content within an amorphous solid dispersion (ASD) drug product? In this Perspective, the origin and significance of crystallinity within amorphous solid dispersions will be considered. Crystallinity can be found within an ASD from one of two pathways: (1) incomplete amorphization, or (2) crystal creation (nucleation and crystal growth). While nucleation and crystal growth is the more commonly considered pathway, where crystals originate as a physical stability failure upon accelerated or prolonged storage, manufacturing-based origins of crystallinity are possible as well. Detecting trace levels of crystallinity is a significant analytical challenge, and orthogonal methods should be employed to develop a holistic assessment of sample properties. Probing the impact of crystallinity on release performance which may translate to meaningful clinical significance is inherently challenging, requiring optimization of dissolution test variables to address the complexity of ASD formulations, in terms of drug physicochemical properties (e.g., crystallization tendency), level of crystallinity, crystal reference material selection, and formulation characteristics. The complexity of risk presented by crystallinity to product performance will be illuminated through several case studies, highlighting that a one-size-fits-all approach cannot be used to set specification limits, as the risk of crystallinity can vary widely based on a multitude of factors. Risk assessment considerations surrounding drug physicochemical properties, formulation fundamentals, physical stability, dissolution, and crystal micromeritic properties will be discussed.

Impact of Poloxamer on Crystal Nucleation and Growth of Amorphous Clotrimazole

Surfactants have been widely used as effective additives to increase the solubility and dissolution rates of amorphous solid dispersions (ASDs). However, they may also generate adverse effects on the physical stability of ASDs. In this study, we systematically investigated the impacts of poloxamer, a frequently used surfactant, on the crystallization of amorphous clotrimazole (CMZ). The added poloxamer significantly decreased the glass transition temperature (Tg) of CMZ and accelerated the growth of Form 1 and Form 2 crystals. It was found that the poloxamer had an accelerating effect on Form 1 and Form 2 but showed a larger accelerating effect on Form 1, which resulted from a combined effect of increased mobility and local phase separation at the crystal-liquid interface. Additionally, the added poloxamer exhibited different effects on nucleation of the CMZ polymorphs, which was more complicated than crystal growth. The nucleation rate of Form 1 was significantly increased by the added poloxamer, and the effect increased with increasing P407 content. However, for Form 2, nucleation was slightly decreased or unchanged. The nucleation of Form 2 may have been influenced by the Form 1 crystallization, and Form 2 converted to Form 1 during nucleation. This study increases our understanding of poloxamer and its impacts on the melt crystallization of drugs.

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.

Considerations in the Development of Physically Stable High Drug Load API- Polymer Amorphous Solid Dispersions in the Glassy State

In this Commentary, the authors expand on their earlier studies of the solid-state long-term isothermal crystallization of amorphous API from the glassy state in amorphous solid dispersions, and focus on the effects of polymer concentration, and its implications for producing high load API doses with minimum polymer concentration. After presenting an overview of the various mechanistic factors which influence the ability of polymers to inhibit API crystallization, including the chemical structure of the polymer relative to the API, the nature and strength of API-polymer noncovalent interactions, polymer molecular weight, impact on primary diffusive molecular mobility, as well as on secondary motions in the bulk and surface phases of the glass, we consider in more detail, the effects of polymer concentration. Here, we examine the factors that appear to allow relatively low polymer concentrations, i.e., less than 10%w/w polymer, to greatly reduce crystallization, including a focus on the heterogeneous structure of the glassy state, and the possible spatial distribution and concentration of polymer in certain key regions of the glass. This is followed by a review and analysis of examples in the recent literature focused on determining the minimum polymer concentration in an amorphous solid dispersion, capable of producing optimally stable high drug load amorphous dispersions.

Amorphous Solid Dispersions: Role of the Polymer and Its Importance in Physical Stability and In Vitro Performance

Amorphous solid dispersions stabilized by one or more polymer(s) have been widely used for delivering amorphous drugs with poor water solubilities, and they have gained great market success. Polymer selection is important for preparing robust amorphous solid dispersions, and considerations should be given as to how the critical attributes of a polymer can enhance the physical stability, and the in vitro and in vivo performances of a drug. This article provides a comprehensive overview for recent developments in the understanding the role of polymers in amorphous solid dispersions from the aspects of nucleation, crystal growth, overall crystallization, miscibility, phase separation, dissolution, and supersaturation. The critical properties of polymers affecting the physical stability and the in vitro performance of amorphous solid dispersions are also highlighted. Moreover, a perspective regarding the current research gaps and novel research directions for better understanding the role of the polymer is provided. This review will provide guidance for the rational design of polymer-based amorphous pharmaceutical solids with desired physicochemical properties from the perspective of physical stability and in vitro performance.

Physical stability and dissolution behaviors of amorphous pharmaceutical solids: Role of surface and interface effects

Amorphous pharmaceutical solids (APS) are single- or multi-component systems in which drugs exist in high-energy states with long-range disordered molecular packing. APSs have become one of the most effective and widely used pharmaceutical delivery approaches for poorly water-soluble drugs in the last several decades. Considerable efforts have been made to investigate the physical stability and dissolution behaviors of APSs, however, the underlying mechanisms remain imperfectly understood. Recent studies reveal that surface and interface properties of APSs could strongly affect the physical stability and dissolution behaviors. This paper provides a comprehensive overview of recent studies focusing on the physical stability and dissolution behaviors of APSs from both surface and interface perspectives. We highlight the role of surface or interface properties in nucleation, crystal growth, phase separation, dissolution, and supersaturation. Meanwhile, the challenges and scope of research on surface and interface properties in the future are also briefly discussed. This review contributes to a better understanding of the surface- and interface-facilitated processes, which will provide more efficient and rational guidance for the design of APSs.

Surface Mobility of Amorphous Indomethacin Containing Moisture and a Surfactant: A Concentration-Temperature Superposition Principle

An amorphous material can have vastly higher mobility on the surface than in the bulk and, as a result, shows fast surface crystallization. Most amorphous materials contain multiple components, but the effect of composition on surface dynamics remains poorly understood. In this study, the surface mobility of amorphous indomethacin was measured using the method of surface-grating decay in the presence of moisture and the surfactant Tween 20. It is found that both components significantly enhance the surface mobility, and their effects are well described by the principle of concentration-temperature superposition (CTS); that is, the same surface dynamics is observed at the same T_g-normalized temperature T/T_g, where T_g is the composition-dependent glass transition temperature. For doped indomethacin showing CTS, the mechanism of surface evolution for a 1000 nm wavelength surface grating transitions from viscous flow at high temperatures to surface diffusion at low temperatures at 1.04 T_g. For the surfactant-doped system, the T_g used is the value for the surface layer that reflects the surface enrichment of the surfactant (measured by X-ray photoelectron spectroscopy). At a high surfactant concentration (>10% by weight), the surface-grating decay rate in the surface-diffusion regime is limited by the large, slow-diffusing surfactant molecules; in this case, CTS holds only for the viscous-flow regime. The CTS principle allows the prediction of the surface dynamics of multicomponent amorphous materials.

Effect of Vehicle Composition on the Preparation of Different Types of Dapsone Crystals for Topical Drug Delivery

Topical formulations composed of API-pure crystals have been increasingly studied, especially in regards to the impact of particle size in penetration efficiency. Less attention, however, has been devoted to the solid-state properties of drugs delivered to the skin. In this study, we address the effect of formulation composition on the crystal form existing in topical products. Dapsone (DAP) gel formulations were prepared by mixing an organic solution containing DAP with an aqueous solution containing polymers and preservatives. The organic solvent was chosen as ethoxydiglycol (DEGEE), polyethylene glycol (PEG), or 1-methyl-2-pirrolidone (MPR) to assess the impact of composition on DAP crystal form. Such solvent variations resulted in different particulate matter. In terms of crystalline nature, the presence of DEGEE in formulations induced the crystallization of DAP hydrate, while PEG cocrystal and a mixture of hydrate and MPR solvate crystallized from the same amounts of PEG and MPR, respectively. Microscopic analysis of the gels showed heterogeneous particles with different characteristics. The behavior of gels after application to the skin was also tested. Interestingly, the different formulations seemed to accumulate in different regions of the skin. This could be the result of the effect of vehicle composition/excipients on the characteristics of the skin, such as hydration. The site-specific accumulation, however, was more pronounced in crystal-loaded gels as opposed to blank formulations. These results indicate that future studies should consider the effect of formulation composition on the API crystal form landscape as part of the strategies used to successfully target drug delivery to the skin.

Fast crystal growth of amorphous nimesulide: implication of surface effects

Understanding crystallization behaviors is of utmost importance for developing robust amorphous pharmaceutical solids. Herein, the crystal growth behaviors of amorphous anti-inflammatory drug nimesulide (NIME) are systemically investigated in the glassy and supercooled liquid state as a function of temperature. A sudden over-tenfold increase is observed in the bulk crystal growth of NIME on cooling below its glass transition temperature (T_g). This fast growth behavior is known as a glass-to-crystal (GC) mode and has been reported in some molecular glasses. Fast surface crystal growth of NIME can persist up to T_g + 57°C with a weak jump in its growth rates at 30-40°C. In addition, surface crystal growth and GC growth of NIME exhibit an almost identical temperature dependence, supporting the view that GC growth is indeed a surface-facilitated process. Moreover, the bubble-induced fast crystal growth of NIME is observed in the interior of its supercooled liquid with approximately the same growth kinetics as surface crystal growth. These findings are relevant for a full understanding of the surface-related crystallization behaviors and physical stability of amorphous pharmaceutical formulations.

Crystallization kinetics and molecular dynamics of binary coamorphous systems of nimesulide and profen analogs

Coamorphous drug delivery systems have emerged as a promising formulation technique for improving the solubility and oral bioavailability of poorly soluble drugs. The selection of a suitable coformer is the key to obtaining a successful coamorphous formulation. This study aims to investigate the impacts of coformers with similar chemical structures but different physical properties on the crystallization behavior and molecular dynamics of binary amorphous systems. The addition of three profen analogs, ibuprofen (IBU), ketoprofen (KETO) and indoprofen (INDO) leads to significantly different effects on the crystallization kinetics of amorphous nimesulide (NIME). The crystal growth rates for amorphous NIME are substantially accelerated in the presence of IBU, but drastically reduced in the presence of INDO, while the incorporation of KETO results in a negligible effect. Broadband dielectric spectroscopy is employed to characterize the molecular dynamics of neat amorphous NIME and coamorphous systems. The addition of three structural analogs alters the molecular mobility of amorphous NIME in different ways, which is consistent with the trend observed for their impacts on the crystallization kinetics, suggesting that the relative mobility between the components of coamorphous mixtures governs the physical stability. In addition, it is found that the temperature dependence of the α-relaxation times for NIME with and without coformers is superimposed once the temperature is scaled by T_g/T, whereas the crystallization kinetics do not overlap on a T_g/T scale. This deviation can result from a complex interplay of thermodynamic and kinetic factors involved in multicomponent amorphous systems. This study provides insights into the crystallization kinetics and molecular dynamics of coamorphous systems containing drug analogs, which can potentially offer more flexibility for the control of physical stability without sacrificing therapeutic efficacy.

What Are the Important Factors That Influence API Crystallization in Miscible Amorphous API-Excipient Mixtures during Long-Term Storage in the Glassy State?

In this Perspective, the authors examine the various factors that should be considered when attempting to use miscible amorphous API-excipient mixtures (amorphous solid dispersions and coamorphous systems) to prevent the solid-state crystallization of API molecules when isothermally stored for long periods of time (a year or more) in the glassy state. After presenting an overview of a variety of studies designed to obtain a better understanding of possible mechanisms by which amorphous API undergo physical instability and by which excipients generally appear to inhibit API crystallization from the amorphous state, we examined 78 studies that reported acceptable physical stability of such systems, stored below T_g under "dry" conditions for one year or more. These results were examined more closely in terms of two major contributing factors: the degree to which a reduction in diffusional molecular mobility and API-excipient molecular interactions operates to inhibit crystallization. These two parameters were chosen because the data are readily available in early development to help compare amorphous systems. Since T_g - T = 50 K is often used as a rule of thumb for the establishing the minimum value below T_g required to reduce diffusional mobility to a period of years, it was interesting to observe that 30 of the 78 studies still produced significant physical stability at values of T_g - T < 50 K (3-47 °C), suggesting that factors besides diffusive molecular mobility likely contribute. A closer look at the T_g - T < 50 systems shows that hydrogen bonding, proton transfer, disruption of API-API self-associations (such as dimers), and possible π-π stacking were reported for most of the systems. In contrast, five crystallized systems that were monitored for a year or more were also examined. These systems exhibited T_g - T values of 9-79, with three of them exhibiting T_g - T < 50. For these three samples, none displayed molecular interactions by infrared spectroscopy. A discussion on the impact of relative humidity on long-term crystallization in the glass was included, with attention paid to the relative water vapor sorption by various excipients and effects on diffusive mobility and molecular interactions between API and excipient.

Effect of polymeric excipients on nucleation and crystal growth kinetics of amorphous fluconazole

Three chemically distinct polymeric excipients show significantly different effects on the nucleation and crystal growth kinetics of amorphous fluconazole, a classical antifungal drug.

Molecular Mobility and Crystal Growth in Amorphous Binary Drug Delivery Systems: Effects of Low-Concentration Poly(Ethylene Oxide)

Polymer additives have been widely reported to affect the crystallization of amorphous drugs, while the underlying mechanism is poorly understood. The present study aims to investigate the relationship between the crystal growth and the molecular mobility of amorphous nifedipine (NIF) in the presence and absence of low-concentration poly(ethylene oxide) (PEO). The addition of 3% w/w PEO yields approximately a 5-fold increase in the crystal growth rate of NIF in the glassy matrix and a 10-fold increase in the supercooled liquid. Broadband dielectric spectroscopy is performed to investigate the molecular mobility of amorphous pure NIF system and NIF doped with low-concentration PEO. With 3% w/w PEO, the structural relaxation time τ_α of amorphous NIF significantly decreases, indicating an increase in the global molecular mobility. However, the increase of the molecular mobility is insufficient to explain the 5- to 10-fold increase of the crystal growth rate at the same τ_α scale. Moreover, we compare the accelerating effect of PEO in NIF-PEO systems to other PEO-doped systems. The accelerating effect of low-concentration PEO on the crystal growth of amorphous drugs is found to be independent of the Flory-Huggins interaction, T_g of the drug, or the increase of the global molecular mobility. These findings suggest that an in-depth understanding regarding the effects of polymer additives on the crystallization of drugs should consider the localized mobility of the host molecules near the crystal-liquid interface.

Physical stability of amorphous pharmaceutical solids: Nucleation, crystal growth, phase separation and effects of the polymers

Compared to their crystalline forms, amorphous pharmaceutical solids present marvelous potential and advantages for effectively improving the oral bioavailability of poorly water-soluble drugs. A central issue in developing amorphous pharmaceutical solids is the stability against crystallization, which is particularly important for maintaining their advantages in solubility and dissolution rate. This review provides a comprehensive overview of recent studies focusing on the physical stability of amorphous pharmaceutical solids affected by nucleation, crystal growth, phase separation and the addition of polymers. Moreover, we highlight the novel technologies and theories in the field of amorphous pharmaceutical solids. Meanwhile, the challenges and strategies in maintaining the physical stability of amorphous pharmaceutical solids are also discussed. With a better understanding of physical stability, the more robust amorphous pharmaceutical formulations with desired pharmaceutical performance would be easier to achieve.

Unconventional Passive Enhancement of Transdermal Drug Delivery: toward a Mechanistic Understanding of Penetration Enhancers Releasing from Acrylic Pressure-Sensitive Adhesive of Patches

PURPOSE

Penetration enhancers (PEs) enhancing efficacy depends on two processes: PEs release from patches and action on skin. Compared with their action on skin, PEs release process was poorly understood. Therefore, the purpose of this study was to make a mechanistic understanding of PEs release from acrylic pressure-sensitive adhesive of patches and propose an unconventional enhancement of PEs efficacy.

METHODS

PEs efficacy was evaluated both in drug permeation study and drug pharmacokinetic study. Confocal Raman spectroscopy was employed to observe PEs release behavior by mapping PEs dynamic distribution in skin. The mechanism of PEs release behavior was provided from molecular interaction and rheology using FT-IR, molecular docking, molecular dynamic simulation and rheometer, separately.

RESULTS

The release behavior of PEs themselves greatly restricted their efficacy. By using PEG 400, an improvement of oleic acid (OA) release behavior was achieved, and the efficacy of OA was significantly enhanced with enhancing ratio (ER) from 2.69 to 4.10 and AUC_last from 1574 ± 87 to 2664 ± 249 ng·h/mL, separately. The improvement of OA release behavior was primarily resulted from reduction of the interaction between OA and adhesive, which was caused by other small molecules with a strong ability in forming hydrogen bonds with adhesive. Also, the rigidity of adhesive was a factor in affecting PEs release behavior.

CONCLUSIONS

An unconventional passive enhancement of transdermal drug delivery was achieved via improving PEs themselves releasing from acrylic pressure-sensitive adhesive. Graphical abstract Influence of PEs release behavior on drug permeation through skin and molecular mechanism.

Manipulation of Pharmaceutical Polymorphic Transformation Process Using Excipients

BACKGROUND

In the pharmaceutical field, it is vital to ensure a consistent product containing a single solid-state form of the active pharmaceutical ingredient (API) in the drug product. However, some APIs are suffering from the risk of transformation of their target forms during processing, formulation and storage.

METHODS

The purpose of this review is to summarize the relevant category of excipients and demonstrate the availability and importance of using excipients as a key strategy to manipulate pharmaceutical polymorphic transformation.

RESULTS

The excipient effects on solvent-mediated phase transformations, solid-state transitions and amorphous crystallization are significant. Common pharmaceutical excipients including amino acids and derivatives, surfactants, and various polymers and their different manipulation effects were summarized and discussed.

CONCLUSION

Appropriate use of excipients plays a role in manipulating polymorphic transformation process of corresponding APIs, with a promising application of guaranteeing the stability and effectiveness of drug dosage forms.