Drug-Rich Phases Induced by Amorphous Solid Dispersion: Arbitrary or Intentional Goal in Oral Drug Delivery?

Kinetic and Thermodynamic Interplay of Polymer-Mediated Liquid-Liquid Phase Separation for Poorly Water-Soluble Drugs

Understanding the interplay between kinetics and thermodynamics of polymer-mediated liquid-liquid phase separation is crucial for designing and implementing an amorphous solid dispersion formulation strategy for poorly water-soluble drugs. This work investigates the phase behaviors of a poorly water-soluble model drug, celecoxib (CXB), in a supersaturated aqueous solution with and without polymeric additives (PVP, PVPVA, HPMCAS, and HPMCP). Drug-polymer-water ternary phase diagrams were also constructed to estimate the thermodynamic behaviors of the mixtures at room temperature. The liquid-liquid phase separation onset point for CXB was detected using an inline UV/vis spectrometer equipped with a fiber optic probe. Varying CXB concentrations were achieved using an accurate syringe pump throughout this study. The appearance of the transient nanodroplets was verified by cryo-EM and total internal reflection fluoresence microscopic techniques. The impacts of various factors, such as polymer composition, drug stock solution pumping rates, and the types of drug-polymer interactions, are tested against the onset points of the CXB liquid-liquid phase separation (LLPS). It was found that the types of drug-polymer interactions, i.e., hydrogen bonding and hydrophobic interactions, are vital to the position and shapes of LLPS in the supersaturation drug solution. A relation between the behaviors of LLPS and its location in the CXB-polymer-water ternary phase diagram was drawn from the findings.

Quantitative Investigation of Intestinal Drug Absorption Enhancement by Drug-Rich Nanodroplets Generated via Liquid-Liquid Phase Separation

Drug-rich droplets formed through liquid-liquid phase separation (LLPS) have the potential to enhance the oral absorption of drugs. This can be attributed to the diffusion of these droplets into the unstirred water layer (UWL) of the gastrointestinal tract and their reservoir effects on maintaining drug supersaturation. However, a quantitative understanding of the effect of drug-rich droplets on intestinal drug absorption is still lacking. In this study, the enhancement of intestinal drug absorption through the formation of drug-rich droplets was quantitatively evaluated on a mechanistic basis. To obtain fenofibrate (FFB)-rich droplets, an amorphous solid dispersion (ASD) of FFB/hypromellose (HPMC) was dispersed in an aqueous medium. Physicochemical characterization confirmed the presence of nanosized FFB-rich droplets in the supercooled liquid state within the FFB/HPMC ASD dispersion. An in situ single-pass intestinal perfusion (SPIP) assay in rats demonstrated that increased quantities of FFB-rich nanodroplets enhanced the intestinal absorption of FFB. The effective diffusion of FFB-rich nanodroplets through UWL would partially contribute to the improved FFB absorption. Additionally, confocal laser scanning microscopy (CLSM) of cross sections of the rat intestine after the administration of fluorescently labeled FFB-rich nanodroplets showed that these nanodroplets were directly taken up by small intestinal epithelial cells. Therefore, the direct uptake of drug-rich nanodroplets by the small intestine is a potential mechanism for improving FFB absorption in the intestine. To quantitatively evaluate the impact of FFB-rich droplets on the FFB absorption enhancement, we determined the apparent permeabilities of the FFB-rich nanodroplets and dissolved FFB based on the SPIP results. The apparent permeability of the FFB-rich nanodroplets was 110-130 times lower than that of dissolved FFB. However, when the FFB-rich nanodroplet concentration was several hundred times higher than that of dissolved FFB, the FFB-rich nanodroplets contributed significantly to FFB absorption improvement. The present study highlights that drug-rich nanodroplets play a direct role in enhancing drug absorption in the gastrointestinal tract, indicating their potential for further improvement of oral absorption from ASD formulations.

Supersaturable diacyl phospholipid dispersion for improving oral bioavailability of brick dust molecule: A case study of Aprepitant

This study aims to investigate the potential use of polymer inclusion in the phospholipid-based solid dispersion approach for augmenting the biopharmaceutical performance of Aprepitant (APT). Initially, different polymers were screened using the microarray plate method to assess their ability to inhibit drug precipitation in the supersaturated solution and HPMCAS outperformed the others. Later, the binary (BD) and ternary (TD) phospholipid dispersions were prepared using the co-solvent evaporation method. Solid-state characterization was performed using SEM and PXRD to examine the physical properties, while molecular interactions were probed through FTIR and NMR analysis. In vitro dissolution studies were performed in both fasted and fed state biorelevant media. The results demonstrated a substantial increase in drug release from BD and TD, approximately 4.8 and 9.9 times higher compared to crystalline APT in FaSSIF. Notably, TD also showed a lowered dissolution difference between fed and fasted states in comparison to crystalline APT, indicating a reduction in the positive food effect of APT. Moreover, we assessed the impact of polymer inclusion on permeation under in vitro biomimetic conditions. In comparison with the crystalline APT suspension, both BD and TD demonstrated approximately 3.3 times and 14 times higher steady-state flux (Jss values), respectively. This can be ascribed to the supersaturation and presence of drug-rich submicron particles (nanodroplets) along with the multiple aggregates of drug with phospholipids and polymer in the donor compartment, consequently resulting in a more substantial driving force for passive diffusion. Lastly, in vivo pharmacokinetic evaluation demonstrated the enhanced absorption of both TD and BD over the free drug suspension in the fasted state. This enhancement was evident through a 2.1-fold and 1.3-fold increase in Cmax and a 2.3-fold and 1.4-fold increase in AUC0-t, respectively. Overall, these findings emphasize the potential of polymer-based phospholipid dispersion in enhancing the overall biopharmaceutical performance of APT.

In-situ formation of nanoparticles from drug-loaded 3D polymeric matrices

The in-situ formation of nanoparticles from polymer-based solid medicines, although previously described, has been overlooked despite its potential to interfere with oral drug bioavailability. Such polymeric pharmaceuticals are becoming increasingly common on the market and can become even more popular due to the dizzying advance of 3D printing medicines. Hence, this work aimed to study this phenomenon during the dissolution of 3D printed tablets produced with three different polymers, hydroxypropylmethylcellulose acetate succinate (HPMCAS), polyvinyl alcohol (PVA), and Eudragit RL PO® (EUD RL) combined with plasticizers and the model drug naringenin (NAR). The components' interaction, dissolution behavior, and characteristics of the formed particles were investigated employing thermal, spectroscopic, mechanical, and chromatographic assays. All the systems generated stable spherical-shaped particles throughout 24 h, encapsulating over 25% of NAR. Results suggest encapsulation efficiencies variations may depend on interactions between polymer-drug, drug-plasticizer, and polymer-plasticizer, which formed stable nanoparticles even in the drug absence, as observed with the HPMCAS and EUD RL formulations. Additionally, components solubility in the medium and previous formulation treatments are also a decisive factor for nanoparticle formation. In particular, the treatment provided by hot-melt extrusion and FDM 3D printing affected the dissolution efficiency enhancing the interaction between the components, reverberating on particle size and particle formation kinetics mainly for HPMCAS and EUD RL. In conclusion, the 3D printing process influences the in-situ formation of nanoparticles, which can directly affect oral drug bioavailability and needs to be monitored.

The Effects of Degree and Duration of Supersaturation on In Vivo Absorption Profiles for Highly Permeable Drugs, Dipyridamole and Ketoconazole

The prediction of oral absorption from a supersaturating drug delivery system (SDDS) remains a significant challenge. Here we evaluated the effects of the degree and duration of supersaturation on in vivoabsorption for dipyridamole and ketoconazole. Various dose concentrations of supersaturated suspensions were prepared by a pH shift method, and in vitro dissolution and in vivo absorption profiles were determined. For dipyridamole, the duration of supersaturation decreased with the increase of the dose concentration owing to rapid precipitation. For ketoconazole, the initially constant dissolved concentrations due probably to the liquid-liquid phase separation (LLPS) as a reservoir were observed at high dose concentrations. However, the LLPS did not delay the peak plasma concentration of ketoconazole in rats, indicating that drug molecules were immediately released from the oil phase to the bulk aqueous phase. For both model drugs, the degree of supersaturation, but not the duration of supersaturation, correlated with systemic exposure, indicating quick drug absorption before precipitation. Therefore, the degree of supersaturation is an important parameter compared with the duration of supersaturation for enhancing the in vivo absorption of highly permeable drugs. These findings would help develop a promising SDDS.

High-throughput kinetic turbidity analysis for determination of amorphous solubility and excipient screening for amorphous solid dispersions

Many poorly water-soluble active pharmaceutical ingredients (APIs) rely on supersaturating formulations, such as amorphous solid dispersions (ASDs), to enhance oral bioavailability. ASDs kinetically trap amorphous solid drugs within polymer excipient matrices to maintain the amorphous drug states. The maximum solution concentration of the API in these formulations is known as the amorphous solubility. In early drug development with scarce material and time, high-throughput approaches to measuring amorphous solubility and screening excipient effects on crystallization risk offer significant benefits to preclinical formulation scientists. Here, we developed a high-throughput screening (HTS) workflow to quantify amorphous solubility and screen ASD excipients by automated kinetic turbidity analysis. Testing 20 model APIs with a wide range of biorelevant solubility, we demonstrated their apparent amorphous solubility determined by the HTS approach strongly correlated with quantification results using conventional liquid chromatography; while the real-time analysis significantly saved analytical time and experimental efforts. Furthermore, kinetic turbidity profiles elucidated distinct excipient effects on the precipitation process of APIs. These results were successfully translated to dissolution and precipitation behaviors of ASD formulations composed of the tested polymers. The high-throughput kinetic turbidity workflow presents a facile and information-rich approach for amorphous solubility screenings against excipients, and helps guide enabling formulation development.

Detecting Crystallinity in Amorphous Solid Dispersions Using Dissolution Testing: Considerations on Properties of Drug Substance, Drug Product, and Selection of Dissolution Media

Dissolution testing has long been used to monitor product quality. Its role in quality control of amorphous solid dispersion (ASD) formulations is relatively new. In the presence of the crystalline phase, the dissolution of ASDs is determined by the dynamics between the dissolution rate of the amorphous solids and the rate of crystal growth. The detection of crystalline phase by dissolution test has not been well understood in the context of drug properties, formulation characteristics and dissolution test variables. This study systematically evaluated the impact of key parameters such as intrinsic crystallization tendency of the API, drug loading, extent of dissolution sink conditions and level of crystallinity on the ASD dissolution behavior. The results indicated diverse dissolution behaviors due to the differences in the intrinsic crystallization propensity of the drug, the drug loading, the ASD polymers and the dissolution sink index. Each of the complex dissolution profiles were interpreted based on visual observations during dissolution, the appropriate sink index based on the amorphous solubility, and the competition between drug dissolution versus crystallization. The findings of this study provide insights towards the various considerations that should be taken into account towards rationally developing a discriminatory dissolution method.

Liquid-liquid phase separation drug aggregate: Merit for oral delivery of amorphous solid dispersions

As a promising strategy, amorphous solid dispersion has been extensively employed in improving the oral bioavailability of insoluble drugs. Despite the numerous advantages, the problems associated with supersaturation stability limit its further application. Recently, the formation and stability of the liquid-liquid phase separation drug aggregate (LLPS-DA) have been found to be vital for supersaturation maintenance. An in-depth review of LLPS-DA was required to further explore the supersaturation maintenance mechanism in vivo. Hence, this study aimed to present a short review to introduce the LLPS-DA, highlight the in vivo advantages for oral administration, and discuss the prospects to help understand the in vivo behavior of LLPS-DA.

Increasing Cellular Uptake and Permeation of Curcumin Using a Novel Polymer-Surfactant Formulation

Several therapeutically active molecules are poorly water-soluble, thereby creating a challenge for pharmaceutical scientists to develop an active solution for their oral drug delivery. This study aimed to investigate the potential for novel polymer-surfactant-based formulations (designated A and B) to improve the solubility and permeability of curcumin. A solubility study and characterization studies (FTIR, DSC and XRD) were conducted for the various formulations. The cytotoxicity of formulations and commercial comparators was tested via MTT and LDH assays, and their permeability by in vitro drug transport and cellular drug uptake was established using the Caco-2 cell model. The apparent permeability coefficients (Papp) are considered a good indicator of drug permeation. However, it can be argued that the magnitude of Papp, when used to reflect the permeability of the cells to the drug, can be influenced by the initial drug concentration (C₀) in the donor chamber. Therefore, Papp (suspension) and Papp (solution) were calculated based on the different values of C₀. It was clear that Papp (solution) can more accurately reflect drug permeation than Papp (suspension). Formulation A, containing Soluplus^® and vitamin E TPGs, significantly increased the permeation and cellular uptake of curcumin compared to other samples, which is believed to be related to the increased aqueous solubility of the drug in this formulation.

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

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

Amorphous and Co-Amorphous Olanzapine Stability in Formulations Intended for Wet Granulation and Pelletization

The preparation of amorphous and co-amorphous systems (CAMs) effectively addresses the solubility and bioavailability issues of poorly water-soluble chemical entities. However, stress conditions imposed during common pharmaceutical processing (e.g., tableting) may cause the recrystallization of the systems, warranting close stability monitoring throughout production. This work aimed at assessing the water and heat stability of amorphous olanzapine (OLZ) and OLZ-CAMs when subject to wet granulation and pelletization. Starting materials and products were characterized using calorimetry, diffractometry and spectroscopy, and their performance behavior was evaluated by dissolution testing. The results indicated that amorphous OLZ was reconverted back to a crystalline state after exposure to water and heat; conversely, OLZ-CAMs stabilized with saccharin (SAC), a sulfonic acid, did not show any significant loss of the amorphous content, confirming the higher stability of OLZ in the CAM. Besides resistance under the processing conditions of the dosage forms considered, OLZ-CAMs presented a higher solubility and dissolution rate than the respective crystalline counterpart. Furthermore, in situ co-amorphization of OLZ and SAC during granule production with high fractions of water unveils the possibility of reducing production steps and associated costs.

Enteric Polymer-Based Amorphous Solid Dispersions Enhance Oral Absorption of the Weakly Basic Drug Nintedanib via Stabilization of Supersaturation

The pH−induced crystallization of weakly basic drugs in the small intestine limits oral bioavailability. In this study, we investigated the solubilization and inhibitory effects on nintedanib in the presence of enteric polymers (HPMCAS LG, HPMCAS MG, Eudragit L100 55, and Eudragit L100). These polymers provided maintenance of supersaturation by increasing the solubility of nintedanib in PBS 6.8 in a concentration-dependent manner, and the improved ranking was as follows: Eudragit L100 > Eudragit L100 55 > HPMCAS MG > HPMCAS LG. After being formulated into amorphous solid dispersions (ASDs) by a solvent evaporation method, the drug exhibited an amorphous state. The pH shift dissolution results of polymer-ASDs demonstrated that four polymers could effectively maintain the drug supersaturation even at the lowest ratio of nintedanib and polymer (1:1, w/w). Eudragit L100−ASD could provide both acid resistance and the favorable mitigation of crystallization in GIF. In comparison to the coarse drug, the relative bioavailability of Eudragit L100−ASD was 245% after oral administration in rats, and Tmax was markedly delayed from 2.8 ± 0.4 h to 5.3 ± 2.7 h. Our findings indicate that enteric ASDs are an effective strategy to increase the intestinal absorption of nintedanib by improving physiologically generated supersaturation and subsequent crystallization.

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.

Co-amorphous systems using epigallocatechin-3-gallate as a co-former: stability, in vitro dissolution, in vivo bioavailability and underlying molecular mechanisms

Co-amorphous strategy has been extensively investigated to improve the dissolution of hydrophobic drugs. Here, epigallocatechin-3-gallate (EGCG) was exploited as a co-former in co-amorphous systems based on its unique structure including phenyl rings, phenolic hydroxyl groups and the galloyl moiety. Two model BCS class II drugs, simvastatin (SIM) and nifedipine (NIF), were selected to be co-amorphized with EGCG. All drug-EGCG systems at three molar ratios became amorphous by the means of spray drying and showed high physically stable either under dry condition and 75% RH at 40 °C or under dry conditions at 25 °C. The optimal feed molar ratios of both EGCG based co-amorphous systems fabricated were determined to be three, under which the significant increases were obtained in the maximum apparent concentrations of 4.90-fold for SIM at 1 h and 106.03-fold for NIF at 0.25 h compared to crystalline drugs by non-sink dissolution studies. The underlying molecular mechanisms of two co-amorphous systems formation were involved in molecular miscibility, hydrogen bonds and π-π stacking interactions unraveled by means of DSC, FTIR and molecular dynamics simulations. More to the point, oral pharmacokinetic studies in rats demonstrated that co-amorphous SIM-EGCG and NIF-EGCG systems at 1:3 have a significant increase in C_max of 1.81- and 5.69-fold, and AUC _{0-24 h} of 1.62- and 4.57-fold compared with those of corresponding crystalline drugs, respectively. In conclusion, EGCG is proved to be a promising co-former in co-amorphous systems.

Revealing the roles of polymers in supersaturation stabilization from the perspective of crystallization behaviors: A case of nimodipine

Formulating drugs into amorphous solid dispersions (ASDs) represents an attractive means to enhance the aqueous solubility of drugs. Furthermore, water-soluble polymers have proven highly advantageous for stabilizing supersaturated solutions of ASDs. However, the performance and mechanism of various polymers in stabilizing supersaturated drug solutions have not been well-studied. The aim of this study was to investigate the effects of different commercial polymers on the dissolution behaviors and supersaturation stabilization of the ASDs and to further explore the mechanism of polymer mediated supersaturation maintenance by studying the crystallization behaviors of the ASDs. In this study, nimodipine (NMD) was used as a model drug because of its poor water-solubility and fast crystallization rate in aqueous solution, and three polymers polyvinylpyrrolidone (PVP), vinylpyrrolidone-vinyl acetate copolymer (PVP VA), and polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft co-polymer (Soluplus) was selected as the drug carriers to form the ASDs with NMD. Solid-state characterizations of the ASDs confirmed the amorphous state of the ASD systems. ASD_{PVP VA} demonstrated superior supersaturation maintenance in dissolution experiments compared to the other two ASD systems. Among the polymers tested, PVP VA most efficiently maintained dissolution of NMD and prevented its crystallization from the supersaturated solution. The ability of PVP VA to most-effectively maintain supersaturation of the drug was manifested by inhibition of crystal nucleation rather than inhibition of crystal growth following nucleation. These results suggest that nucleation inhibition was instrumental in enabling the polymer-mediated supersaturation maintenance, at least with NMD.

pH-Dependent supersaturation from amorphous solid dispersions of weakly basic drugs

PURPOSE

In amorphous solid dispersions (ASDs), the chemical potential of a drug can be reduced due to mixing with the polymer in the solid matrix, and this can lead to reduced drug release when the polymer is insoluble in the dissolution media. If both the drug and the polymer composing an ASD are ionizable, drug release from the ASD becomes pH-dependent. The goal of this study was to gain insights into the pH-dependent solubility suppression from ASD formulations.

METHODS

The maximum release of clotrimazole, a weakly basic drug, from ASDs formulated with insoluble and pH-responsive polymers, was determined as a function of solution pH. Drug-polymer interactions in ASDs were probed using melting point depression, moisture sorption, and solid-state Nuclear Magnetic Resonance spectroscopy (SSNMR) measurements.

RESULTS

The extent of solubility suppression was dependent on polymer type and drug loading. The strength of drug-polymer interactions was found to correlate well with the degree of solubility suppression. For the same ASD, the degree of solubility suppression was nearly constant across the solution pH range studied, suggesting that polymer-drug interactions in residual ASD solids was independent of solution pH. The total drug release agrees with the Henderson-Hasselbalch relationship if the suppressed amorphous solubility of the free drug is independent of solution pH.

CONCLUSIONS

The mechanism of solubility suppression at different solution pHs appeared to be drug-polymer interactions in the solid-state, where the concentration of the free drug remains the same at variable pHs and the total drug concentration follows the Henderson-Hasselbalch relationship.

Dissolving microneedle patches loaded with amphotericin B microparticles for localised and sustained intradermal delivery: Potential for enhanced treatment of cutaneous fungal infections

Fungal infections affect millions of people globally and are often unreceptive to conventional topical or oral preparations because of low drug bioavailability at the infection site, lack of sustained therapeutic effect, and the development of drug resistance. Amphotericin B (AmB) is one of the most potent antifungal agents. It is increasingly important since fungal co-infections associated with COVID-19 are frequently reported. AmB is only administered via injections (IV) and restricted to life-threatening infections due to its nephrotoxicity and administration-related side effects. In this work, we introduce, for the first time, dissolving microneedle patches (DMP) loaded with micronised particles of AmB to achieve localised and long-acting intradermal delivery of AmB for treatment of cutaneous fungal infections. AmB was pulverised with poly (vinyl alcohol) and poly (vinyl pyrrolidone) to form micronised particles-loaded gels, which were then cast into DMP moulds to form the tips. The mean particle size of AmB in AmB DMP tips after pulverisation was 1.67 ± 0.01 μm. This is an easy way to fabricate and load microparticles into DMP, as few steps are required, and no organic solvents are needed. AmB had no covalent chemical interaction with the excipients, but the crystallinity of AmB was reduced in the tips. AmB was completely released from the tips within 4 days in vitro. AmB DMP presented inhibition of Candida albicans (CA) and the killing rate of AmB DMP against CA biofilm inside porcine skin reached 100% within 24 h. AmB DMP were able to pierce excised neonatal porcine skin at an insertion depth of 301.34 ± 46.86 μm. Ex vivo dermatokinetic and drug deposition studies showed that AmB was mainly deposited in the dermis. An in vivo dermatokinetic study revealed that the area under curve (AUC_0-inf) values of AmB DMP and IV (Fungizone® bolus injection 1 mg/kg) groups were 8823.0 d∙μg/g and 33.4 d∙μg/g, respectively (264-fold higher). AmB remained at high levels (219.07 ± 102.81 μg/g or more) in the skin until 7 days after the application of AmB DMP. Pharmacokinetic and biodistribution studies showed that AmB concentration in plasma, kidney, liver, and spleen in the AmB DMP group was significantly lower than that in the IV group. Accordingly, this system addressed the systemic side effects of intravenous injection of AmB and localised the drug inside the skin for a week. This work establishes a novel, easy and effective method for long-acting and localised intradermal drug delivery.