Influence of Additives on the Properties of Nanodroplets Formed in Highly Supersaturated Aqueous Solutions of Ritonavir

Impact of colloidal drug-rich droplet size and amorphous solubility on drug membrane permeability: A comprehensive analysis

This study aimed to investigate the impact of amorphous solubility and colloidal drug-rich droplets on drug absorption. The amorphous solubility of cilnidipine (CND) in AS-HF grade of hypromellose acetate succinate (HPMC-AS) solution was significantly reduced compared to that in non-polymer solution due to AS-HF partitioning into the CND-rich phase. In contrast, AS-LF grade of HPMC-AS has minimal effect on the amorphous solubility. The size of colloidal CND-rich droplets formed in the CND-supersaturated solution was less than 100 nm in the presence of AS-HF, while 200-450 nm in the presence of AS-LF. When the CND concentrations were near the amorphous solubility, CND membrane flux was reduced in the presence of AS-HF due to the decrease in the amorphous solubility of CND. However, the CND flux increased with the increase in CND-rich droplets, especially in the AS-HF solution. The size reduction of the CND-rich droplets led to their effective diffusion into the unstirred water layer, enhancing CND flux. In higher CND concentration regions, the CND flux became higher in the AS-HF solution than in the AS-LF solution. Thus, it is essential to elucidate the drug concentration-dependent impact of the colloidal drug-rich droplets on the drug absorption performance to optimize supersaturating formulations.

Growth mechanisms of amorphous nanoparticles in solution and during heat drying

The purpose of this study was twofold: to identify the growth mechanisms of amorphous nanoparticles in solution and during the drying process at high temperatures, and to guide the process condition and stabilizer selection for amorphous nanoparticle formulations. In contrast to nanocrystals that are mostly mechanically robust, amorphous nanoparticles tend to undergo deformation under stress. As a result, development of a stable formulation and evaluation of the drying process for re-dispersible amorphous nanoparticles present considerable challenges. Although amorphous nanoparticles have stability issues, they have several pros in terms of production, high monodispersity, and diverse applications in drug delivery. In this study, amorphous nanoparticles were prepared via liquid-liquid phase separation, and their growth mechanisms were investigated both in solution and during the drying process. In solution, particles were found to be susceptible to flocculation, crystallization, coalescence, and Ostwald ripening, with coalescence being a preliminary step providing the driving force for Ostwald ripening. However, during the heat drying process, coalescence and crystallization were found to be the primary mechanisms for particle growth, with Ostwald ripening being negligible due to reduced molecular mobility. The glass transition temperature (Tg) of these amorphous nanoparticles was found to be a crucial factor both in solution and during the drying process. At temperatures < Tg, particles remained in a rigid, glassy state thereby inhibiting coalescence, whereas at or above Tg, particles transition from glassy to rubbery state, making them more susceptible to deformation and coalescence. The mechanistic understanding of particle growth from this study can also be extended to the stabilization of other types of soft nanoparticles.

Excipient effects on supersaturation, particle size dynamics, and thermodynamic activity of multidrug amorphous formulations

Multidrug formulations enhance patient compliance and extend the life cycle of pharmaceutical products. To overcome solubility challenges for multidrug combinations, amorphous formulations are commonly used. However, the excipients for creating amorphous formulations are often selected without an understanding of their effects on the bioavailability of the drugs. In this context, we investigated the impact of three types of excipients (polymers, surfactants and amino acids) on the supersaturation and thermodynamic activity of multidrug amorphous formulations. Additionally, we studied the particle size dynamics of the colloidal phase formed as a result of liquid-liquid phase separation. The amorphous solubility of two drugs, atazanavir and ritonavir, was determined in solutions containing predissolved excipients and the particle size dynamics of the colloidal particles was measured by dynamic light scattering. Dissolution experiments of atazanavir and ritonavir were conducted in predissolved sodium dodecyl sulfate (SDS), an anionic surfactant, and alanine solutions under non-sink conditions. Membrane transport of the drugs was evaluated using a MicroFLUX setup. The polymers had only minor effects on the amorphous solubility, but SDS significantly increased the solubilities of both drugs. In contrast, the other non-ionic surfactants and amino acids reduced the solubility of atazanavir but had no negative effect on ritonavir. Polymers were effective in maintaining supersaturation and preventing the coarsening of the colloidal particles. Conversely, alanine was neither able to inhibit the solution crystallization nor increase the flux of either drug. Despite the increase in the amorphous solubility of both drugs in SDS, flux was reduced. These results highlight the importance of properly selecting excipients for supersaturating amorphous formulations. The choice of excipient impacts the thermodynamic activity, the phase behaviour of the drugs and hence, the resulting absorption after oral intake.

6-Carboxycellulose Acetate Butyrate: Effectiveness as an Amorphous Solid Dispersion Polymer

Amorphous solid dispersion (ASD) in a polymer matrix is a powerful method for enhancing the solubility and bioavailability of otherwise crystalline, poorly water-soluble drugs. 6-Carboxycellulose acetate butyrate (CCAB) is a relatively new commercial cellulose derivative that was introduced for use in waterborne coating applications. As CCAB is an amphiphilic, carboxyl-containing, high glass transition temperature (Tg) polymer, characteristics essential to excellent ASD polymer performance, we chose to explore its ASD potential. Structurally diverse drugs quercetin, ibuprofen, ritonavir, loratadine, and clarithromycin were dispersed in CCAB matrices. We evaluated the ability of CCAB to create ASDs with these drugs and its ability to provide solubility enhancement and effective drug release. CCAB/drug dispersions prepared by spray drying were amorphous up to 25 wt % drug, with loratadine remaining amorphous up to 50% drug. CCAB formulations with 10% drug proved effective at providing in vitro solubility enhancement for the crystalline flavonoid drug quercetin as well as ritonavir, but not for the more soluble APIs ibuprofen and clarithromycin and the more hydrophobic loratadine. CCAB did provide slow and controlled release of ibuprofen, offering a simple and promising Long-duration ibuprofen formulation. Formulation with clarithromycin showed the ability of the polymer to protect against degradation of the drug at stomach pH. Furthermore, CCAB ASDs with both loratadine and ibuprofen could be improved by the addition of the water-soluble polymer poly(vinylpyrrolidone) (PVP), with which CCAB shows good miscibility. CCAB provided solubility enhancement in some cases, and the slower drug release exhibited by CCAB, especially in the stomach, could be especially beneficial, for example, in formulations containing known stomach irritants like ibuprofen.

Investigation of Stabilized Amorphous Solid Dispersions to Improve Oral Olaparib Absorption

In this study, we investigated the formulation of stable solid dispersions to enhance the bioavailability of olaparib (OLA), a therapeutic agent for ovarian cancer and breast cancer characterized as a BCS class IV drug with low solubility and low permeability. Various polymers were screened based on solubility tests, and OLA-loaded solid dispersions were prepared using spray drying. The physicochemical properties of these dispersions were investigated via scanning electron microscopy (SEM), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and Fourier Transform Infrared Spectroscopy (FT-IR). Subsequent dissolution tests, along with assessments of morphological and crystallinity changes in aqueous solutions, led to the selection of a hypromellose (HPMC)-based OLA solid dispersion as the optimal formulation. HPMC was effective at maintaining the supersaturation of OLA in aqueous solutions and exhibited a stable amorphous state without recrystallization. In an in vivo study, this HPMC-based OLA solid dispersion significantly enhanced bioavailability, increasing AUC0-24 by 4.19-fold and Cmax by more than 10.68-fold compared to OLA drug powder (crystalline OLA). Our results highlight the effectiveness of HPMC-based solid dispersions in enhancing the oral bioavailability of OLA and suggest that they could be an effective tool for the development of oral drug formulations.

Enhanced Stability and Improved Oral Absorption of Enzalutamide with Self-Nanoemulsifying Drug Delivery System

The purpose of this study is to develop and evaluate a self-nanoemulsifying drug delivery system (SNEDDS) to improve the oral absorption of poorly water-soluble enzalutamide (ENZ). Considering the rapid recrystallization of the drug, based on solubility and crystallization tests in various oils, surfactants and co-surfactants, Labrafac PG 10%, Solutol HS15 80%, and Transcutol P 10%, which showed the most stable particle size and polydispersity index (PDI) without drug precipitation, were selected as the optimal SNEDDS formulation. The optimized SNEDDS formulation showed excellent dissolution profiles for all the drugs released at 10 min of dissolution due to the increased surface area with a small particle size of approximately 16 nm. Additionally, it was confirmed to be stable without significant differences in physical and chemical properties for 6 months under accelerated conditions (40 ± 2 °C, 75 ± 5% RH) and stressed conditions (60 ± 2 °C). Associated with the high dissolutions of ENZ, pharmacokinetic parameters were also greatly improved. Specifically, the AUC was 1.9 times higher and the Cmax was 1.8 times higher than those of commercial products (Xtandi® soft capsule), resulting in improved oral absorption. Taken together with the results mentioned above, the SNEDDS could be an effective tool as a formulation for ENZ and other similar drugs.

The Development of an Oral Solution Containing Nirmatrelvir and Ritonavir and Assessment of Its Pharmacokinetics and Stability

Paxlovid®, a co-packaged medication comprised of separate tablets containing two active ingredients, nirmatrelvir (NRV) and ritonavir (RTV), exhibits good effectiveness against coronavirus disease 2019 (COVID-19). However, the size of the NRV/RTV tablets makes them difficult for some patients to swallow, especially the elderly and those with dysphagia. Therefore, an oral liquid formulation that can overcome this shortcoming and improve patient compliance is required. In this study, we developed a liquid formulation containing NRV and RTV by adopting strategies that used co-solvents and surfactants to enhance the solubility and inhibit possible recrystallization. The in vitro release results showed that NRV and RTV could be maintained at high concentrations in solution for a certain period in the investigated media. In vivo studies in rats showed that the oral bioavailability of NRV/RTV solution was significantly enhanced. Compared to Paxlovid® tablets, the AUC(0-t) of NRV and RTV increased by 6.1 and 3.8 times, respectively, while the Cmax increased by 5.5 times for both. Furthermore, the promoting effect of the absorption of RTV on the bioavailability of NRV was confirmed. Experiments with a beagle showed a similar trend. Stability studies were also conducted at 4 °C, 25 °C, and 40 °C for 90 days, indicating that the oral liquid formulation was physically and chemically stable. This study can be used as a valuable resource for developing and applying oral liquid NRV/RTV formulations in a clinical context.

Spray-dried paracetamol/polyvinylpyrrolidone amorphous solid dispersions: Part II - Solubility and in vitro drug permeation behavior

Amorphous solid dispersions (ASDs) comprising an active pharmaceutical ingredient (API) and polymer are a frequently described approach in the formulation of new drug candidates. This study aimed to evaluate the saturation solubility and dissolution behavior of ASDs consisting of paracetamol (PCM) and polyvinylpyrrolidone/vinyl acetate (PVP/VA) in water and their influence on the transepithelial in vitro permeation of PCM. With increasing amounts of PVP/VA, the water solubility of ASDs containing PCM increased up to six times compared to that of a saturated PCM solution. In the case of preparations with 30 % PCM, two-phase separation was observed in water at room temperature, consisting of a polymer-rich phase with high API loading and an aqueous, polymer-poor phase. This result was attributed to the thermoresponsive behavior of PVP/VA with lower critical solution temperature (LCST). As the PCM content in the ASD increased, the LCST decreased. This behavior was analyzed by measuring the demixing temperature (T_dem) values with differential scanning calorimetry (DSC). Furthermore, the permeation behavior of PCM from these phase-separated preparations through Caco-2 cells was analyzed. Additionally, the effect of these preparations on cell viability was evaluated using the MTT assay. Preparations with relatively high PCM concentrations showed a reduction in cell viability.

Synergistic effect of miscible cellulose-based microparticles and pH modulators on the bioavailability of a weakly basic drug and its metabolites

This study aimed to evaluate the miscibility of cellulose derivatives to improve the release rate and stability of microparticles containing the weakly basic drug itraconazole (ITZ). We also investigated the effect of some organic acids on the microenvironmental pH (pH_m) and the release rate of ITZ from the cellulose-based microparticles. The synergistic effect of cellulose-based microparticles and pH_m modulators on the bioavailability of ITZ compared with the reference product was investigated in a rabbit model. Differential scanning calorimetry and Fourier-transform infrared spectroscopy (FTIR) analysis showed that ITZ, hydroxypropyl methylcellulose, and hydroxypropyl methylcellulose phthalate were miscible at a ratio of 1.5:3:1 (w/w/w), and the stability of the microparticles was maintained for 6 months under accelerated conditions. In addition, X-ray diffraction, FTIR, and scanning electron microscopy were used to characterize the properties of the microparticles. Through the titration technique and determination of pH_m, the combination of fumaric acid and maleic acid (1:2, w/w) was found to be the most effective pH_m modulator for microparticles. The integration of cellulose-based microparticles and pH_m modulators showed a synergistic effect on the flux and relative bioavailability of ITZ and its active metabolite OH-ITZ (182.60 % and 217.67 %, respectively) when compared with the reference product.

Supersaturation and phase behavior during dissolution of amorphous solid dispersions

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

Dissolution Mechanisms of Amorphous Solid Dispersions: Role of Drug Load and Molecular Interactions

High drug load amorphous solid dispersions (ASDs) have been a challenge to formulate partially because drug release is inhibited at high drug loads. The maximum drug load prior to inhibition of release has been termed the limit of congruency (LoC) and has been most widely studied for copovidone (PVPVA)-based ASDs. The terminology was derived from the observation that below LoC, the polymer controlled the kinetics and the drug and the polymer released congruently, while above LoC, the release rates diverged and were impaired. Recent studies show a correlation between the LoC value and drug-polymer interaction strength, where a lower LoC was observed for systems with stronger interactions. The aim of this study was to investigate the causality between drug-PVPVA interaction strength and LoC. Four chemical analogues with diverse abilities to interact with PVPVA were used as model drugs. The distribution of the polymer between the dilute aqueous phase and the insoluble nanoparticles containing drug was studied with solution nuclear magnetic resonance spectroscopy and traditional separation techniques to understand the thermodynamics of the systems in a dilute environment. Polymer diffusion to and from ASD particles suspended in aqueous solution was monitored for drug loads above the LoC to investigate the thermodynamic driving force for polymer release. The surface composition of ASD compacts before and after exposure to buffer was studied with Fourier transform infrared spectroscopy to capture potential kinetic barriers to release. It was found that ASD compacts with drug loads above the LoC formed an insoluble barrier on the surface that was in pseudo-equilibrium with the aqueous phase and prevented further release of drugs and polymers during dissolution. The insoluble barrier contained a substantial amount of the polymer for the strongly interacting drug-polymer systems. In contrast, a negligible amount was found for the weakly interacting systems. This observation provides an explanation for the ability of strongly interacting systems to form an insoluble barrier at lower drug loads. The study highlights the importance of thermodynamic and kinetic factors on the dissolution behavior of ASDs and provides a potential framework for maximizing the drug load in ASDs.

Comparisons of in Vitro Models to Evaluate the Membrane Permeability of Amorphous Drug Nanoparticles

The spontaneous formation of amorphous drug nanoparticles following the release of a drug from a supersaturating formulation is gaining increasing attention due to their potential contribution to increased oral bioavailability. The formation of nanosized drug particles also has considerable implications for the interpretation of in vitro and in vivo data. However, the membrane transport properties of these drug particles remain less well understood. Herein, the membrane permeation of nanosized amorphous drug particles of a model drug atazanavir was evaluated using different artificial membrane-based, cell-based, and animal tissue-based models. Results showed that flux enhancement by particles was different for the various systems used. Generally, good agreement was obtained among experiments performed using the same apparatus with different model membranes, with the exception of the Madin-Darby canine kidney cell monolayer and the Long-Evans rat intestine tissue, which showed lower flux enhancements. Franz cell-based models showed slightly higher flux enhancements by particles compared to Transwell and intestinal tissue sac models. Mass transport analysis suggested that the extent of flux enhancement by particles is dependent on the geometry of the apparatus as well as the properties of the membrane and buffer used, whereas the flux plateau concentration is dependent on the unstirred water later (UWL) asymmetry. These results highlight the complexity in characterizing the permeability advantage of these nonmembrane permeable drug particles and suggest that caution should be used in selecting the appropriate in vitro model to evaluate the overall permeability of colloidal drug particles.

Phase Behavior and Crystallization Kinetics of a Poorly Water-Soluble Weakly Basic Drug as a Function of Supersaturation and Media Composition

Understanding the supersaturation and precipitation behavior of poorly water-soluble compounds in vivo and the impact on oral absorption is critical to design consistently performing products with optimized bioavailability. Weakly basic compounds are of particular importance in this context since they have an inherent tendency to undergo supersaturation in vivo upon exit from the stomach and entry into the small intestine because of their pH-dependent solubility. To understand and probe potential in vivo variability of supersaturating systems, rigorous understanding of compound physical properties and phase behavior landscape is essential. Herein, we extensively characterize the solution phase behavior of a model, poorly soluble and weakly basic compound, posaconazole. Phase boundaries for crystal-solution and amorphous-solution were established as a function of pH, allowing possible phase transformations, namely, crystallization or liquid-liquid phase separation, to be mapped for different initial doses and fluid volumes. Endogenous surfactants including sodium taurocholate, lecithin, glycerol monooleate, and sodium oleate in biorelevant media significantly extended the phase boundaries due to solubilization, to an extent that was dependent on the concentration of the surface-active agents. The nucleation induction time of posaconazole was much shorter in biorelevant media in comparison to the corresponding buffer solution, with two distinct regions observed in all media that could be attributed to a change in the nucleation mechanism at high and low supersaturation. The presence of undissolved nanocrystals accelerated the desupersaturation. This work enhances our understanding of biorelevant factors impacting precipitation kinetics, which might affect absorption in vivo. It is expected that findings from this study with posaconazole could be broadly applicable to other weakly basic compounds, after taking into consideration differences in pK_a, solubility, and molecular structure.

Impact of Surfactants on the Performance of Clopidogrel-Copovidone Amorphous Solid Dispersions: Increased Drug Loading and Stabilization of Nanodroplets

PURPOSE

Surfactants are increasingly being added to amorphous solid dispersion (ASDs) formulations to enhance processability and release performance. The goal of the current work was to investigate the impact of cationic, anionic and non-ionic surfactants on the rate and extent of clopidogrel (CPD) release from copovidone-based ASDs.

METHODS

CPD release was evaluated for ASDs with different drug loadings using a surface normalized intrinsic dissolution apparatus. Studies were also carried out using dynamic light scattering, zeta potential measurements, and nuclear magnetic resonance spectroscopy to probe the impact of surfactants on drug-rich nanodroplet physical stability and clopidogrel-surfactant interactions.

RESULTS

CPD ASDs showed good release for drug loadings as high as 40%, before the release fell off a cliff at higher drug loadings. Only sodium dodecyl sulfate, added at a 5% level, was able to improve the release at 50% drug loading, with other surfactants proving to be ineffective. However, some of the surfactants evaluated did show some benefits in improving nanodroplet stability against size enlargement. Ionic and non-ionic surfactants were observed to interact differently with CPD-rich nanodroplets, and variations in the kinetics and morphology of water-induced phase separation were noted in the presence and absence of surfactants in ASD films.

CONCLUSIONS

In summary, addition of surfactants to ASD formulations may lead to some improvements in formulation performance, but predictive capabilities and mechanisms of surfactant effect still require further studies.

Recent Advances in Enhancement of Dissolution and Supersaturation of Poorly Water-Soluble Drug in Amorphous Pharmaceutical Solids: A Review

Amorphization is one of the most effective pharmaceutical approaches to enhance the dissolution and oral bioavailability of poorly water-soluble drugs. In recent years, amorphous formulations have been experiencing rapid development both in theoretical and practical application. Based on using different types of stabilizing agents, amorphous formulations can be mainly classified as polymer-based amorphous solid dispersion, coamorphous formulation, mesoporous silica-based amorphous formulation, etc. This paper summarizes recent advances in the dissolution and supersaturation of these amorphous formulations. Moreover, we also highlight the roles of stabilizing agents such as polymers, low molecular weight co-formers, and mesoporous silica. Maintaining supersaturation in solution is a key factor for the enhancement of dissolution profile and oral bioavailability, and thus, the strategies and challenges for maintaining supersaturation are also discussed. With an in-depth understanding of the inherent mechanisms of dissolution behaviors, the design of amorphous pharmaceutical formulations will become more scientific and reasonable, leading to vigorous development of commercial amorphous drug products.

Role of Permeability on the Biopredictive Dissolution of Amorphous Solid Dispersions

An ideal dissolution test for amorphous solid dispersions (ASDs) should reflect physicochemical, physiological, and hydrodynamic conditions which accurately represent in vivo dissolution. However, this is confounded by the evolution of different molecular and colloidal species during dissolution, generating a supersaturated state of the drug. The supersaturated state of a drug is thermodynamically unstable which drives the process of precipitation resulting in a loss of solubility advantage. Maintaining a supersaturated state of the drug with the help of precipitation inhibiting excipients is a key component in the design of ASDs. Therefore, a biopredictive dissolution test is critical for proper risk assessment during the development of an optimal ASD formulation. One of the overlooked components of biopredictive dissolution is the role of drug permeability. The kinetic changes in the phase behavior of a drug during dissolution of ASDs are influenced by drug permeability across a membrane. Conventionally, drug dissolution and permeation are analyzed separately although they occur simultaneously in vivo. The kinetic phase changes occurring during dissolution of ASDs can influence the thermodynamic activity and membrane flux of a drug. The present review evaluates the feasibility, predictability, and practicability of permeability/dissolution for the optimal development and risk assessment of ASD formulations.

Balancing Solid-State Stability and Dissolution Performance of Lumefantrine Amorphous Solid Dispersions: The Role of Polymer Choice and Drug-Polymer Interactions

Amorphous solid dispersions (ASDs) are of great interest due to their ability to enhance the delivery of poorly soluble drugs. Recent studies have shown that, in addition to acting as a crystallization inhibitor, the polymer in an ASD plays a role in controlling the rate of drug release, notably in congruently releasing formulations, where both the drug and polymer have similar normalized release rates. The aim of this study was to compare the solid-state stability and release performance of ASDs when formulated with neutral and enteric polymers. One neutral (polyvinylpyrrolidone-vinyl acetate copolymer, PVPVA) and four enteric polymers (hypromellose acetate succinate; hypromellose phthalate; cellulose acetate phthalate, CAP; methacrylic acid-methyl methacrylate copolymer, Eudragit L 100) were used to formulate binary ASDs with lumefantrine, a hydrophobic and weakly basic antimalarial drug. The normalized drug and polymer release rates of lumefantrine-PVPVA ASDs up to 35% drug loading (DL) were similar and rapid. No drug release from PVPVA systems was detected when the DL was increased to 40%. In contrast, ASDs formulated with enteric polymers showed a DL-dependent decrease in the release rates of both the drug and polymer, whereby release was slower than for PVPVA ASDs for DLs < 40% DL. Drug release from CAP and Eudragit L 100 systems was the slowest and drug amorphous solubility was not achieved even at 5% DL. Although lumefantrine-PVPVA ASDs showed fast release, they also showed rapid drug crystallization under accelerated stability conditions, while the ASDs with enteric polymers showed much greater resistance to crystallization. This study highlights the importance of polymer selection in the formulation of ASDs, where a balance between physical stability and dissolution release must be achieved.

Revealing the mechanism of morphological variation of amorphous drug nanoparticles formed by aqueous dispersion of ternary solid dispersion

Probucol (PBC)/hypromellose (HPMC)/sodium dodecyl sulfate (SDS) ternary solid dispersions (SDs) of various weight ratios were prepared and evaluated to unveil the effect of HPMC and SDS on the formation of amorphous PBC nanoparticles. The morphological variation of the PBC nanoparticles prepared using SDs of different compositions was determined using dynamic light scattering and cryogenic transmission electron microscopy (cryo-TEM). Statistical analysis of particle size versus roundness of PBC nanoparticles was carried out based on cryo-TEM images. A clear correlation was observed between the morphologies of the PBC nanoparticles and the amounts of HPMC and SDS, either admixed in SDs or pre-dissolved in an aqueous solution. The admixed HPMC in SDs was demonstrated to play the major role in determining the primary particle sizes of discrete amorphous PBC nanoparticles. Based on ¹³C solid-state NMR spectroscopy, this phenomenon should be due to the enlarged size of the PBC-rich domains in SDs, which depended on the decreasing amounts of admixed HPMC. Although the pre-dissolved part of HPMC had less impact on the primary particle sizes, it was found to inhibit the particle agglomeration and recrystallization of amorphous PBC nanoparticles. On the other hand, sufficient SDS admixed in SDs could suppress the size enhancement of the PBC-rich domains during water immersion and nanoparticle evolution (agglomeration and crystallization) after aqueous dispersion. The pre-dissolved SDS could restrain the agglomeration of amorphous PBC nanoparticles, ultimately forming hundreds of irregular nanometer-order structures. Since the increase in size during water immersion, their sizes were still slightly larger than those obtained with a high portion of admixed SDS. The findings of this study clarified the usefulness and necessity of adding polymers and surfactants to SDs to fabricate drug nanoparticle formulations.

Effect of surfactant on the in vitro dissolution and the oral bioavailability of a weakly basic drug from an amorphous solid dispersion

This study aimed to investigate the effect of a surfactant on the liquid-liquid phase separation, dissolution, diffusion, and the oral bioavailability of a weakly basic drug (l-tetrahydropalmatine; l-THP) from an amorphous solid dispersion (ASD). The carrier used in the ASD was optimized by the application of casting film, solvent shift, and pH shift methods. The interaction between the optimized carrier (HPMCP) and l-THP was then evaluated by Fourier transform-infrared spectroscopy and powder X-ray diffraction. The impact of the surfactant on ASD prepared by the spray-drying method was evaluated by both in vitro and in vivo studies. The results of in vitro studies, including liquid-liquid phase separation, drug diffusion, and pH-shift dissolution, indicated that the addition of a surfactant at a certain concentration below critical micelle concentration to ASD caused the precipitation of and a reduction in the membrane diffusion of l-THP in pH 6.8. This observation was confirmed in an in vivo study in which the drug concentration of l-THP in rabbit plasma was determined by the LC-MS/MS analysis method. Then the absolute and relative bioavailability of l-THP was calculated from the obtained pharmacokinetic parameters. Specifically, the addition of 1.5% surfactant (Poloxamer 188) to the binary ASD decreased the relative bioavailability of l-THP by approximately 2.4 times compared with the original binary ASD. Besides, the study proved that l-THP had low absolute bioavailability (around 1.24%), and the application of binary ASD was meaningful in enhancing the oral bioavailability of l-THP by around 334.77% compared to the raw material. The study is expected to provide a better understanding of how different dosage forms influence the bioavailability of l-THP, thereby allowing the selection of the optimal approach for this weakly basic drug.

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

Among many methods to mitigate the solubility limitations of drug compounds, amorphous solid dispersion (ASD) is considered to be one of the most promising strategies to enhance the dissolution and bioavailability of poorly water-soluble drugs. The enhancement of ASD in the oral absorption of drugs has been mainly attributed to the high apparent drug solubility during the dissolution. In the last decade, with the implementations of new knowledge and advanced analytical techniques, a drug-rich transient metastable phase was frequently highlighted within the supersaturation stage of the ASD dissolution. The extended drug absorption and bioavailability enhancement may be attributed to the metastability of such drug-rich phases. In this paper, we have reviewed (i) the possible theory behind the formation and stabilization of such metastable drug-rich phases, with a focus on non-classical nucleation; (ii) the additional benefits of the ASD-induced drug-rich phases for bioavailability enhancements. It is envisaged that a greater understanding of the non-classical nucleation theory and its application on the ASD design might accelerate the drug product development process in the future.

A Crowding Barrier to Protein Inhibition in Colloidal Aggregates

Small molecule colloidal aggregates adsorb and partially denature proteins, inhibiting them artifactually. Oddly, this inhibition is typically time-dependent. Two mechanisms might explain this: low concentrations of the colloid and enzyme might mean low encounter rates, or colloid-based protein denaturation might impose a kinetic barrier. These two mechanisms should have different concentration dependencies. Perplexingly, when enzyme concentration was increased, incubation times actually lengthened, inconsistent with both models and with classical chemical kinetics of solution species. We therefore considered molecular crowding, where colloids with lower protein surface density demand a shorter incubation time than more crowded colloids. To test this, we grew and shrank colloid surface area. As the surface area shrank, the incubation time lengthened, while as it increased, the converse was true. These observations support a crowding effect on protein binding to colloidal aggregates. Implications for drug delivery and for detecting aggregation-based inhibition will be discussed.

A mechanistic review on the dissolution phase behavior and supersaturation stabilization of amorphous solid dispersions

Amorphous solid dispersion (ASD) technology is an attractive formulation approach for poorly soluble drugs because of the supersaturated state acquired during its dissolution. The high thermodynamic activity of the supersaturated state of the drug is also a driver for the enhanced absorptive flux across a membrane. However, this advantage can easily be lost due to the inherent instability of supersaturation, causing drug precipitation. Stabilizing the supersaturated state during the dissolution of ASD for the relevant absorption time frame is a challenging area in formulation research. Stabilizing the supersaturated state by using polymeric excipients and understanding the phase behavior of drugs during dissolution are required for the optimal performance of ASD formulations. A number of confounding kinetic, formulation and physiological factors can influence the evolution of supersaturation and phase changes during dissolution of ASDs. The review highlights the complex nature of dissolution of ASDs and the need of biorelevant dissolution for proper risk assessment and optimizing formulation development.

Amorphous solid dispersions of enzalutamide and novel polysaccharide derivatives: investigation of relationships between polymer structure and performance

Amorphous solid dispersion (ASD) is a widely employed formulation technique for drugs with poor aqueous solubility. Polymers are integral components of ASDs, but mechanisms by which polymers lead to the generation and maintenance of supersaturated solutions, which enhance oral absorption in vivo, are poorly understood. Herein, a diverse group of newly synthesized cellulose derivatives was evaluated for their ability to inhibit crystallization of enzalutamide, a poorly soluble compound used to treat prostate cancer. ASDs were prepared from selected polymers, specifically a somewhat hydrophobic polymer that was extremely effective at inhibiting drug crystallization, and a less effective, but more hydrophilic, crystallization inhibitor, that might afford better release. Drug membrane transport rate was evaluated in vitro and compared to in vivo performance, following oral dosing in rats. Good correlation was noted between the in vitro diffusion cell studies and the in vivo data. The ASD formulated with the less effective crystallization inhibitor outperformed the ASD prepared with the highly effective crystallization inhibitor in terms of the amount and rate of drug absorbed in vivo. This study provides valuable insight into key factors impacting oral absorption from enabling ASD formulations, and how best to evaluate such formulations using in vitro approaches.

Comparison of Drug Release and Adsorption under Supersaturating Conditions for Ordered Mesoporous Silica with Indomethacin or Indomethacin Methyl Ester

Incomplete drug release from mesoporous silica systems has been observed in several studies. This work aims to increase the understanding of this phenomenon by investigating the mechanism of drug-silica interactions and adsorption behavior from supersaturated aqueous solutions of two similar drug molecules with different hydrogen bonding capabilities. Drug-silica interactions between indomethacin or its methyl ester and SBA-15 were investigated using spectroscopic techniques (infrared, fluorescence and X-ray photoelectron) and adsorption experiments. The results demonstrate that the predominant mechanism of interaction of both drugs with silica is hydrogen bonding between drug acceptor carbonyl groups with donor groups on the silica surface. The presence of a drug hydrogen bond donor group did not enhance drug adsorption. No evidence was obtained for drug adsorption through nonspecific hydrophobic interactions. Drug adsorption onto the silica surface was investigated under supersaturating conditions through the generation of adsorption isotherms. Similar adsorption isotherms were observed for each compound when the concentration scale was normalized to the drug amorphous solubility. In other words, the equilibrium between the drug adsorbed on the silica surface and free drug in solution was related to the drug activity in solution. The high tendency of the drug to adsorb when the solution is supersaturated was, in turn, found to limit the extent of drug release during dissolution under nonsink conditions. Thus, adsorption provides an explanation for incomplete drug release.

Mechanisms of increased bioavailability through amorphous solid dispersions: a review

Amorphous solid dispersions (ASDs) can increase the oral bioavailability of poorly soluble drugs. However, their use in drug development is comparably rare due to a lack of basic understanding of mechanisms governing drug liberation and absorption in vivo. Furthermore, the lack of a unified nomenclature hampers the interpretation and classification of research data. In this review, we therefore summarize and conceptualize mechanisms covering the dissolution of ASDs, formation of supersaturated ASD solutions, factors responsible for solution stabilization, drug uptake from ASD solutions, and drug distribution within these complex systems as well as effects of excipients. Furthermore, we discuss the importance of these findings on the development of ASDs. This improved overall understanding of these mechanisms will facilitate a rational ASD formulation development and will serve as a basis for further mechanistic research on drug delivery by ASDs.

Polymer Type Impacts Amorphous Solubility and Drug-Rich Phase Colloidal Stability: A Mechanistic Study Using Nuclear Magnetic Resonance Spectroscopy

The polymer used in an amorphous solid dispersion (ASD) formulation plays a critical role in dosage form performance. Herein, drug-polymer interactions in aqueous solution were evaluated in order to better understand the dispersion stability of the colloidal drug-rich phase generated when the amorphous solubility is exceeded. The amorphous solubility (S_a,IBP) of ibuprofen (IBP) decreased when hypromellose (HPMC) or polyvinylpyrrolidone/vinyl acetate (PVP-VA) were present in solution. Solution nuclear magnetic resonance (NMR) spectroscopy revealed that a large amount of HPMC and PVP-VA distributed into the IBP-rich phase. The mixing of HPMC and PVP-VA with the IBP-rich phase led to the decreased S_a,IBP. In contrast, the charged amino methacrylate copolymer (Eudragit E PO, EUD-E) showed minimal mixing with the IBP-rich phase; however, this polymer did lead to solubilization of IBP in the bulk aqueous phase. Although the IBP-rich phase generated by dissolving IBP at concentrations above S_a,IBP rapidly coarsened followed by creaming in the absence of polymer, all of the polymers stabilized the IBP dispersion to some extent. The droplet size of the IBP-rich phase immediately after formation was around 300 nm in HPMC and PVP-VA solutions, and around 800 nm in the EUD-E solution. The mixing of the former two polymers with the drug-rich phase is thought to account for the smaller droplet size. Despite a smaller initial size, the dispersion stability of the IBP-rich droplets was relatively poor in the presence of PVP-VA. In contrast, the coalescence of the IBP-rich droplets was effectively suppressed by the steric repulsion and electrostatic repulsion derived from adsorbed HPMC and EUD-E, respectively. The present study highlights the complex effects of a polymer on the drug amorphous solubility and colloidal stability, which should be considered when optimizing ASD formulations with the goal of maximizing drug absorption.

Interplay of Supersaturation and Solubilization: Lack of Correlation between Concentration-Based Supersaturation Measurements and Membrane Transport Rates in Simulated and Aspirated Human Fluids

Supersaturating formulations are increasingly being used to improve the absorption of orally administered poorly water-soluble drugs. To better predict outcomes in vivo, we must be able to accurately determine the degree of supersaturation in complex media designed to provide a surrogate for the gastrointestinal environment. Herein, we demonstrate that relying on measurements based on consideration of the total dissolved concentration leads to underestimation of supersaturation and consequently membrane transport rates. Crystalline and amorphous solubilities of two compounds, atazanavir and posaconazole, were evaluated in six different media. Concurrently, diffusive flux measurements were performed in a side-by-side diffusion cell to determine the activity-based supersaturation by evaluating membrane transport rates at the crystalline and amorphous solubilities. Solubility values were found to vary in each medium because of different solubilization capacities. Concentration-based supersaturation ratios were also found to vary for the different media. Activity-based measurements, however, were largely independent of the medium, leading to relatively constant values for the estimated supersaturation. These findings have important consequences for modeling and prediction of supersaturation impact on the absorption rate as well as for better defining the thermodynamic driving force for crystallization in complex media.

Recent Advances in Understanding the Micro- and Nanoscale Phenomena of Amorphous Solid Dispersions

Many pharmaceutical drugs in the marketplace and discovery pipeline suffer from poor aqueous solubility, thereby limiting their effectiveness for oral delivery. The use of an amorphous solid dispersion (ASD), a mixture of an active pharmaceutical ingredient and a polymer excipient, greatly enhances the aqueous dissolution performance of a drug without the need for chemical modification. Although this method is versatile and scalable, deficient understanding of the interactions between drugs and polymers inhibits ASD rational design. This current Review details recent progress in understanding the mechanisms that control ASD performance. In the solid-state, the use of high-resolution theoretical, computational, and experimental tools resolved the influence of drug/polymer phase behavior and dynamics on stability during storage. During dissolution in aqueous media, novel characterization methods revealed that ASDs can form complex nanostructures, which maintain and improve supersaturation of the drug. The studies discussed here illustrate that nanoscale phenomena, which have been directly observed and quantified, strongly affect the stability and bioavailability of ASD systems, and provide a promising direction for optimizing drug/polymer formulations.

Colloidal Drug Aggregate Stability in High Serum Conditions and Pharmacokinetic Consequence

Colloidal drug aggregates have been a nuisance in drug screening, yet, because they inherently comprise drug-rich particles, they may be useful in vivo if issues of stability can be addressed. As the first step toward answering this question, we optimized colloidal drug aggregate formulations using a fluorescence-based assay to study fulvestrant colloidal formation and stability in high (90%) serum conditions in vitro. We show, for the first time, that the critical aggregation concentration of fulvestrant depends on media composition and increases with serum concentration. Excipients, such as polysorbate 80, stabilize fulvestrant colloids in 90% serum in vitro for over 48 h. Using fulvestrant and an investigational pro-drug, pentyloxycarbonyl-( p-aminobenzyl) doxazolidinylcarbamate (PPD), as proof-of-concept colloidal formulations, we demonstrate that the in vivo plasma half-life for stabilized colloids is greater than their respective monomeric forms. These studies demonstrate the potential of turning the nuisance of colloidal drug aggregation into an opportunity for drug-rich formulations.

Mechanistic elucidation of formation of drug-rich amorphous nanodroplets by dissolution of the solid dispersion formulation

Drug-rich amorphous nanodroplets have great potential to improve intestinal absorption of poorly water-soluble drugs. Spray-dried samples (SPDs) of glibenclamide (GLB) with hypromellose (HPMC) or hypromellose acetate succinate (HPMC-AS, grade AS-LF and AS-HF) were prepared to investigate how GLB-rich amorphous nanodroplets form during the dissolution of solid dispersions. The co-spray drying of AS-LF significantly enhanced GLB dissolution from the SPD, leading to the temporary formation of GLB-rich amorphous nanodroplets. However, the droplets gradually coarsened as AS-LF fails to inhibit coarsening. In contrast, the addition of HPMC to the SPD failed to aid GLB-rich amorphous nanodroplet formation during dissolution. The failure of formation of GLB-rich amorphous nanodroplet was caused by slow GLB dissolution, due to the poor controllability of the GLB dissolution by HPMC. The addition of AS-HF to the SPD produced amorphous GLB particles that contained a large amount of AS-HF during dissolution. Gel-like particles formed instead of GLB-rich amorphous nanodroplets. When the SPD containing AS-LF was dissolved in AS-HF solution, stably-dispersed GLB-rich amorphous nanodroplets were successfully formed owing to rapid GLB dissolution from the SPD containing AS-LF and strong coarsening inhibition by AS-HF. Formulation optimization considering both aqueous dissolution of the solid dispersion and the inhibition of nanodroplet coarsening achieved stably-dispersed drug-rich amorphous nanodroplets.

Aggregation of Hydroxypropyl Methylcellulose Acetate Succinate under Its Dissolving pH and the Impact on Drug Supersaturation

Hydroxypropyl methylcellulose acetate succinate (HPMC-AS) is one of the commonly selected polymers used in amorphous solid dispersions (ASD) with excellent capabilities to maintain aqueous supersaturation of poorly water-soluble drugs and inhibit their crystallization, but the underlying mechanisms remain elusive. In this study, posaconazole was chosen as the model drug to study the supersaturation maintaining and crystallization inhibition capabilities of different types of HPMC-AS under pH 5.5-7.5. We analyzed the HPMC-AS aggregation status in solution using combination of static and dynamic light scattering and observed higher polymer aggregation number when higher grade HPMC-AS or lower pH was used, which correlates well with prolonged drug supersaturation or crystallization inhibition. The amount of HPMC-AS coprecipitated with PSZ, a direct indicator of drug/HPMC-AS affinity, also showed positive correlation with the drug supersaturation and crystallization inhibition in the dissolution process. Therefore, we conclude that the aggregation behavior of HPMC-AS and the drug/HPMC-AS affinity are the key mechanisms that lead to posaconazole supersaturation and crystallization inhibition when HPMC-AS was applied.

Pharmaceutical Applications of Cellulose Ethers and Cellulose Ether Esters

Cellulose ethers have proven to be highly useful natural-based polymers, finding application in areas including food, personal care products, oil field chemicals, construction, paper, adhesives, and textiles. They have particular value in pharmaceutical applications due to characteristics including high glass transition temperatures, high chemical and photochemical stability, solubility, limited crystallinity, hydrogen bonding capability, and low toxicity. With regard to toxicity, cellulose ethers have essentially no ability to permeate through gastrointestinal enterocytes and many are already in formulations approved by the U.S. Food and Drug Administration. We review pharmaceutical applications of these valuable polymers from a structure-property-function perspective, discussing each important commercial cellulose ether class; carboxymethyl cellulose, methyl cellulose, hydroxypropylcellulose, hydroxypropyl methyl cellulose, and ethyl cellulose, and cellulose ether esters including hydroxypropyl methyl cellulose acetate succinate and carboxymethyl cellulose acetate butyrate. We also summarize their syntheses, basic material properties, and key pharmaceutical applications.

Colloidal aggregation: from screening nuisance to formulation nuance

It is well known that small molecule colloidal aggregation is a leading cause of false positives in early drug discovery. Colloid-formers are diverse and well represented among corporate and academic screening decks, and even among approved drugs. Less appreciated is how colloid formation by drug-like compounds fits into the wider understanding of colloid physical chemistry. Here we introduce the impact that colloidal aggregation has had on early drug discovery, and then turn to the physical and thermodynamic driving forces for small molecule colloidal aggregation, including the particulate nature of the colloids, their critical aggregation concentration-governed formation, their mechanism of protein adsorption and subsequent inhibition, and their sensitivity to detergent. We describe methods that have been used extensively to both identify aggregate-formers and to study and control their physical chemistry. While colloidal aggregation is widely recognized as a problem in early drug discovery, we highlight the opportunities for exploiting this phenomenon in biological milieus and for drug formulation.

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.

Direct NMR Monitoring of Phase Separation Behavior of Highly Supersaturated Nifedipine Solution Stabilized with Hypromellose Derivatives

We investigated the phase separation behavior and maintenance mechanism of the supersaturated state of poorly water-soluble nifedipine (NIF) in hypromellose (HPMC) derivative solutions. Highly supersaturated NIF formed NIF-rich nanodroplets through phase separation from aqueous solution containing HPMC derivative. Dissolvable NIF concentration in the bulk water phase was limited by the phase separation of NIF from the aqueous solution. HPMC derivatives stabilized the NIF-rich nanodroplets and maintained the NIF supersaturation with phase-separated NIF for several hours. The size of the NIF-rich phase was different depending on the HPMC derivatives dissolved in aqueous solution, although the droplet size had no correlation with the time for which NIF supersaturation was maintained without NIF crystallization. HPMC acetate and HPMC acetate succinate (HPMC-AS) effectively maintained the NIF supersaturation containing phase-separated NIF compared with HPMC. Furthermore, HPMC-AS stabilized NIF supersaturation more effectively in acidic conditions. Solution ¹H NMR measurements of NIF-supersaturated solution revealed that HPMC derivatives distributed into the NIF-rich phase during the phase separation of NIF from the aqueous solution. The hydrophobicity of HPMC derivative strongly affected its distribution into the NIF-rich phase. Moreover, the distribution of HPMC-AS into the NIF-rich phase was promoted at lower pH due to the lower aqueous solubility of HPMC-AS. The distribution of a large amount of HPMC derivatives into NIF-rich phase induced the strong inhibition of NIF crystallization from the NIF-rich phase. Polymer distribution into the drug-rich phase directly monitored by solution NMR technique can be a useful index for the stabilization efficiency of drug-supersaturated solution containing a drug-rich phase.