Solid-state analysis of amorphous solid dispersions: Why DSC and XRPD may not be regarded as stand-alone techniques

Drug-polymer interactions are of great importance in amorphous solid dispersion (ASD) formulation for both dissolution performance and physical stability considerations. In this work, three felodipine ASD systems with drug loading ranging from 5 to 20% were prepared using PVP, PVP-VA, or HPMC-AS as the polymer matrix. The amorphization and homogeneity were confirmed by differential scanning calorimetry and powder X-ray diffraction. The intrinsic dissolution behavior of these ASDs was studied in 0.05 M HCl and phosphate-buffered saline (PBS) (pH 6.5). In 0.05 M HCl, PVP-VA ASDs with low drug loading (<15%) showed rapid dissolution accompanied with nano-species generation, while in the PVP system, rapid dissolution and nano-species generation were observed only when drug loading was less than 10%, and HPMC-AS ASDs always released slowly with no nano-species formation. In PBS, PVP-VA ASDs with drug loading less than 10% showed rapid dissolution accompanied with nano-species generation, while for PVP ASDs, rapid dissolution and nano-species generation were observed only when drug loading was 5%. However, 20% drug loading HPMC-AS ASDs exhibited rapid dissolution of felodipine and nano-species generation. When the drug loading was above the transition point of PVP-VA ASDs and PVP ASDs, the release rate was significantly lowered, and no nano-species was generated. To understand this phenomenon, drug-polymer interactions were studied using the melting point depression method and the Flory-Huggins model fitting. The Flory-Huggins interaction parameters (χ) for felodipine/HPMC-AS, felodipine/PVP, and felodipine/PVP-VA were determined to be 0.62 ± 0.07, -0.55 ± 0.20, and -1.02 ± 0.21, respectively, indicating the existence of the strongest attractive molecular interaction between felodipine and PVP-VA, followed by felodipine/PVP, but not in felodipine/HPMC-AS. Furthermore, dynamic vapor sorption further revealed that the molecular interactions between felodipine and PVP or PVP-VA were resistant to water. We concluded that water-resistant drug-polymer interactions in felodipine/polymer systems were responsible for the formation of nano-species, which further facilitated the rapid initial drug dissolution.

Development of stability-enhanced ternary solid dispersions via combinations of HPMCP and Soluplus® processed by hot melt extrusion

Effect of temperature and moisture on the miscibility of amorphous dispersions of felodipine and poly(vinyl pyrrolidone)

This study investigated the development of high drug loading amorphous solid dispersions (ASDs) of itraconazole (ITZ) using single screw hot melt extrusion (HME) for fused deposition modelling (FDM) 3D printing (3DP). ITZ ASDs containing 20-22% w/w ITZ were prepared with Hydroxypropyl methylcellulose acetate succinate, medium grade, medium particle (HPMCAS-MMP) and processed into filaments for 3DP, while a conventional direct compression ASD was produced as a benchmark to assess the influence of manufacturing method on drug release. While both dosage forms were based on the same ASD system, the final tablet compositions differed due to the requirements of each manufacturing method. Solid-state characterisation using differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) confirmed the amorphous nature of the formulations. Dissolution studies were conducted in phosphate buffer saline (PBS, pH 7.4). The direct compressed ASD tablets showed rapid drug release (~ 63% in 30min) while much slower release was observed for the 3D printed tablets. At 30min F1 (10% triethyl citrate (TEC)) released only 3% and F2 (12.5% TEC) released 6%. This behaviour may be attributed to the printed tablet's dense structure, buoyancy, and formation of a viscous hydrogel barrier at the surface. This study shows that single screw HME can be used to produce ITZ ASDs for both 3DP and conventional tabletting, while also demonstrating that the dense microstructure of 3D printed tablets limits their ability to achieve an immediate release profile. Further optimisation of formulation and tablet design, such as infill will be needed to improve release performance. These findings provide a basis for future formulation and design strategies to enhance the performance of 3D printed dosage forms.

Long-Term Physical Stability of Amorphous Solid Dispersions: Comparison of Detection Powers of Common Evaluation Methods for Spray-Dried and Hot-Melt Extruded Formulations

Hot-melt extrudability of amorphous solid dispersions of flubendazole-copovidone: An exploratory study of the effect of drug loading and the balance of adjuvants on extrudability and dissolution

Investigation of Atypical Dissolution Behavior of an Encapsulated Amorphous Solid Dispersion

The co-administration of curcumin and hesperetin might be beneficial in terms of neuroprotective activity; therefore, in this study, we attempted to develop a fixed-dose formulation comprising these two compounds in an amorphous state. The aim of obtaining an amorphous state was to overcome the limitations of the low solubility of the active compounds. First, we assessed the possibility of using popular sweeteners (erythritol, xylitol, and sorbitol) as plasticizers to reduce the glass transition temperature of PVP K30 to prepare the polymer-excipient blends, which allowed the preparation of amorphous solid dispersions via hot-melt extrusion at a temperature below the original glass transition of PVP K30. Erythritol proved to be the superior plasticizer. Then, we focused on the development of fixed-dose amorphous solid dispersions of curcumin and hesperetin. Powder X-ray diffraction and thermal analysis confirmed the amorphous character of dispersions, whereas infrared spectroscopy helped to assess the presence of intermolecular interactions. The amorphous state of the produced dispersions was maintained for 6 months, as shown in a stability study. Pharmaceutical parameters such as dissolution rate, solubility, and in vitro permeability through artificial membranes were evaluated. The best improvement in these features was noted for the dispersion, which contained 15% of the total content of the active compounds with erythritol used as the plasticizer.

Simvastatin(SMV) is poorly soluble drug classified as belonging to Class II of BiopharmaceuticsClassification System. Common approach to improve apparent solubility of drugsis production of amorphous solid dispersions (ASD) by means of spray drying(SD) or hot-melt extrusion. Spray drying of low-glass transition temperature(Tg) ASDs is challenging due to the risk of material being exposed to SD outlettemperatures close to its Tg which may result in melting of ASD and subsequentcrystallisation of amorphous drug. It was hypothesised that addition ofeasily-crystallising material to ASD will improve its SD processability. Inaddition, it was hypothesised that produced ternary solid dispersions (TSD)composed of amorphous composite of drug and the polymer (PVP K17, 55 and 150) andcrystalline, soluble nanoparticles (NaCl) will improve dissolution of TSDtablets. The dissolution of SMV fromTSDs was faster compared with that of binary solid dispersion in case of SMV-TSDsproduced with PVP K55 and 150. The tabletabilityassessment showed increase in compression led to increase in tensile strengthand decrease in porosities of SDs tablets.

Introduction. Ebastine is a second-generation antihistamine drug available in the form of orally disintegrating tablets and film-coated tablets. Ebastine substance exhibits high bioavailability, but low solubility in water and gastrointestinal tract media. The technology of solid dispersions based on polymer carriers by hot melt extrusion is proposed to solve the problem of ebastine low solubility.Aim. Composition development of extrudate and its production technology to create an amorphous solid dispersion of ebastine in oder to increase the recovery rate and bioavailability.Materials and methods. Ebastin micronized (JSC "Active Component", Russia); ebastin crystalline (Arevipharma GmbH, Germany); VIVAPHARM® PVP/VA 64 (JRS Pharma GMbH &amp; Co. KG, Germany). Extrudates were obtained on a HAAKE™ miniCTW co-rotating twin-screw laboratory extruder (Thermo Fisher Scientific, Germany). Extrudates were studied by differential scanning calorimetry, synchronous thermal analysis, powder X-ray diffraction and FTIR-spectroscopy. The quantitative content of the active ingredient was determined by spectrophotometry. The content of related impurities in the amorphous solid dispersion of ebastine was determined by HPLC.Results and discussion. The technology of amorphous solid dispersion of ebastine by hot melt extrusion was developed. The pharmacokinetic properties of ebastine were significantly improved. The process of obtaining solid dispersion with 20 % of ebastine was optimized in order to reduce the content of impurities in the extrudate.Conclusion. The maximum concentration of ebastine for proper quality amorphous solid dispersion based on PVP/VA64 amounted to 20 %. Obtaining a solid dispersion by hot melt extrusion with ebastine content in PVP/VA64 higher than 30 % is impossible because the melt does not possess the glass transition property.

Spray drying is one of the most commonly used manufacturing techniques for amorphous solid dispersions (ASDs). During spray drying, very fast solvent evaporation is enabled by the generation of small droplets and exposure of these droplets to a heated drying gas. This fast solvent evaporation leads to an increased viscosity that enables kinetic trapping of an active pharmaceutical ingredient (API) in a polymer matrix, which is favorable for the formulation of supersaturated, kinetically stabilized ASDs. In this work, the relation between the solvent evaporation rate and the kinetic stabilization of highly drug-loaded ASDs was investigated. Accordingly, thermal gravimetric analysis (TGA) was employed to study the evaporation kinetics of seven organic solvents and the influence of solutes, i.e., poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA), fenofibrate (FNB), and naproxen (NAP), on the evaporation behavior. At 10 °C below the boiling point of the respective solvent, methanol (MeOH) had the lowest evaporation rate and dichloromethane (DCM) had the highest. PVPVA decreased the evaporation rate for all solvents, yet this effect was more pronounced for the relatively faster evaporating solvents. The APIs had opposite effects on the evaporation process: FNB increased the evaporation rate, while NAP decreased it. The latter might indicate the presence of interactions between NAP and the solvent or NAP and PVPVA, which was further investigated using Fourier transform-InfraRed (FT-IR) spectroscopy. Based on these findings, spray drying process parameters were adapted to alter the evaporation rate. Increasing the evaporation rate of MeOH and DCM enabled the kinetic stabilization of higher drug loadings of FNB, while the opposite trend was observed for ASDs of NAP. Even when higher drug loadings could be kinetically stabilized by adapting the process parameters, the improvement was limited, demonstrating that the phase behavior of these ASDs of FNB and NAP immediately after preparation was predominantly determined by the API-polymer-solvent combination rather than the process parameters applied.

Bottom-Up and Top-Down Approaches to Explore Sodium Dodecyl Sulfate and Soluplus on the Crystallization Inhibition and Dissolution of Felodipine Extrudates

Weakly acid polymerswith pH-responsive solubility arebeing usedwith increasing frequency in amorphous solid dispersion (ASD) formulationsof drugs with low aqueous solubility. However, drug release and crystallizationin a pH environment where the polymer is insoluble are not well understood.The aim of the current study was to develop ASD formulations optimizedfor release and supersaturation longevity of a rapidly crystallizingdrug, pretomanid (PTM), and to evaluate a subset of these formulationsin vivo. Following screening of several polymers for their abilityto inhibit crystallization, hypromellose acetate succinate HF grade(HPMCAS-HF; HF) was selected to prepare PTM ASDs. In vitro releasestudies were conducted in simulated fasted- and fed-state media. Drugcrystallization in ASDs following exposure to dissolution media wasevaluated by powder X-ray diffraction, scanning electron microscopy,and polarized light microscopy. In vivo oral pharmacokinetic evaluationwas conducted in male cynomolgus monkeys (n = 4)given 30 mg PTM under both fasted and fed conditions in a crossoverdesign. Three HPMCAS-based ASDs of PTM were selected for fasted-stateanimal studies based on their in vitro release performance. Enhancedbioavailability was observed for each of these formulations relativeto the reference product that contained crystalline drug. The 20%drug loading PTM-HF ASD gave the best performance in the fasted state,with subsequent dosing in the fed state. Interestingly, while foodimproved drug absorption of the crystalline reference product, theexposure of the ASD formulation was negatively impacted. The failureof the HPMCAS-HF ASD to enhance absorption in the fed state was hypothesizedto result from poor release in the reduced pH intestinal environmentresulting from the fed state. In vitro experiments confirmed a reducedrelease rate under lower pH conditions, which was attributed to reducedpolymer solubility and an enhanced crystallization tendency of thedrug. These findings emphasize the limitations of in vitro assessmentof ASD performance using standardized media conditions. Future studiesare needed for improved understanding of food effects on ASD releaseand how this variability can be captured by in vitro testing methodologiesfor better prediction of in vivo outcomes, in particular for ASDsformulated with enteric polymers.

The present study was designed to determine the applicability of a newly derived dimensionless number precipitation parameter, "supersaturation holding capacity (SHC)" in development of amorphous solid dispersion (ASD) of a rapidly crystallizing drug, nisoldipine. Also, ASD preparation from lab scale formulation technique to scalable spray drying technique followed by oral bioavailability study was demonstrated. Solution state screening of polymers was performed by determining nucleation induction time (tin) and SHC. With screened polymers, lab scale ASDs of nisoldipine were prepared using rotary evaporation (solvent evaporation) method, and the optimized stable ASDs were scaled up by spray drying. The ASDs were characterized by DSC, PXRD, and FTIR for amorphous nature and evaluated for apparent solubility, dissolution, and solid-state stability improvement. The spray dried ASDs were additionally evaluated for micrometric properties and oral bioavailability study.PVP grades demonstrated superior crystal growth inhibition properties (with 2-4-fold enhancements in SHC). ASDs prepared by both lab scale and scale-up technique using PVP stabilized the amorphous nisoldipine via antiplasticization effect that maintained the stability under accelerated stability conditions (40°C/75% RH) for 6months. Additionally, FTIR study confirmed the role of intermolecular interactions in amorphous state stabilization of PVP-based solid dispersions. PVP-based spray dried ASDs improved the apparent solubility 4-fold for PVP K17 and more than 3-fold for remaining spray dried ASDs. The enhanced solubility was translated to improved dissolution of the drug when compared with crystalline and amorphous form complementing the outcome of the solution state study. The spray dried ASD showed 2.3 and > 3-fold the improvement in Cmax and AUC (0-24h) respectively when compared with crystalline nisoldipine during oral bioavailability study which highlights the significance of SHC parameter of polymers. The spray dried ASD has shown improved micromeritics properties then crystalline nisoldipine in terms of flow behavior.This unique study provides a rational strategy for selection of appropriate polymer in development of ASDs that can tackle both precipitation during dissolution and amorphous state stabilization in solid state and also considers the SHC in scale-up study. Graphical abstract.

Context: Serious efforts have been made to overcome the bioavailability problems of ever increasing number of poorly soluble drugs, including atorvastatin (ATO); however, enhancing its gastric solubility has not received much attention.Objectives: To improve the bioavailability of ATO by increasing its gastric solubility in a stable oral disintegration tablet (ODT) formulation.Materials and methods: Amorphous solid dispersion (ASD) of ATO with Eudragit® EPO was used as API in ODT formulation. Characterization using Differential scanning calorimetry, Powder X-ray diffraction, Fourier transform infrared drug–polymer interaction simulated by molecular modeling, solubility, dissolution and stability studies together with in vivo evaluation.Results and discussion: In ASD there was uniform distribution of drug in the polymer and it retained the amorphous nature without any chemical interactions except the possibility of hydrogen bond formation, with substantially higher gastric solubility. The dissolution profile of the ODT containing ASD was significantly improved >90% within 15 min compared with 25% of plain ATO formulation. In vivo results showed an overall enhancement in the apparent bioavailability (83% and 434% more than Lipitor® and plain amorphous ATO tablets, respectively). Combining the ASD with ODT presents a reliable solution to overcome the low solubility and bioavailability problems of ATO in a simple, robust and cost effective formulation.