Challenges and Strategies in Thermal Processing of Amorphous Solid Dispersions: A Review

Amorphous solid dispersions: An update for preparation, characterization, mechanism on bioavailability, stability, regulatory considerations and marketed products

Amorphous solid dispersions (ASDs) are being employed frequently to improve bioavailability of poorly soluble molecules by enhancing the rate and extant of dissolution in drug product development process. These systems comprise of an amorphous active pharmaceutical ingredient stabilized by a polymer matrix to provide enhanced stability. This review discussed the methodologies of preparation and characterization of ASDs with an emphasis on understanding and predicting stability. Rational selection of polymers, preparation techniques with its advantages and disadvantages and characterization of polymeric amorphous solid dispersions have discussed. Stability aspects have been described as per ICH guidelines which intend to depend on selection of polymers and preparation methods of ASD. The mechanism involved on improvement of bioavailability also considered. Regulatory importance of ASD and current evolving details of QBD approach were reviewed. Amorphous products and particularly ASDs are currently most emerging area in the pharmaceutical field. This strategic approach presents huge impact and advantageous features concerning the overall improvement of drug product performance in clinical settings which ultimately lead to drug product approval by leading regulatory agencies into the market.

A Mechanistic Model for Predicting the Physical Stability of Amorphous Solid Dispersions

In this paper, we establish a mechanistic model for the prediction of amorphous solid dispersion (ASD) stability. The novel approach incorporates fundamental physical parameters, principally supersaturation, diffusivity, and interfacial energy, to model crystallization in ASDs accounting for both kinetic and thermodynamic drivers. API dependent decoupling coefficients were also considered which allowed dynamic mechanical analysis to probe molecular mobility, with viscosity measurements, across an exceptionally broad range of temperatures to support ASD stability simulations. ASDs are multicomponent systems in which the amorphous form of active pharmaceutical ingredients (APIs) are molecularly dispersed within a carrier. This gives rise to a transiently supersaturated API solution upon dissolution which increases the driving force for oral absorption and results in increased bioavailability as compared to that of the crystalline API. A major shortcoming of ASDs, however, is that there is the potential for amorphous APIs to revert to their more stable crystalline form during storage, despite the use of polymer carriers to stabilize formulations and limit recrystallization. Hot melt extrusion (HME) has been employed as the preparation method for ASDs used in this study as it is well-suited for the formation of uniform dispersions. The ASDs were stored under controlled temperature conditions, in the absence of humidity, to determine recrystallization kinetics. Our mechanistic model, considering both crystal nucleation and growth processes, describes temporal ASD stability through a system of coupled differential equations that connect the physiochemical properties of the ASD system to drug recrystallization. The model and prolonged time scale of crystallization observed highlight the importance of considering both thermodynamic and kinetic factors in the preparation of stable ASDs. Experimental observations were found to be in good agreement with predictions of the model confirming its utility in predicting the temporal physical stability of amorphous solid dispersions through a mechanistic lens.

Solvent-Assisted Secondary Drying of Spray-Dried Polymers

Purpose

The purpose of this work is to introduce solvent-assisted secondary drying, a method used to accelerate the residual solvent removal from spray dried materials. Spray-drying is used to manufacture amorphous solid dispersions, which enhance the bioavailability of active pharmaceutical ingredients (APIs) with low aqueous solubility. In the spray-drying process, API and excipients are co-dissolved in a volatile organic solvent, atomized into droplets through a nozzle, and introduced to a drying chamber containing heated nitrogen gas. The product dries rapidly to form a powder, but small amounts of residual solvent (typically, 1 to 10 wt%) remain in the product and must be removed in a secondary-drying process. For some spray-dried materials, secondary drying by traditional techniques can take days and requires balancing stability risks with process time.

Methods

Spray-dried polymers were secondary dried, comparing the results for three state-of-the-art methods that employed a jacketed, agitated-vessel dryer: (1) vacuum-only drying, (2) water-assisted drying, or (3) methanol-assisted drying. Samples of material were pulled at various time points and analyzed by gas chromatography (GC) and Karl Fischer (KF) titration to track the drying process.

Results

Model systems were chosen for which secondary drying is slow. For all cases studied, methanol-assisted drying outperformed the vacuum-only and water-assisted drying methods.

Conclusions

The observation that methanol-assisted drying is more effective than the other drying techniques is consistent with the free-volume theory of solvent diffusion in polymers.

Electronic supplementary material

The online version of this article (10.1007/s11095-020-02890-0) contains supplementary material, which is available to authorized users.

Orodispersible Polymer Films with the Poorly Water-Soluble Drug, Olanzapine: Hot-Melt Pneumatic Extrusion for Single-Process 3D Printing

Amorphous solid dispersions (ASDs) improve the oral delivery of poorly water-soluble drugs. ASDs of olanzapine (OLZ), which have a high melting point and low solubility, are performed using a complicated process. Three-dimensional (3D) printing based on hot-melt pneumatic extrusion (HMPE) is a simplified method for producing ASDs. Unlike general 3D printing, printlet extrusion is possible without the preparation of drug-loaded filaments. By heating powder blends, direct fused deposition modeling (FDM) printing through a nozzle is possible, and this step produces ASDs of drugs. In this study, we developed orodispersible films (ODFs) loaded with OLZ as a poorly water-soluble drug. Various ratios of film-forming polymers and plasticizers were investigated to enhance the printability and optimize the printing temperature. Scanning electron microscopy (SEM) showed the surface morphology of the film for the optimization of the polymer carrier ratios. Differential scanning calorimetry (DSC) was used to evaluate thermal properties. Powder X-ray diffraction (PXRD) confirmed the physical form of the drug during printing. The 3D printed ODF formulations successfully loaded ASDs of OLZ using HMPE. Our ODFs showed fast disintegration patterns within 22 s, and rapidly dissolved and reached up to 88% dissolution within 5 min in the dissolution test. ODFs fabricated using HMPE in a single process of 3D printing increased the dissolution rates of the poorly water-soluble drug, which could be a suitable formulation for fast drug absorption. Moreover, this new technology showed prompt fabrication feasibility of various formulations and ASD formation of poorly water-soluble drugs as a single process. The immediate dissolution within a few minutes of ODFs with OLZ, an atypical antipsychotic, is preferred for drug compliance and administration convenience.

A Novel Approach to Optimize Hot Melt Impregnation in Terms of Amorphization Efficiency

In this study, an innovative methodology to optimize amorphization during the hot melt impregnation (HMI) process was proposed. The novelty of this report revolves around the use of thermal analysis in combination with design of experiments (DoEs) to reduce residual crystallinity during the HMI process. As a model formulation, a mixture of ibuprofen (IBU) and Neusilin was used. The main aim of the study was to identify the critical process parameters of HMI and determine their optimal values to assure a robust impregnation process and possibly the highest possible amorphization rate of IBU. In order to realize this, a DoE approach was proposed based on a face-centered composite design involving three factors. The IBU/Neusilin ratio, the feeding rate, and the screw speed were considered as variables, while the residual crystallinity level of IBU, determined using differential scanning calorimetry (DSC), was measured as the response. Additionally, the stability of IBU under HMI was analyzed using high-performance liquid chromatography to estimate the extent of potential degradation. In order to verify the correctness of the DoE model, tested extrudates were manufactured by HMI and the obtained extrudates were thoroughly examined using scanning electron micrography, X-ray powder diffraction, and DSC.

Improved Dissolution and Pharmacokinetics of Abiraterone through KinetiSol® Enabled Amorphous Solid Dispersions

Abiraterone is a poorly water-soluble drug. It has a high melting point and limited solubility in organic solvents, making it difficult to formulate as an amorphous solid dispersion (ASD) with conventional technologies. KinetiSol^® is a high-energy, fusion-based, solvent-free technology that can produce ASDs. The aim of this study was to evaluate the application of KinetiSol to make abiraterone ASDs. We developed binary KinetiSol ASDs (KSDs) using both polymers and oligomers. For the first time, we reported that KinetiSol can process hydroxypropyl-β-cyclodextrin (HPBCD), a low molecular-weight oligomer. Upon X-ray diffractometry and modulated differential scanning calorimetry analysis, we found the KSDs to be amorphous. In vitro dissolution analysis revealed that maximum abiraterone dissolution enhancement was achieved using a HPBCD binary KSD. However, the KSD showed significant abiraterone precipitation in fasted state simulated intestinal fluid (FaSSIF) media. Hence, hypromellose acetate succinate (HPMCAS126G) was selected as an abiraterone precipitation inhibitor and an optimized ternary KSD was developed. A pharmacokinetic study revealed that HPBCD based binary and ternary KSDs enhanced abiraterone bioavailability by 12.4-fold and 13.8-fold, respectively, compared to a generic abiraterone acetate tablet. Thus, this study is the first to demonstrate the successful production of an abiraterone ASD that exhibited enhanced dissolution and bioavailability.

Processing of Polyvinyl Acetate Phthalate in Hot-Melt Extrusion-Preparation of Amorphous Solid Dispersions

The preparation of amorphous solid dispersions (ASDs) is a suitable approach to overcome solubility-limited absorption of poorly soluble drugs. In particular, pH-dependent soluble polymers have proven to be an excellently suitable carrier material for ASDs. Polyvinyl acetate phthalate (PVAP) is a polymer with a pH-dependent solubility, which is as yet not thoroughly characterized regarding its suitability for a hot-melt extrusion process. The objective of this study was to assess the processability of PVAP within a hot-melt extrusion process with the aim of preparing an ASD. Therefore, the influence of different process parameters (temperature, feed-rate) on the degree of degradation, solid-state and dissolution time of the neat polymer was studied. Subsequently, drug-containing ASDs with indomethacin (IND) and dipyridamole (DPD) were prepared, respectively, and analyzed regarding drug content, solid-state, non-sink dissolution performance and storage stability. PVAP was extrudable in combination with 10% (w/w) PEG 3000 as plasticizer. The dissolution time of PVAP was only slightly influenced by different process parameters. For IND no degradation occurred in combination with PVAP and single phased ASDs could be generated. The dissolution performance of the IND-PVAP ASD at pH 5.5 was superior and at pH 6.8 equivalent compared to commonly used polymers hydroxypropylmethylcellulose acetate succinate (HPMCAS) and Eudragit L100-55.

Injection Molded Capsules for Colon Delivery Combining Time-Controlled and Enzyme-Triggered Approaches

A new type of colon targeting system is presented, combining time-controlled and enzyme-triggered approaches. Empty capsule shells were prepared by injection molding of blends of a high-amylose starch and hydroxypropyl methylcellulose (HPMC) of different chain lengths. The dissolution/erosion of the HPMC network assures a time-controlled drug release, i.e., drug release starts upon sufficient shell swelling/dissolution/erosion. In addition, the presence of high-amylose starch ensures enzyme-triggered drug release. Once the colon is reached, the local highly concentrated bacterial enzymes effectively degrade this polysaccharide, resulting in accelerated drug release. Importantly, the concentration of bacterial enzymes is much lower in the upper gastrointestinal tract, thus enabling site-specific drug delivery. The proposed capsules were filled with acetaminophen and exposed to several aqueous media, simulating the contents of the gastrointestinal tract using different experimental setups. Importantly, drug release was pulsatile and occurred much faster in the presence of fecal samples from patients. The respective lag times were reduced and the release rates increased once the drug started to be released. It can be expected that variations in the device design (e.g., polymer blend ratio, capsule shell geometry and thickness) allow for a large variety of possible colon targeting release profiles.

Harnessing the therapeutic potential of anticancer drugs through amorphous solid dispersions

The treatment of cancer is still a major challenge. But tremendous progress in anticancer drug discovery and development has occurred in the last few decades. However, this progress has resulted in few effective oncology products due to challenges associated with anticancer drug delivery. Oral administration is the most preferred route for anticancer drug delivery, but the majority of anticancer drugs currently in product pipelines and the majority of those that have been commercially approved have inherently poor water solubility, and this cannot be mitigated without compromising their potency and stability. The poor water solubility of anticancer drugs, in conjunction with other factors, leads to suboptimal pharmacokinetic performance. Thus, these drugs have limited efficacy and safety when administered orally. The amorphous solid dispersion (ASD) is a promising formulation technology that primarily enhances the aqueous solubility of poorly water-soluble drugs. In this review, we discuss the challenges associated with the oral administration of anticancer drugs and the use of ASD technology in alleviating these challenges. We emphasize the ability of ASDs to improve not only the pharmacokinetics of poorly water-soluble anticancer drugs, but also their efficacy and safety. The goal of this paper is to rationalize the application of ASD technology in the formulation of anticancer drugs, thereby creating superior oncology products that lead to improved therapeutic outcomes.

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.

Intermolecular Interactions between Drugs and Aminoalkyl Methacrylate Copolymer in Solution to Enhance the Concentration of Poorly Water-Soluble Drugs

An aminoalkyl methacrylate copolymer, Eudragit^® E (EUD-E), has gained tremendous attention as a solid dispersion carrier because it efficiently stabilizes drugs in the amorphous state. Furthermore, EUD-E remarkably enhances drug dissolution in water. This review focuses on the interaction between drugs and EUD-E in solution, which contributes to the enhancement of drug concentration. Studies examining interactions between acidic drugs and EUD-E in organic solvents have revealed that the interaction occurs predominantly by electrostatic interaction, including hydrogen bonding and dipolar interactions. Other studies on interactions in aqueous solution found evidence for strong electrostatic interactions between acidic drugs and EUD-E in ion exchange experiments. ¹H-NMR studies using high-resolution magic-angle spinning, nuclear Overhauser effect spectroscopy, diffusion, and relaxation time measurements successfully identified the interaction site and strength in aqueous solution. Hydrophobic and ionic interactions occurred between drugs and EUD-E. The conformation of EUD-E, which was affected by the ionic strength and pH of the aqueous media, also influenced the interaction. The knowledge discussed in this review will be helpful in designing solid dispersion formulations with EUD-E, which will efficiently enhance drug concentration and subsequent absorption into the body.

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

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

Holistic QbD approach for hot-melt extrusion process design space evaluation: Linking materials science, experimentation and process modeling

The aim of this work was to investigate the relationship between formulation material properties, process parameters and process performance for the manufacturing of amorphous solid dispersions via hot-melt extrusion (HME) using experimentation coupled with process modeling. Specifically, we evaluated the impact of the matrix copovidone melt rheology with and without the addition of a plasticizing surfactant, polysorbate 80, while also varying the process parameters, barrel temperature and screw speed, and keeping fill volume constant. To correlate the process performance to a critical quality attribute, we used telmisartan as an indicator substance by processing at temperatures below its solubility temperature in the polymeric matrix. We observed a broader design space of HME processes for the plasticized formulation with respect to screw speed than for the copovidone-only matrix formulation. This observation was determined by the range of observed melt temperatures in the extruder, both measured and simulated. The reason was not primarily linked to a reduced shear-thinning behavior, characterized by the power law index, n, but instead more to an overall reduced melt viscosity during extrusion and zero-shear rate viscosity, η₀, accordingly. We also found that the amount of residual crystallinity of telmisartan correlated with the simulated maximum melt temperature in the extruder barrel. This finding confirmed the applicability of the temperature-dependent API-matrix solubility phase diagram for HME to process development. Given the complex inter-dependent relationships between material properties, process and performance, process modeling combined with reduced laboratory experimentation was established as a holistic approach for the evaluation of Quality-by-Design-based HME process design spaces.

Micro-Injection Moulding of Poly(vinylpyrrolidone-vinyl acetate) Binary and Ternary Amorphous Solid Dispersions

Micro-injection moulding (µIM) was used for the production of enteric tablets of plasticised and unplasticised solid dispersions of poly(vinylpyrrolidone-vinyl acetate) (PVPVA), and the effect of the mechanical and thermal treatment on the properties of the dispersions was investigated. The physical state of the systems showed to be unaltered by the µIM step, maintaining the drug in the amorphous state. The dissolution profile of the tablets showed a slower dissolution rate due to the lower surface to volume ratio compared to the extruded strands. The lack of solubility of the doses in the acidic medium as a consequence of the acidity of indomethacin (IND) was observed. However, in neutral pH the drug dissolution showed slower rates without affecting the dissolution extent, showing a potential application for the development of controlled release doses. Overall, the production of tablets of amorphous solid dispersions (ASD), coupling hot-melt extrusion (HME) and µIM, proved to be a successful approach towards a continuous automated manufacturing process to improve the aqueous solubility of poorly water-soluble drugs.

Processability of AquaSolve™ LG polymer by hot-melt extrusion: Effects of pressurized CO2 on physicomechanical properties and API stability

The objective of this study was to investigate the processability of AquaSolve™ hydroxypropyl methylcellulose acetate succinate L grade (HPMCAS LG) via hot-melt extrusion and to examine the effect of pressurized carbon dioxide (P-CO₂) on the physicomechanical properties of efavirenz (EFA)-loaded extrudates. To optimize the process parameters and formulations, various physical mixtures of EFA (30%, 40%, and 50%, w/w) and HPMCAS LG (70%, 60%, and 50%, w/w), respectively, were extruded using a co-rotating twin-screw extruder with a standard screw configuration, with P-CO₂ injected into zone 8 of the extruder. Thermal characterization of the extrudates was performed using differential scanning calorimetry and thermogravimetric analysis. Scanning electron microscopy was employed to study the morphology and porosity of the formulations. Notably, the macroscopic morphology changed to a foam-like structure by P-CO₂ injection resulting in an increased specific surface area, porosity, and dissolution rate. Thus, HPMCAS LG extrusion, coupled with P-CO₂ injection, yielded faster dissolving extrudates. Stability studies indicated that HPMCAS LG was able to physically and chemically stabilize the amorphous state of high-dose EFA. Furthermore, the milling efficiency of the extrudates produced with P-CO₂ injection improved because of their increased porosity.

Characterization of amorphous celecoxib mixed with plasticizing (TPGS) and anti-plasticizing (PVP) ingredients using Hot Melt Extrusion

Purpose

Hot melt extrusion (HME) has demonstrated to be an adequate compounding method for poorly-soluble pharmaceutical drugs, as it increases its solubility by fixing its amorphous solid-state using polymers (plasticizing) and other ingredients (non- plasticizing). However, it's amorphous state of the drug and the stability of the amorphous state will greatly depend on its interactions with these (plasticizing or not).

Methods

In this study, we aimed at characterizing the impact of the combination of plasticizing (TPGS) and anti-plasticizing (PVP) ingredients in amorphous celecoxib prepared using HME in terms of chemical interactions between the components (FTIR, Raman and NMR), viscoelasticity (loss and storage modulus) and required energy for flow (activation energy). Different celecoxib/PVP/TPGS ratios were studied to understand the synergistic effect of PVP and TPGS in inhibiting the crystallization of celecoxib when preparing amorphous dispersions using HME. We aimed at linking the viscoelastic properties of the melt with the resulting amorphous state described by the chemical interactions upon extrusion.

Results

The amorphous state of celecoxib was evidenced by strengthening of H-bonding between celecoxib and PVP, lack of characteristic crystalline peaks of celecoxib, and deshielding of aromatic protons. The melt was also characterized in terms of viscoelastic temperature dependent behavior (liquid G"; elastic G'), where increasing amounts of TPGS and PVP showed opposites effects; TPGS reduced the viscoelastic response whereas PVP increased it. Calculated melt activation energies (Ea) from the temperature dependent viscosity revealed a threshold of TPGS concentration where samples with 1% w/w of TPGS showed higher flow activation energies (higher Ea) independent of the drug/polymer ratios, compared to samples with higher amounts of TPGS.

Conclusions

Low drug content combined with anti-plasticizing (PVP) amounts and relatively low plasticizing (TPGS) amounts yields an amorphous dispersion that is characterized with strong H-bonding due to efficient mixing using HME.

Homogeneity of amorphous solid dispersions - an example with KinetiSol®

KinetiSol^® is a high-shear, fusion-based technology capable of producing stable amorphous solid dispersions (ASDs) without the assistance of solvent. KinetiSol^® has proven successful with multiple challenging BCS class II and IV drugs, where drug properties like thermal instability or lack of appreciable solubility in volatile solvents make hot melt extrusion or spray drying unfeasible. However, there is a necessity to characterize the ASDs like those made by the KinetiSol^® process, in order to better understand whether KinetiSol^® is capable of homogeneously dispersing drug throughout a carrier in a short (<40 s) processing time. Our study utilized the high melting point, BCS class II drug, meloxicam, in order to evaluate the degree of homogeneity of 1, 5, and 10% w/w KinetiSol^®-processed samples. Powder blend homogeneity and content uniformity were evaluated, and all samples demonstrated a meloxicam concentration % relative standard deviation of ≤2.0%. SEM/EDS was utilized to map elemental distribution of the processed samples, which confirmed KinetiSol^®-processed materials were homogeneous at a 25 µm² area. Utilizing Raman spectroscopy, we were able to verify the amorphous content of the processed samples. Finally, we utilized ssNMR ¹H spin-lattice relaxation measurement to evaluate the molecular miscibility of meloxicam with the polymer at 1% w/w drug load, for the first time, and determined the processed sample was highly miscible at ∼200 nm scale. In conclusion, we determined the KinetiSol^® process is capable of producing ASDs that are homogeneously and molecularly well-dispersed drug-in-polymer at drug concentrations as low as 1% w/w.

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

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

Scale-Up and In-line Monitoring During Continuous Melt Extrusion of an Amorphous Solid Dispersion

Chemical degradation of drug substances remains a major drawback of extrusion. Larger-scale extrusion equipment has advantages over smaller equipment due to deeper flight elements and added flexibility in terms of screw design, unit operations, and residence time. In a previous study, we extruded a meloxicam-copovidone amorphous solid dispersion (ASD) on a Nano-16 extruder and achieved 96.7% purity. The purpose of this study is to introduce a strategy for scaling the process to an extruder with dissimilar geometry and to investigate the impact on the purity of the ASD. The formulation previously optimized on the Nano-16, 10:90 meloxicam and copovidone, was used for scale-up. Our approach to scale-up to the ZSE-18, utilized specific mechanical energy input and degree of fill from the Nano-16. Vacuum was added to prevent hydrolysis of meloxicam. Downstream feeding and micronization of meloxicam were introduced to reduce the residence time. In-line monitoring of the solubilization of meloxicam was monitored with a UV probe positioned at the die. We were able to achieve the same purity of meloxicam with the Micro-18 as we achieved with Nano-16. When process conditions alone were not sufficient, meglumine was added to further stabilize meloxicam. In addition to the chemical stability advantage that meglumine provided, we also observed solubility enhancement which allowed for an increase in drug loading to 20% while maintaining 100% purity.

Validation of Model-Based Melt Viscosity in Hot-Melt Extrusion Numerical Simulation

A validation for the use of model-based melt viscosity in hot-melt extrusion numerical simulations was presented. Here, the melt viscosity of an amorphous solid dispersion (ASD) was calculated by using its glass transition temperature (T_g) and the rheological flow profile of the pure polymeric matrix. All further required physical properties were taken from the pure polymer. For forming the ASDs, four active pharmaceutical ingredients (APIs), that had not been considered in first place to establish the correlation between T_g and melt viscosity were examined. The ASDs were characterized in terms of density, specific heat capacity, melt rheology, API solubility in the polymeric matrix, and deviation from the Couchman⁻Karasz fit to, identify the influencing factors of the accuracy of the simulation using model-based melt viscosity. Furthermore, the energy consumption of the hot-melt extrusion (HME) experiments, conventional simulation, and simulation using model-based melt viscosity were compared. It was shown, with few exceptions, that the use of model-based melt viscosity in terms of the HME simulation did not reduce the accuracy of the computation outcome. The commercial one-dimensional (1D) simulation software Ludovic^® was used to conduct all of the numerical computation. As model excipients, vinylpyrrolidone-vinyl acetate copolymer (COP) in combination with four APIs (celecoxib, loratadine, naproxen, and praziquantel) were investigated to form the ASDs.

Improved Vemurafenib Dissolution and Pharmacokinetics as an Amorphous Solid Dispersion Produced by KinetiSol® Processing

Vemurafenib is a poorly soluble, low permeability drug that has a demonstrated need for a solubility-enhanced formulation. However, conventional approaches for amorphous solid dispersion production are challenging due to the physiochemical properties of the compound. A suitable and novel method for creating an amorphous solid dispersion, known as solvent-controlled coprecipitation, was developed to make a material known as microprecipitated bulk powder (MBP). However, this approach has limitations in its processing and formulation space. In this study, it was hypothesized that vemurafenib can be processed by KinetiSol into the same amorphous formulation as MBP. The KinetiSol process utilizes high shear to rapidly process amorphous solid dispersions containing vemurafenib. Analysis of the material demonstrated that KinetiSol produced amorphous, single-phase material with acceptable chemical purity and stability. Values obtained were congruent to analysis conducted on the comparator material. However, the materials differed in particle morphology as the KinetiSol material was dense, smooth, and uniform while the MBP comparator was porous in structure and exhibited high surface area. The particles produced by KinetiSol had improved in-vitro dissolution and pharmacokinetic performance for vemurafenib compared to MBP due to slower drug nucleation and recrystallization which resulted in superior supersaturation maintenance during drug release. In the in-vivo rat pharmacokinetic study, both amorphous solid dispersions produced by KinetiSol exhibited mean AUC values at least two-fold that of MBP when dosed as a suspension. It was concluded that the KinetiSol process produced superior dosage forms containing vemurafenib with the potential for substantial reduction in patient pill burden.

Generation of a Weakly Acidic Amorphous Solid Dispersion of the Weak Base Ritonavir with Equivalent In Vitro and In Vivo Performance to Norvir Tablet

Ritonavir is an anti-viral compound that has also been employed extensively as a CYP3A4 and P-glycoprotein (Pgp) inhibitor to boost the pharmacokinetic performance of compounds that undergo first pass metabolism. For use in combination products, there is a desire to minimize the mass contribution of the ritonavir system to reduce patient pill burden in these combination products. In this study, KinetiSol® processing was utilized to produce an amorphous solid dispersion of ritonavir at two times the drug load of the commercially available form of ritonavir, and the composition was subsequently developed into a tablet dosage form. The amorphous intermediate was demonstrated to be amorphous by X-ray powder diffraction and ¹³C solid-state nuclear magnetic resonance and an intimately mixed single-phase system by modulated differential scanning calorimetry and ¹H T₁/¹H T_1ρ solid-state nuclear magnetic resonance relaxation. In vitro transmembrane flux analysis showed similar permeation rates for the KinetiSol-made tablet and the reference tablet dosage form, Norvir®. In vivo pharmacokinetic comparison between the two dosage forms resulted in equivalent exposure with approximately 20% Cmax reduction for the KinetiSol tablet. These performance gains were realized with a concurrent reduction in dosage form mass of 45%.

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

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

Pharmaceutical Dispersion Techniques for Dissolution and Bioavailability Enhancement of Poorly Water-Soluble Drugs

Over the past decades, a large number of drugs as well as drug candidates with poor dissolution characteristics have been witnessed, which invokes great interest in enabling formulation of these active ingredients. Poorly water-soluble drugs, especially biopharmaceutical classification system (BCS) II ones, are preferably designed as oral dosage forms if the dissolution limit can be broken through. Minimizing a drug’s size is an effective means to increase its dissolution and hence the bioavailability, which can be achieved by specialized dispersion techniques. This article reviews the most commonly used dispersion techniques for pharmaceutical processing that can practically enhance the dissolution and bioavailability of poorly water-soluble drugs. Major interests focus on solid dispersion, lipid-based dispersion (nanoencapsulation), and liquisolid dispersion (drug solubilized in a non-volatile solvent and dispersed in suitable solid excipients for tableting or capsulizing), covering the formulation development, preparative technique and potential applications for oral drug delivery. Otherwise, some other techniques that can increase the dispersibility of a drug such as co-precipitation, concomitant crystallization and inclusion complexation are also discussed. Various dispersion techniques provide a productive platform for addressing the formulation challenge of poorly water-soluble drugs. Solid dispersion and liquisolid dispersion are most likely to be successful in developing oral dosage forms. Lipid-based dispersion represents a promising approach to surmounting the bioavailability of low-permeable drugs, though the technique needs to traverse the obstacle from liquid to solid transformation. Novel dispersion techniques are highly encouraged to develop for formulation of poorly water-soluble drugs.

A Miniaturized Extruder to Prototype Amorphous Solid Dispersions: Selection of Plasticizers for Hot Melt Extrusion

Hot-melt extrusion is an option to fabricate amorphous solid dispersions and to enhance oral bioavailability of poorly soluble compounds. The selection of suitable polymer carriers and processing aids determines the dissolution, homogeneity and stability performance of this solid dosage form. A miniaturized extrusion device (MinEx) was developed and Hypromellose acetate succinate type L (HPMCAS-L) based extrudates containing the model drugs neurokinin-1 (NK1) and cholesterylester transfer protein (CETP) were manufactured, plasticizers were added and their impact on dissolution and solid-state properties were assessed. Similar mixtures were manufactured with a lab-scale extruder, for face to face comparison. The properties of MinEx extrudates widely translated to those manufactured with a lab-scale extruder. Plasticizers, Polyethyleneglycol 4000 (PEG4000) and Poloxamer 188, were homogenously distributed but decreased the storage stability of the extrudates. Stearic acid was found condensed in ultrathin nanoplatelets which did not impact the storage stability of the system. Depending on their distribution and physicochemical properties, plasticizers can modulate storage stability and dissolution performance of extrudates. MinEx is a valuable prototyping-screening method and enables rational selection of plasticizers in a time and material sparing manner. In eight out of eight cases the properties of the extrudates translated to products manufactured in lab-scale extrusion trials.

Predictive Modeling of Micellar Solubilization by Single and Mixed Nonionic Surfactants

Micellar solubilization is an important concept in the delivery of poorly water-soluble drugs. The rational selection of the type and the amount of surfactant to be incorporated in a formulation require comprehensive solubility studies. These studies are time and material demanding, both of which are scarce, especially during late discovery and early development stages. We hypothesized that, if the solubilization mechanism or molecular interaction is similar, the solubilization capacity ratio (a newly defined parameter) is dictated by micellar structures, independent of drugs. We tested this hypothesis by performing solubility studies using 8 commonly used nonionic surfactants and 17 insoluble compounds with diverse characteristics. The results show a striking constant solubilization capacity ratio among the 8 nonionic surfactants, which allow us to develop predictive solubility models for both single and mixed surfactant systems. The vast majority of the predicted solubility values, using our developed models, fall within 2-fold of the experimentally determined values with high correlation coefficients. As expected, systems involving ionic surfactant sodium dodecyl sulfate, used as a negative control, do not follow this trend. Deviations from the model, observed in this study or envisioned, were discussed. In conclusion, we have established predictive models that are capable of predicting solubility in a wide range of nonionic micellar solutions with only 1 experimental measurement. The application of such a model will significantly reduce resource and greatly enhance drug product development efficiency.

Improving Solubility and Oral Bioavailability of Febuxostat by Polymer-Coated Nanomatrix

Here, the mesoporous silica (Sylysia 350) was selected as mesoporous material, hydroxypropyl methylcellulose (HPMC) was selected as crystallization inhibitor, and febuxostat (FBT) was selected as model drug, respectively. The FBT-Sylysia-HPMC nanomatrix (FBT@SHN) was prepared. The characteristics of FBT@SHN were investigated in vitro and in vivo. Our results indicated that the FBT in FBT@SHN was in amorphous form. The solubility and dissolution of FBT in FBT@SHN were significantly increased. The oral bioavailability of FBT in FBT@SHN was greatly improved 5.8-fold compared with that in FBT suspension. This nanomatrix could be used as a drug delivery platform for improving the oral bioavailability.

Advances in Polymer Design for Enhancing Oral Drug Solubility and Delivery

Synthetic polymers have enabled amorphous solid dispersions (ASDs) to emerge as an oral delivery strategy for overcoming poor drug solubility in aqueous environments. Modern ASD products noninvasively treat a range of chronic diseases (for example, hepatitis C, cystic fibrosis, and HIV). In such formulations, polymeric carriers generate and maintain drug supersaturation upon dissolution, increasing the apparent drug solubility to enhance gastrointestinal barrier absorption and oral bioavailability. In this Review, we outline several approaches in designing polymeric excipients to drive interactions with active pharmaceutical ingredients (APIs) in spray-dried ASDs, highlighting polymer-drug formulation guidelines from industrial and academic perspectives. Special attention is given to new commercial and specialized polymer design strategies that can solubilize highly hydrophobic APIs and suppress the propensity for rapid drug recrystallization. These molecularly customized excipients and hierarchical excipient assemblies are promising toward informing early-stage drug-discovery development and reformulating existing API candidates into potentially lifesaving oral medicines for our growing global population.

Unexpected solvent impact in the crystallinity of praziquantel/poly(vinylpyrrolidone) formulations. A solubility, DSC and solid-state NMR study

The saturation solubility of PVP:PZQ physical mixtures (PMs) and solid dispersions (SDs) prepared from ethanol (E/E) or ethanol/water (E/W) by the solvent evaporation method at 1:1, 2:1 and 3:1 ratio (w/w) was determined. The presence of PVP improves the solubility of PZQ (0.31±0.01mg/mL). A maximum of 1.29±0.03mg/mL of PZQ in solution was achieved for the 3:1 SD (E/E). The amount of PZQ in solution depends on the amount of polymer and on the preparation method. Solid-state NMR (ssNMR) and DSC were used to understand this behavior. Results show that PMs are a mixture of crystalline PZQ with the polymer, while SDs show different degrees of drug amorphization depending on the solvent used. For E/W SDs, PZQ exists in amorphous and crystalline states, with no clear correlation between the amount of crystalline PZQ and the amount of PVP. For E/E SDs, formulations with a higher percentage of PZQ are amorphous with the components miscible in domains larger than 3nm ((1)H ssNMR relaxation measurements). Albeit its higher saturation solubility, the 3:1 E/E PVP:PZQ sample has a significant crystalline content, probably due to the water introduced by the polymer. High PVP content and small crystal size account for this result.