An investigation into the influence of drug-polymer interactions on the miscibility, processability and structure of polyvinylpyrrolidone-based hot melt extrusion formulations

Exploring the influence of hydrogen bond donor groups on the microstructure and intermolecular interactions of amorphous solid dispersions containing diflunisal structural analogues

Drug-polymer intermolecular interactions, and H-bonds specifically, play an important role in the stabilization process of a compound in an amorphous solid dispersion (ASD). However, it is still difficult to predict whether or not interactions will form and what the strength of those interactions would be, based on the structure of drug and polymer. Therefore, in this study, structural analogues of diflunisal (DIF) were synthesized and incorporated in ASDs with poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA) as a stabilizing polymer. The respective DIF derivatives contained different types and numbers of H-bond donor groups, which allowed to assess the influence of these structural differences on the phase behavior and the actual interactions formed in the ASDs. The highest possible drug loading of these derivatives in PVPVA were evaluated through film casting. Subsequently, a lower drug loading of each compound was spray dried. These spray dried ASDs were subjected to an in-depth solid-state nuclear magnetic resonance (ssNMR) study, including 1D spectroscopy and relaxometry, as well as 2D dipolar HETCOR experiments. The drug loading study revealed the highest possible loading of 50 wt% for the native DIF in PVPVA. The methoxy DIF derivative reached the second highest drug loading of 35 wt%, while methylation of the carboxyl group of DIF led to a sharp decrease in the maximum loading, to around 10 wt% only. Unexpectedly, the maximum loading increased again when both the COOH and OH groups of diflunisal were methylated in the dimethyl DIF derivative, to around 30 wt%. The ssNMR study on the spray dried ASD samples confirmed intermolecular H-bonding with PVPVA for native DIF and methoxy DIF. Studies of the proton relaxation decay times and 2D 1H-13C dipolar HETCOR experiments indicated that the ASDs with native DIF and methoxy DIF were homogenously mixed, while the ASDs containing DIF methyl ester and dimethyl DIF were phase separated at the nm level. It was established that, for these systems, the availability of the carboxyl group was imperative in the formation of intermolecular H-bonds with PVPVA and in the generation of homogenously mixed ASDs.

Utilizing the allyl-terminated copolymer methoxy(poly(ethylene glycol))-block-poly(jasmine lactone) in the development of amorphous solid dispersions: A comparative study of functionalized and non-functionalized polymer

Molecular interactions are crucial to stabilize amorphous drugs in amorphous solid dispersions (ASDs). Most polymers, however, have only a limited ability to form strong molecular interactions with drugs. Polymers tailored to fit the physicochemical properties of the drug molecule to be incorporated, for instance by allowing the incorporation of specific functional groups, would be highly sought-for in this regard. For this purpose, the novel allyl-terminated polymer methoxy(polyethylene glycol)-block-poly(jasmine lactone) (mPEG-b-PJL) has been synthesized and functionalized to potentially enhance specific drug-polymer interactions. This study investigated the use of mPEG-b-PJL in ASDs, using carvedilol (CAR), a weakly basic model drug. The findings revealed that the acidic functionalized form of the polymer (mPEG-b-PJL-COOH) indeed established stronger molecular interactions with CAR compared to its non-functionalized counterpart mPEG-b-PJL. Evaluations on polymer effectiveness in forming ASDs demonstrated that mPEG-b-PJL-COOH outperformed its non-functionalized counterpart in miscibility, drug loading ability, and stability, inferred from reduced molecular mobility. However, dissolution tests indicated that ASDs with mPEG-b-PJL-COOH did not significantly improve the dissolution behaviour compared to amorphous CAR alone, despite potential solubility enhancement through micelle formation. Overall, this study confirms the potential of functionalized polymers in ASD formulations, while the challenge of improving dissolution performance in these ASDs remains an area of further development.

Strategies to improve the stability of amorphous solid dispersions in view of the hot melt extrusion (HME) method

Oral administration of drugs is preferred over other routes for several reasons: it is non-invasive, easy to administer, and easy to store. However, drug formulation for oral administration is often hindered by the drug's poor solubility, which limits its bioavailability and reduces its commercial value. As a solution, amorphous solid dispersion (ASD) was introduced as a drug formulation method that improves drug solubility by changing the molecular structure of the drugs from crystalline to amorphous. The hot melt extrusion (HME) method is emerging in the pharmaceutical industry as an alternative to manufacture ASD. However, despite solving solubility issues, ASD also exposes the drug to a high risk of crystallisation, either during processing or storage. Formulating a successful oral administration drug using ASD requires optimisation of the formulation, polymers, and HME manufacturing processes applied. This review presents some important considerations in ASD formulation, including strategies to improve the stability of the final product using HME to allow more new drugs to be formulated using this method.

Influence of Intermolecular Interactions on Crystallite Size in Crystalline Solid Dispersions

Crystalline solid dispersions (CSDs) represent a thermodynamically stable system capable of effectively reducing the crystallite size of drugs, thereby enhancing their solubility and bioavailability. This study uses flavonoid drugs with the same core structures but varying numbers of hydroxyl groups as model drugs and poloxamer 188 as a carrier to explore the intrinsic relationships between drug-polymer interactions, crystallite size, and in vitro dissolution behavior in CSDs. Initially, we investigate the interactions between flavonoid drugs and P188 by calculating Hansen solubility parameters, determination of Flory-Huggins interaction parameters, and other methods. Subsequently, we explore the crystallization kinetics of flavonoid drugs and P188 in CSD systems using polarized optical microscopy and powder X-ray diffraction. We monitor the domain size and crystallite size of flavonoids in CSDs through powder X-ray diffraction and a laser-particle-size analyzer. Finally, we validate the relationship between crystallite size and in vitro dissolution behavior through powder dissolution. The results demonstrate that, as the number of hydroxyl groups increases, the interactions between drugs and polymers become stronger, making drug crystallization in the CSD system less likely. Consequently, reductions in crystalline domain size and crystallite size become more pronounced, leading to a more significant enhancement in drug dissolution.

Analysis of the Dissolution Mechanism of Drugs into Polymers: The Case of the PVP/Sulindac System

This paper is dealing with the dissolution mechanism of crystalline sulindac into amorphous Polyvinylpyrrolidone (PVP) upon heating and annealing at high temperatures. Special attention is paid on the diffusion mechanism of drug molecules in the polymer which leads to a homogeneous amorphous solid dispersion of the two components. The results show that isothermal dissolution proceeds through the growth of polymer zones saturated by the drug, and not by a progressive increase in the uniform drug concentration in the whole polymer matrix. The investigations also show the exceptional ability of temperature Modulated Differential Scanning Calorimetry (MDSC) to identify the equilibrium and out of equilibrium stages of dissolution corresponding to the trajectory of the mixture into its state diagram.

Investigating and Comparing the Applicability of the R3m Molecular Descriptor and Solubility Parameter Estimation Approaches in Predicting Dispersion Formation Potential of APIs in a Random Co-Polymer Polyvinylpyrrolidone Vinyl Acetate and its Homopolymer

Evaluation of different amorphous solid dispersion carrier matrices is enabled by active pharmaceutical ingredient (API) structure-based predictions. This study compares the utility of Hansen Solubility Parameters with the R3m molecular descriptor for identifying dispersion polymers based on the structure of the drug molecule. Twelve API-polymer combinations (4 APIs and 3 interrelated polymers) were used to test each approach. Co-solidified mixtures containing 75% API were prepared by melt-quenching. Phase behavior was evaluated and classified using differential scanning calorimetry, powder X-ray diffraction, polarized light microscopy, and hot stage microscopy. Observations of dispersion behavior were compared to predictions made using the Hansen Solubility Parameter and R3m. The solubility parameter approach misclassified the dispersion behavior of 1 API-polymer combination and also did not produce definite predictions in 3 out of 12 of the API-polymer combinations. In contrast, R3m classifications of dispersion behavior were correct in all but two cases, with one misclassification and one ambiguous prediction. The solubility parameters best classify dispersion behavior when specific drug-polymer intermolecular interactions are present, but may be less useful otherwise. Ultimately, these two methods are most effectively used together, as they are based on distinct features of the same molecular structure.

Application of Twin-Screw Melt Granulation to Overcome the Poor Tabletability of a High Dose Drug

Pharmaceutical tablet manufacturing has seen a paradigm shift toward continuous manufacturing and twin-screw granulation-based technologies have catalyzed this shift. Twin-screw granulator can simultaneously perform unit operations like mixing, granulation, and drying of the granules. The present study investigates the impact of polymer concentration and processing parameters of twin-screw melt granulation, on flow properties and compaction characteristics of a model drug having high dose and poor tabletability. Acetaminophen (AAP) and polyvinylpyrrolidone vinyl acetate (PVPVA) were used as a model drug (90-95% w/w) and polymeric binder (5-10%w/w), respectively, for the current study. Feed rate (~650-1150 g/h), extruder screw speed (150-300 rpm), and temperature (60-150°C) were used as processing variables. Results showed the reduction in particle size of drug in the extrudates (D₉₀ of 15-25 μm from ~80 μm), irrespective of processing condition, while flow properties were a function of polymer concentration. Overall, good flowability of the products and their tablets with optimum tensile strength can be obtained through using high polymer concentration (i.e., 10% w/w), lower feed rate (~650 g/h), lower extruder screw speed (150 rpm), and higher processing temperatures (up to 120°C). The findings from the current study can be useful for continuous manufacturing of tablets of high dose drugs with minimal excipient loading in the final dosage form.

The Value of Bead Coating in the Manufacturing of Amorphous Solid Dispersions: A Comparative Evaluation with Spray Drying

Despite the fact that an amorphous solid dispersion (ASD)-coated pellet formulation offers potential advantages regarding the minimization of physical stability issues, there is still a lack of in-depth understanding of the bead coating process and its value in relation to spray drying. Therefore, bead coating and spray drying were both evaluated for their ability to manufacture high drug-loaded ASDs and for their ability to generate physically stable formulations. For this purpose, naproxen (NAP)–poly(vinyl-pyrrolidone-co-vinyl acetate) (PVP-VA) was selected as an interacting drug–polymer model system, whilst naproxen methyl ester (NAPME)–PVP-VA served as a non-interacting model system. The solvent employed in this study was methanol (MeOH). First, a crystallization tendency study revealed the rapid crystallization behavior of both model drugs. In the next step, ASDs were manufactured with bead coating as well as with spray drying and for each technique the highest possible drug load that still results in an amorphous system was defined via a drug loading screening approach. Bead coating showed greater ability to manufacture high drug-loaded ASDs as compared to spray drying, with a rather small difference for the interacting drug–polymer model system studied but with a remarkable difference for the non-interacting system. In addition, the importance of drug–polymer interactions in achieving high drug loadings is demonstrated. Finally, ASDs coated onto pellets were found to be more physically stable in comparison to the spray dried formulations, strengthening the value of bead coating for ASD manufacturing purposes.

Impact of Drug-Polymer Intermolecular Interactions on Dissolution Performance of Copovidone-Based Amorphous Solid Dispersions

For poorly soluble drugs formulated as amorphous solid dispersions (ASDs), fast and complete release with the generation of drug-rich colloidal particles is beneficial for optimizing drug absorption. However, this ideal dissolution profile can only be achieved when the drug releases at the same normalized rate as the polymer, also known as congruent release. This phenomenon only occurs when the drug loading (DL) is below a certain value. The maximal DL at which congruent release occurs is defined as the limit of congruency (LoC). The purpose of this study was to investigate the relationship between drug chemical structure and LoC for PVPVA-based ASDs. The compounds investigated shared a common scaffold substituted with different functional groups, capable of forming hydrogen bonds only, halogen bonds only, both hydrogen and halogen bonds, or nonspecific interactions only with the polymer. Intermolecular interactions were studied and confirmed by X-ray photoelectron spectroscopy and infrared spectroscopy. The release rates of ASDs with different DLs were investigated using surface area normalized dissolution. ASDs with hydrogen bond formation between the drug and polymer had lower LoCs, while compounds that were only able to form halogen bonds or nonspecific interactions with the polymer achieved considerably higher LoCs. This study highlights the impact of different types of drug-polymer interactions on ASD dissolution performance, providing insights into the role of drug and polymer chemical structures on the LoC and ASD performance in general.

Hot-Melt Extrusion: a Roadmap for Product Development

Hot-melt extrusion has found extensive application as a feasible pharmaceutical technological option over recent years. HME applications include solubility enhancement, taste masking, and sustained drug release. As bioavailability enhancement is a hot topic of today's science, one of the main applications of HME is centered on amorphous solid dispersions. This review describes the most significant aspects of HME technology and its use to prepare solid dispersions as a drug formulation strategy to enhance the solubility of poorly soluble drugs. It also addresses molecular and thermodynamic features critical for the physicochemical properties of these systems, mainly in what concerns miscibility and physical stability. Moreover, the importance of applying the Quality by Design philosophy in drug development is also discussed, as well as process analytical technologies in pharmaceutical HME monitoring, under the current standards of product development and regulatory guidance. Graphical Abstract.

Effect of Temperature and Additives on the Interaction of Ciprofloxacin Hydrochloride Drug with Polyvinylpyrrolidone and Bovine Serum Albumin: Spectroscopic and Molecular Docking Study

The fluoroquinolone antibiotic drug namely ciprofloxacin hydrochloride (CFH) is widely prescribed for the treatment of different bacterial infections. The interaction of CFH with a synthetic polymer, polyvinyl pyrrolidone (PVP), and biopolymer, bovine serum albumin (BSA) was studied by UVvisible and fluorescence spectroscopic methods at different temperatures. The binding constant (K _b ) for the CFH-PVP complex was determined from the Benesi-Hildebrand plot. PVP of different molecular weights (MW) (such as 24,000, 40,000, 360,000, and 700,000 g. mole^-1) were used for the interaction between CFH and PVP. The gradual increase in K _b value and the complexation reaction was found to be much enhanced with the augmentation of the MW of PVP. The values of K _b were also found to be increased with increasing temperatures as well as with the increase of electrolyte/acetic acid concentration. The Gibbs free energy of binding (∆G ⁰) values of the interaction process was negative which indicates the complex formation is thermodynamically spontaneous. The positive values of enthalpy (∆H ⁰) and entropy (∆S ⁰) of binding connote that the binding force for CFH-PVP complexation is hydrophobic in nature and the complexation is entropy controlled. The negative intrinsic enthalpy (∆H ^*,0) values indicate the high stability of CFH-PVP complexes. Molecular docking calculation discloses the existence of similar binding forces between CFH and PVP obtained by the analysis of experimental data from UV-visible spectroscopic method. The binding constant between CFH and BSA (K _b ), quenching constant (K _sv ), the number of binding sites (n), and the quenching rate constant (K _q ) for the CFH-BSA system were also calculated. The values of K _sv , K _q , and n for the CFH-BSA system are lower in 0.05 mol L^-1 urea solution and higher in PVP solutions compared to those of aqueous medium.

Paracetamol Sensing with a Pencil Lead Electrode Modified with Carbon Nanotubes and Polyvinylpyrrolidone

The determination of paracetamol is a common need in pharmaceutical and environmental samples for which a low-cost, rapid, and accurate sensor would be highly desirable. We develop a novel pencil graphite lead electrode (PGE) modified with single-wall carbon nanotubes (SWCNTs) and polyvinylpyrrolidone (PVP) polymer (PVP/SWCNT/PGE) for the voltammetric quantification of paracetamol. The sensor shows remarkable analytical performance in the determination of paracetamol at neutral pH, with a limit of detection of 0.38 μM and a linear response from 1 to 500 μM using square-wave voltammetry (SWV), which are well suited to the analysis of pharmaceutical preparations. The introduction of the polymer PVP can cause dramatic changes in the sensing performance of the electrode, depending on its specific architecture. These effects were investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results indicate that the co-localization and dispersion of PVP throughout the carbon nanotubes on the electrode are key to its superior electrochemical performance, facilitating the electrical contact between the nanotubes and with the electrode surface. The application of this sensor to commercial syrup and tablet preparations is demonstrated with excellent results.

Characterizing and Exploring the Differences in Dissolution and Stability Between Crystalline Solid Dispersion and Amorphous Solid Dispersion

Solid dispersion is one of the most effective ways to improve the dissolution of insoluble drugs. When the carrier can highly disperse the drug, it will increase the wettability of the drug and reduce the surface tension, thus improving the solubility, dissolution, and bioavailability. However, amorphous solid dispersions usually have low drug loading and poor stability. Therefore, the goal of this work is to study the increased dissolution and high stability of high drug-loading crystalline solid dispersion (CSD), and the difference in dissolution and stability of high-loading and low-loading amorphous solid dispersion (ASD). A CSD of nimodipine with a drug loading of 90% was prepared by wet milling, with hydroxypropyl cellulose (model: HPC-SL) and sodium dodecyl sulfate as stabilizers and spray drying. At the same time, the gradient drug-loaded ASD was prepared by hot melt extrusion with HPC-SL as the carrier. Each preparation was characterized by DSC, PXRD, FT-IR, SEM, and in vitro dissolution testing. The results indicated that the drug in CSD existed in a crystalline state. The amorphous drug molecules in the low drug-loading ASD were uniformly dispersed in the carrier, while the drug state in the high drug-loading ASD was aggregates of the amorphous drug. At the end of the dissolution assay, the 90% drug-loading CSD increased cumulative dissolution to 60%, and the 10% drug-loading ASD achieved a cumulative dissolution rate of 90%.

Hot-Melt Extrusion as an Advantageous Technology to Obtain Effervescent Drug Products

Here, we assessed the feasibility of hot-melt extrusion (HME) to obtain effervescent drug products for the first time. For this, a combined mixture design was employed using paracetamol as a model drug. Extrudates were obtained under reduced torque (up to 0.3 Nm) at 100 °C to preserve the stability of the effervescent salts. Formulations showed vigorous and rapid effervescent disintegration (<3 min), adequate flow characteristics, and complete solubilization of paracetamol instantly after the effervescent reaction. Formulations containing PVPVA in the concentration range of 15–20% m/m were demonstrated to be sensitive to accelerated aging conditions, undergoing marked microstructural changes, since the capture of water led to the agglomeration and loss of their functional characteristics. HPMC matrices, in contrast, proved to be resistant to storage conditions in high relative humidity, showing superior performance to controls, including the commercial product. Moreover, the combined mixture design allowed us to identify significant interactions between the polymeric materials and the disintegrating agents, showing the formulation regions in which the responses are kept within the required levels. In conclusion, this study demonstrates that HME can bring important benefits to the elaboration of effervescent drug products, simplifying the production process and obtaining formulations with improved characteristics, such as faster disintegration, higher drug solubilization, and better stability.

Probing the Molecular-Level Interactions in an Active Pharmaceutical Ingredient (API) - Polymer Dispersion and the Resulting Impact on Drug Product Formulation

PURPOSE

An investigation of underlying mechanisms of API-polymer interaction patterns has the potential to provide valuable insights for selecting appropriate formulations with superior physical stability and processability.

MATERIALS AND METHODS

In this study, copovidone was used as a polymeric carrier for several model compounds including clotrimazole, nifedipine, and posaconazole. The varied chemical structures conferred the ability for the model compounds to form distinct interactions with copovidone. Rheology and nuclear magnetic resonance (NMR) were combined to investigate the molecular pattern and relative strength of active pharmaceutical ingredient (API)-polymer interactions. In addition, the impact of the interactions on formulation processability via hot melt extrusion (HME) and physical stability were evaluated.

RESULTS

The rheological response of an API-polymer system was found to be highly sensitive to API-polymer interaction, depending both on API chemistry and API-polymer miscibility. In the systems studied, dispersed API induced a stronger plasticizer effect on the polymer matrix compared to crystalline/aggregated API. Correspondingly, the processing torque via HME showed a proportional relationship with the maximum complex viscosity of the API-polymer system. In order to quantitatively evaluate the relative strength of the API-polymer interaction, homogeneously dispersed API-polymer amorphous samples were prepared by HME at an elevated temperature. DSC, XRD, and rheology were employed to confirm the amorphous integrity and homogeneity of the resultant extrudates. Subsequently, the homogeneously dispersed API-polymer amorphous dispersions were interrogated by rheology and NMR to provide a qualitative and quantitative assessment of the nature of the API-polymer interaction, both macroscopically and microscopically. Rheological master curves of frequency sweeps of the extrudates exhibited a strong dependence on the API chemistry and revealed a rank ordering of the relative strength of API-copovidone interactions, in the order of posaconazole > nifedipine > clotrimazole. NMR data provided the means to precisely map the API-polymer interaction pattern and identify the specific sites of interaction from a molecular perspective. Finally, the impact of API-polymer interactions on the physical stability of the resultant extrudates was studied.

CONCLUSION

Qualitative and quantitative evaluation of the relative strength of the API-polymer interaction was successfully accomplished by utilizing combined rheology and NMR. Graphical Abstract.

Manufacturing strategies to develop amorphous solid dispersions: An overview

Since the past several decades, poor water solubility of existing and new drugs in the pipeline have remained a challenging issue for the pharmaceutical industry. Literature describes several approaches to improve the overall solubility, dissolution rate, and bioavailability of drugs with poor water solubility. Moreover, the development of amorphous solid dispersion (SD) using suitable polymers and methods have gained considerable importance in the recent past. In the present review, we attempt to discuss the important and industrially scalable thermal strategies for the development of amorphous SD. These include both solvent (spray drying and fluid bed processing) and fusion (hot melt extrusion and KinetiSol®) based techniques. The current review also provides insights into the thermodynamic properties of drugs, their polymer miscibility and solubility, and their molecular dynamics to develop stable and more efficient amorphous SD.

Analytical and Computational Methods for the Estimation of Drug-Polymer Solubility and Miscibility in Solid Dispersions Development

The development of stable solid dispersion formulations that maintain desired improvement of drug dissolution rate during the entire shelf life requires the analysis of drug-polymer solubility and miscibility. Only if the drug concentration is below the solubility limit in the polymer, the physical stability of solid dispersions is guaranteed without risk for drug (re)crystallization. If the drug concentration is above the solubility, but below the miscibility limit, the system is stabilized through intimate drug-polymer mixing, with additional kinetic stabilization if stored sufficiently below the mixture glass transition temperature. Therefore, it is of particular importance to assess the drug-polymer solubility and miscibility, to select suitable formulation (a type of polymer and drug loading), manufacturing process, and storage conditions, with the aim to ensure physical stability during the product shelf life. Drug-polymer solubility and miscibility can be assessed using analytical methods, which can detect whether the system is single-phase or not. Thermodynamic modeling enables a mechanistic understanding of drug-polymer solubility and miscibility and identification of formulation compositions with the expected formation of the stable single-phase system. Advance molecular modeling and simulation techniques enable getting insight into interactions between the drug and polymer at the molecular level, which determine whether the single-phase system formation will occur or not.

Modelling phase separation in amorphous solid dispersions

Much work has been devoted to analysing thermodynamic models for solid dispersions with a view to identifying regions in the phase diagram where amorphous phase separation or drug recrystallization can occur. However, detailed partial differential equation non-equilibrium models that track the evolution of solid dispersions in time and space are lacking. Hence theoretical predictions for the timescale over which phase separation occurs in a solid dispersion are not available. In this paper, we address some of these deficiencies by (i) constructing a general multicomponent diffusion model for a dissolving solid dispersion; (ii) specializing the model to a binary drug/polymer system in storage; (iii) deriving an effective concentration dependent drug diffusion coefficient for the binary system, thereby obtaining a theoretical prediction for the timescale over which phase separation occurs; (iv) calculating the phase diagram for the Felodipine/HPMCAS system; and (iv) presenting a detailed numerical investigation of the Felodipine/HPMCAS system assuming a Flory-Huggins activity coefficient. The numerical simulations exhibit numerous interesting phenomena, such as the formation of polymer droplets and strings, Ostwald ripening/coarsening, phase inversion, and droplet-to-string transitions. A numerical simulation of the fabrication process for a solid dispersion in a hot melt extruder was also presented. STATEMENT OF SIGNIFICANCE: Solid dispersions are products that contain mixtures of drug and other materials e.g. polymer. These are liable to separate-out over time - a phenomenon known as phase separation. This means that it is possible the product differs both compositionally and structurally between the time of manufacture and the time it is taken by the patient, leading to poor bioavailability and so ultimately the shelf-life of the product has to be reduced. Theoretical predictions for the timescale over which phase separation occurs are not currently available. Also lacking are detailed partial differential equation non-equilibrium models that track the evolution of solid dispersions in time and space. This study addresses these issues, before presenting a detailed investigation of a particular drug-polymer system.

Theoretical and practical evaluation of lowly hydrolyzed polyvinyl alcohol as a potential carrier for hot-melt extrusion

Polyvinyl alcohol (PVA) is considered to be an unsuitable carrier for hot-melt extrusion (HME) due to its low processability. In this study, we focused on a lowly hydrolyzed PVA (JR-05, 70.0-74.0% hydrolyzed, L-PVA) to evaluate the potential use of L-PVA as a carrier for HME using the Hoftyzer and Krevelen method and thermodynamic models. These evaluations for drug-polymer systems based on the Flory-Huggins theory predicted the physicochemical properties of the solubility and miscibility between indomethacin (IND) and PVAs. Prior to initiating formulation studies, construction of IND and PVA phase diagrams provided guidance for design process conditions in HME. On the basis of the results of the validation studies, a conventional grade of PVA (JP-05, 87.0-89.0% hydrolyzed) is unlikely to be suitable as a carrier of HME due to its low plasticity, resulting in rapid recrystallization in the evaluation of in vitro dissolution and stability caused by poor miscibility. On the other hand, JR-05 demonstrated high processability, leading to the preparation of miscible extrudate with a high stability and an excellent in vitro dissolution profile due to its unique micelle-forming capability. These findings suggest that L-PVA brings about new carrier options among non-ionic polymers for HME.

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.

Numerical simulation of hot-melt extrusion processes for amorphous solid dispersions using model-based melt viscosity

Simulation of HME processes is a valuable tool for increased process understanding and ease of scale-up. However, the experimental determination of all required input parameters is tedious, namely the melt rheology of the amorphous solid dispersion (ASD) in question. Hence, a procedure to simplify the application of hot-melt extrusion (HME) simulation for forming amorphous solid dispersions (ASD) is presented. The commercial 1D simulation software Ludovic^® was used to conduct (i) simulations using a full experimental data set of all input variables including melt rheology and (ii) simulations using model-based melt viscosity data based on the ASDs glass transition and the physical properties of polymeric matrix only. Both types of HME computation were further compared to experimental HME results. Variation in physical properties (e.g. heat capacity, density) and several process characteristics of HME (residence time distribution, energy consumption) among the simulations and experiments were evaluated. The model-based melt viscosity was calculated by using the glass transition temperature (T_g) of the investigated blend and the melt viscosity of the polymeric matrix by means of a T_g-viscosity correlation. The results of measured melt viscosity and model-based melt viscosity were similar with only few exceptions, leading to similar HME simulation outcomes. At the end, the experimental effort prior to HME simulation could be minimized and the procedure enables a good starting point for rational development of ASDs by means of HME. As model excipients, Vinylpyrrolidone-vinyl acetate copolymer (COP) in combination with various APIs (carbamazepine, dipyridamole, indomethacin, and ibuprofen) or polyethylene glycol (PEG 1500) as plasticizer were used to form the ASDs.

Continuous manufacturing via hot-melt extrusion and scale up: regulatory matters

Currently, because globalization, the pharmaceutical industry is facing enormous challenges to comply with regulatory matters. Reduced patent life and overall decreased profitability of newly discovered drugs are also forcing the pharmaceutical industry to shorten the drug development time with maximum throughput. Therefore, continuous manufacturing (CM) processes via hot melt extrusion (HME) can be a promising alternative for achieving these goals. HME offers solvent-free green technology with a process that is easy to scale up. Moreover, CM provides better product quality assurance compared with batch processes, with fewer labor costs and shorter time to development. In this review, we primarily focus on various aspects of CM and the emerging application of HME to bridge the current manufacturing gap in pharmaceutical sphere.

Application of hot melt extrusion to enhance the dissolution and oral bioavailability of oleanolic acid

The aim of this study was to improve the in vitro dissolution rate and oral bioavailability of oleanolic acid (OA), a water insoluble drug belonging to BCS class IV. Hot melt extrusion (HME) was applied to develop OA amorphous solid dispersions. The characterizations of the optimal formulation were performed by differential scanning calorimetry, X-ray powder diffraction, Fourier transform infrared spectroscopy and in vitro dissolution test. The in vivo pharmacokinetic study was conducted in rats. As a result, OA solid dispersion based on PVP VA 64 (OA-PVP) was successfully prepared. In the dissolution medium containing 0.3% SDS, OA-PVP dramatically increased the releasing rate of OA compared with the physical mixture (PM-PVP) and commercial tablet. Furthermore, OA-PVP exhibited higher AUC (P < 0.05) and C_max (P < 0.05) than PM-PVP and commercial tablet. The superior dissolution property and bioavailability of OA-PVP mainly attributed to the amorphous state of OA in PVP VA64 and the well dispersion caused by thermal melting and shearing. Overall, hot melt extrusion was an efficient strategy to enhance the dissolution rate and oral bioavailability of OA.

Amorphous solid dispersions: Rational selection of a manufacturing process

Amorphous products and particularly amorphous solid dispersions are currently one of the most exciting areas in the pharmaceutical field. This approach presents huge potential and advantageous features concerning the overall improvement of drug bioavailability. Currently, different manufacturing processes are being developed to produce amorphous solid dispersions with suitable robustness and reproducibility, ranging from solvent evaporation to melting processes. In the present paper, laboratorial and industrial scale processes were reviewed, and guidelines for a rationale selection of manufacturing processes were proposed. This would ensure an adequate development (laboratorial scale) and production according to the good manufacturing practices (GMP) (industrial scale) of amorphous solid dispersions, with further implications on the process validations and drug development pipeline.