Elucidation and visualization of solid-state transformation and mixing in a pharmaceutical mini hot melt extrusion process using in-line Raman spectroscopy

Probing the interplay between drug saturation, processing temperature and microstructure of amorphous solid dispersions with synchrotron X-ray phase-contrast tomography

The impact of drug saturation and processing regime on the microstructure of amorphous solid dispersions (ASDs) produced by hot-melt extrusion (HME) has been investigated. By exploring various combinations of drug loadings and processing temperatures, a range of drug saturation points were obtained by HME. The process was monitored with an in-line low-frequency Raman probe to construct the respective solubility phase diagram (i.e., solubility of crystalline drug in molten/soften polymer). The resulting ASDs were analysed with synchrotron X-ray phase-contrast micro computed tomography (Sync-XPC-μCT) in conjunction with a tailored image segmentation strategy to extract quantitative and qualitative descriptors. Despite minimal elemental variability between the drug (paracetamol) and the polymer (HPMC), Sync-XPC-μCT provided sufficient contrast to identify multiple structural domains, including drug-rich crystalline clusters, impurities, polymer-related heterogeneities and voids/pores. Supersaturated ASDs (> 20 wt% drug loading) displayed higher structural complexity and showed a plethora of highly defective API-rich crystalline domains upon ageing, which were absent in the undersaturated ASDs. Beyond its impact on the API physical state, the HME processing regime influenced the degree of homogeneity within the polymer fraction, as well as total porosity, size, shape and pore connectivity. By correlating with fundamental API-polymer solubility data, this study offers additional insight into the dynamics of the drug's solubilisation process during extrusion and the subsequent formation of microstructures within the ASD system, which have potential implications on product performance and stability.

In-line NIR coupled with machine learning to predict mechanical properties and dissolution profile of PLA-Aspirin

In the production of polymeric drug delivery devices, dissolution profile and mechanical properties of the drug loaded polymeric matrix are considered important Critical Quality Attributes (CQA) for quality assurance. However, currently the industry relies on offline testing methods which are destructive, slow, labour intensive, and costly. In this work, a real-time method for predicting these CQAs in a Hot Melt Extrusion (HME) process is explored using in-line NIR and temperature sensors together with Machine Learning (ML) algorithms. The mechanical and drug dissolution properties were found to vary significantly with changes in processing conditions, highlighting that real-time methods to accurately predict product properties are highly desirable for process monitoring and optimisation. Nonlinear ML methods including Random Forest (RF), K-Nearest Neighbours (KNN) and Recursive Feature Elimination with RF (RFE-RF) outperformed commonly used linear machine learning methods. For the prediction of tensile strength RFE-RF and KNN achieved R 2 values 98% and 99%, respectively. For the prediction of drug dissolution, two time points were considered with drug release at t = 6 h as a measure of the extent of burst release, and t = 96 h as a measure of sustained release. KNN and RFE-RF achieved R 2 values of 97% and 96%, respectively in predicting the drug release at t = 96 h. This work for the first time reports the prediction of drug dissolution and mechanical properties of drug loaded polymer product from in-line data collected during the HME process.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42252-024-00063-5.

Exploiting common ion addition to accelerate zolpidem hemitartrate release from Eudragit EPO extrudates

The current study aimed at optimizing a previously developed non-clinical formulation for use in zolpidem deprescribing. The formulation under investigation consists of extruded zolpidem hemitartrate (30% w/w) and Eudragit EPO (70% w/w) mixtures which display unsatisfactory dissolution behavior. Both milled extrudates and physical mixtures were compressed to produce tablets with identical target weight and solid fraction. First, the susceptibility of zolpidem hemitartrate towards heat and shear degradation was identified utilizing thermal and HPLC-DAD analysis. The drug salt proved prone to thermally induced disproportionation. Moreover, the impurity content increased after applying hot melt extrusion although ICH guidelines were still attained. Secondly, extrudates and physical mixtures were subjected to FTIR analysis. As a result, interaction and protonation of the dimethyl aminoethyl group from Eudragit EPO resulting from zolpidem disproportionation was elucidated. As such, the formulations' slow dissolution kinetics in comparison to formulations containing non-ionizable polymers (e.g. Kollidon 12PF and Kollidon VA64) is explained. Finally, addition of tartaric acid, a microenvironmental pH modulator and common ion, proved a successful method to increase dissolution kinetics. The amount of drug released after 15 min increased drastically from 10 to 40% upon the addition of 5% tartaric acid. Immediate release behavior (80% within 15 min) was however not yet attained.

Advances in numerical simulation of unit operations for tablet preparation

Recently, there has been an increase in the use of numerical simulation technology in pharmaceutical preparation processes. Numerical simulation can contribute to a better understanding of processes, reduce experimental costs, optimize preparation processes, and improve product quality. The intermediate material of most dosage forms is powder or granules, especially in the case of solid preparations. The macroscopic behavior of particle materials is controlled by the interactions of individual particles with each other and surrounding fluids. Therefore, it is very important to analyze and control the microscopic details of the preparation process for solid preparations. Since tablets are one of the most widely used oral solid preparations, and the preparation process is relatively complex and involves numerous units of operation, it is especially important to analyze and control the tablet production process. The present paper discusses recent advances in numerical simulation technology for the preparation of tablets, including drying, mixing, granulation, tableting, and coating. It covers computational fluid dynamics (CFD), discrete element method (DEM), population balance model (PBM), finite element method (FEM), Lattice-Boltzmann model (LBM), and Monte Carlo model (MC). The application and deficiencies of these models in tablet preparation unit operations are discussed. Furthermore, the paper provides a systematic reference for the control and analysis of the tablet preparation process and provides insight into the future direction of numerical simulation technology in the pharmaceutical industry.

Machine Learning for Process Monitoring and Control of Hot-Melt Extrusion: Current State of the Art and Future Directions

In the last few decades, hot-melt extrusion (HME) has emerged as a rapidly growing technology in the pharmaceutical industry, due to its various advantages over other fabrication routes for drug delivery systems. After the introduction of the ‘quality by design’ (QbD) approach by the Food and Drug Administration (FDA), many research studies have focused on implementing process analytical technology (PAT), including near-infrared (NIR), Raman, and UV–Vis, coupled with various machine learning algorithms, to monitor and control the HME process in real time. This review gives a comprehensive overview of the application of machine learning algorithms for HME processes, with a focus on pharmaceutical HME applications. The main current challenges in the application of machine learning algorithms for pharmaceutical processes are discussed, with potential future directions for the industry.

Spectrophotometry and pharmaceutical PAT/RTRT: Practical challenges and regulatory landscape from development to product lifecycle

European Pharmacopoeia includes dedicated chapters for Raman, NIR and Chemometrics, as well as there is a lot of Academia research on the matter. Despite that, the word innovation is often associated to such tools and there is a still slow implementation at industry. The paper is the outcome of the Associazione Farmaceutici dell'Industria (AFI) Study Group on Process Innovation and Product Lifecycle; the aim is to describe some case studies referring to practical approaches in pharmaceutical industry, in order to depict challenges and opportunities for the implementation of spectroscopic techniques. Case studies include: feasibility and pre-screening evaluations, chemometric model development approaches, way for the method maintenance during commercial manufacturing, challenges for implementation on existing equipment and on sterile processes. Case studies refer to oral solid products, liquid products and sterile Active Pharmaceutical Ingradient (API) manufacturing. There are already successful and robust spectroscopic applications in pharmaceutical industry and the technology is mature: this is the outcome of a strong applied research performed at pharmaceutical production departments. It is necessary to acknowledge efforts done by industry as Research for strengthening the cooperation with Academia, so that advantage of process innovation might reach the patients in a fastest way.

Quality-by-design in hot melt extrusion based amorphous solid dispersions: An industrial perspective on product development

An industrially feasible approach to overcome the solubility and bioavailability limitations of poorly soluble active pharmaceutical ingredients is the development of amorphous solid dispersions (ASDs) using hot-melt extrusion (HME) technique. The application of Quality by Design (QbD) had a profound impact on the development of HME-based ASDs. The formulation and process optimization of ASDs manufactured via HME techniques require an understanding of critical quality attributes, critical material attributes, critical process parameters, risk assessment tools, and experimental designs. The knowledge gained from each of these QbD elements helps ensure the consistency of product quality. The selection and implementation of appropriate Design of Experiments (DoE) methodology to screen and optimize the formulation and process variables remain a major challenge. This review provides a comprehensive overview on QbD concepts in HME-based ASDs with an emphasis on DoE methodologies. Further, the information provided in this review can assist researchers in selecting a suitable design with optimal experimental conditions. Specifically, this review has focused on the prediction of drug-polymer miscibility, the elements and sequence of QbD, and various screening and optimization designs, to provide insights into the formulation and process variables that are encountered routinely in the production of HME-based ASDs.

Exploring the Complexity of Processing-Induced Dehydration during Hot Melt Extrusion Using In-Line Raman Spectroscopy

The specific aim in this study was to understand the effect of critical process parameters on the solid form composition of model drug compounds during hot melt extrusion using in-line Raman spectroscopy combined with Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) modeling for semi-quantitative kinetic profiling. It was observed that the hydrate and anhydrate solid forms of two model drugs in the melts of nitrofurantoin (NF):polyethylene oxide (PEO) and piroxicam (PRX):PEO could be resolved from a MCR-ALS model without an external calibration dataset. Based on this model, the influence of two critical process parameters (shear and temperature) on the solid form composition could be evaluated in a real-time mode and the kinetics of complex transformation pathways could be explored. Additionally, the dehydration pathways of NF monohydrate and PRX monohydrate in molten PEO could be derived. It can be concluded that dehydration of both hydrates in PEO occurs via competing mechanisms—a solution-mediated transformation pathway and a solid–solid transformation, and that the balance between these mechanisms is determined by the combined effect of both temperature and shear. Another important observation was that the water released from these hydrate compounds has a detectable effect on the rheological characteristics of this mixture.

In-Line Monitoring the Degradation of Polypropylene under Multiple Extrusions Based on Raman Spectroscopy

Polymer degradation is a common problem in the extrusion process. In this work, Raman spectroscopy, a robust, rapid, and non-destructive tool for in-line monitoring, was utilized to in-line monitor the degradation of polypropylene (PP) under multiple extrusions. Raw spectra were pretreated by chemometrics methods to extract variations of spectra and eliminate noise. The variation of Raman intensity with the increasing number of extrusions was caused by the scission of PP chains and oxidative degradation, and the variation trend of Raman intensity indicated that long chains were more likely to be damaged by the extrusion. For the quantitative analysis of degradation, the partial least square was used to build a model to predict the degree of PP degradation measured by gel permeation chromatography (GPC). For the calibration set, the coefficient of determination (R2) and the root mean square error of cross-validation (RMSECV) were 0.9859 and 1.2676%, and for the prediction set, R2 and the root mean square error of prediction (RMSEP) were 0.9752 and 1.7228%, which demonstrated the accuracy of the proposed model. The in-line Raman spectroscopy combined with the chemometrics methods was proved to be an accurate and highly effective tool, which can monitor the degradation of polymer in real time.

Assessment of volumetric scale-up law for processing of a sustained release formulation on co-rotating hot-melt extruders

In this research, the volumetric scale-up law was assessed for its applicability to scale-up from a laboratory-scale extruder (11 mm diameter) to a pilot-scale extruder (16 mm diameter) with geometric similarity using low feed rates (0.1-0.26 kg/h at lab-scale). A sustained release formulation was extruded on both scales using scaled feed rates according to the volumetric scale-up law. The specific mechanical energies, drug solid-state, drug dissolution and the residence time distribution responses (i.e. axial mixing degree, mean residence time, width of distribution) were compared between both scales. The results showed that the difference in mean residence time between both scale extruders reduced with higher throughput and thus fill level. Overall, the specific mechanical energies (SME) were comparable between scales when using the volumetric scale-up law (i.e. applying scaling factor q = 3) and were exactly matching with a scaling factor of q = 2.6. Furthermore, plug flow conditions at lab-scale should be avoided before scaling up to obtain similar SMEs. The same degree of axial mixing (represented by the Peclet number) was demonstrated at a scaling factor of q = 2. If drug solid-state is a critical quality attribute (CQA), focus should be on the screw speed and cooling capacity of the larger scale extruder. The drug dissolution showed similarity between scales and was independent of drug solid-state for this formulation, indicating that successful scale-up was possible.

Novel Hot Melt Extruded Matrices of Hydroxypropyl Cellulose and Amorphous Felodipine-Plasticized Hydroxypropyl Methylcellulose as Controlled Release Systems

Hydroxypropyl methylcellulose (HPMC) is a hydrophilic retarding-release polymer with the limited application in hot melt extrusion (HME) due to its high glass transition temperature (T_g 181-191°C) and melt viscosity. The aim of this study is to develop hot melt extruded matrices using hydroxypropyl cellulose (HPC) and felodipine (FLDP) with HPMC for controlled release and explore the relations of their specialty, processability, and structure with the product properties. Results showed that FLDP/HPC_EF/HPMC can be extruded at 160°C with torques not more than 0.5 N·m. The extruded matrices of FLDP/HPC_EF/HPMC_K15M (10:45:45 and 30:35:35) achieved the controlled release for 24 h. Rheological behaviors demonstrated that HPC_EF and FLDP were miscible with HPMC_K15M, attaining maximum 30% FLDP soluble in the molten mixtures. HPC_EF and FLDP decreased the complex viscosity and plasticized HPMC_K15M to improve the extrusion processing. DSC and FT-IR indicated that the molten soluble FLDP was amorphous in the extruded matrices by hydrogen bonding with HPC_EF/HPMC_K15M. SEM/energy-dispersive X-ray microanalysis illustrated that the microstructure of extrudates was surface dense and interior loose, and FLDP was homogenously dispersed. Three-point bending test revealed that the plasticizers of HPC_EF and FLDP contributed differently to the mechanical properties. HPC_EF decreased the flexural modulus of HPMC_K15M while that of HPC_EF/HPMC_K15M was increased by FLDP. Besides controlled release, low moisture absorption and enhanced stability were also the correlated achievements. Therefore, HPC_EF-combined poorly water-soluble drugs to plasticize HPMC_K15M provide an alternative novel potential approach to realize the controlled-release delivery via HME.

Process analytical technologies and injectable drug products: Is there a future?

Parametric release was the first subset of real time release testing (RTRT), applied to terminally sterilised injectable drug products. The objective was to offer the industry an alternative to the time and money consuming sterility testing, without compromising the sterility of the products. The rationale was that quality cannot be tested into products, instead it must be planned (the principle of quality by design, QbD). This can be implemented by setting appropriate in-process controls supported on process analytical technologies (PAT). Two of the most versatile and promising PAT tools are the near infrared spectroscopy (NIRS) and the Raman spectroscopy. However, their application to injectable drug product development and manufacturing has been scarce. This review has the objective to provide a framework for the practical implementation of the QbD approach to injectable formulations, including application of diverse risk assessment and factorial design tools. Finally, the actual application of PAT, namely NIRS and Raman spectroscopy, to injectable drug product analysis is addressed.

The application of temperature-composition phase diagrams for hot melt extrusion processing of amorphous solid dispersions to prevent residual crystallinity

Hot melt extrusion (HME) can be used to produce amorphous solid dispersions (ASDs) at temperatures below the drug's melting point if the drug and polymer exhibit melting point depression. However, the risk of residual crystallinity becomes significant. The purpose of this study was to apply the temperature-composition phase diagram to the HME process, correlating process conditions to ASD residual crystallinity, and identifying the formulation critical temperature, which defines the theoretical minimum processing temperature. The phase diagram of indomethacin (IDM) and polyvinylpyrrolidone/vinyl acetate copolymer (PVPVA) was generated using melting point depression measurements coupled with Flory-Huggins theory. Extrudates were manufactured above, at, and below the formulation critical temperature (T_c) as identified from the phase diagram, with a range of residence times, and characterized for crystallinity. Below the T_c, a fully amorphous sample could not be prepared. Above T_c, sufficient residence time led to amorphous samples. A processing operating design space diagram with three regimes was generated to correlate temperature and residence time factors with process outcome. In conclusion, phase diagrams provide a rational basis for designing hot melt extrusion processes of amorphous solid dispersions to minimize residual crystalline content, delineating the minimum processing temperature based on thermodynamic considerations.

Application of Raman Spectroscopy for In-Line Measurement of Dispersion Uniformity of Polypropylene-Polystyrene Blends During Melt Extrusion

At present, there is a widespread phenomenon that product quality is difficult to monitor during the process of polymer melt modification such as blending, filling, and reinforcement. In consideration of this problem, this paper proposes an in-line Raman spectroscopy technique for measuring dispersion uniformity of polystyrene (PS) in polypropylene (PP)/PS blends during melt extrusion. On the basis of the optimal partial least squares (PLS) calibration model for quantitative determination of PS content in PP/PS, the fluctuations of PS content in extruding PP/PS with a mass percentage of 70 : 30 at different screw rotation speeds were predicted. The coefficient of variation (CV) of PS content at each screw rotation speed was obtained to accurately compare the dispersion uniformity, which was in agreement with the PS dispersion result characterized by the scanning electron microscope (SEM). In addition, the sensitivity of the measurement was validated by calculating the CV of PP/PS with mass percentages of 69 : 31 and 71 : 29. All of the above demonstrated that the in-line measurement system of Raman spectroscopy was able to accurately measure the dispersion uniformity of PS during the blending extrusion of PP/PS and demonstrated good sensitivity to minor changes in the blends composition.

Hot Melt Extrusion: Highlighting Physicochemical Factors to Be Investigated While Designing and Optimizing a Hot Melt Extrusion Process

Hot-melt extrusion (HME) is a well-accepted and extensively studied method for preparing numerous types of drug delivery systems and dosage forms. It offers several advantages: no solvents are required, it is easy to scale up and employ on the industrial level, and, in particular, it offers the possibility of improving drug bioavailability. HME involves the mixing of a drug with one or more excipients, in general polymers and even plasticizers, which can melt, often forming a solid dispersion of the drug in the polymer. The molten mass is extruded and cooled, giving rise to a solid material with designed properties. This process, which can be realized using different kinds of special equipment, may involve modifications in the drug physicochemical properties, such as chemical, thermal and mechanical characteristics thus affecting the drug physicochemical stability and bioavailability. During process optimization, the evaluation of the drug solid state and stability is thus of paramount importance to guarantee stable drug properties for the duration of the drug product shelf life. This manuscript reviews the most important physicochemical factors that should be investigated while designing and optimizing a hot melt extrusion process, and by extension, during the different pre-formulation, formulation and process, and post-formulation phases. It offers a comprehensive evaluation of the chemical and thermal stability of extrudates, the solid physical state of extrudates, possible drug-polymer interactions, the miscibility/solubility of the drug-polymer system, the rheological properties of extrudates, the physicomechanical properties of films produced by hot melt extrusion, and drug particle dissolution from extrudates. It draws upon the last ten years of research, extending inquiry as broadly as possible.

Facile formation of co-amorphous atenolol and hydrochlorothiazide mixtures via cryogenic-milling: Enhanced physical stability, dissolution and pharmacokinetic profile

The development of poorly water-soluble drugs faces the risk of low bioavailability and therapeutic efficacy. The co-amorphous drug delivery system has recently gained considerable interest because it offers an alternative approach to modify properties of poorly water-soluble drugs. Herein, we developed a co-amorphous system of atenolol (ATE) and poorly water-soluble hydrochlorothiazide (HCT) by means of cryogenic milling. The co-administration of ATE and HCT has been reported to show therapeutic advantages for patients with uncomplicated hypertension. The co-amorphous ATE-HCT sample with 1:1 molar ratio showed excellent physical stability, which could be attributed to the formation of strong molecular interactions between ATE and HCT as evidenced by FT-IR spectra. Compared to the pure crystalline form, amorphous form and physical mixture, HCT in the co-amorphous form exhibited the significantly increased intrinsic dissolution rate, as well as the enhanced bioavailability in the pharmacokinetic study. It was found that the enhanced bioavailability of HCT in the co-amorphous formulation was achieved by the synergistic effect of amorphized HCT and the water-soluble coformer ATE. The present study provides an improved approach to implement the combination therapy of ATE and HCT for potential clinical treatments.

Global approach for the validation of an in-line Raman spectroscopic method to determine the API content in real-time during a hot-melt extrusion process

Since the Food and Drug Administration (FDA) published a guidance based on the Process Analytical Technology (PAT) approach, real-time analyses during manufacturing processes are in real expansion. In this study, in-line Raman spectroscopic analyses were performed during a Hot-Melt Extrusion (HME) process to determine the Active Pharmaceutical Ingredient (API) content in real-time. The method was validated based on a univariate and a multivariate approach and the analytical performances of the obtained models were compared. Moreover, on one hand, in-line data were correlated with the real API concentration present in the sample quantified by a previously validated off-line confocal Raman microspectroscopic method. On the other hand, in-line data were also treated in function of the concentration based on the weighing of the components in the prepared mixture. The importance of developing quantitative methods based on the use of a reference method was thus highlighted. The method was validated according to the total error approach fixing the acceptance limits at ±15% and the α risk at ±5%. This method reaches the requirements of the European Pharmacopeia norms for the uniformity of content of single-dose preparations. The validation proves that future results will be in the acceptance limits with a previously defined probability. Finally, the in-line validated method was compared with the off-line one to demonstrate its ability to be used in routine analyses.