Use of Terahertz-Raman Spectroscopy to Determine Solubility of the Crystalline Active Pharmaceutical Ingredient in Polymeric Matrices during Hot Melt Extrusion

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.

A Quantitative Chemometric Study of Pharmaceutical Tablet Formulations Using Multi-Spectroscopic Fibre Optic Probes

Background/Objectives: Two fibre optic probes were custom designed to perform Raman and near-infrared spectroscopic measurements. Our long-term objective is to develop a non-destructive tool able to collect data in hard-to-access locations for real-time analysis or diagnostic purposes. This study evaluated the quantitative performances of Probe A and Probe B using model pharmaceutical tablets. Methods: Measurements were performed using pharmaceutical tablets containing hydroxyl propylcellulose, titanium dioxide (anatase), lactose monohydrate, and indomethacin (γ form). Material content and thickness of bilayer samples (samples consisting of a top layer and a bottom layer of differing materials) were also assessed using Probe A to evaluate its capabilities to collect sub-surface information. Principal component analysis and partial least squares regression models were using individual and fused data to evaluate the performances of the different probe configurations. Results: Hydroxymethyl cellulose (RP2=0.98, RMSEP = 2.27% w/w) and lactose monohydrate (RP2=0.97, RMSEP = 2.96% w/w) content were most effectively estimated by near-infrared spectroscopy data collected using Probe A. Titanium dioxide (RP2=0.99, RMSEP = 0.21% w/w) content was most effectively estimated using a combination of 785 nm Raman spectroscopy and near-infrared spectroscopy using Probe B. Indomethacin (RP2=0.97, RMSEP = 1.01% w/w) was best estimated using a low-level fused dataset collected using 0 mm, 2.5 mm, and 5.0 mm lateral offsets of 785 nm spatially offset Raman spectroscopy using Probe A. Conclusions: The different probe configurations were able to reliably collect data and demonstrated robust quantitative performances. These results highlight the advantage of using multiple techniques for analysing different structures.

Thermal degradation of Affinisol HPMC: Optimum Processing Temperatures for Hot Melt Extrusion and 3D Printing

PURPOSE

Affinisol HPMC HME is a new popular form of hypromellose specifically designed for the hot melt extrusion and 3D printing of pharmaceutical products. However, reports of its thermal stability include only data obtained under inert N2 atmosphere, which is not consistent with the common pharmaceutical practice. Therefore, detailed investigation of its real-life thermal stability in air is paramount for identification of potential risks and limitations during its high-temperature processing.

METHODS

In this work, the Affinisol HPMC HME 15LV powder as well as extruded filaments will be investigated by means of thermogravimetry, differential scanning calorimetry and infrared spectroscopy with respect to its thermal stability.

RESULTS

The decomposition in N2 was proceeded in accordance with the literature data and manufacturer's specifications: onset at ~260°C at 0.5°C·min-1, single-step mass loss of 90-95%. However, in laboratory or industrial practice, high-temperature processing is performed in the air, where oxidation-induced degradation drastically changes. The thermogravimetric mass loss in air proceeded in three stages: ~ 5% mass loss with onset at 150°C, ~ 70% mass loss at 200°C, and ~ 15% mass loss at 380°C. Diffusion of O2 into the Affinisol material was identified as the rate-determining step.

CONCLUSION

For extrusion temperatures ≥170°C, Affinisol exhibits a significant degree of degradation within the 5 min extruder retention time. Hot melt extrusion of pure Affinisol can be comfortably performed below this temperature. Utilization of plasticizers may be necessary for safe 3D printing.

Exploring the Solid-State Landscape of Carbamazepine during Dehydration: A Low Frequency Raman Spectroscopy Perspective

The solid-state landscape of carbamazepine during its dehydration was explored using Raman spectroscopy in the low- (-300 to -15, 15 to 300) and mid- (300 to 1800 cm^-1) frequency spectral regions. Carbamazepine dihydrate and forms I, III, and IV were also characterized using density functional theory with periodic boundary conditions and showed good agreement with experimental Raman spectra with mean average deviations less than 10 cm^-1. The dehydration of carbamazepine dihydrate was examined under different temperatures (40, 45, 50, 55, and 60 °C). Principal component analysis and multivariate curve resolution were used to explore the transformation pathways of different solid-state forms during the dehydration of carbamazepine dihydrate. The low-frequency Raman domain was able to detect the rapid growth and subsequent decline of carbamazepine form IV, which was not as effectively observed by mid-frequency Raman spectroscopy. These results showcased the potential benefits of low-frequency Raman spectroscopy for pharmaceutical process monitoring and control.

Selective laser sintering additive manufacturing of dosage forms: Effect of powder formulation and process parameters on the physical properties of printed tablets

Large batches of placebo and drug-loaded solid dosage forms were successfully fabricated using selective laser sintering (SLS) 3D printing in this study. The tablet batches were prepared using either copovidone (N-vinyl-2-pyrrolidone and vinyl acetate, PVP/VA) or polyvinyl alcohol (PVA) and activated carbon (AC) as radiation absorbent, which was added to improve the sintering of the polymer. The physical properties of the dosage forms were evaluated at different pigment concentrations (i.e., 0.5 and 1.0 wt%) and at different laser energy inputs. The mass, hardness, and friability of the tablets were found to be tunable and structures with greater mass and mechanical strength were obtained with increasing carbon concentration and energy input. Amorphization of the active pharmaceutical ingredient in the drug-loaded batches, containing 10 wt% naproxen and 1 wt% AC, was achieved in-situ during printing. Thus, amorphous solid dispersions were prepared in a single-step process and produced tablets with mass losses below 1 wt%. These findings show how the properties of dosage forms can be tuned by careful selection of the process parameters and the powder formulation. SLS 3D printing can therefore be considered to be an interesting and promising technique for the fabrication of personalized medicines.

Palatable Levocetirizine Dihydrochloride Solid Dispersed Fast-Dissolving Films: Formulation and In Vitro and In Vivo Characterization

One of the most important issues for bitter-tasting drugs such as levocetirizine dihydrochloride (LCD) is the production of palatable dosage forms. LCD also has a delayed onset of action following oral administration. In this study, solid dispersed fast-dissolving films (FDFs) of LCD using the solvent casting method for oral application were prepared and evaluated. The FDF is composed of HPMC as the film forming polymer and different types of superdisintegrants (sodium starch glycolate, croscarmellose sodium, or crospovidone). FDF containing crospovidone showed the highest percentage release of the drug (100.54% ± 1.47 within 3 min.) and was chosen for fabricating into palatable solid dispersed FDFs using different ratios of gelatine. The results of Raman and FTIR revealed that the drug's crystalline structure has been disrupted, and the drug has intermolecular hydrogen bonds with gelatine. The solid dispersed FDF (LF-7), which contained the drug in the form of a 1 : 1 solid dispersion with gelatine, showed a rapid in vitro disintegration (25 seconds) and a burst release of the drug (99.22% ± 2.22 within one min). The in vivo studies were conducted on human participants and showed a significant (p < 0.05) reduction in disintegration time (9.43 ± 2.16 sec.) and higher taste masking ability of the solid dispersed FDF (LF-7) compared to the nonsolid dispersed FDF (LF-4). The stability studies indicated that the prepared FDF remained stable over three months. Overall, FDFs of levocetirizine dihydrochloride with a palatable and rapid onset of action were developed to relieve allergic symptoms.

Lipid-based solubilization technology via hot melt extrusion: promises and challenges

INTRODUCTION

Self-emulsifying drug delivery systems (SEDDS) are a promising strategy to improve the oral bioavailability of poorly water-soluble drugs (PWSD). The excipients of SEDDS enable permeation through the mucus and gastro-intestinal barrier, inhibiting efflux transporters (e.g. P-glycoprotein) of drugs. Poor drug loading capacity and formulation instability are the main setbacks of traditional SEDDS. The use of polymeric precipitation inhibitors was shown to create supersaturable SEDDS with increased drug payload, and their solidification can help to overcome the instability challenge. As an alternative to several existing SEDDS solidification technologies, hot melt extrusion (HME) holds the potential for lean and continuous manufacturing of supersaturable solid-SEDDS. Despite being ubiquitously applied in solid lipid and polymeric processing, HME has not yet been widely considered for the preparation of SEDDS.

AREAS COVERED

The review begins with the rationale why SEDDS as the preferred lipid-based delivery systems (LBDS) is suitable for the oral delivery of PWSD and discusses the common barriers to oral administration. The potential of LBDS to surmount them is discussed. SEDDS as the flagship of LBDS for PWSD is proposed with a special emphasis on solid-SEDDS. Finally, the opportunities and challenges of HME from the lipid-based excipient (LBE) processing and product performance standpoint are highlighted.

EXPERT OPINION

HME can be a continuous, solvent-free, cost-effective, and scalable technology for manufacturing solid supersaturable SEDDS. Several critical formulations and process parameters in successfully preparing SEDDS via HME are identified.

Mefenamic acid solid dispersions: Impact of formulation composition on processing parameters, product properties and performance

The objective of this study was to develop an immediate release (IR), crystalline solid dispersion (CSD) formulation of Mefenamic acid (MFA) by hot-melt-extrusion (HME) and assess the impact of drug loading on process parameters, product physico-chemical properties and product performance. An HME process to produce a range of MFA-Soluplus®-Sorbitol polymer matrix CSD formulations was developed based on rheological screening assays of physical mixtures (PM). The impact of drug loading on process parameters was compared to the impact of drug loading on the physico-chemical properties of formulations. Based on process and product data, three groupings of API drug loading were identified: sub-saturated, saturated, and supersaturated systems. CSD formulations were obtained for 20 - 50% (w/w) drug loading containing the stable polymorphic form I of MFA. CSD formulations predominantly improved the consistency of the product performance. An Amorphous Solid Dispersion (ASD) was obtained for 10% (w/w) drug loading, exhibiting faster drug release even at physiologically relevant pH. This study illustrates the impact of drug loading on process and product characteristics and how a better understanding of maximum API solubility in a given polymer system can improve targeted formulation development.

Analytical and Computational Methods for the Determination of Drug-Polymer Solubility and Miscibility

In the pharmaceutical industry, poorly water-soluble drugs require enabling technologies to increase apparent solubility in the biological environment. Amorphous solid dispersion (ASD) has emerged as an attractive strategy that has been used to market more than 20 oral pharmaceutical products. The amorphous form is inherently unstable and exhibits phase separation and crystallization during shelf life storage. Polymers stabilize the amorphous drug by antiplasticization, reducing molecular mobility, reducing chemical potential of drug, and increasing glass transition temperature in ASD. Here, drug-polymer miscibility is an important contributor to the physical stability of ASDs. The current Review discusses the basics of drug-polymer interactions with the major focus on the methods for the evaluation of solubility and miscibility of the drug in the polymer. Methods for the evaluation of drug-polymer solubility and miscibility have been classified as thermal, spectroscopic, microscopic, solid-liquid equilibrium-based, rheological, and computational methods. Thermal methods have been commonly used to determine the solubility of the drug in the polymer, while other methods provide qualitative information about drug-polymer miscibility. Despite advancements, the majority of these methods are still inadequate to provide the value of drug-polymer miscibility at room temperature. There is still a need for methods that can accurately determine drug-polymer miscibility at pharmaceutically relevant temperatures.

Monitoring the Isothermal Dehydration of Crystalline Hydrates Using Low-Frequency Raman Spectroscopy

Detection of the solid-state forms of pharmaceutical compounds is important from the drug performance point of view. Low-frequency Raman (LFR) spectroscopy has been demonstrated to be very sensitive in detecting the different solid-state forms of pharmaceutically relevant compounds. The potential of LFR spectroscopy to probe the in situ isothermal dehydration was studied using piroxicam monohydrate (PXM) and theophylline monohydrate (TPMH) as the model drugs. The dehydration of PXM and TPMH at four different temperatures (95, 100, 105, and 110 °C and 50, 60, 70, and 80 °C, respectively) was monitored in both the low- (20-300 cm^-1) and mid-frequency (335-1800 cm^-1) regions of the Raman spectra. Principal component analysis and multivariate curve resolution were applied for the analysis of the Raman data. Spectral differences observed in both regions highlighted the formation of specific anhydrous forms of piroxicam and theophylline from their respective monohydrates. The formation of the anhydrous forms was detected on different timescales (approx. 2 min) between the low and mid-frequency Raman regions. This finding highlights the differing nature of the vibrations being detected between these two spectral regions. Computational simulations performed were also in agreement with the experimental results, and allowed elucidating the origin of different spectral features.

Innovations in Thermal Processing: Hot-Melt Extrusion and KinetiSol® Dispersing

Thermal processing has gained much interest in the pharmaceutical industry, particularly for the enhancement of solubility, bioavailability, and dissolution of active pharmaceutical ingredients (APIs) with poor aqueous solubility. Formulation scientists have developed various techniques which may include physical and chemical modifications to achieve solubility enhancement. One of the most commonly used methods for solubility enhancement is through the use of amorphous solid dispersions (ASDs). Examples of commercialized ASDs include Kaletra®, Kalydeco®, and Onmel®. Various technologies produce ASDs; some of the approaches, such as spray-drying, solvent evaporation, and lyophilization, involve the use of solvents, whereas thermal approaches often do not require solvents. Processes that do not require solvents are usually preferred, as some solvents may induce toxicity due to residual solvents and are often considered to be damaging to the environment. The purpose of this review is to provide an update on recent innovations reported for using hot-melt extrusion and KinetiSol® Dispersing technologies to formulate poorly water-soluble APIs in amorphous solid dispersions. We will address development challenges for poorly water-soluble APIs and how these two processes meet these challenges.

Improving Consistency for a Mefenamic Acid Immediate Release Formulation

The objective of this study was to develop an immediate release dose form containing 250 mg Mefenamic acid (MFA) presented as a crystalline solid dispersion in order to achieve improved consistency in drug release through a simplified formulation compared to a commercial product. An MFA-Soluplus®-Sorbitol polymer matrix was developed using an HME process based on rheological screening assays of physical mixtures. The physico-chemical properties of these formulations were assessed by thermal analysis, FTIR, mechanical testing and SEM image analysis, confirming the crystalline character and stable polymorphic form I of the API in the polymer matrix. A faster release and a significant improvement in consistency (±6%) of drug release was observed compared to a commercially available MFA product (±17%) (250 mg capsule). This study illustrates advantages of applying a structured development program aimed at retaining API physical properties in the final dosage form.

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.