Optimizing twin-screw melt granulation: The role of overflight clearance on granulation behavior

Twin-screw melt granulation (TSMG) relies on the dispersive and distributive mixing at the kneading zone for granule growth to happen highlighting the critical role played by the kneading elements in TSMG. Despite extensive research conducted on the impact of screw geometry in melt compounding, there is not enough literature for TSMG. Disc width for the kneading elements was 2 mm, contrary to the standard 5 mm. The objective of this study was to evaluate if varying overflight clearance (OC) can alter the paradigm for TSMG. The new elements reduce the peak shear at kneading zone however a higher barrel temperature and degree of fill (DoF) is required to compensate to attain similar granule attributes. The change in DoF was achieved through a combination of modified screw configuration to pre-densify powders before kneading and processing at a lower screw speed. Despite the higher barrel temperature, process optimization of thermally unstable gabapentin was carried out. Using the new elements, compressible granules (Tensile strength > 2 MPa) with low % GABA-L content were manufactured despite increasing OC to 0.4 mm. Granule stability at 40 °C, ambient humidity for 6 months indicated gabapentin was stable (% GABA-L ≪0.4 %) despite a high barrel temperature of 120 °C.

Visualization of the granule temperature using thermal imaging to improve understanding of the granulation mechanism in continuous twin-screw melt granulation

The aim of this study is to increase process understanding of the granulation mechanism in twin-screw melt granulation by evaluating the influence of different screw configurations on granule formation and granule temperature via thermal imaging. The study used a Design of Experiments (DoE) to process a miscible and immiscible formulation (85% API/binder w/w) using a twin-screw extruder with varying screw configurations. The barrel temperature (°C), screw speed (rpm), throughput (kg/h), and kneading zone (direction and stagger angle) were varied. Granule and process properties were evaluated for samples collected at four different locations along the length of the granulation barrel to visualize the granule formation, and granule temperature was monitored by an infrared camera to measure heat transfer on the granules. The resulting temperature was linked to the granule properties and the granule formation along the length of the barrel. The most influencing factors on the granule temperature are the direction of the kneading zone and the set barrel temperature. It was observed that granule formation mainly occurred in the zones that apply more kneading on the granules. The highest temperature increase was observed when the smallest stagger angle in reverse configuration was used, and could be linked to better granule quality attributes.

Material Transport Characteristics in Planetary Roller Melt Granulation

Melt granulation for improving material handling by modifying particle size distribution offers significant advantages compared to the standard methods of dry and wet granulation in dust reduction, obviating a subsequent drying step. Furthermore, current research in pharmaceutical technology aims for continuous methods, as these have an enhanced potential to reduce product quality fluctuations. Concerning both aspects, the use of a planetary roller granulator is consequential. The process control with these machines benefits from the enhanced ratio of heated surface to processed volume, compared to the usually-applied twin-screw systems. This is related to the unique concept of planetary spindles flowing around a central spindle in a roller cylinder. Herein, the movement pattern defines the transport characteristics, which determine the energy input and overall processing conditions. The aim of this study is to investigate the residence time distribution in planetary roller melt granulation (PRMG) as an indicator for the material transport. By altering feed rate and rotation speed, the fill level in the granulator is adjusted, which directly affects the average transport velocity and mixing volume. The two-compartment model was utilized to reflect these coherences, as the model parameters symbolize the sub-processes of axial material transport and mixing.

Integrated continuous melt granulation-based powder-to-tablet line: process investigation and scale-up on the same equipment

In the last decades, continuous manufacturing (CM) has become a research priority in the pharmaceutical industry. However, significantly fewer scientific researches address the investigation of integrated, continuous systems, a field that needs further exploration to facilitate the implementation of CM lines. This research outlines the development and optimization of an integrated, polyethylene glycol aided melt granulation-based powder-to-tablet line that operates fully continuously. The flowability and tabletability of a caffeine-containing powder mixture were improved through twin-screw melt granulation resulting in the production of tablets with improved breaking force (from 15 N to over 80 N), excellent friability, and immediate release dissolution. The system was also conveniently scaleable: the production speed could be increased from 0.5 kg/h to 8 kg/h with only minimal changes in the process parameters and using the same equipment. Thereby the frequent challenges of scale-up can be avoided, such as the need for new equipment and separate optimization.

Elucidation of Granulation Mechanisms along the Length of the Barrel in Continuous Twin-Screw Melt Granulation

In the pharmaceutical industry, innovative continuous manufacturing technologies such as twin-screw melt granulation (TSMG) are gaining more and more interest to process challenging formulations. To enable the implementation of TSMG, more elucidation of the process is required and this study provides a better understanding of the granule formation along the length of the barrel. By sampling at four different zones, the influence of screw configuration, process parameters and formulation is investigated for the granule properties next to the residence time distribution. It showed that conveying elements initiate the granulation by providing a limited heat transfer into the powder bed. In the kneading zones, the consolidation stage takes place, shear elongation combined with breakage and layering is occurring for the reversed configurations and densification with breakage and layering for the forward and neutral configurations. Due to the material build-up in the reversed configurations, these granules are larger, stronger, more elongated and less porous due to the higher degree of shear and densification. This configuration also shows a significantly longer residence time compared to the forward configuration. Hence, the higher level of shear and the longer period of time enables more melting of the binder resulting in successful granulation.

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.

Moisture Sorption by Polymeric Excipients Commonly Used in Amorphous Solid Dispersions and its Effect on Glass Transition Temperature: II. Cellulosic Polymers

Moisture sorption by polymeric carriers used for the development of amorphous solid dispersions (ASDs) plays a critical role in the physical stability of dispersed drugs since moisture may decrease glass transition temperature (T_g) and thereby increase molecular mobility of drugs leading to their crystallization. To assist the selection of appropriate polymers for ASDs, we conducted moisture sorption by five types of cellulosic polymers, namely, hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC), hydroxypropyl methyl cellulose acetate succinate (HPMCAS), hydroxypropyl methyl cellulose phthalate (HPMCP), and ethyl cellulose (EC), as functions of relative humidity (10 to 90% RH) and temperature (25 and 40 °C). The moisture sorption was in the order of HPC>HPMC>HPMCP>HPMCAS>EC, and there was no significant effect of the molecular weights of polymers on moisture uptake. There was also less moisture sorption at 40 °C than that at 25 °C. Glass transition temperatures (T_g) of the polymers decreased with the increase in moisture content. However, the plasticizing effect by moisture on HPC could not be determined fully since, despite being amorphous, there were very little baseline shifts in DSC scans. There was also very shallow baseline shift for HPMC at >1% moisture content. In contrast, T_g of HPMCAS and HPMCP decreased in general agreement with the Gordon-Taylor/Kelley-Bueche equation, and EC was semicrystalline having both T_g and melting endotherm, with only minor effect of moisture on T_g. The results of the present investigation would lead to a systematic selection of polymeric carriers for ASDs.

Identification of continuous twin-screw melt granulation mechanisms for different screw configurations, process settings and formulation

Twin-screw melt granulation (TSMG) is a promising continuous manufacturing technology for the processing of high drug load formulations and to formulate heat- and moisture-sensitive active pharmaceutical ingredients (APIs). This study evaluates the influence of process parameters for TSMG, mainly focusing on the effect of the screw configuration combined with screw speed, throughput and barrel temperature, to elucidate the melt granulation mechanisms. For the kneading zone, the stagger angle was varied between 30°, 60° and 90°, and investigated for both the forward and the reversed direction. In addition to the process parameters, the influence of the formulation differing in their API-binder miscibility was evaluated. As responses, the granule (size, friability and porosity) and process properties such as torque were evaluated, indicating that the screw configuration is the most influential factor. Nucleation, consolidation and breakage are the granulation mechanisms for the forward and the neutral configuration, while consolidation and densification with shear elongation are identified for the reversed configuration. The formulations differ mainly in the forward and neutral configuration since the immiscible formulation shows a bimodal granule size distribution with a larger fraction of fines and weaker granules is obtained. For the reversed configuration, similar granulation mechanisms are seen for both formulations.

Commercial scale transfer of a twin-screw melt granulation process for high drug load fevipiprant tablets

OBJECTIVE

This work summarizes select methodology of twin-screw melt granulation and process analytical technology that were used in the successful scaling-up and commercial transfer of high drug load (80.5% w/w) immediate release fevipiprant tablets.

SIGNIFICANCE

The unique and compelling learnings from this industry work are (1) insights into Novartis AG's commercial scale transfer using twin-screw melt granulation (2) rapid, non-destructive NIR methodology as a PAT tool for RTR testing. No prior literature combines these two aspects at the level of detail we present/disclose.

METHODS

Scaling up of twin-screw melt granulation (TSMG) was guided by specific energy values obtained for the 27 mm (pilot scale) and 50 mm (commercial scale) twin-screw extruders (TSE). Proven acceptable ranges (PAR) were confirmed by varying the critical process parameters (CPPs) for granulation (screw speed) and tableting (dwell time, crushing strength) at three process levels (upper, target, lower). An at-line NIR method was developed and validated for real-time release testing.

RESULTS

The combination of CPPs were selected to have the same effect on critical quality attributes (CQAs) i.e., lower (-) and upper (+) process level challenged tablet aspect/appearance and dissolution, respectively. TSMG was performed using a 50 mm extruder at constant feed rate. Compression of the six final blends (∼300 kg) showed no impact of varied granulation and compression process conditions on both CQAs. A near-infrared spectroscopy method was validated to determine content uniformity, assay, identity, and to predict CQAs on uncoated tablets in preparation for a real time release testing (RTRT) of future batches.

Physicochemical Changes and Chemical Degradation of Gliclazide during Twin-Screw Melt Granulation

Using a miscible model formulation consisting of 80% gliclazide (GLZ) and 20% hydroxypropyl cellulose, we investigate how the twin-screw melt granulation process affects the chemical stability and process-induced physicochemical changes of the drug. No degradation was observed in the conveying section that leads to kneading element. Approximately 1/3 of the GLZ degradant was generated at the kneading section, while the remaining 2/3 was generated in the conveying section post-kneading and during cooling outside the barrel. A strong correlation was observed between the overall degradation and the temperature of the granules at the barrel exit. In the kneading section, the degradant content correlates best with the specific mechanical energy. With higher specific mechanical energies, the size of the GLZ crystals was reduced further, resulting in more surface defects. In the section post-kneading element, GLZ degradation correlates best with the granule temperature measured at the kneading section. This knowledge of drug degradation during twin-screw melt granulation can be used to develop processing strategies to maintain drug stability during and post processing.

Metamorphosis of Twin Screw Extruder-Based Granulation Technology: Applications Focusing on Its Impact on Conventional Granulation Technology

In order to be at pace with the market requirements of solid dosage forms and regulatory standards, a transformation towards systematic processing using continuous manufacturing (CM) and automated model-based control is being thought through for its fundamental advantages over conventional batch manufacturing. CM eliminates the key gaps through the integration of various processes while preserving quality attributes via the use of process analytical technology (PAT). The twin screw extruder (TSE) is one such equipment adopted by the pharmaceutical industry as a substitute for the traditional batch granulation process. Various types of granulation techniques using twin screw extrusion technology have been explored in the article. Furthermore, individual components of a TSE and their conjugation with PAT tools and the advancements and applications in the field of nutraceuticals and nanotechnology have also been discussed. Thus, the future of granulation lies on the shoulders of continuous TSE, where it can be coupled with computational mathematical studies to mitigate its complications.

Binder-free twin-screw melt granulation: An effective approach to manufacture high-dose API formulations

This study investigates the use of twin-screw binder-free melt granulation (BFMG) in the development of high-dose solid dose formulations for low melting point thermally stable drugs. Both ibuprofen and guaifenesin are examined. By granulating pure API powder, it is shown that BFMG can successfully be used to produce granules that contain 100% API. A design of experiments (DoE) response surface methodology was used to establish the design space for the end-product. The effects of the most relevant process variables (barrel operating temperature, powder feed rate, screw speed and screw configuration) on granule properties (outlet temperature, size distribution, morphology, flowability, compressibility, porosity) and tablet attributes (tensile strength and in-vitro dissolution) were thoroughly studied. Barrel temperature (alone or in interactions with the other variables) represented the most significant variable for both drugs since it governs the formation of granules by partial melting and subsequent agglomeration of the fed powder. Interestingly, the shear action originated by screw speed and screw configuration resulted in various significant responses depending on the drug substance, indicating that it can also be affected by the nature of the processed molecule. Flow properties were improved (i.e., lower Hausner ratio) for both drugs after formation of granules. Tabletability was also tested by preparing 600 mg tablets for all samples. Surprisingly, the resulting granules were highly compactible, requiring only 1% lubricant to form strong tablets containing 96% API and 3% disintegrant. The results also showed that tablets become harder as the granule size increased, especially for guaifenesin. As expected, in-vitro dissolution results indicated that tablets and capsules showed slightly slower dissolution rates than the granules.

Selection of Small Amounts of Glidant Capable of Improving the Tensile Strength of Ibuprofen Tablets

This study examined the selection of small amounts of excipients capable of improving the compactability of ibuprofen, thereby enabling the miniaturization of ibuprofen tablets. Various glidants in amounts of 1% of the total volume were added to dry surface-modified ibuprofen, and the tensile strengths of the resulting tablets were evaluated. The characteristics of the excipients that affected the tensile strengths of the tablets were then extracted using a tensile strength prediction model. We confirmed that the effective angle of the internal friction of the mixed powder, the coating form of the glidant, the packing fraction of the raw material, and the mixed powder affect the tensile strength of the tablet. A smooth particle layer was formed on the surface of the ibuprofen particles when a glidant with a packing fraction of <0.05 was used. In the sample with a smooth particle layer, the angle of the critical state line increased significantly and the tensile strength improved. We inferred that the smoothness of the particle layer allowed the ibuprofen particles to come into close contact with each other. Consequently, the number of junctions increased, and the frictional force between the particles improved, resulting in tablets with improved tensile strengths. In conclusion, the compactability of ibuprofen was improved by adding 1% glidant with a packing fraction of <0.05. The reduction in excipients will allow the creation of smaller tablets, making them easier to swallow. Therefore, the medication adherence of customers will be improved.

Immediate-Release Formulations Produced via Twin-Screw Melt Granulation: Systematic Evaluation of the Addition of Disintegrants

The current study evaluated the effect of location and amount of various superdisintegrants on the properties of tablets made by twin-screw melt granulation (TSMG). Sodium-croscarmellose (CCS), crospovidone (CPV), and sodium starch glycolate (SSG) were used in various proportions intra- and extra-granular. Tabletability, compactibility, compressibility as well as friability, disintegration, and dissolution performance were assessed. The extra-granular addition resulted in the fasted disintegration and dissolution. CPV performed superior to CCS and SSG. Even if the solid fraction (SF) of the granules was lower for CPV, only a minor decrease in tabletability was observed, due to the high plastic deformation of the melt granules. The intra-granular addition of CPV resulted in a more prolonged dissolution profile, which could be correlated to a loss in porosity during tableting. The 100% intra-granular addition of the CPV resulted in a distinct decrease of the disintegration efficiency, whereas the performance of SSG was unaffected by the granulation process. CCS was not suitable to be used for the production of an immediate-release formulation, when added in total proportion into the granulation phase, but its efficiency was less impaired compared to CPV. Shortest disintegration (78 s) and dissolution (Q₈₀: 4.2 min) was achieved with CPV extra-granular. Using CPV and CCS intra-granular resulted in increased disintegration time and Q₈₀. However, at a higher level of appx. 500 s and appx. 15 min, only SSG showed a process and location independent disintegration and dissolution performance.

The Effect of Process Variables and Binder Concentration on Tabletability of Metformin Hydrochloride and Acetaminophen Granules Produced by Twin Screw Melt Granulation with Different Polymeric Binders

In twin screw melt granulation, granules are produced by passing mixtures of drug substances and polymeric binders through twin screw extruder such that temperatures are maintained below melting point of drugs but above glass transition of polymers used, whereby the polymers coat surfaces of drug particles and cause their agglomeration into granules. Since various formulation factors, such as binder type and concentration, and processing variables like extrusion temperature, screw configuration, and screw speed, can influence the granulation process, the present investigation was undertaken to study their effects on tabletability of granules produced. Three different types of polymeric binders, Klucel® EXF (hydroxypropyl cellulose), Eudragit® EPO (polyacrylate binder), and Soluplus® (polyvinyl caprolactam-co-vinyl acetate-ethylene glycol graft polymer), were used at 2, 5, and 10% concentrations. Metformin hydrochloride (HCl) (mp: 222°C) and acetaminophen (mp: 169°C) were used as model drugs, and drug-polymer mixtures with metformin HCl were extruded at 180, 160, and 130°C, while those with acetaminophen were extruded at 130 and 110°C. Other process variables included screw configurations: low, medium, and high shear for metformin HCl, and low and medium shear for acetaminophen; feed rates: 20 and 60 g/min; and screw speed of 100 and 300 RPM. Formulation and process variables had significant impact on tabletability. The target tensile strength of ≥2 MPa could be obtained with all polymers and at all processing temperatures when metformin HCl was granulated at 180°C and acetaminophen at 130°C. At other temperatures, the target tensile strength could be achieved at certain specific sets of processing conditions.

Twin-Screw Melt Granulation for Oral Solid Pharmaceutical Products

This article highlights the advantages of pharmaceutical continuous melt granulation by twin-screw extrusion. The different melt granulation process options and excipients are described and compared, and a case is made for expanded use of twin-screw melt granulation since it is a flexible and continuous process. Methods for binder selection are profiled with a focus on rheology and physical stability impacts. For twin-screw melt granulation, the mechanism of granulation and process impact on granule properties are described. Pharmaceutical applications of melt granulation ranging from immediate release of soluble and insoluble APIs, taste-masking, and sustained release formulation are reviewed, demonstrating the range of possibilities afforded by twin-screw melt granulation.

Application of Machine-Learning Algorithms for Better Understanding of Tableting Properties of Lactose Co-Processed with Lipid Excipients

Co-processing (CP) provides superior properties to excipients and has become a reliable option to facilitated formulation and manufacturing of variety of solid dosage forms. Development of directly compressible formulations with high doses of poorly flowing/compressible active pharmaceutical ingredients, such as paracetamol, remains a great challenge for the pharmaceutical industry due to the lack of understanding of the interplay between the formulation properties, process of compaction, and stages of tablets’ detachment and ejection. The aim of this study was to analyze the influence of the compression load, excipients’ co-processing and the addition of paracetamol on the obtained tablets’ tensile strength and the specific parameters of the tableting process, such as (net) compression work, elastic recovery, detachment, and ejection work, as well as the ejection force. Two types of neural networks were used to analyze the data: classification (Kohonen network) and regression networks (multilayer perceptron and radial basis function), to build prediction models and identify the variables that are predominantly affecting the tableting process and the obtained tablets’ tensile strength. It has been demonstrated that sophisticated data-mining methods are necessary to interpret complex phenomena regarding the effect of co-processing on tableting properties of directly compressible excipients.

How Does the Dissimilarity of Screw Geometry Impact Twin-screw Melt Granulation?

Using a model formulation of 80% gabapentin and 20% hydroxypropyl cellulose (Klucel^TM), we investigate how differences in the geometry of mixing elements in the Leistritz Nano-16 and Micro-18 extruders affect granulation mechanisms and the properties of the resulting granules. Two extruders, Leistritz Nano-16 and Micro-18, commonly used in development and manufacturing, respectively, were used. The kneading blocks of the Nano-16 extruder are less efficient in dispersive mixing than the kneading blocks of the Micro-18 due to the thinner discs (2.5 mm wide) of the Nano-16. Therefore, our model formulation could be granulated only under a higher degree of fill (DF) by enhancing the axial compaction and heating of the barrel. In contrast, the thicker (5 mm wide) kneading blocks of the Micro-18 extruder provide efficient dispersive mixing that enables granulation without axial compaction and barrel heating. The higher specific mechanical energy (SME) achieved at higher screw speeds and lower feed rates led to more granulation. Because of the difference in granulation mechanisms between the two extruders, critical processing parameters also differed. Tabletability and degradant content of granules correlated positively with DF for the Nano-16 but with SME for the Micro-18 extruder.

Pre-plasticization of thermal binder facilitates processing and granule growth during melt granulation of gabapentin using co-rotating twin screw extruder

Plasticization, a common method of reducing the polymer melt viscosity in plastics extrusion, was investigated to improve the processability of a pharmaceutical formulation during twin-screw melt granulation. The thermolabile drug gabapentin was used as a model compound given previous work showed the benefit of preparing 80% drug loading gabapentin granules with hydroxypropyl cellulose as thermal binder. The plasticizer triethyl citrate was selected based on physicochemical compatibility with both the thermal binder and gabapentin by assessing polymer melt rheology and drug stability, respectively. Gabapentin was melt granulated at 80% drug loading with pre-plasticized binder using a co-rotating twin-screw extruder. The chemical stability and tabletability of the pre-plasticized granules were assessed to evaluate granule tabletability, drug stability, and process robustness. The granulation of gabapentin was facilitated by pre-plasticization, showing both increased granule growth and the ability to optimize processing conditions by lowering processing temperature. Pre-plasticization of thermal binder was therefore shown to be beneficial during melt granulation as a method of optimizing processing conditions while maintaining granule robustness.

Melt granulation: A comparison of granules produced via high-shear mixing and twin-screw granulation

Melt granules of DI-CAFOS® A12 and 15% (w/w) Kolliphor® P407 were manufactured in a twin-screw granulator (TSG) at five different conditions (screw speed and throughput varied) and compared to granules manufactured in a high-shear granulator (HSG) (rotation speed of chopper/impeller and granulation time varied). Evaluated granules characteristics were process yield, particle-size distribution (PSD), particle morphology, flowability, porosity, specific surface area (SSA), tabletability, compressibility and binder distribution. Compared to TSG, granules produced from HSG were more spherical in shape with lower porosity, smaller mean particle size and a superior flowability. Granules made by TSG showed a more elongated structure, higher porosity and larger mean particle size with smaller SSA instead. Concerning the compression process of granules, tablets made of TSG granules exhibited a higher tabletability compared to HSG granules, whereas the compressibility remained similar. In the case of the TSG granules, energy-dispersive-X-ray (EDX) measurements of the tablet surface indicated an enhanced homogenous binder distribution. Additionally, the EDX-analyses determined that more binder was available between the individual particles, resulting in a stronger bonding.

Effect of Hydroxypropyl Cellulose Level on Twin-Screw Melt Granulation of Acetaminophen

This study investigated the effect of binder level on the physicochemical changes and tabletability of acetaminophen (APAP)-hydroxypropyl cellulose (HPC) granulated using twin-screw melt granulation. Even at 5% HPC level, the tablet tensile strength achieved up to 3.5 MPa. A minimum of 10% HPC was required for the process robustness. However, 20% HPC led to tabletability loss, attributable to the high mechanical strength of APAP granules. The over-granulated APAP granules had thick connected HPC scaffold and low porosity. Consequently, these granules were so strong that they underwent a lower degree of fracture under compression and higher elastic recovery during decompression. HPC was enriched on the surface of APAP extrudates at all HPC levels. Amorphous APAP was also observed on the extrudate surface at 20% HPC level, and it recrystallized within 24 h storage. To achieve a robust process and optimal improvement in APAP tabletability, the preferred HPC level was 10 to 15%.

Twin-screw melt granulation: Current progress and challenges

Twin-screw melt granulation (TSMG) is a new alternative method for granulation that offers several advantages over wet and dry granulation methods. TSMG has rapidly gained interest over recent years in the pharmaceutical industry. Since it is an inherently continuous process with controlled temperature and shear history, TSMG produces products with more consistent quality than the batch process. Several studies have investigated how various formulation and processing parameters influence granulation behavior and granule properties; however, there are still challenges that require a better mechanistic understanding. This review summarizes the current progress of TSMG while highlighting how various formulation and process parameters affect the physicochemical properties of granules. The challenges related to the process-induced physicochemical changes of drug substances are also discussed.

Continuous twin screw granulation - An advanced alternative granulation technology for use in the pharmaceutical industry

Hot melt extrusion has been an exciting technology in the pharmaceutical field owing to its novel applicability. Twin-screw granulation presents a great potential and offers many advantages relative to conventional granulation processes. Different twin-screw granulation techniques, such as twin-screw dry granulation, twin-screw wet granulation, and twin-screw melt granulation, are currently being developed as robust and reproducible granulation processes. The competence of twin-screw granulation as a continuous manufacturing process has contributed to its suitability as an alternative granulation option within the pharmaceutical industry. In this article, different types of twin-screw granulation techniques were discussed. In addition, the screw elements, scale-up process, continuous twin-screw granulation which involves process analytical tools, and excipients were explored. This economical, industrially scalable process can be automated for continuous manufacturing to produce granules for the development of oral solid dosage forms. However, extensive research using process analytical tools is warranted to develop processes for the continuous manufacture of granules.

Metformin Hydrochloride and Sitagliptin Phosphate Fixed-Dose Combination Product Prepared Using Melt Granulation Continuous Processing Technology

The development of oral solid dosage forms, such as tablets that contain a high dose of drug(s), requires polymers and other additives to be incorporated at low levels as possible, to keep the final tablet weight low, and, correspondingly, the dosage form size small enough to be acceptable from a patient perspective. Additionally, a multi-step batch-based manufacturing process is usually required for production of solid dosage forms. This study presents the development and production, by twin-screw melt granulation technology, of a high-dose immediate-release fixed-dose combination (FDC) product of metformin hydrochloride (MET) and sitagliptin phosphate (SIT), with drug loads of 80% w/w and 6% w/w, respectively. For an 850/63 mg dose of MET/SIT, the final weight of the caplets was approximately 1063 mg compared with 1143 mg for the equivalent dose in Janumet®, the marketed product. Mixtures of the two drugs and polymers were melt-granulated at temperatures below the individual melting temperatures of MET and SIT (231.65 and 213.89°C, respectively) but above the glass transition temperature or melting temperature of the binder(s) used. By careful selection of binders, and processing conditions, direct compressed immediate-release caplets with desired product profiles were successfully produced. The melt granule formulations before compression showed good flow properties, were larger in particle size than individual starting API materials and were easily compressible. Melt granulation is a suitable platform for developing direct compressible high-dose immediate-release solid dosage forms of FDC products.

Tablet Scoring: Current Practice, Fundamentals, and Knowledge Gaps

Oral solid dosage formulations and/or tablets have remained the preferred route of administration by both patients and health care practitioners. Oral tablets are easy to administer, they are non-invasive and cause less risk adversity. Because of the lack of commercially available tablet dose options, tablets are being split or partitioned by users. Tablet scoring refers to the breakage of a tablet to attain a desired efficacy dose and is an emerging concept in the pharmaceutical industry. The primary reason for the tablet scoring practice is to adjust the dose: dose tapering or dose titrating. Other reasons for tablet partitioning are to facilitate dose administration, particularly among the pediatric and the geriatric patient population, and to mitigating the high cost of prescription drugs. The scope of this review is to: (1) evaluate the advantages and inconveniences associated with tablet scoring/portioning, and (2) identify factors in the formulation and the manufacturing of tablets that influence tablet splitting. Whereas tablet partitioning has been a common practice, there is a lack of understanding regarding the fundamentals underpinning the performance of tablets with respect to splitting. Several factors can influence tablet partitioning: tablet size, shape, and thickness. A requirement has recently been set by the European Pharmacopoeia and the U.S. Food and Drug Administration for the uniformity of mass of subdivided tablets. For breaking ease, an in-vivo reference test and a routinely applicable in-vitro test need to be established.

An update on the contribution of hot-melt extrusion technology to novel drug delivery in the twenty-first century: part II

INTRODUCTION

Interest in hot-melt extrusion (HME) technology for novel applications is growing day by day, which is evident from several hundred publications within the last 5 years. HME is a cost-effective, solvent free, 'green' technology utilized for various formulations with low investment costs compared to conventional technologies. HME has also earned the attention of the pharmaceutical industry by the transformation of this technology for application in continuous manufacturing.

AREAS COVERED

Part II of the review focuses on various novel opportunities or innovations of HME such as multiple component systems (co-crystals, co-amorphous systems and salts), twin-screw granulation, semi-solids, co-extrusion, abuse deterrent formulations, solid self-emulsifying drug delivery systems, chronotherapeutic drug delivery systems, and miscellaneous applications.

EXPERT OPINION

HME is being investigated as an alternative technology for preparation of multicomponent systems such as co-crystals and co-amorphous techniques. Twin-screw granulation has gained increased interest in preparation of granules via twin-screw melt granulation or twin-screw dry granulation. This novel application of the HME process provides a promising alternate approach in the formulation of granules and solid dosage forms. However, this technology may need to be further investigated for scalability aspects of these novel applications for industrial production.

Effects of Processing on a Sustained Release Formulation Prepared by Twin-Screw Dry Granulation

Dry granulation is an indispensable process used to improve the flow property of moisture-sensitive materials. Considering the limitations of currently available dry granulation techniques, it is necessary to develop a novel technique. In this study, a twin-screw dry granulation (TSDG) technology was successfully applied to produce a sustained-release dry granule formulation, which was subsequently compressed into sustained-release tablets. Based on a preliminary study, theophylline was selected as model drug, Klucel^™ EF, Ethocel^™, and magnesium stearate were selected as excipients. A Resolution V Irregular Fraction Design was applied to determine the effect of different processing parameters (screw speed, feeding rate, barrel temperature, and screw configuration) on product properties (flow properties, particle size distribution, and dissolution time). A reliable model was achieved by combining the data obtained, and processing parameters were automatically optimized to attain the setting goal. In general, TSDG was demonstrated to be an alternative method for the preparation of dry granules. The continuous processing nature, simplicity of operation, and ease of optimization made TSDG competitive compared with other conventional dry granulation techniques.

Effects of thermal binders on chemical stabilities and tabletability of gabapentin granules prepared by twin-screw melt granulation

The effect of thermal binders on the physicochemical properties of gabapentin, a thermally labile drug, in granules prepared using twin-screw melt granulation was investigated in this study. Hydroxypropyl cellulose (HPC), a thermoplastic high molecular-weight binder, was compared against conventional low molecular-weight semi-crystalline thermal binders PEG 8000 and Compritol. Both the chemical degradation and polymorph form change of gabapentin were analyzed. The effects of particle size and molecular weight of HPC on the properties of granules were also studied. To overcome the high melt viscosity of HPC, higher barrel temperatures and higher specific mechanical energy were required to attain suitable granules. As a result, higher levels of gabapentin degradant were observed in HPC-based formulations. However, gabapentin form change was not observed in all formulations. Smaller particle size and lower molecular weight of HPC led to faster granule growth. The tabletability of granules was insensitive to the variations in particle size and molecular weight of HPC. Gabapentin crystal size reduction, HPC size reduction, and HPC enrichment on granule surface were observed for HPC-based granules.

Comparison of fused-filament fabrication to direct compression and injection molding in the manufacture of oral tablets

Oral tablets are a convenient form to deliver active pharmaceutical ingredients (API) and have a high level of acceptance from clinicians and patients. There is a wide range of excipients available for the fabrication of tablets thereby offering a versatile platform for the delivery of therapeutic agents to the gastrointestinal tract. However, the geometry of tablets is limited by conventional manufacturing processes. This study aimed to compare three manufacturing processes in the production of flat-faced oral tablets using the same formulation composed of a polymer blend and caffeine as a model drug: fused-filament fabrication (FFF), direct compression (DC) and injection molding (IM). Hot-melt extrusion was used to convert a powder blend into feedstock material for FFF and IM processes, while DC was performed on the powder mixture. Tablets were produced with the same dimensions and were characterized for their physical and dissolution properties. There were statistical differences in the physical properties and drug release profiles of the tablets produced by the different manufacturing processes. DC tablets displayed immediate release, IM provided sustained release over 48 h, and FFF tablets displayed both release types depending on the printing parameters. FFF continues to demonstrate high potential as a manufacturing process for the efficient production of personalized oral tablets.

Exploratory studies in heat-assisted continuous twin-screw dry granulation: A novel alternative technique to conventional dry granulation

Dry granulation is the preferred technique for solvent-sensitive products, especially drugs with stability problems such as hydrolysis. Twin-screw granulation is a continuous granulation technique, offering a potential alternative to conventional dry granulation techniques such as roller compaction. The major advantage of twin-screw granulation is the ability to adjust process parameters of dry granulation without compromising the compression properties. This study was aimed to perform exploratory studies of heat-assisted continuous twin-screw dry granulation process to formulate sustained release tablets for APIs with different melting points: theophylline, acetaminophen and lidocaine hydrochloride hydrate. Granulation feasibility was studied with different binders (e.g. Klucel™ EF, Kollidon® VA64), sustained release agents (e.g. Klucel™ MF, Eudragit® RSPO) and diluents at various drug loads. The processing conditions were below the melting point or glass transition temperature of the formulation ingredients. After successful granulation, DSC and XRD studies revealed the crystalline nature of the granules and FTIR studies showed no interaction of the API with the excipients. The granules were compressed into sustained release tablets without any compressibility issues. The tablets were stable after testing for 6 months at 25 °C/60% RH. This novel continuous dry granulation technique may offer an excellent alternative to conventional dry granulation techniques.

Effect of formulation and process variables on lipid based sustained release tablets via continuous twin screw granulation: A comparative study

The current study's aim is to prepare lipid based sustained release tablets via a twin-screw granulation technique and compare those dosage forms with conventional techniques, namely wet granulation and direct compression. The granules were successfully manufactured in a single-step, continuous twin-screw granulation process with a low proportion of binder (Klucel™ EF, HPC SSL) using Compritol® 888 ATO, Precirol® ATO 5 and Geleol™ as sustained release agents. The granules prepared showed good flow characteristics and compaction properties. DSC and XRD studies were conducted to characterize the granules prepared via a twin-screw granulation method and the results demonstrated the crystalline nature of lipids within the granules. FTIR data indicated that there were no interactions with the formulation components investigated. The formulations developed by all three methods were compressed into tablets with a mechanical strength of 14-16 KP. The tablets formulated were characterized for physicochemical properties, in vitro drug release studies, water uptake and erosion studies. These results showed that the drug was not completely released after 24 h for tablets developed by the wet granulation process using all three lipids. The tablets prepared by the direct compression method demonstrated a burst release within 8 to 10 h from Precirol ATO 5® and Geleol™ formulations compared to Compritol® 888 ATO. However, tablets prepared using twin-screw granulation exhibited sustained release of the drug over 24 h and the water uptake and erosion results were in accordance with dissolution data. Stability data for 45 days at accelerated conditions (40 °C/75% RH) showed similar release profiles with ƒ2 values above 50 for all of the twin screw granulation formulations, indicating the suitability of the process for formulating sustained release tablets. These findings of a single-step, continuous twin-screw granulation process are novel and demonstrate new opportunities for development of sustained release tablets.

Pharmaceutical Applications of Cellulose Ethers and Cellulose Ether Esters

Cellulose ethers have proven to be highly useful natural-based polymers, finding application in areas including food, personal care products, oil field chemicals, construction, paper, adhesives, and textiles. They have particular value in pharmaceutical applications due to characteristics including high glass transition temperatures, high chemical and photochemical stability, solubility, limited crystallinity, hydrogen bonding capability, and low toxicity. With regard to toxicity, cellulose ethers have essentially no ability to permeate through gastrointestinal enterocytes and many are already in formulations approved by the U.S. Food and Drug Administration. We review pharmaceutical applications of these valuable polymers from a structure-property-function perspective, discussing each important commercial cellulose ether class; carboxymethyl cellulose, methyl cellulose, hydroxypropylcellulose, hydroxypropyl methyl cellulose, and ethyl cellulose, and cellulose ether esters including hydroxypropyl methyl cellulose acetate succinate and carboxymethyl cellulose acetate butyrate. We also summarize their syntheses, basic material properties, and key pharmaceutical applications.

Development and Optimization of a Wet Granulation Process at Elevated Temperature for a Poorly Compactible Drug Using Twin Screw Extruder for Continuous Manufacturing

The objective of this study was to enhance tabletability of a poorly compactible drug, acetaminophen, by wet granulation using twin screw extruder at high temperature. It was desired that there would be minimum amounts of excipients used and the granules obtained after extrusion would be dry and fall within a size range suitable for tableting without any further processing. Mixtures of acetaminophen (95%) with binders (5% povidone or partially pregelatinized starch) were wet granulated through twin screw extruder at 70°C by adding 7% w/w water. The process had a short granulation time (<1 min), and, on account of the elevated processing temperature used, no drying after extrusion was needed. By optimizing formulation and processing parameters, >90% granules in the size range of 125 to 1000 μm (<3% above 1000 μm and <7% below 125 μm) were obtained without any milling. When the granules were compressed by adding 1% disintegrant and 0.5% lubricant extragranularly, tablets produced (93.6% drug load) had good mechanical strength having hardness >1.7 MPa, which was superior to that of tablets prepared by conventional high shear wet granulation. As the granules could be extruded continuously and did not require drying and milling, the method was amenable to continuous processing.

Investigating the Use of Polymeric Binders in Twin Screw Melt Granulation Process for Improving Compactibility of Drugs

Traditionally, the melt granulation for pharmaceutical products was performed at low temperature (<90°C) with high-shear granulators using low-melting waxy binders, and tablets produced using such granules were not amenable to large-scale manufacturing. The situation has changed in recent years by the use of twin screw extruder where the processing temperature could be increased to as high as 180°C and polymers with high T_g could be used as binders. In this study, different polymeric binders were screened for their suitability in improving compactibility of 2 drugs, metformin hydrochloride and acetaminophen, by twin screw melt granulation. Processing temperatures for the 2 drugs were set at 180°C and 130°C, respectively. Screw configuration, screw speed, and feed rate were optimized such that all polymeric binders used produced granules. Several hydroxypropyl cellulose, hydroxypropyl methylcellulose, polyvinylpyrrolidone, and methacrylate-based polymers, including Klucel^® EXF, Eudragit^® EPO, and Soluplus^®, demonstrated good tablet tensile strength (>2 MPa) when granules were produced using only 10% wt/wt polymer concentration. Certain polymers provided acceptable compactibility even at 5% wt/wt. Thus, twin screw melt granulation process may be used with different polymers at a wide range of temperature. Due to low excipient concentration, this granulation method is especially suitable for high-dose tablets.

Stearic acid and high molecular weight PEO as matrix for the highly water soluble metoprolol tartrate in continuous twin-screw melt granulation

Granules with release-sustaining properties were developed by twin screw hot melt granulation (HMG) using a combination of stearic acid (SA) and high molecular weight polyethylene oxide (PEO) as matrix for a highly water soluble model drug, metoprolol tartrate (MPT). Earlier studies demonstrated that mixing molten SA and PEO resulted in hydrogen bond formation between hydroxyl groups of fatty acid molecules and ether groups in PEO chains. These molecular interactions might be beneficial in order to elevate the sustained release effect of drugs from a SA/PEO matrix. This study aims to investigate the continuous twin screw melt granulation technique to study the impact of a SA/PEO matrix on the dissolution rate of a highly water soluble drug (MPT). Decreasing the SA/PEO ratio improved the release-sustaining properties of the matrix. The solid state of the granules was characterized using differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) and near infrared chemical imaging (NIR-CI) in order to understand the dissolution behavior. The results revealed a preferential interaction of the MPT molecules with stearic acid impeding the PEO to form hydrogen bonds with the stearic acid chains. However, this allowed the PEO chains to recrystallize inside the stearic acid matrix after granulation, hence, elevating the release-sustaining characteristics of the formulation.