Solid-state properties of powders in the formulation and processing of solid dosage forms

Characterization of Pharmaceutical Tablets by X-ray Tomography

Solid dosage forms such as tablets are extensively used in drug administration for their simplicity and large-scale manufacturing capabilities. High-resolution X-ray tomography is one of the most valuable non-destructive techniques to investigate the internal structure of the tablets for drug product development as well as for a cost effective production process. In this work, we review the recent developments in high-resolution X-ray microtomography and its application towards different tablet characterizations. The increased availability of powerful laboratory instrumentation, as well as the advent of high brilliance and coherent 3rd generation synchrotron light sources, combined with advanced data processing techniques, are driving the application of X-ray microtomography forward as an indispensable tool in the pharmaceutical industry.

Characterization of Mass Transfer within the Crystal-Solution Boundary Layer of l-Alanine {120} Faces Using Laser Interferometry during Growth and Dissolution

Crystallization and dissolution are important processes to consider in drug development as well as many other industrial processes. Many current growth and dissolution models are based on bulk solution properties and do not implicitly consider concentration variation close to the crystal surface-solution interface and how this is mediated by solute diffusive mass transfer. Solution boundary layer thickness and concentration distribution, for the {120} crystal habit face of single crystals of l-alanine in saturated aqueous solutions during both growth and dissolution processes, is measured as a function of super/undersaturation using a Mach-Zehnder optical interferometer system. Further analysis allows determination of the diffusion coefficient and mass flux within the boundary layer as well as whether the processes are controlled by mass transfer or crystal interfacial kinetics. The measurement of this study revealed that the {120} face was not saturated at its surface during growth or dissolution meaning both processes were somewhat limited by their crystal interfacial kinetics. Growth was limited by crystal interfacial kinetics at all supersaturations to the same degree, whereas dissolution had a mixed dependency on crystal interfacial kinetics and mass transfer at lower undersaturations becoming more limited by mass transfer at higher undersaturations. Boundary layer thickness increased with super/undersaturation but to a lesser degree than the increase in the concentration difference between the crystal surface and bulk solution leading to a higher mass flux of solute molecules through the boundary layer. At the same relative super/undersaturation mass flux of solute molecules was faster during dissolution which was concurrent with its increased surface to bulk solution concentration difference and boundary layer thickness.

Strategies for Managing Solid Form Transformation Risk in Drug Product

The International Conference of Harmonization (ICH) Q6A document provides guidance on setting specifications for new drug substances and drug products.¹ In this paper we focus on decision trees 4 (#1) to (#3) in the guidance related to solid-state form transformation. Form transformation could occur from use of high energy forms to overcome solubility challenges or stresses from manufacturing processes. The decision trees provide guidance on when and how polymorphic form changes should be monitored and controlled. However, guidance is high level and does not capture aspects related to assessments needed to understand if there is a risk of transformation or tools that can be integrated to understand the severity of bioavailability impact at different stages of development. The objective of this paper is therefore to provide comprehensive chemistry manufacturing and controls (CMC) and regulatory strategies to manage the risk of form transformation. This includes practical workflows for form transformation risk assessment, analytical tools to detect and quantify the transformation including their shortcomings, biopharmaceutical tools to understand the severity of transformation risk and if needed justify the limits based on clinical relevance. Finally, a few case studies are discussed that capture how the workflow can be used to manage transformation risk.

Relating Crystal Structure to Surface Properties: A Study on Quercetin Solid Forms

The surface energy and surface chemistry of a crystal are of great importance when designing particles for a specific application, as these will impact both downstream manufacturing processes as well as final product quality. In this work, the surface properties of two different quercetin solvates (quercetin dihydrate and quercetin DMSO solvate) were studied using molecular (synthonic) modeling and experimental techniques, including inverse gas chromatography (IGC) and contact angle measurements, to establish a relationship between crystal structure and surface properties. The attachment energy model was used to predict morphologies and calculate surface properties through the study of their growth synthons. The modeling results confirmed the surface chemistry anisotropy for the two forms. For quercetin dihydrate, the {010} facets were found to grow mainly by nonpolar offset quercetin-quercetin stacking interactions, thus being hydrophobic, while the {100} facets were expected to be hydrophilic, growing by a polar quercetin-water hydrogen bond. For QDMSO, the dominant facet {002} grows by a strong polar quercetin-quercetin hydrogen bonding interaction, while the second most dominant facet {011} grows by nonpolar π-π stacking interactions. Water contact angle measurements and IGC confirmed a greater overall surface hydrophilicity for QDMSO compared to QDH and demonstrated surface energy heterogeneity for both structures. This work shows how synthonic modeling can help in the prediction of the surface nature of crystalline particles and guide the choice of parameters that will determine the optimal crystal form and final morphology for targeted surface properties, for example, the choice of crystallization conditions, choice of solvent, or presence of additives or impurities, which can direct the crystallization of a specific crystal form or crystal shape.

A novel soluble lornoxicam-sodium chelate monohydrate with improved plasticity and tabletability

Lornoxicam (LOR), a BCS Ⅱ nonsteroidal anti-inflammatory drug, has been clinically utilized for moderate to severe acute pain management. However, it has poor water solubility and insufficient tabletability, leading to erratic absorption and challenge in tablet processability. This study reported a novel solid state of LOR (i.e., LOR sodium chelate monohydrate, LOR-Na·H₂O) with significantly improved solubility, dissolution rate and tabletability. The prepared chelate (CCDC No.: 2125157) contains LOR^-, Na⁺, and H₂O in a molar ratio of 1:1:1, where Na⁺ ions bridged with O(5) of amide group, and N(2) of pyridine group on LOR^-, as well as O(4) on H₂O through coordination bonds. LOR-Na·H₂O displayed a superior dissolution rate (5∼465 folds) than commercial LOR due to its increased wettability (contact angle: 74.5° vs 85.6°) and lower solvation free energy (∼2-fold). In addition, the significant improvement in tabletability was caused by high plasticity and deformability, which was attributed to its special interlayer gliding with weak bonding interactions across layers but strong coordination bonding interactions within layers. The novel LOR-Na·H₂O with significantly enhanced pharmaceutical performance offers a promising strategy for further product development.

A Digital Mechanistic Workflow for Predicting Solvent-Mediated Crystal Morphology: The α and β Forms of l-Glutamic Acid

The solvent-mediated crystal morphologies of the α and β polymorphic forms of l-glutamic acid are presented. This work applies a digital mechanistically based workflow that encompasses calculation of the crystal lattice energy and its constituent intermolecular synthons, their interaction energies, and their key role in understanding and predicting crystal morphology as well as assessing the surface chemistry, topology, and solvent binding on crystal habit growth surfaces. Through a comparison between the contrasting morphologies of the conformational polymorphs of l-glutamic acid, this approach highlights how the interfacial chemistry of organic crystalline materials and their inherent anisotropic interactions with their solvation environments direct their crystal habit with potential impact on their further downstream processing behavior.

Raman spectroscopic evaluation of crystallinity, chemical composition and stability of pharmaceutical powder aerosols

Raman spectroscopy was used to evaluate the effects of temperature and humidity on the physicochemical stability of inhalable spray-dried (SD) powders containing budesonide (BUD) and crystalline or amorphous lactose. Powders prepared by spray drying of BUD-lactose solution or suspension containing lactose crystals in BUD solution were stored for 0, 1 and 7 days at 25 °C/60 RH or 40 °C/75 RH. Bulk powders along with the large and small particle size fractions collected on stages 2 and 5, respectively, of the Next Generation Impactor (NGI) were chemically characterised. SD powder from solution contained BUD and lactose in amorphous form and both components were homogeneously distributed in bulk and in the particles collected from the two NGI stages. In contrast, SD powder from suspension showed heterogeneous distribution of lactose and drug in the particles containing crystalline lactose. After 1 day of storage at either condition, recrystallisation and changes in the chemical composition of the particles for the SD powder from solution occurred. The number of drug-only particles increased by 70 on stage 5, whereas most particles on stage 2 still contained both drug and lactose. These changes were not observed in the SD powder from suspension after storage, confirming superior stability of the SD powder obtained from suspension.

Sensing technologies and experimental platforms for the characterization of advanced oral drug delivery systems

Complex and miniaturized oral drug delivery systems are being developed rapidly for targeted, controlled drug release and improved bioavailability. Standard analytical techniques are widely used to characterize i) drug carrier and active pharmaceutical ingredients before loading into a delivery device (to ensure the solid form), and ii) the entire drug delivery system during the development process. However, in light of the complexity and the size of some of these systems, standard techniques as well as novel sensing technologies and experimental platforms need to be used in tandem. These technologies and platforms are discussed in this review, with a special focus on passive delivery systems in size range from a few 100 µm to a few mm. Challenges associated with characterizing these systems and evaluating their effect on oral drug delivery in the preclinical phase are also discussed.

Reduced deliquescency of isosorbide by cocrystallization and mechanisms for hygroscopicity

Isosorbide (ISO) is an effective hyperosmotic agent that can be administrated orally and is used as a therapeutic agent for brain pressure drop, glaucoma, and Meniere's disease. However, the critical relative humidity (CRH) of ISO is about 48% RH at 25 °C, and it deliquesces in humid environments. In this study, we attempted to reduce the deliquescence of ISO using cocrystallization and analyze the water adsorption mechanism from the crystal structure. Four new ISO cocrystals with piperazine (PZ), hydrochlorothiazide (HCT), 3,5-dihydroxybenzoic acid (35DHBA), or gallic acid (GA) were identified. The dynamic vapor sorption analyses demonstrated that all the cocrystals showed higher CRHs than the ISO crystal. Although water adsorption below the CRH was observed for all cocrystals, the water molecules adsorbed in the ISO-PZ and ISO-GA cocrystals were lower than those in the ISO crystal. Investigation of the crystal structures suggested that the amount of water adsorbed might be related to the degree of exposure of the ISO hydroxyl groups on the crystal surface. Given the CRH, water adsorption below the CRH, thermal stability, apparent dissolution rate, and toxicity level of the coformer, the ISO-GA cocrystal is the most suitable for preparing a solid formulation of ISO.

The impact of carbamazepine crystallinity on carbamazepine-loaded microparticle formulations

Crystallinity plays a vital role in the pharmaceutical industry. It affects drug manufacturing, development processes, and the stability of pharmaceutical dosage forms. An objective of this study was to measure and analyze the carbamazepine (CBZ) crystallinity before and after formulation. Moreover, it intended to determine the extent to which the crystallinity of CBZ would affect the drug loading, the particle size, and the release of CBZ from the microparticles. The CBZ microparticles were prepared by encapsulating CBZ in ethyl cellulose (EC) polymer using a solvent evaporation method. EC was used here as a release modifier polymer and polyvinyl alcohol (PVA) as an aqueous phase stabilizer. Factorial design was used to prepare the CBZ microparticle formulations, including polymer concentration, solvent (dichloromethane, ethyl acetate), PVA concentrations factor, the homogenization time, and homogenization speed. The crystallinity of CBZ was calculated utilizing differential scanning calorimetry (DSC) thermal analysis. The crystallinity was calculated from the enthalpy of CBZ. Enthalpy was analyzed from the area under the curve peak of CBZ standard and CBZ-loaded microparticles. DSC and ATR-FTIR assessed the possible interaction between CBZ and excipients in the microparticle. The prepared CBZ microparticles showed various changes in the crystallinity rate of CBZ. The changes in the rate of CBZ crystallinity had different effects on the particle size, the drug loading, and the release of CBZ from the polymer. Statistically, all studied factors significantly affected the crystallinity of CBZ after formulation to microparticles.

Transfer and scale-up of the manufacturing of orodispersible mini-tablets from a compaction simulator to an industrial rotary tablet press

Orodispersible mini-tablets (ODMTs) are a promising dosage form for the pediatric use showing increasing interest from pharmaceutical industry. However, a scale-up process for ODMTs from a compaction simulator to a rotary tablet press following FDA and EMA guidelines has not been performed and investigated yet. Isomalt (galenIQ™721) and Ludiflash® both excipients with proven suitability for the development of ODMTs have been investigated in transfer and scale-up from a compaction simulator to a rotary tablet press. ODMTs with isomalt and Ludiflash® were produced on the rotary tablet press monitoring the product temperature over time and assessing the properties of the residual powder in the feed shoe. Critical quality attributes like tensile strength, mass and disintegration time were evaluated. The transfer from compaction simulator to rotary tablet press succeeded as for both excipients similar disintegration times, tabletability and compactibility profiles were obtained. However, during scale-up, disintegration time significantly increases over time for both excipients. Monitoring of the product temperature revealed that with increasing batch size the product temperature increases as well having a significant impact on disintegration time. The properties of ODMTs produced with the residual powder are comparable in tabletability and disintegration time compared with ODMTs produced from fresh powder.

Interplay between packing, dimer interaction energy and morphology in a series of tricyclic imide crystals

Crystal morphology is a very important feature in many industrial applications. Tricyclic imides, derivatives of 10-oxa-4-azatricyclo[5.2.1.0^2,6]dec-8-ene-3,5-dione with differing small hydrophobic groups (Me, Et), were studied and grouped based on Etter's rule. Using experimental X-ray studies, dimer energy calculations, framework analysis and periodic DFT-D calculations, it is shown that knowledge of the hydrogen-bond pattern can be used to determine the final crystal shape. Molecules forming a ring hydrogen-bond motif crystallize as plate crystals with the {100} facet as the slowest growing, whereas those molecules forming an infinite hydrogen-bond motif in the crystal structure crystallize as needles with the {101} facet having the largest surface area.

Effect of drying procedures on the physicochemical properties and antioxidant activities of polysaccharides from Crassostrea gigas

Crassostrea gigas polysaccharides (CGP) were obtained by different drying methods: freeze-drying (FD), spray-drying (SD) or rotary evaporation-drying (RED). The physicochemical properties of CGP were evaluated on the basis of polysaccharide content, protein content, color characteristics, FT-IR spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Antioxidant activities were researched three different free radicals, including DPPH free radicals, ABTS free radicals and reducing power. The results demonstrated that FDCGP, SDCGP and REDCGP have different physicochemical properties and antioxidant activities. Contrasted with FDCGP and REDCGP, SDCGP exhibited stronger antioxidant abilities. Therefore, considering the polysaccharides appearances and antioxidant activities, the spray drying method is a decent selection for the preparation of such polysaccharides, and it should be selected for application in the food industry.

Humidity induced phase transformation of poloxamer 188 and its effect on physical stability of amorphous solid dispersion of AMG 579, a PDE10A inhibitor

Poloxamer 188, a commonly used emulsifying and solubilizing agent, was found to be the cause of crystallization of an investigational drug, AMG 579, from its amorphous solid dispersion at accelerated storage conditions. Investigation of this physical stability issue included thorough characterization of poloxamer 188 at non-ambient conditions. At 40°C, poloxamer 188 becomes deliquescent above relative humidity of 75%. Upon returning to ambient conditions, the deliquescent poloxamer 188 loses water and re-solidifies. The reversible phase transformation of poloxamer 188 may cause physical and chemical stability issues and this risk should be assessed when selecting it as an excipient for formulation development.

On the effects of blending, physicochemical properties, and their interactions on the performance of carrier-based dry powders for inhalation - A review

Blending drug and carrier powders to produce homogeneous drug-carrier adhesive mixtures is a key step in the production of dry powder inhaler (DPI) formulations. Although the blending conditions can result in different conclusions or probably change the outcome of a study entirely if being selected differently, there is a scarcity of data on the influence of blending processes on the physicochemical properties of bulk powder formulations and the follow-on effects on DPI performance. This paper provides an overview of the interactions between variables related to blending conditions (e.g. blending equipment, time, speed and sequence as well as environmental humidity) and powder physicochemical properties (e.g. size distribution, shape distribution, density, anomeric composition, electrostatic charge, surface, and bulk properties), and their effects on the performance of adhesive mixtures for inhalation in terms of drug content homogeneity, drug-carrier adhesion, and drug aerosolisation behaviour. The relevance of carrier payload, batch size and segregation was also discussed. Challenges and future directions were identified. This review therefore contributes towards a better understanding of the blending process, powder physicochemical properties, and their interlinked effects on the fundamental understanding of adhesive mixtures for inhalation. The knowledge gained is essential to ensure optimum blending and thereby controlled functionality of DPIs.

Recent advances and potential applications of modulated differential scanning calorimetry (mDSC) in drug development

Differential scanning calorimetry (DSC) is frequently the thermal analysis technique of choice within preformulation and formulation sciences because of its ability to provide detailed information about both the physical and energetic properties of a substance and/or formulation. However, conventional DSC has shortcomings with respect to weak transitions and overlapping events, which could be solved by the use of the more sophisticated modulated DSC (mDSC). mDSC has multiple potential applications within the pharmaceutical field and the present review provides an up-to-date overview of these applications. It is aimed to serve as a broad introduction to newcomers, and also as a valuable reference for those already practising in the field. Complex mDSC was introduced more than two decades ago and has been an important tool for the quantification of amorphous materials and development of freeze-dried formulations. However, as discussed in the present review, a number of other potential applications could also be relevant for the pharmaceutical scientist.

The Future of Pharmaceutical Manufacturing Sciences

The entire pharmaceutical sector is in an urgent need of both innovative technological solutions and fundamental scientific work, enabling the production of highly engineered drug products. Commercial-scale manufacturing of complex drug delivery systems (DDSs) using the existing technologies is challenging. This review covers important elements of manufacturing sciences, beginning with risk management strategies and design of experiments (DoE) techniques. Experimental techniques should, where possible, be supported by computational approaches. With that regard, state-of-art mechanistic process modeling techniques are described in detail. Implementation of materials science tools paves the way to molecular-based processing of future DDSs. A snapshot of some of the existing tools is presented. Additionally, general engineering principles are discussed covering process measurement and process control solutions. Last part of the review addresses future manufacturing solutions, covering continuous processing and, specifically, hot-melt processing and printing-based technologies. Finally, challenges related to implementing these technologies as a part of future health care systems are discussed.

Tribo-electrification and Powder Adhesion Studies in the Development of Polymeric Hydrophilic Drug Matrices

The generation of tribo-electric charge during pharmaceutical powder processing can cause a range of complications, including segregation of components leading to content uniformity and particle surface adhesion. This phenomenon becomes problematical when excipients are introduced to a powder mixture alongside the highly charging active pharmaceutical ingredient(s) (APIs). The aim of this study was to investigate the tribo-electric charging and adhesion properties of a model drug, theophylline. Moreover, binary powder mixtures of theophylline with methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC), having different polymer to drug ratios, were formed in order to study the impact of polymer concentration, particle size, substitution ratio and molecular size on the tribo-electric charging and surface adhesion properties of the drug. Furthermore, the relationship between tribo-electric charging and surface adhesion was also studied. The diversity in physicochemical properties of MC/HPMC has shown a significant impact on the tribo-electric charging and adhesion behaviour of theophylline. It was found that the magnitude of electrostatic charge and the level of surface adhesion of the API were significantly reduced with an increase in MC and HPMC concentration, substitution ratios and molecular size. In addition, the tribo-electric charge showed a linear relationship with particle surface adhesion, but the involvement of other forces cannot be neglected.

Effect of different drying methods on chemical composition and bioactivity of finger citron polysaccharides

Traditionally, people like to take dried finger citron fruits (FC) as adjuvant herbal medicines to treat a diversity of chronic diseases like asthma, hypertension and respiratory tract infections. Many healing properties are attributed to FC polysaccharides (FCPs), one of the main active ingredients of FC. Three drying methods, freeze drying (FDM), hot air drying (HDM) and vacuum drying methods (VDM) were comparatively studied on the physicochemical and antioxidant properties of FCPs. The results showed these FCPs were similar in UV and FT-IR spectrum. However, they showed significant differences (p<0.05) in yields of crude polysaccharides and contents of protein and ash. Compared with VDM and HDM, FDM resulted in the properties of FCPs with lower molecular weight distribution, higher reducing power and scavenging abilities on DPPH, OH, and O2(-). Available data obtained in vitro models suggested that FDM was an appropriate and effective treatment for obtaining crude polysaccharides from FC fruits. Hence, drying methods used for preparation of FCPs can affect physicochemical and associated functional properties.

Physicochemical characterization of the polysaccharide from Bletilla striata: effect of drying method

The polysaccharide from Bletilla striata, a traditional Chinese herbal medicine, was obtained by different drying techniques: vacuum-drying (BVPS) or vacuum freeze-drying (BFPS). The effect of drying method on the physicochemical properties of the B striata polysaccharide was evaluated using high size exclusion chromatography coupled to multiangle laser light scattering (HPSEC-MALLS), FT-IR and UV spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The monosaccharide analysis and pH test revealed that the polysaccharide derived from B. striata was a neutral polysaccharide that is composed of glucose and mannose. The solubility and moisture content test's results demonstrated that BFPS was greater than BVPS. The number average molecular weight (Mn) and the computed average molecular weight (Mw) of 99.3% BFPS were 7.297×10(4)g/mol and 9.545×10(4)g/mol, respectively, whereas the Mn and Mw of 97.6% BVPS were 1.218×10(5)g/mol and 1.472×10(5)g/mol, respectively. The FT-IR and UV results indicated that drying technique has little effect on the structure of the polysaccharide. The thermal analysis showed that weight loss event was at 307.85°C and 305.50°C to BVPS and BFPS, respectively. Furthermore, the XRD confirmed that the polysaccharide was the amorphous nature. However, both SEM and AFM images exhibited that the drying technique had a significant impact on the morphology and conformation of the polysaccharide.

The solid state, surface and morphological properties of p-aminobenzoic acid in terms of the strength and directionality of its intermolecular synthons

The lattice energy and crystal morphologies of the α and β forms of p-aminobenzoic acid are correlated to experimentally grown crystals by calculating their strength, directionality and chemical state of their bulk (intrinsic) and surface (extrinsic) synthons.

Tribo-electric charging and adhesion of cellulose ethers and their mixtures with flurbiprofen

The pervasiveness of tribo-electric charge during pharmaceutical processing can lead to the exacerbation of a range of problems including segregation, content heterogeneity and particle surface adhesion. The excipients, hydroxypropyl methylcellulose (HPMC) and methylcellulose (MC), are often used in drug delivery systems and so it is important to understand the impact of associated factors on their charging and adhesion mechanisms, however, little work has been reported in this area. Such phenomena become more prominent when excipients are introduced to a powder mixture alongside the active pharmaceutical ingredient(s) (APIs) with inter- and intra-particulate interactions giving rise to electrification and surface adhesion of powder particles. The aim of this study was to understand the impact of material attributes (particle size, hydroxypropyl (Hpo) to methoxyl (Meo) ratio and molecular size) on the charging and adhesion characteristics of cellulose ethers. Furthermore, a poorly compactible and highly electrostatically charged drug, flurbiprofen, was used to develop binary powder mixtures having different polymer to drug ratios and the relationship between tribo-electric charging and surface adhesion was studied. Charge was induced on powder particles and measured using a custom built device based on a shaking concept, consisting of a Faraday cup connected to an electrometer. The diversity in physicochemical properties has shown a significant impact on the tribo-electric charging and adhesion behaviour of MC and HPMC. Moreover, the adhesion and electrostatic charge of the API was significantly reduced when MC and HPMC were incorporated and tribo-electric charging showed a linear relationship (R(2)=0.81-0.98) with particle surface adhesion, however, other factors were also involved. It is anticipated that such a reduction in charge and particle surface adhesion would improve flow and compaction properties during processing.

Evidence-based nanoscopic and molecular framework for excipient functionality in compressed orally disintegrating tablets

The work investigates the adhesive/cohesive molecular and physical interactions together with nanoscopic features of commonly used orally disintegrating tablet (ODT) excipients microcrystalline cellulose (MCC) and D-mannitol. This helps to elucidate the underlying physico-chemical and mechanical mechanisms responsible for powder densification and optimum product functionality. Atomic force microscopy (AFM) contact mode analysis was performed to measure nano-adhesion forces and surface energies between excipient-drug particles (6-10 different particles per each pair). Moreover, surface topography images (100 nm2-10 µm2) and roughness data were acquired from AFM tapping mode. AFM data were related to ODT macro/microscopic properties obtained from SEM, FTIR, XRD, thermal analysis using DSC and TGA, disintegration testing, Heckel and tabletability profiles. The study results showed a good association between the adhesive molecular and physical forces of paired particles and the resultant densification mechanisms responsible for mechanical strength of tablets. MCC micro roughness was 3 times that of D-mannitol which explains the high hardness of MCC ODTs due to mechanical interlocking. Hydrogen bonding between MCC particles could not be established from both AFM and FTIR solid state investigation. On the contrary, D-mannitol produced fragile ODTs due to fragmentation of surface crystallites during compression attained from its weak crystal structure. Furthermore, AFM analysis has shown the presence of extensive micro fibril structures inhabiting nano pores which further supports the use of MCC as a disintegrant. Overall, excipients (and model drugs) showed mechanistic behaviour on the nano/micro scale that could be related to the functionality of materials on the macro scale.

Compressed orally disintegrating tablets: excipients evolution and formulation strategies

INTRODUCTION

Orally disintegrating tablets (ODTs) have emerged as one of the novel solid oral dosage forms with a potential to deliver a wide range of drug candidates to both paediatric and geriatric patient populations. Of the plethora of available technologies, compression of excipients offers a cost-effective and translatable methodology for the manufacture of ODTs.

AREAS COVERED

The review is a modest endeavour from the authors to assemble literature published over the last couple of decades on formulation development of compressed ODT. It describes the main ODT excipients used since the introduction of this dosage form in the 1990s and explores the switch from cellulose-based excipients towards sugar/polyols. Furthermore, it unfolds the key properties of ODT fillers, binders and disintegrants with an emphasis on their advantages and drawbacks. The review also provides a critical assessment of the various strategies employed for performance enhancement of compressed ODT with a focus on the underlying mechanisms for fast disintegration and acceptable mechanical strength.

EXPERT OPINION

Recent increase in the total number of compression-based technologies for ODT development promises to reduce the manufacturing cost of this dosage form in the future. However, some of the developed methods may affect the stability of tablets due to susceptibility to moisture, collapse of pores or the generation of less stable polymorphs which require rigorous testing prior to commercialization.

Probing interfaces between pharmaceutical crystals and polymers by neutron reflectometry

Pharmaceutical powder engineering often involves forming interfaces between the drug and a suitable polymer. The structure at the interface plays a critical role in the properties and performance of the composite. However, interface structures have not been well understood due to a lack of suitable characterization tool. In this work, we have used ellipsometry and neutron reflectometry to characterize the structure of such interfaces in detail. Ellipsometry provided a quick estimate of the number of layers and their thicknesses, whereas neutron reflectometry provided richer structural information such as density, thickness, roughness, and intermixing of different layers. The combined information allowed us to develop an accurate model about the layered structure and provided information about intermixing of different layer components. Systematic use of these characterization techniques on several model systems suggests that the nature of the polymer had a small effect on the interfacial structure, while the solvent used in polymer coating had a large effect. These results provide useful information on the efforts of engineering particle properties through the control of the interfacial chemistry.

An insight into water of crystallization during processing using vibrational spectroscopy

Many organic molecules used as drugs can incorporate water into their crystal lattice. These compounds are also prone to processing-induced transformations (PITs) because processing often exposes the compounds to moisture, heat and mechanical stress. The aim of this review is to provide an overview of the possibilities for following and understanding hydrate/anhydrate transformations using vibrational spectroscopy (mid-infrared, near-infrared, Raman and terahertz). The review begins with a general section on hydrates, followed by considerations on the impact of these on drug products and a description of transformation mechanisms of hydrates. Moreover, a general introduction is given for the spectroscopic techniques together with a discussion of critical issues for quantification models. Unit operations that may induce transformations in hydrate systems are discussed with focus on the published work on the use of spectroscopy to derive information from these processes. Finally, the effect of excipients on PITs is discussed.

Effects of drying methods on the physicochemical and compressional characteristics of Okra powder and the release properties of its metronidazole tablet formulation

A study has been made of the effects of sun and oven drying methods on the physicochemical characteristics and compressibility of Okra powder and the release properties of its metronidazole tablet formulation. Corn starch was used as the reference standard. The mechanical properties of the tablets were evaluated using crushing strength and friability, while the release properties were determined using the disintegration times and dissolution rates. The results obtained showed that sun-dried Okra powder had smaller particle size, exhibited good flow and possessed higher hydration and swelling capacities compared to the oven dried samples. The compressibility of Okra powders assessed by the indices of plasticity from Heckel (Py) and Kawakita plots (Pk) showed that sun dried Okra powders had higher Py but lower Pk values than the oven-dried Okra powder. Metronidazole tablets formulated with oven dried Okra powder formed stronger tablets than tablets containing sun dried Okra powder. Generally, tablets containing sun dried Okra powders had faster disintegration and dissolution than tablets formulated with oven-dried powder. The results suggest that the choice of drying method during the processing of pharmaceutical raw materials is critical to its physicochemical properties and the release properties of its tablet formulations.