A material science perspective of pharmaceutical solids

Amorphous Solid Dispersion as Drug Delivery Vehicles in Cancer

Cancer treatment has improved over the past decades, but a major challenge lies in drug formulation, specifically for oral administration. Most anticancer drugs have poor water solubility which can affect their bioavailability. This causes suboptimal pharmacokinetic performance, resulting in limited efficacy and safety when administered orally. As a result, it is essential to develop a strategy to modify the solubility of anticancer drugs in oral formulations to improve their efficacy and safety. A promising approach that can be implemented is amorphous solid dispersion (ASD) which can enhance the aqueous solubility and bioavailability of poorly water-soluble drugs. The addition of a polymer can cause stability in the formulations and maintain a high supersaturation in bulk medium. Therefore, this study aimed to summarize and elucidate the mechanisms and impact of an amorphous solid dispersion system on cancer therapy. To gather relevant information, a comprehensive search was conducted using keywords such as "anticancer drug" and "amorphous solid dispersion" in the PubMed, Scopus, and Google Scholar databases. The review provides an overview and discussion of the issues related to the ASD system used to improve the bioavailability of anticancer drugs based on molecular pharmaceutics. A thorough understanding of anticancer drugs in this system at a molecular level is imperative for the rational design of the products.

Fundamental advances in hydrogels for the development of the next generation of smart delivery systems as biopharmaceuticals

Recent advances in developing and applying therapeutic peptides for anticancer, antimicrobial and immunomodulatory remedies have opened a new era in therapeutics. This development has resulted in the engineering of new biologics as part of a concerted effort by the pharmaceutical industry. Many alternative routes of administration and delivery vehicles, targeting better patient compliance and optimal therapeutic bioavailability, have emerged. However, the design of drug delivery systems to protect a range of unstable macromolecules, including peptides and proteins, from high temperatures, acidic environments, and enzymatic degradation remains a priority. Herein, we give chronological insights in the development of controlled-release drug delivery systems that occurred in the last 70 years or so. Subsequently, we summarise the key physicochemical characteristics of hydrogels contributing to the development of protective delivery systems concerning drug-targeted delivery in the chronospatial domain for biopharmaceuticals. Furthermore, we shed some light on promising hydrogels that can be utilised for systemic bioactive administration.

Cocrystals; basic concepts, properties and formation strategies

Cocrystallization is an old technique and remains the focus of several research groups working in the field of Chemistry and Pharmacy. This technique is basically in field for improving physicochemical properties of material which can be active pharmaceutical ingredients (APIs) or other chemicals with poor profile. So this review article has been presented in order to combine various concepts for scientists working in the field of chemistry, pharmacy or crystal engineering, also it was attempt to elaborate concepts belonging to crystal designing, their structures and applications. A handsome efforts have been made to bring scientists together working in different fields and to make chemistry easier for a pharmacist and pharmacy for chemists pertaining to cocrystals. Various aspects of chemicals being used as co-formers have been explored which predict the formation of co-crystals or molecular salts and even inorganic cocrystals.

On the dimorphism of prednisolone: The topological pressure-temperature phase diagram involving forms I and II

The dimorphism of the corticosteroid anti-inflammatory drug prednisolone has been investigated by the construction of a topological pressure-temperature phase diagram, using crystallographic and calorimetric data. The system is enantiotropic, because the temperature of the I-II equilibrium under atmospheric conditions (400 - 463 K) is lower than that of the two melting equilibria (518.7 K for form II and 526.3 K for form I). The slope of the I-II equilibrium in the pressure-temperature phase diagram is negative and relatively steep; therefore, form II, which is the stable form at room temperature, will not easily encounter conditions where form I will become stable even under industrial processing conditions. On the other hand, extreme small amounts of form I have been observed to spontaneously transform into form II in a time interval of about six years at room temperature and it can be concluded that although form I is very persistent under ambient conditions, it does slowly convert into form II. Moreover, the system does not obey the density rule.

Pharmacokinetics of rifampicin after repeated intra-tracheal administration of amorphous and crystalline powder formulations to Sprague Dawley rats

Rifampicin is one of the key drugs used to treat tuberculosis and is currently used orally. The use of higher oral doses of rifampicin is desired for better therapeutic efficacy, but this is accompanied by increased risk of systemic toxicity thus limiting its recommended oral dose to 10 mg/kg per day. Inhaled delivery of rifampicin is a potential alternative mode of delivery, to achieve high drug concentrations in both the lung and potentially the systemic circulation. In addition, rifampicin exists either as amorphous or crystalline particles, which may show different pharmacokinetic behaviour. However, disposition behaviour of amorphous and crystalline rifampicin formulations after inhaled high-dose delivery is unknown. In this study, rifampicin pharmacokinetics after intra-tracheal administration of carrier-free, amorphous and crystalline powder formulations to Sprague Dawley rats were evaluated. The formulations were administered once daily for seven days by oral, intra-tracheal and oral plus intra-tracheal delivery, and the pharmacokinetics were studied on day 0 and day 6. Intra-tracheal administration of the amorphous formulation resulted in a higher area under the plasma concentration curve (AUC) compared to the crystalline formulation. For both formulations, the intra-tracheal delivery led to significantly higher AUC compared to the oral delivery at the same dose suggesting higher rifampicin bioavailability from the inhaled route. Increasing the intra-tracheal dose resulted in a more than dose proportional AUC suggesting non-linear pharmacokinetics of rifampicin from the inhaled route. Upon repeated administration for seven days, no significant decrease in the AUCs were observed suggesting the absence of rifampicin induced enzyme auto-induction in this study. The present study suggests an advantage of inhaled delivery of rifampicin in achieving higher drug bioavailability compared to the oral route.

Quantification of Uncoupled Spin Domains in Spin-Abundant Disordered Solids

Materials often contain minor heterogeneous phases that are difficult to characterize yet nonetheless significantly influence important properties. Here we describe a solid-state NMR strategy for quantifying minor heterogenous sample regions containing dilute, essentially uncoupled nuclei in materials where the remaining nuclei experience heteronuclear dipolar couplings. NMR signals from the coupled nuclei are dephased while NMR signals from the uncoupled nuclei can be amplified by one or two orders of magnitude using Carr-Meiboom-Purcell-Gill (CPMG) acquisition. The signal amplification by CPMG can be estimated allowing the concentration of the uncoupled spin regions to be determined even when direct observation of the uncoupled spin NMR signal in a single pulse experiment would require an impractically long duration of signal averaging. We use this method to quantify residual graphitic carbon using 13C CPMG NMR in poly(carbon monofluoride) samples synthesized by direct fluorination of carbon from various sources. Our detection limit for graphitic carbon in these materials is better than 0.05 mol%. The accuracy of the method is discussed and comparisons to other methods are drawn.

Application of Differential Scanning Calorimetry (DSC) and Modulated Differential Scanning Calorimetry (MDSC) in Food and Drug Industries

Phase transition issues in the field of foods and drugs have significantly influenced these industries and consequently attracted the attention of scientists and engineers. The study of thermodynamic parameters such as the glass transition temperature (Tg), melting temperature (Tm), crystallization temperature (Tc), enthalpy (H), and heat capacity (Cp) may provide important information that can be used in the development of new products and improvement of those already in the market. The techniques most commonly employed for characterizing phase transitions are thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), thermomechanical analysis (TMA), and differential scanning calorimetry (DSC). Among these techniques, DSC is preferred because it allows the detection of transitions in a wide range of temperatures (−90 to 550 °C) and ease in the quantitative and qualitative analysis of the transitions. However, the standard DSC still presents some limitations that may reduce the accuracy and precision of measurements. The modulated differential scanning calorimetry (MDSC) has overcome some of these issues by employing sinusoidally modulated heating rates, which are used to determine the heat capacity. Another variant of the MDSC is the supercooling MDSC (SMDSC). SMDSC allows the detection of more complex thermal events such as solid–solid (Ts-s) transitions, liquid–liquid (Tl-l) transitions, and vitrification and devitrification temperatures (Tv and Tdv, respectively), which are typically found at the supercooling temperatures (Tco). The main advantage of MDSC relies on the accurate detection of complex transitions and the possibility of distinguishing reversible events (dependent on the heat capacity) from non-reversible events (dependent on kinetics).

Secondary nucleation in amyloid formation

Nucleation of new peptide and protein aggregates on the surfaces of amyloid fibrils of the same peptide or protein has emerged in the past two decades as a major pathway for both the generation of molecular species responsible for cellular toxicity and for the autocatalytic proliferation of peptide and protein aggregates. A key question in current research is the molecular mechanism and driving forces governing such processes, known as secondary nucleation. In this context, the analogies with other self-assembling systems for which monomer-dependent secondary nucleation has been studied for more than a century provide a valuable source of inspiration. Here, we present a short overview of this background and then review recent results regarding secondary nucleation of amyloid-forming peptides and proteins, focusing in particular on the amyloid β peptide (Aβ) from Alzheimer's disease, with some examples regarding α-synuclein from Parkinson's disease. Monomer-dependent secondary nucleation of Aβ was discovered using a combination of kinetic experiments, global analysis, seeding experiments and selective isotope-enrichment, which pinpoint the monomer as the origin of new aggregates in a fibril-catalyzed reaction. Insights into driving forces are gained from variations of solution conditions, temperature and peptide sequence. Selective inhibition of secondary nucleation is explored as an effective means to limit oligomer production and toxicity. We also review experiments aimed at finding interaction partners of oligomers generated by secondary nucleation in an ongoing aggregation process. At the end of this feature article we bring forward outstanding questions and testable mechanistic hypotheses regarding monomer-dependent secondary nucleation in amyloid formation.

Emergence of a substrate-temperature-dependent dielectric process in a prototypical vapor deposited hole-transport glass

Since the discovery of ultrastability, vapor deposition has emerged as a relevant tool to further understand the nature of glasses. By this route, the density and average orientation of glasses can be tuned by selecting the proper deposition conditions. Dielectric spectroscopy, on the other hand, is a basic technique to study the properties of glasses at a molecular level, probing the dynamics of dipoles or charge carriers. Here, and for the first time, we explore the dielectric behavior of vapor deposited N,N-Diphenyl-N,N’bis(methylphenyl)-1,1′-biphenyl-4,4′-diamines (TPD), a prototypical hole-transport material, prepared at different deposition temperatures. We report the emergence of a new relaxation process which is not present in the ordinary glass. We associate this process to the Maxwell-Wagner polarization observed in heterogeneous systems, and induced by the enhanced mobility of charge carriers in the more ordered vapor deposited glasses. Furthermore, the associated activation energy establishes a clear distinction between two families of glasses, depending on the selected substrate-temperature range. This finding positions dielectric spectroscopy as a unique tool to investigate the structural and electronic properties of charge transport materials and remarks the importance of controlling the deposition conditions, historically forgotten in the preparation of optoelectronic devices.

Impact of Supramolecular Aggregation on the Crystallization Kinetics of Organic Compounds from the Supercooled Liquid State

Despite numerous challenges in their theoretical description and practical implementation, amorphous drugs are of growing importance to the pharmaceutical industry. One such challenge is to gain molecular level understanding of the propensity of a molecule to form and remain as a glassy solid. In this study, a series of structurally similar diarylamine compounds was examined to elucidate the role of supramolecular aggregation on crystallization kinetics from supercooled liquid state. The structural similarity of the compounds makes it easier to isolate the molecular features that affect crystallization kinetics and glass forming ability of these compounds. To examine the role of hydrogen-bonded aggregation and motifs on crystallization kinetics, a combination of thermal and spectroscopic techniques was employed. Using variable temperature FTIR, Raman, and solid-state NMR spectroscopies, the presence of hydrogen bonding in the melt and glassy state was examined and correlated with observed phase transition behaviors. Spectroscopic results revealed that the formation of hydrogen-bonded aggregates involving carboxylic acid and pyridine nitrogen (acid-pyridine aggregates) between neighboring molecules in the melt state impedes crystallization, while the presence of carboxylic acid dimers (acid-acid dimers) in the melt favors crystallization. This study suggests that glass formation of small molecules is influenced by the type of intermolecular interactions present in the melt state and the kinetics associated with the molecules to assemble into a crystalline lattice. For the compounds that form acid-pyridine aggregates, the formation of energy degenerate chains, produced due to conformational flexibility of the molecules, presents a kinetic barrier to crystallization. The poor crystallization tendency of these aggregates stems from the highly directional hydrogen-bonding interactions needed to form the acid-pyridine chains. Conversely, for the compounds that form acid-acid dimers, the nondirectional van der Waals forces needed to construct a nucleus promote rapid assembly and crystallization.

Amorphous Sulfadoxine: A Physical Stability and Crystallization Kinetics Study

Poor aqueous solubility of drugs and the improvement thereof has always been a challenge for the pharmaceutical industry. With this, one of the focuses of the pharmaceutical research scientist involves investigating possible metastable forms of a given drug to be incorporated into solid dosage forms. The rationale being, the improved solubility offered by the metastable solid-state forms of drugs. Solubility remains a major challenge for formulation scientists, especially with antimicrobial agents where the emergence of resistance is directly dependent on the concentration and duration of the parasite exposed to the drug. Sulfadoxine-pyrimethamine combination therapies are still the recommended treatments for uncomplicated Plasmodium falciparum malaria. The aim of this study was to prepare an amorphous form of sulfadoxine and to investigate the stability and recrystallization behavior thereof. The amorphous form was prepared by the well-known quench cooling of the melt. The physico-chemical properties and stability of amorphous sulfadoxine were studied using hot-stage microscopy (HSM), scanning electron microscopy (SEM), x-ray powder diffractometry (XRPD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), as well as microcalorimetry. The recrystallization kinetics were studied isothermally by applying the Johnson-Mehl-Avrami model and non-isothermally by applying the Kissinger model. The physical stabilization of the amorphous form was investigated using physical mixtures of amorphous sulfadoxine with polyvinylpyrrolidone-25 (PVP-25). It was proved that sulfadoxine is a good glass former with relative high physical stability; however, water acts as a strong plasticizer for amorphous sulfadoxine, detrimentally affecting the stability during exposure to high moisture conditions.

Unintended and in situ amorphisation of pharmaceuticals

Amorphisation of poorly water-soluble drugs is one approach that can be applied to improve their solubility and thus their bioavailability. Amorphisation is a process that usually requires deliberate external energy input. However, amorphisation can happen both unintentionally, as in process-induced amorphisation during manufacturing, or in situ during dissolution, vaporisation, or lipolysis. The systems in which unintended and in situ amorphisation has been observed normally contain a drug and a carrier. Common carriers include polymers and mesoporous silica particles. However, the precise mechanisms by which in situ amorphisation occurs are often not fully understood. In situ amorphisation can be exploited and performed before administration of the drug or possibly even within the gastrointestinal tract, as can be inferred from in situ amorphisation observed during in vitro lipolysis. The use of in situ amorphisation can thus confer the advantages of the amorphous form, such as higher apparent solubility and faster dissolution rate, without the disadvantage of its physical instability.

Crystalline mesophases: Structure, mobility, and pharmaceutical properties

Crystalline mesophases, which are commonly classified according to their translational, orientational, and conformational order as liquid crystals, plastic crystals, and conformationally disordered crystals, represent a common state of condensed matter. As an intermediate state between crystalline and amorphous materials, crystalline mesophases resemble amorphous materials in relation to their molecular mobility, with the glass transition being their common property, and at the same time possessing a certain degree of translational periodicity (with the exception of nematic phase), with corresponding narrow peaks in X-ray diffraction patterns. For example, plastic crystals, which can be formed both by near-spherical molecules and molecules of lower symmetry, such as planar or chain molecules, can have both extremely sharp X-ray diffraction lines and exhibit glass transition. Fundamentals of structural arrangements in mesophases are compared with several types of disorder in crystalline materials, as well as with short-range ordering in amorphous solids. Main features of the molecular mobility in crystalline mesophases are found to be generally similar to amorphous materials, although some important differences do exist, depending on a particular type of mobility modes involved in relaxation processes. In several case studies reviewed, chemical stability appears to follow the extent of disorder, with the stability of crystalline mesophase found to be intermediate between amorphous (least stable) and crystalline (most stable) materials. Finally, detection of crystalline mesophases during manufacturing of two different types of dosage forms is discussed.

(14) N nuclear quadrupole resonance study of piroxicam: confirmation of new polymorphic form V

A new polymorphic crystal form of piroxicam was discovered while preparing crystalline samples of piroxicam for (14) N nuclear quadrupole resonance (NQR) analysis. The new crystal form, designated as V, was prepared by evaporative recrystallization from dichloromethane. Three known polymorphic forms (I, II, and III) were also prepared. Our aim was to apply (14) N NQR to characterize the new polymorphic form of piroxicam and compare the results with those of the other known polymorphic forms. Additional analytical methods used for characterization were X-ray powder diffraction (XRPD), thermal analysis, and vibrational spectroscopy. For the first time, a complete set of nine characteristic (14) N NQR frequencies was found for each prepared polymorph of piroxicam. The consistent set of measured frequencies and calculated characteristic quadrupole parameters found for the new polymorphic form V is a convincing evidence that we are dealing with a new form. The already known piroxicam polymorphic forms were characterized similarly. The XRPD results were in accordance with the conclusions of (14) N NQR analysis. The performed study clearly demonstrates a strong potential of (14) N NQR method to be applied as a highly discriminative spectroscopic analytical tool to characterize polymorphic forms.

Computational predictions of glass-forming ability and crystallization tendency of drug molecules

Amorphization is an attractive formulation technique for drugs suffering from poor aqueous solubility as a result of their high lattice energy. Computational models that can predict the material properties associated with amorphization, such as glass-forming ability (GFA) and crystallization behavior in the dry state, would be a time-saving, cost-effective, and material-sparing approach compared to traditional experimental procedures. This article presents predictive models of these properties developed using support vector machine (SVM) algorithm. The GFA and crystallization tendency were investigated by melt-quenching 131 drug molecules in situ using differential scanning calorimetry. The SVM algorithm was used to develop computational models based on calculated molecular descriptors. The analyses confirmed the previously suggested cutoff molecular weight (MW) of 300 for glass-formers, and also clarified the extent to which MW can be used to predict the GFA of compounds with MW < 300. The topological equivalent of Grav3_3D, which is related to molecular size and shape, was a better descriptor than MW for GFA; it was able to accurately predict 86% of the data set regardless of MW. The potential for crystallization was predicted using molecular descriptors reflecting Hückel pi atomic charges and the number of hydrogen bond acceptors. The models developed could be used in the early drug development stage to indicate whether amorphization would be a suitable formulation strategy for improving the dissolution and/or apparent solubility of poorly soluble compounds.

Alginate Particles as Platform for Drug Delivery by the Oral Route: State-of-the-Art

Pharmaceutical research and development aims to design products with ensured safety, quality, and efficacy to treat disease. To make the process more rational, coherent, efficient, and cost-effective, the field of Pharmaceutical Materials Science has emerged as the systematic study of the physicochemical properties and behavior of materials of pharmaceutical interest in relation to product performance. The oral route is the most patient preferred for drug administration. The presence of a mucus layer that covers the entire gastrointestinal tract has been exploited to expand the use of the oral route by developing a mucoadhesive drug delivery system that showed a prolonged residence time. Alginic acid and sodium and potassium alginates have emerged as one of the most extensively explored mucoadhesive biomaterials owing to very good cytocompatibility and biocompatibility, biodegradation, sol-gel transition properties, and chemical versatility that make possible further modifications to tailor their properties. The present review overviews the most relevant applications of alginate microparticles and nanoparticles for drug administration by the oral route and discusses the perspectives of this biomaterial in the future.

Formulation of tablets containing an 'in-process' amorphized active pharmaceutical ingredient

The aim of this work was a preliminary study of the "in-process" amorphization of clopidogrel hydrogensulfate (CLP) as model drug during the production of tablets as dosage form. A solvent method was used for amorphization and the crystalline phase of CLP was detected by differential scanning calorimetry; the physical parameters of fresh and stored tablets were investigated. For the amorphous form, Aerosil 200 was selected as crystallization inhibitor as the most suitable of eight auxiliary agents. The optimum composition of the product for amorphization in the scaling-up process (100-fold) was 7 parts of CLP to 3 parts of Aerosil 200. In this scaled-up product, the amorphous CLP was fixed on the surface of microcrystalline cellulose. The tablet form further stabilized the amorphous form. Finally, the steps of an "in-process" amorphization are given as a protocol, which can promote stabilization of an amorphized active pharmaceutical ingredient.

Following the surface response of caffeine cocrystals to controlled humidity storage by atomic force microscopy

Active pharmaceutical ingredient (API) stability in solid state tablet formulation is frequently a function of the relative humidity (RH) environment in which the drug is stored. Caffeine is one such problematic API. Previously reported caffeine cocrystals, however, were found to offer increased resistance to caffeine hydrate formation. Here we report on the use of atomic force microscopy (AFM) to image the surface of two caffeine cocrystal systems to look for differences between the surface and bulk response of the cocrystal to storage in controlled humidity environments. Bulk responses have previously been assessed by powder X-ray diffraction. With AFM, pinning sites were identified at step edges on caffeine/oxalic acid, with these sites leading to non-uniform step movement on going from ambient to 0% RH. At RH >75%, areas of fresh crystal growth were seen on the cocrystal surface. In the case of caffeine/malonic acid the cocrystals were observed to absorb water anisotropically after storage at 75% RH for 2 days, affecting the surface topography of the cocrystal. These results show that AFM expands on the data gathered by bulk analytical techniques, such as powder X-ray diffraction, by providing localised surface information. This surface information may be important for better predicting API stability in isolation and at a solid state API-excipient interface.

Near-infrared analysis of hydrogen-bonding in glass- and rubber-state amorphous saccharide solids

Near-infrared (NIR) spectroscopic analysis of noncrystalline polyols and saccharides (e.g., glycerol, sorbitol, maltitol, glucose, sucrose, maltose) was performed at different temperatures (30-80 degrees C) to elucidate the effect of glass transition on molecular interaction. Transmission NIR spectra (4,000-12,000 cm(-1)) of the liquids and cooled-melt amorphous solids showed broad absorption bands that indicate random configuration of molecules. Heating of the samples decreased an intermolecular hydrogen-bonding OH vibration band intensity (6,200-6,500 cm(-1)) with a concomitant increase in a free and intramolecular hydrogen-bonding OH group band (6,600-7,100 cm(-1)). Large reduction of the intermolecular hydrogen-bonding band intensity at temperatures above the glass transition (T(g)) of the individual solids should explain the higher molecular mobility and lower viscosity in the rubber state. Mixing of the polyols with a high T(g) saccharide (maltose) or an inorganic salt (sodium tetraborate) shifted both the glass transition and the inflection point of the hydrogen-bonding band intensity to higher temperatures. The implications of these results for pharmaceutical formulation design and process monitoring (PAT) are discussed.