Inhibition of Crystal Nucleation and Growth by Water-Soluble Polymers and its Impact on the Supersaturation Profiles of Amorphous Drugs

Screening of Organic Small Molecule Excipients on Ternary Solid Dispersions Based on Miscibility and Hydrogen Bonding Analysis: Experiments and Molecular Simulation

The preparation of solid dispersions by mixing insoluble drugs with polymers is the main way to improve the aqueous solubility of drugs. The introduction of organic small molecule excipients into binary solid dispersions is expected to further enhance drug solubility by regulating intermolecular hydrogen bonding within the system at the microscopic level. In this study, we used carbamazepine (CBZ) as the target drug and polyvinylpyrrolidone as the solid dispersion matrix and screened the third component from 13 organic small molecules with good miscibility in the solid dispersion based on the principle of similarity of solubility parameters. The hydrogen bonding parameters and dissociation Gibbs free energy of the 13 organic small molecule-CBZ dimer were calculated by quantum mechanical simulation, and the tryptophan (Try) was identified as the optimal third component of organic small molecule. The migration of CBZ in binary and ternary systems was also analyzed by molecular dynamics simulation. On this theoretical basis, the corresponding solid dispersions were prepared, characterized, and tested for solubility analysis, which verified that the drug solubility was stronger for the system with the addition of polar fractions and the Try was indeed the best third component of organic small molecule compound, which was consistent with the simulation predictions. This screening method may provide theoretical guidance for drug modification design and clinical studies.

Supersaturation Behavior: Investigation of Polymers Impact on Nucleation Kinetic Profile for Rationalizing the Polymeric Precipitation Inhibitors

BACKGROUND

Although nucleation kinetic data is quite important for the concept of supersaturation behavior, its part in rationalizing the crystallization inhibitor has not been well understood.

OBJECTIVE

This study aimed to investigate the nucleation kinetic profile of Dextromethorphan HBr (as an ideal drug, BCS-II) by measuring liquid-liquid phase segregation, nucleation induction time, and Metastable Zone width.

METHODS

Surfeit action was examined by a superfluity assay of the drug. The concentration was scrutinized by light scattering techniques (UV spectrum (novel method) and Fluorometer (CL 53)).

RESULTS

The drug induction time was 20 min without polymer and 90 and 110 min with polymers, such as HPMC K15M and Xanthan Gum, respectively. Therefore, the order of the polymer's ability to inhibit nucleation was Xanthan Gum > HPMC K15M in the medium (7.4 pH). Similarly, the drug induction time was 30 min without polymer and 20, 110, and 90 min with polymers, such as Sodium CMC, HPMC K15M, and Xanthan Gum, respectively. Therefore, the order of the polymer's ability to inhibit nucleation was HPMC K15M > Xanthan Gum > Sodium CMC in SIFsp (6.8 pH), which synchronizes the polymer's potentiality to interdict the drug precipitation.

CONCLUSION

The HPMC K15M and xanthan Gum showed the best crystallization inhibitor effect for the maintenance of superfluity conditions till the drug absorption time. The xanthan gum is based on the "glider" concept, and this shows the novelty of this preliminary research. The screening methodology used for rationalizing the best polymers used in the superfluity formulations development successfully.

Designing a Novel Coamorphous Salt Formulation of Telmisartan with Amlodipine to Enhance Permeability and Oral Absorption

Coamorphous formulation is a useful approach for enhancing the solubility of poorly water-soluble drugs via intermolecular interactions. In this study, a hydrogen-bonding-based coamorphous system was developed to improve drug solubility, but it barely changed the apparent permeability (Papp) of the drug. This study aimed to design a novel coamorphous salt using ionic interactions to improve drug permeability and absorption. Telmisartan (TMS), with an acidic group, was used to form a coamorphous salt with basic amlodipine (AML). Evaluation of the physicochemical properties confirmed the formation of a coamorphous salt via ionic interactions between the amine group of AML and the carboxyl group of TMS at a molar ratio of 1:1. The coamorphous salt of TMS/AML enhanced the partitioning of both drugs into octanol, indicating increased lipophilicity owing to the interaction between TMS and AML. The coamorphous salt dramatically enhanced TMS solubility (99.8 times that of untreated TMS) and decreased AML solubility owing to the interaction between TMS and AML. Although the coamorphous salt showed a decreased Papp in the permeation study in the presence of a thicker unstirred water layer (UWL) without stirring, Papp increased in the presence of a thinner UWL with stirring. The oral absorption of TMS from the coamorphous salt increased by up to 4.1 times compared to that of untreated TMS, whereas that of AML remained unchanged. Although the coamorphous salt with increased lipophilicity has a disadvantage in terms of diffusion through the UWL, the UWL is thin in human/animal bodies owing to the peristaltic action of the digestive tract. Dissociation of the coamorphous salt on the membrane surface could contribute to the partitioning of the neutral form of drugs to the membrane cells compared with untreated drugs. As a result, coamorphous salt formation has the advantage of improving the membrane permeation and oral absorption of TMS, owing to the enhanced solubility and supply of membrane-permeable free TMS on the surface of the membrane.

Precellys® Evolution Homogenizer - a versatile instrument for milling, mixing, and amorphization of drugs in preformulation

The aim of this work was the evaluation and introduction of the Bertin Precellys® Evolution homogenizer with Cryolys® as a valuable and versatile tool for the improvement of workflows in the preformulation phase of drug development. The presented pilot experiments indicate that the instrument can be applied for (1) screening of appropriate vehicles for the generation of micro- and nano suspensions, (2) small-scale manufacturing of suspension formulations for preclinical animal studies, (3) drug amorphization and identification of appropriate excipients for amorphous systems, and (4) preparation of homogenous powder blends. The instrument allows the rapid, parallel, and compound-sparing screening of formulation approaches and small-scale formulation manufacturing, in particular for low solubility compounds. For the characterization of generated formulations, miniaturized methods are introduced such as a screening tool for suspension sedimentation and redispersion and a non-sink dissolution model in biorelevant media in microtiter plates. This work summarizes exploratory, proof-of-concept studies and opens up new opportunities for more extended studies with this instrument in various application areas.

Small molecules interfacial assembly regulate the crystallization transition process for nobiletin stabilization

Many bioactive nutraceuticals naturally occurring in food materials possess beneficial biological activities, while their use as functional supplements is subjected to hydrophobicity and crystallinity. Currently, inhibiting crystallization for such nutrients is of immense scientific interest. Here, we exploited diverse structural polyphenols as potential inhibitors for restraining Nobiletin crystallization. Specifically, the crystallization transition process could be influenced by the polyphenol gallol density, Nobiletin supersaturation (1, 1.5, 2, 2.5 mM), temperature (4, 10, 15, 25 and 37 ℃), and pH (3.5, 4, 4.5, 5), important factors for regulating the binding attachment and interactions. The optimized samples could be guided by NT100 lied in 4 ℃ at pH 4. Besides, the main assembly driving force was hydrogen-bonding cooperated with π-π stacking and electrostatic interaction, leading to a Nobiletin/TA combination ratio of ∼ 3:1. Our findings proposed an innovative synergistic strategy for inhibiting crystallization and broaden potential applications of polyphenol-based materials in advanced biological fields.

Effect of Polymer Additives on the Crystal Habit of Metformin HCl

The crystal habit can have a profound influence on the physical properties of crystalline materials, and thus controlling the crystal morphology is of great practical relevance across many industries. Herein, this work investigates the effect of polymer additives on the crystal habit of metformin HCl with both experiments and computational methods with the aim of developing a combined screening approach for crystal morphology engineering. Crystallization experiments of metformin HCl are conducted in methanol and in an isopropanol-water mixture (8:2 V/V). Polyethylene glycol, polyvinylpyrrolidone, Tween80, and hydroxypropyl methylcellulose polymer additives are used in low concentrations (1-2% w/w) in the experiments to study the effect they have on modifying the crystal habit. Additionally, this work has developed computational methods to characterize the morphology "landscape" and quantifies the overall effect of solvent and additives on the predicted crystal habits. Further analysis of the molecular dynamics simulations is used to rationalize the effect of additives on specific crystal faces. This work demonstrates that the effects of additives on the crystal habit are a result of their absorption and interactions with the slow growing {100} and {020} faces.

Enabling direct compression tablet formulation of celecoxib by simultaneously eliminating punch sticking, improving manufacturability, and enhancing dissolution through co-processing with a mesoporous carrier

The development of a high quality tablet of Celecoxib (CEL) is challenged by poor dissolution, poor flowability, and high punch sticking propensity of CEL. In this work, we demonstrate a particle engineering approach, by loading a solution of CEL in an organic solvent into a mesoporous carrier to form a coprocessed composite, to enable the development of tablet formulations up to 40% (w/w) of CEL loading with excellent flowability and tabletability, negligible punch sticking propensity, and a 3-fold increase in in vitro dissolution compared to a standard formulation of crystalline CEL. CEL is amorphous in the drug-carrier composite and remained physically stable after 6 months under accelerated stability conditions when the CEL loading in the composite was ≤ 20% (w/w). However, crystallization of CEL to different extents from the composites was observed under the same stability condition when CEL loading was 30-50% (w/w). The success with CEL encourages broader exploration of this particle engineering approach in enabling direct compression tablet formulations for other challenging active pharmaceutical ingredients.

Supersaturation and phase behavior during dissolution of amorphous solid dispersions

Amorphous solid dispersion (ASD) is a promising strategy to enhance solubility and bioavailability of poorly water-soluble drugs. Due to higher free energy of ASD, supersaturated drug solution could be generated during dissolution. When amorphous solubility of a drug is exceeded, drug-rich nanodroplets could form and act as a reservoir to maintain the maximum free drug concentration in solution, facilitating the absorption of the drug in vivo. Dissolution behavior of ASD has received increasing interests. This review will focus on the recent advances in ASD dissolution, including the generation and maintenance of supersaturated drug solution in absence or presence of liquid-liquid phase separation. Mechanism of drug release from ASD including polymer-controlled dissolution and drug-controlled dissolution will be introduced. Formation of amorphous drug-rich nanodroplets during dissolution and the underlying mechanism will be discussed. Phase separation morphology of hydrated ASD plays a critical role in dissolution behavior of ASD, which will be highlighted. Supersaturated drug solution shows poor physical stability and tends to crystallize. The effect of polymer and surfactant on supersaturated drug solution will be demonstrated and some unexpected results will be shown. Physicochemical properties of drug and polymer could impact ASD dissolution and some of them even show opposite effect on dissolution and physical stability of ASD in solid state, respectively. This review will contribute to a better understanding of ASD dissolution and facilitate a rational design of ASD formulation.

Nano-Spray-Dried Levocetirizine Dihydrochloride with Mucoadhesive Carriers and Cyclodextrins for Nasal Administration

Antihistamines such as levocetirizine dihydrochloride (LC) are commercially used in oral tablets and oral drops to reduce allergic symptoms. In this study, LC was nano-spray-dried using three mucoadhesive polymers and four cyclodextrin species to form composite powders for nasal administration. The product was composed of hydroxypropyl methylcellulose polymer, including LC as a zwitterion, after neutralization by NaOH, and XRD investigations verified its amorphous state. This and a sulfobutylated-beta-cyclodextrin sodium salt-containing sample showed crystal peaks due to NaCl content as products of the neutralization reaction in the solutions before drying. The average particle size of the spherical microparticles was between 2.42 and 3.44 µm, except for those containing a polyvinyl alcohol excipient, which were characterized by a medium diameter of 29.80 µm. The drug was completely and immediately liberated from all the samples at pH 5.6 and 32 °C; i.e., the carriers did not change the good dissolution behavior of LC. A permeability test was carried out by dipping the synthetic cellulose ester membrane in isopropyl myristate using modified horizontal diffusion cells. The spray-dried powder with β-cyclodextrin showed the highest permeability (188.37 µg/cm²/h), as this additive was the least hydrophilic. Products prepared with other cyclodextrins (randomly methylated-beta-cyclodextrin, sulfobutylated-beta-cyclodextrin sodium salt and (hydroxypropyl)-beta-cyclodextrin) showed similar or slightly higher penetration abilities than LC. Other polymer excipients resulted in lower penetration of the active agent than the pure LC.

The Impact of Water-Soluble Chitosan on the Inhibition of Crystal Nucleation of Alpha-Mangostin from Supersaturated Solutions

The use of an amorphous drugs system to generate supersaturated solutions is generally developed to improve the solubility and dissolution of poorly soluble drugs. This is because the drug in the supersaturation system has a high energy state with a tendency to precipitate. In the amorphous solid dispersion (ASD) formulation, it was discovered that polymer plays a critical role in inhibiting nucleation or crystal growth of the drugs. Therefore, this study aimed to evaluate the crystallization inhibition of water-soluble chitosan (WSC) on nucleation as well as crystal growth from alpha-mangostin (AM) and elucidate its inhibition mechanism in the supersaturated solutions. During the experiment, WSC was used as a polymer to evaluate its ability to inhibit AM nucleation. The interaction between WSC and AM was also estimated using FT-IR, NMR, and in silico study. The result showed that in the absence of polymer, the concentration of AM rapidly decreased due to the precipitation in one minute. Meanwhile, the addition of WSC effectively inhibited AM crystallization and maintained a supersaturated state for the long term. FT-IR measurement also revealed that the shift in the amine primer of WSC occurred because of the interaction between WSC and AM. In the 1H NMR spectra, the proton peaks of WSC showed an upfield shift with the presence of AM, indicating the intermolecular interactions between AM and WSC. Moreover, in silico study revealed the hydrogen bond interaction between the carbonyl group of AM with hydrocarbon groups of WSC. This indicated that WSC interacted with AM in the supersaturated solution and suppressed their molecular mobility, thereby inhibiting the formation of the crystal nucleus. Based on these results, it can be concluded that the interaction between drug polymers contributed to the maintenance of the drug supersaturation by inhibiting both nucleation and growth.

Phase Behavior and Crystallization Kinetics of a Poorly Water-Soluble Weakly Basic Drug as a Function of Supersaturation and Media Composition

Understanding the supersaturation and precipitation behavior of poorly water-soluble compounds in vivo and the impact on oral absorption is critical to design consistently performing products with optimized bioavailability. Weakly basic compounds are of particular importance in this context since they have an inherent tendency to undergo supersaturation in vivo upon exit from the stomach and entry into the small intestine because of their pH-dependent solubility. To understand and probe potential in vivo variability of supersaturating systems, rigorous understanding of compound physical properties and phase behavior landscape is essential. Herein, we extensively characterize the solution phase behavior of a model, poorly soluble and weakly basic compound, posaconazole. Phase boundaries for crystal-solution and amorphous-solution were established as a function of pH, allowing possible phase transformations, namely, crystallization or liquid-liquid phase separation, to be mapped for different initial doses and fluid volumes. Endogenous surfactants including sodium taurocholate, lecithin, glycerol monooleate, and sodium oleate in biorelevant media significantly extended the phase boundaries due to solubilization, to an extent that was dependent on the concentration of the surface-active agents. The nucleation induction time of posaconazole was much shorter in biorelevant media in comparison to the corresponding buffer solution, with two distinct regions observed in all media that could be attributed to a change in the nucleation mechanism at high and low supersaturation. The presence of undissolved nanocrystals accelerated the desupersaturation. This work enhances our understanding of biorelevant factors impacting precipitation kinetics, which might affect absorption in vivo. It is expected that findings from this study with posaconazole could be broadly applicable to other weakly basic compounds, after taking into consideration differences in pK_a, solubility, and molecular structure.

Towards a better understanding of the role of stabilizers in QESD crystallizations

Quasi-emulsion solvent-diffusion crystallization (QESD) is a type of spherical crystallization which can be used as a particle design method to improve the flowability and micromeritic properties of drugs or excipients. Spherical particles are generated by dispersing a solvent phase in an antisolvent so that a transient emulsion is formed. Within the droplets the material can crystallize and agglomerate into spherical, hollow particles. Surfactants, such as surface-active polymers like hypromellose, are often required to stabilize the quasi-emulsion. To gain further understanding for the role of the stabilizer, a new screening-method was developed which compared different surface active polymers in solution at similar dynamic viscosities rather than at a set concentration. The dynamic viscosities of a low-viscosity grade hypromellose solution used in the previous publications describing the QESD crystallization of metformin hydrochloride by the authors was used as a target value. QESD crystallizations of metformin hydrochloride (MF) and celecoxib showed that the type of stabilizer and whether it is dissolved in the solvent or antisolvent has an effect on the agglomerates. For MF, the type of hypromellose used can have a significant influence on the properties of the agglomerates. More polymers could be used to stabilize the transient emulsion of celecoxib than previously found in literature. Furthermore, QESD crystallizations seem to be more robust when the stabilizer is dissolved in the antisolvent, however this can lead to a reduced drug load of the agglomerates.

Explicating the molecular level drug-polymer interactions at the interface of supersaturated solution of the model drug: Albendazole

Supersaturation as a formulation principle relates to the aqueous solubility of poorly soluble drugs in solution . However, supersaturation state of drugs tends to crystallize because of its thermodynamic instability thereby compromising the solubility and biopharmaceutical performance of drugs. The present study aims to investigate the supersaturation potential of albendazole (ABZ) and its precipitation via nucleation and crystal growth. We hypothesized the use of polymers will avoid ABZ precipitation by interacting with drug molecules. The drug polymer interactions are characterized using conventional methods of Fourier transform infrared (FTIR), Nuclear magnetic resonance (NMR) and Polarized light microscopy (PLM). We have used a novel approach of sum frequency generation (SFG) vibrational spectroscopic in exploring the drug polymer interactions at air-water interface. Recently we have reported the SFG for e rifaximin-polymer interactions (Singh et al., 2021). The supersaturation assay, saturation solubility studies and nucleation induction time analysis revealed polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP K30) as effective precipitation inhibitors thereby enhancing the ABZ equilibrium solubility and in vitro supersaturation maintenance of ABZ. Further, modification in the solid state of ABZ has confirmed the influence of polymers on its precipitation behaviour. We conclude that PVA and PVP K30 act as nucleation and crystal growth inhibitor, respectively for the precipitation inhibition of ABZ.

Application of Polymers as a Tool in Crystallization-A Review

The application of polymers as a tool in the crystallization process is gaining more and more interest among the scientific community. According to Web of Science statistics the number of papers dealing with “Polymer induced crystallization” increased from 2 in 1990 to 436 in 2020, and for “Polymer controlled crystallization”—from 4 in 1990 to 344 in 2020. This is clear evidence that both topics are vivid, attractive and intensively investigated nowadays. Efficient control of crystallization and crystal properties still represents a bottleneck in the manufacturing of crystalline materials ranging from pigments, antiscalants, nanoporous materials and pharmaceuticals to semiconductor particles. However, a rapid development in precise and reliable measuring methods and techniques would enable one to better describe phenomena involved, to formulate theoretical models, and probably most importantly, to develop practical indications for how to appropriately lead many important processes in the industry. It is clearly visible at the first glance through a number of representative papers in the area, that many of them are preoccupied with the testing and production of pharmaceuticals, while the rest are addressed to new crystalline materials, renewable energy, water and wastewater technology and other branches of industry where the crystallization process takes place. In this work, authors gathered and briefly discuss over 100 papers, published in leading scientific periodicals, devoted to the influence of polymers on crystallizing solutions.

A novel architecture for achieving high drug loading in amorphous spray dried dispersion tablets

Although Amorphous Solid Dispersions (ASDs) effectively increase bioavailability, tablet mass can be high due to the large fraction of excipients needed to stabilize the amorphous drug in the solid state, extend drug supersaturation in solution and achieve robust manufacturability. The aim of this work was to reduce tablet mass of an ASD tablet comprising a low glass transition temperature (Tg), rapidly crystallizing drug without compromising these key attributes. In this approach, erlotinib (Tg = 42 °C, Tm/Tg = 1.4 K/K) was spray dried with the high Tg polymer poly(methyl methacrylate-co-methacrylic acid) (Eudragit® L100, Evonik) (Tg = 187 °C) to facilitate high drug loading while maintaining physical stability. Hydroxypropyl methylcellulose acetate succinate (HPMCAS) (AQOAT® HF, Shin-Etsu) was granulated with the ASD to extend supersaturation in solution. For comparison, a benchmark ASD was spray dried at a lower drug loading with HPMCAS-H (Tg = 119 °C). This High Loaded Dosage Form (HLDF) approach reduced tablet mass by 40%, demonstrated similar physical stability and in vitro performance as the benchmark and exhibited excellent downstream manufacturability. Strategically combining two different polymers in a tablet to maintain physical stability and sustain supersaturation in solution can decrease tablet mass of some low Tg, rapidly crystallizing amorphous drugs.

Insights into Dissolution and Solution Chemistry of Multidrug Formulations of Antihypertensive Drugs

Using fixed dose combinations of drugs instead of administering drugs separately can be beneficial for both patients and the health care system, but the current understanding of how multidrug formulations work at the molecular level is still in its infancy. Here, we explore dissolution, solubility, and supersaturation of various drug combinations in amorphous formulations. The effect of chemical structural similarity on combination behavior was investigated by using structurally related compounds of both drugs. The effect of polymer type on solution behavior was also evaluated using chemically diverse polymers. Indapamide (IPM) concentration decreased when combined with felodipine (FDN) or its analogues, which occurred even when the IPM solution was undersaturated. The extent of solubility decrease of FDN was less than that of IPM from the dissolution of an equimolar formulation of the drugs. No significant solubility decrease was observed for FDN at low contents of IPM which was also observed for other dihydropyridines, whereas FDN decreases at high contents of IPM. This was explained by the complex nature of the colloidal precipitates of the combinations which impacts the chemical potential of the drugs in solution at different levels. The maximum achievable concentration of FDN and IPM during dissolution of the polyvinylpyrrolidone-based amorphous solid dispersion was higher than the value measured with the hydroxypropyl methylcellulose acetate succinate-based formulation. This emphasizes the significance of molecular properties and chemical diversity of drugs and polymers on solution chemistry and solubility profiles. These findings may apply to drugs administered as a single dosage form or in separate dosage forms and hence need to be well controlled to assure effective treatments and patient safety.

Surface stabilized atorvastatin nanocrystals with improved bioavailability, safety and antihyperlipidemic potential

Atorvastatin, a favored option for hyperlipidemia exhibits the problem of poor gastric solubility and low absolute bioavailability (12%) along with higher pre-systemic clearance (>80%). Therefore, to circumvent these limitations, atorvastatin nanocrystals were prepared using poloxamer-188 as stabilizer via high pressure homogenization technique followed by lyophilization. Various variables like drug to poloxamer-188 ratio, homogenization cycle, homogenization pressure, type and concentration of cryoprotectant were optimized to achieve uniform nanosized crystals with good dispersibility. Solid state characterization by ATR-FTIR and DSC revealed no incompatible physicochemical interaction between drug and excipients in formulation while DSC and PXRD collectively corroborated the reduced crystallinity of drug in nanocrystals. Size analysis and SEM confirmed nanometric size range of nanocrystals (225.43 ± 24.36 nm). Substantial improvement in gastric solubility (~40 folds) and dissolution rate of drug in nanocrystals was observed. Pharmacokinetic study in wistar rats revealed significant improvement in oral bioavailability (~2.66 folds) with atorvastatin nanocrystals compared to pure drug. Furthermore, reduction in serum total lipid cholesterol, LDL and triglyceride content justified the effectiveness of formulation at 50% less dose of atorvastatin along with improved plasma safety profile in comparison of pure drug. In conclusion, atorvastatin nanocrystals are safe and efficacious drug delivery system confirming potent competence in treatment of hyperlipidemic conditions with ease of scalability for commercialization.

Polymeric precipitation inhibitor as an effective trigger to convert supersaturated into supersaturable state in vivo

The supersaturated state of the drug in vivo is thermodynamically unstable resulting in a delayed response and reduced efficacy. The use of polymeric precipitation inhibitor (PPI) has been demonstrated as an effective trigger for the conversion of supersaturated state to supersaturable state for improving solubilization, thermodynamic maintenance of drug concentration and oral absorption of poorly water-soluble compounds. PPI retards drug precipitation and provides a kinetically stabilized supersaturation state for an extended period in gastric and intestinal fluids. However, the selection of appropriate PPI and understanding its mechanism is a challenge for formulating a stable pharmaceutical formulation. The present review is aimed at understanding the intricacies of selecting PPIs and their applications in pharmaceutical formulations.

Sericin Inhibits Devitrification of Amorphous Drugs

The purpose of the present investigation was to analyze devitrification of amorphous drugs such as lornoxicam, meloxicam, and felodipine in the presence of sericin. The binary solid dispersions comprising varying mass ratios of drug and sericin were subject to amorphization by spray drying, solvent evaporation, ball milling, and physical mixing. Further, obtained solid dispersions (SDs) were characterized by HPLC, ATR-FTIR, H¹NMR, molecular docking, accelerated stability study at 40°C and 75 ± 2% RH (XRD and DSC), and in vitro dissolution studies. The HPLC analysis indicated no decomposition of the drugs during the spray drying process. From ATR-FTIR, NMR, and molecular docking study, it was revealed that H-bonding played a vital role in amorphous drug stabilization. An excellent devitrification inhibition was observed in case of lornoxicam (SDLS3) and meloxicam (SDMS3) SDs prepared by spray drying. On the other hand, spray-dried SD of felodipine (SDFS3) showed traces of microcrystals. The percent crystallinity of SDLS3, SDMS3, and SDFS3 was found to be 7.4%, 8.23%, and 18.31% respectively indicating adequate amorphization. The dissolution performance of SDLS, SDMS, and SDFS after 3 months showed > 85% than SDs prepared by other methods. Thus, sericin significantly inhibited crystallization and was responsible for amorphous state stabilization of pharmaceuticals.

Impacts of Polymeric Additives on Nucleation and Crystal Growth of Indomethacin from Supersaturated Solutions

Three polymers, polyvinylpyrrolidone (PVP K30), hydroxypropyl methyl cellulose (HPMC E5), and Kollidone VA64 (PVP-VA64), have been assessed for their impact on the nucleation and crystal growth of indomethacin (IND) from supersaturation solutions. PVP was the most effective inhibitor on IND nucleation among three polymers, but the effect of three polymers on inhibiting nucleation is quite limited when the degree of supersaturation S is higher than about 9. Analysis of the nucleation data by classical nucleation theory model generally afforded good data fitting with the model and showed that addition of polymers may affect the crystal/solution interfacial free energy γ and also the pre-exponential kinetic factor. PVP-VA showed better inhibitory effects on crystal growth of IND when the polymer concentration is high (0.1%, w/w) as reflected by the crystal growth inhibition factor R, and PVP exhibited relatively stronger effects on inhibiting crystal growth at low polymer concentrations (0.005%, w/w). The crystal growth inhibitory effect of polymers should be attributable to the retardation of the surface integration of the drug, and such effect should also be polymer and drug dependent. The enhancement of supersaturation level of IND should be attributable to both nucleation and crystal growth inhibition by polymers. The nucleation and crystal growth rate of α-polymorph IND is higher than that of γ-polymorph, and α-polymorph is the predominant form appeared in supersaturated solutions. A rational selection of the appropriate polymer for specific drug is critical for developing supersaturated drug delivery formulations.

In Vitro Assessment of Supersaturation/Precipitation and Biological Membrane Permeation of Poorly Water-Soluble Drugs: A Case Study With Albendazole and Ketoconazole

This study aimed to elucidate the relationship between supersaturation and precipitation and the effect of a supersaturated state on drug membrane permeation. Stock solutions of albendazole (ALB) and ketoconazole (KTZ) dissolved in dimethyl sulfoxide (0.1-50 mg/mL) were diluted 100-fold with buffer solution (pH 6.8, 37°C). In the case of ALB, a supersaturated state and immediate precipitation were observed at 10 μg/mL or less and 20 μg/mL or higher, respectively. When KTZ was used, at an initial concentration of 200 μg/mL or higher, precipitation was observed, although the dissolved concentration remained at approximately 120 μg/mL for at least 30 min. These dissolved concentrations of ALB and KTZ related to approximately 10-fold and 14-fold over the saturated solubility from respective bulk powder. An in vitro permeation study implied that the rate of drug permeation across a biological membrane increased with increasing supersaturation. These results suggested favorable strategies for development of a supersaturable formulation could depend on the precipitation properties of the drug. Immediate- and controlled-release forms might be suitable for supersaturable formulations for KTZ and ALB, respectively.

The inhibiting role of hydroxypropylmethylcellulose acetate succinate on piperine crystallization to enhance its dissolution from its amorphous solid dispersion and permeability

The purpose of this study was to demonstrate that inhibiting crystallization by HPMCAS played a key role in enhancing dissolution and absorption of piperine (Pip) from its amorphous solid dispersion (ASD). Nucleation induction time and supersaturation tests were used to evaluate the ability of the polymers to inhibit crystallization of Pip. The prepared solid dispersions were characterized by DSC and FTIR. The dissolution rate of Pip from its ASDs was assayed by a dissolution test. Pip permeability was investigated by single-pass intestinal perfusion studies. The order of the ability of polymers to inhibit Pip crystallization was HF > MF > LF > L100-55. The best inhibition effect of HF can be attributed to its hydrophobicity and steric hindrance. Pip is amorphous in polymer matrices when the ratio of Pip/HPMCAS is lower than 1 : 1 and Pip/L100-55 is lower than 3 : 1. IR spectra show that there are hydrogen bonds between the amide groups of Pip and the carboxyl groups of polymer. The order of the ability of polymers to enhance Pip dissolution is HF > MF > LF > L100-55, which coincided with the ability of polymers to inhibit Pip crystallization. Increased apparent permeability via HF-induced supersaturation and decreased apparent permeability via solubilization with L100-55 are demonstrated. Nucleation induction time and supersaturation tests may be used to screen appropriate polymers for preparing ASDs.

HPMCAS enhances piperine dissolution and permeability in amorphous solid dispersion by inhibiting crystallization.

Stabilizing supersaturated drug-delivery system through mechanism of nucleation and crystal growth inhibition of drugs

A supersaturated drug-delivery system is capable of enhancing oral bioavailability of hydrophobic drugs. Maintenance of the supersaturated system both in vitro and in vivo is one of the most challenging parts, for that it is required to keenly understand the nucleation and crystal growth behavior. Polymers are widely used to stabilize supersaturated solutions; screening of polymers is done on the basis of their interaction with drug. Nucleation and crystal growth inhibition and drug–polymer interactions can be investigated by using various spectroscopic methods. Various formulations are prepared as supersaturated systems using different drug-delivery systems utilizing different polymers, which illustrates that supersaturation is worthwhile to increase the solubility and hence oral bioavailability of poorly soluble drugs.

Cellulose based polymers in development of amorphous solid dispersions

Cellulose derivatives have gained immense popularity as stabilizers for amorphous solid dispersion owing to their diverse physicochemical properties. More than 20 amorphous solid dispersion-based products that have been approved for marketing consist of cellulose derivatives as stabilizers, thus highlighting their importance in generation of amorphous solid dispersions. These polymers offer numerous advantages like drug solubilization, crystallization inhibition and improvement in release patterns of drugs. Exploring their potential and exploiting their chemistry and pH responsive behaviour have led to the synthesis of new derivatives that has broadened the scope of the use of cellulose derivatives in amorphous formulation development. The present review aims to provide an overview of different mechanisms by which these cellulose derivatives inhibit the crystallization of drugs in the solid state and from supersaturated solution. A summary of different categories of cellulose derivatives along with the newly explored polymers has been provided. A special segment on strengths, weaknesses, opportunities, and threats (SWOT) analysis and critical quality attributes (CQAs) which affect the performance of the cellulose based amorphous solid dispersion will aid the researchers in identifying the major challenges in the development of cellulose based solid dispersion and serve as a guide for further formulation development.

A case study where pharmaceutical salts were used to address the issue of low in vivo exposure

The present active pharmaceutical ingredient (API) is a lipophilic compound with a significant risk of not achieving therapeutic plasma concentrations due to solubility-limited absorption. The aim of the presented studies was to investigate whether three novel salts of a new selected candidate in the cardiovascular therapy area could be applied to improve intestinal absorption and the subsequent in vivo exposure. Three salts (chloride, hydrogen sulfate, and hemi-1.5-naphtalenedisulphonate) of the compound were manufactured and investigated regarding solubility, dissolution rate, and in vivo exposure in rats. The chemical and physical stability of the salt forms (and the crystalline parent compound) were followed in solid state, when dissolved and when formulated as microsuspensions. All salts showed improved solubility in investigated media, increased dissolution rate, and elevated in vivo exposures compared to a nanocrystal formulation (top-down) of the parent free base of the compound. The chloride- and the hydrogen sulfate salts of the API showed similar patterns regarding the chemical stability in solid state as the crystalline free base, while the salt formed of the hemi-1.5-naphtalenedisulphonic acid showed significantly improved stability. In conclusion, this study showed that three salts of a new selected candidate drug could be used to improve solubility, increase dissolution rate, and enhance oral absorption compared with a more commonly used nanocrystal formulation of the API. However, the identity of the counter ion appeared to be of less importance. On the other hand, only the salt of the hemi-1.5-naphtalenedisulphonic acid seemed to improve chemical stability compared with the API.

Poly(2-Ethyl-2-Oxazoline) as an Alternative to Poly(Vinylpyrrolidone) in Solid Dispersions for Solubility and Dissolution Rate Enhancement of Drugs

Poly(2-ethyl-2-oxazoline) (PEOX), a biocompatible polymer considered as pseudopolypeptide, was introduced as a potential alternative to the commonly used polymer, poly(vinylpyrrolidone) (PVP) for the preparation of solid dispersion with a poorly soluble drug. Glipizide (GPZ), a Biopharmaceutical Classification System class II model drug, was selected for solubility and dissolution rate study. GPZ-polymer solid dispersions and physical mixtures were characterized and investigated by X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy, and FTIR spectroscopy. The impact of polymers on crystal nucleation kinetics was studied, and PEOX exhibited strong inhibitory effect compared with PVP. Solubility and dissolution behavior of the prepared solid dispersions and their physical blends were in vitro examined and evaluated. A significant enhancement in GPZ solubility was obtained with PEOX compared with the pure drug and solid dispersion with PVP. A big improvement in the intrinsic dissolution rate (45 times) and dissolved amount of GPZ (58 times) was achieved with PEOX in fasted state simulated intestinal fluid, against comparable enhancement observed with PEOX and PVP in phosphate buffer at pH 6.8. Lower molecular weight of PEOX-5K (5000 g/mol) was found to be superior to higher molecular weight PEOX-50K (50,000 g/mol) in the improvement of dissolution behavior. The findings of this study with GPZ as a model drug introduce lower molecular weight PEOX as a promising polymeric carrier toward better oral bioavailability of poorly soluble drugs.

Impact of Physicochemical Properties of Cellulosic Polymers on Supersaturation Maintenance in Aqueous Drug Solutions

The precipitation inhibitory effect of cellulosic polymers in relation to their physicochemical properties was studied. Using a poorly water-soluble model drug, griseofulvin, the precipitation inhibitory effect of a series of hydroxypropyl methylcellulose (HPMC) and methylcellulose polymers was studied using solvent-shift method. The extent of supersaturation maintenance of each polymer was then quantified by the parameter, supersaturation factor (SF). Partial least square (PLS) regression analysis was employed to understand the relative contribution from viscosity, hydroxypropyl content (HC), methoxyl content, methoxyl/hydroxypropyl ratio, and drug-polymer interaction parameter (χ) on SF. All grades of cellulosic polymers effectively prolonged supersaturation of griseofulvin. PLS regression analysis revealed that HC and χ appeared to have the strongest influence on SF response. A regression model of SF = 1.65-0.16 χ + 0.05 HC with a high correlation coefficient, r of 0.921, was obtained. Since the value of χ is inversely related to the strength of drug-polymer interaction, the result shows that SF increases with increasing drug-polymer interaction and increasing HC. As such, it can be implied that strong drug-polymer interaction and presence of hydroxypropyl groups in cellulosic polymers for hydrogen bonding are two key parameters for effective supersaturation maintenance. This knowledge on the relative contribution of polymer physicochemical properties on precipitation inhibition will allow the selection of suitable cellulosic polymers for systematic development of supersaturating drug delivery systems.

Formulation and Evaluation of Naringenin Nanosuspensions for Bioavailability Enhancement

The clinical potential of naringenin (NRG) is compromised due to its poor aqueous solubility and low oral bioavailability. The study is aimed at addressing these issues by means of naringenin nanosuspensions (NRG-NS) formulated using polyvinylpyrrolidone (PVP K-90) as stabiliser via antisolvent sonoprecipitation method. Optimisation of sonication time, drug concentration and stabilisers was done based on particle size. Characterisation of pure NRG and NRG-NS was carried out by scanning electron microscopy, differential scanning calorimetry (DSC), x-ray powder diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR). In vitro dissolution, intestinal absorption by non-everted rat intestinal sac model and in situ single pass intestinal perfusion techniques were performed for further investigation. Nanosuspensions prepared using PVP K-90 lead to minimum particle size (117 ± 5 nm) with zeta potential of -14.6 ± 5.6 mV. The particle size was affected by increasing sonication time, concentration of stabiliser and drug. Nanosizing process converted the crystalline drug into amorphous form as predicted from DSC and XRD patterns. FTIR demonstrated the formation of hydrogen bonds between drug and polymer. NRG-NS displayed a higher dissolution amount (91 ± 4.4% during 60 min) compared to NRG powder (42 ± 0.41%). The apparent and effective permeability of NRG-NS was increased as compared to the pure NRG. The in vivo pharmacokinetics demonstrated that the C _max and AUC_0-24 h values of NRG-NS were approximately 2- and 1.8-fold superior than the pure drug. Hence, overall results confirmed nanosuspensions as promising approach for NRG delivery with high absorption in gastrointestinal tract, improved dissolution and oral bioavailability.

Solution electrostatic levitator for measuring surface properties and bulk structures of an extremely supersaturated solution drop above metastable zone width limit

We report on the first integrated apparatus for measuring surface and thermophysical properties and bulk structures of a highly supersaturated solution by combining electrostatic levitation with real-time laser/x-ray scattering. Even today, a proper characterization of supersaturated solutions far above their solubility limits is extremely challenging because heterogeneous nucleation sites such as container walls or impurities readily initiate crystallization before the measurements can be performed. In this work, we demonstrate simultaneous measurements of drying kinetics and surface tension of a potassium dihydrogen phosphate (KH₂PO₄) aqueous solution droplet and its bulk structural evolution beyond the metastable zone width limit. Our experimental finding shows that the noticeable changes of the surface properties are accompanied by polymerizations of hydrated monomer clusters. The novel electrostatic levitation apparatus presented here provides an effective means for studying a wide range of highly concentrated solutions and liquids in deep metastable states.

Mechanism-based selection of stabilization strategy for amorphous formulations: Insights into crystallization pathways

We developed a step-by-step experimental protocol using differential scanning calorimetry (DSC), dynamic vapour sorption (DVS), polarized light microscopy (PLM) and a small-scale dissolution apparatus (μDISS Profiler) to investigate the mechanism (solid-to-solid or solution-mediated) by which crystallization of amorphous drugs occurs upon dissolution. This protocol then guided how to stabilize the amorphous formulation. Indapamide, metolazone, glibenclamide and glipizide were selected as model drugs and HPMC (Pharmacoat 606) and PVP (K30) as stabilizing polymers. Spray-dried amorphous indapamide, metolazone and glibenclamide crystallized via solution-mediated nucleation while glipizide suffered from solid-to-solid crystallization. The addition of 0.001%–0.01% (w/v) HPMC into the dissolution medium successfully prevented the crystallization of supersaturated solutions of indapamide and metolazone whereas it only reduced the crystallization rate for glibenclamide. Amorphous solid dispersion (ASD) formulation of glipizide and PVP K30, at a ratio of 50:50% (w/w) reduced but did not completely eliminate the solid-to-solid crystallization of glipizide even though the overall dissolution rate was enhanced both in the absence and presence of HPMC. Raman spectroscopy indicated the formation of a glipizide polymorph in the dissolution medium with higher solubility than the stable polymorph. As a complementary technique, molecular dynamics (MD) simulations of indapamide and glibenclamide with HPMC was performed. It was revealed that hydrogen bonding patterns of the two drugs with HPMC differed significantly, suggesting that hydrogen bonding may play a role in the greater stabilizing effect on supersaturation of indapamide, compared to glibenclamide.

Amorphous is not always better-A dissolution study on solid state forms of carbamazepine

Poor aqueous solubility is a major concern for many new drugs. One possibility to overcome this issue is to formulate the drug as a high energy form, i.e. a metastable polymorph, an amorphous neat drug or a glass solution with polymers. In this study the dissolution properties of different solid state forms of carbamazepine, crystalline or amorphous drug, with or without either polyvinylpyrrolidone (PVP) or hydroxypropylmethylcellulose (HPMC) and glass solutions of the drug with both polymers (2:1, 4:1 and 10:1 (w/w) drug-to-polymer ratio) were tested with respect to their dissolution behaviour in a biorelevant gastric medium (for 30min) and subsequently in intestinal conditions (for 2h). Carbamazepine form III in the absence of polymer dissolved to a drug concentration of 540μg/ml, but the concentration decreased after around 70min due to precipitation of the dihydrate form, and reached 436μg/ml after 2.5h dissolution testing. The presence of PVP led to a similar dissolution profile with a slightly earlier onset of decrease in drug concentration, while in the presence of HPMC no decline in dissolved drug concentration was observed. Surprisingly, amorphous carbamazepine did not result in any supersaturation and the drug concentration was lower than that measured for crystalline carbamazepine. The addition of polymers further decreased the concentration of dissolved drug (290-310μg/ml, depending on polymer type and concentration). Amorphous drug converted quickly into the dihydrate form and thus no supersaturation was achieved. Glass solutions of carbamazepine with PVP reached drug concentrations between 348 and 408μg/ml after 2.5h, i.e. lower than for the crystalline drug, whilst glass solutions with HPMC reached concentrations similar to the crystalline drug.

Stabilizing ability of surfactant on physicochemical properties of drug nanoparticles generated from solid dispersions

This study was aimed to examine the nanoparticle formation from redispersion of binary and ternary solid dispersions. Binary systems are composed of various ratios of glibenclamide (GBM) and polyvinylpyrrolidone K30 (PVP-K30), whereas a constant amount at 2.5%w/w of a surfactant, sodium lauryl sulfate (SLS) or Gelucire44/14 (GLC), was added to create ternary systems. GBM nanoparticles were collected after the systems were dispersed in water for 15 min. The obtained nanoparticles were characterized for size distribution, crystallinity, thermal behavior, molecular structure, and dissolution properties. The results indicated that GBM nanoparticles could be formed when the drug content of the systems was lower than 30%w/w in binary systems and ternary systems containing SLS. The particle size ranged from 200 to 500 nm in diameter with narrow size distribution. The particle size was increased with increasing drug content in the systems. The obtained nanoparticles were spherical and showed the amorphous state. Furthermore, because of being amorphous form and reduced particle size, the dissolution of the generated nanoparticles was markedly improved compared with the GBM powder. In contrast, all the ternary solid dispersions prepared with GLC anomalously provided the crystalline particles with the size ranging over 5 µm and irregular shape. Interestingly, this was irrelevant to the drug content in the systems. These results indicated the ability of GLC to destabilize the polymer network surrounding the particles during particle precipitation. Therefore, this study suggested that drug content, quantity, and type of surfactant incorporated in solid dispersions drastically affected the physicochemical properties of the precipitated particles.

Mechanistic Design of Chemically Diverse Polymers with Applications in Oral Drug Delivery

Polymers play a key role in stabilizing amorphous drug formulations, a recent strategy employed to improve solubility and bioavailability of drugs delivered orally. However, the molecular mechanism of stabilization is unclear, therefore, the rational design of new crystallization-inhibiting excipients remains a substantial challenge. This article presents a combined experimental and computational approach to elucidate the molecular features that improve the effectiveness of cellulose polymers as solution crystallization inhibitors, a crucial first step toward their rational design. Polymers with chemically diverse substituents including carboxylic acids, esters, ethers, alcohols, amides, amines, and sulfides were synthesized. Measurements of nucleation induction times of the model drug, telaprevir, show that the only effective polymers contained carboxylate groups in combination with an optimal hydrocarbon chain length. Computational results indicate that polymer conformation as well as solvation free energy are important determinants of effectiveness at inhibiting crystallization and show that simulations are a promising predictive tool in the screening of polymers. This study suggests that polymers need to have an adequate hydrophilicity to promote solvation in an aqueous environment, and sufficient hydrophobic regions to drive interactions with the drug. Particularly, the right balance between key substituent groups and lengths of hydrocarbon side chains is needed to create effective materials.

The Combined Use of Imaging Approaches to Assess Drug Release from Multicomponent Solid Dispersions

Purpose

Imaging methods were used as tools to provide an understanding of phenomena that occur during dissolution experiments, and ultimately to select the best ratio of two polymers in a matrix in terms of enhancement of the dissolution rate and prevention of crystallization during dissolution.

Methods

Magnetic resonance imaging, ATR-FTIR spectroscopic imaging and Raman mapping have been used to study the release mechanism of a poorly water soluble drug, aprepitant, from multicomponent amorphous solid dispersions. Solid dispersions were prepared based on the combination of two selected polymers - Soluplus, as a solubilizer, and PVP, as a dissolution enhancer. Formulations were prepared in a ratio of Soluplus:PVP 1:10, 1:5, 1:3, and 1:1, in order to obtain favorable properties of the polymer carrier.

Results

The crystallization of aprepitant during dissolution has occurred to a varying degree in the polymer ratios 1:10, 1:5, and 1:3, but the increasing presence of Soluplus in the formulation delayed the onset of crystallization. The Soluplus:PVP 1:1 solid dispersion proved to be the best matrix studied, combining the abilities of both polymers in a synergistic manner.

Conclusions

Aprepitant dissolution rate has been significantly enhanced. This study highlights the benefits of combining imaging methods in order to understand the release process.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-016-2018-x) contains supplementary material, which is available to authorized users.

The impact of polymeric excipients on the particle size of poorly soluble drugs after pH-induced precipitation

Active pharmaceutical ingredients (APIs) with strongly pH-dependent aqueous solubility can face the problem of precipitating from solution when the pH changes from acidic in the stomach to neutral in the intestine. The present work investigates the effect of two polymeric excipients - polyvinylpyrrolidone (PVP) and Soluplus - on the ability to either prevent precipitation, or to control the size distribution of precipitated particles when precipitation cannot be prevented. Two different APIs were compared, Dabigatran etexilate mesylate and Rilpivirine hydrochloride. The effect of excipient concentration on the precipitation behaviour during pH titration was systematically investigated and qualitatively different trends were observed: in case of Soluplus, which forms a micellar solution when critical micelle concentration is exceeded, precipitation was inhibited in the case of Dabigatran etexilate, which partitioned into the micelles. On the other hand, Rilpivirine precipitated independently of Soluplus concentration. In the case of PVP, which does not form micelles, precipitation could not be avoided. Increased polymer concentration, however prevented the aggregation of precipitated particles into larger cluster. The observed effect of PVP was especially pronounced for Rilpivirine. The main conclusion of this study is that a suitably chosen polymeric excipient can either prevent precipitation altogether or reduce the size of the resulting particles. The mechanism of action, however, seems-specific to a given molecule. It was also shown that the polymer-stabilised particles have a potential to redissolve.