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

Influence of Polyvinylpyrrolidone Molecular Weight and Concentration on the Precipitation Inhibition of Supersaturated Solutions of Poorly Soluble Drugs

Supersaturating drug delivery systems such as solid dispersions of a drug in a polymer are frequently used in pharmaceutical development to enable oral delivery of poorly soluble drugs. In this study, the influence of the concentration and molecular weight of polyvinylpyrrolidone (PVP) on the precipitation inhibition of the poorly soluble drugs albendazole, ketoconazole and tadalafil is investigated to expand the understanding of the mechanism of PVP as a polymeric precipitation inhibitor. A three-level full-factorial design was used to delineate the influence of polymer concentration and viscosity of the dissolution medium on precipitation inhibition. Solutions of PVP K15, K30, K60 or K120 at concentrations of 0.1, 0.5 and 1% (w/v), as well as isoviscous solutions of PVP of increasing molecular weight, were prepared. Supersaturation of the three model drugs was induced by the use of a solvent-shift method. Precipitation of the three model drugs from supersaturated solutions in the absence and presence of polymer was investigated by the use of a solvent-shift method. Time-concentration profiles of the respective drugs in the absence and presence of polymer pre-dissolved in the dissolution medium were obtained by the use of a μDISS Profiler™ to determine the onset of nucleation and the precipitation rate. Multiple linear regression was used to evaluate the hypothesis that precipitation inhibition is influenced by the PVP concentration (i.e., the number of repeat units of the polymer) and the medium viscosity of the polymer for the three model drugs. This study showed that an increased concentration of PVP (i.e., an increased concentration of the PVP repeat units, independent of the molecular weight of the polymer) in solution increased the onset of nucleation and decreased the precipitation rate of the respective drugs during supersaturation, which can be explained by an increase in molecular interactions between the drug and polymer with increasing concentrations of polymer. In contrast, the medium viscosity had no significant influence on the onset of the nucleation and precipitation rate of the drugs, which can be explained by solution viscosity having a negligible effect on the rate of drug diffusion from bulk solution to the crystal nuclei. In conclusion, the precipitation inhibition of the respective drugs is influenced by the concentration of PVP, i.e., by molecular interactions between the drug and polymer. In contrast, the molecular mobility of the drug in solution, i.e., the medium viscosity, has no influence on the precipitation inhibition of the drugs.

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.

Lipopolysaccharide Nanosystems for the Enhancement of Oral Bioavailability

Nanosystems that incorporate both polymers and lipids have garnered attention as emerging nanotechnology approach for oral drug delivery. These hybrid systems leverage on the combined properties of polymeric and lipid-based nanocarriers while eliminating their inherent limitations. In view of the safety-related benefits of naturally occurring polymers, we have focused on systems incorporating polysaccharides and derivatives into the hybrid structure. The aim of this review is to evaluate existing biopolymers with specific focus on lipopolysaccharide hybrid systems and their advancement toward enhancing oral drug delivery. Furthermore, we shall identify future research areas that require further exploration toward achieving an optimized hybrid system for easy translation into clinical use. In this review, we have appraised formulations that combined polysaccharides/derivatives with lipids in a single nanocarrier system. These formulations were grouped into lipid-core-polysaccharide-shell systems, polysaccharide-core-lipid-shell systems, self-emulsifying lipopolysaccharide hybrid systems, and hybrid lipopolysaccharide matrix systems. In these systems, we highlighted how the polysaccharide phase enhances the oral absorption of encapsulated bioactives with regard to their function and mechanism. The various lipopolysaccharide designs presented in this review demonstrated significant improvement in pharmacokinetics of bioactives. A multitude of studies found lipopolysaccharide hybrid systems as nascent nanoplatforms for the oral delivery of challenging bioactives due to features that favor gastrointestinal absorption and bioavailability improvement. With future research already geared toward product optimization and scaling up processes, as well as detailed pharmacological and toxicology pre-clinical testing, these versatile systems will have remarkable impact in clinical application.

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.

Hierarchical Particle Approach for Co-Precipitated Amorphous Solid Dispersions for Use in Preclinical In Vivo Studies

Amorphous solid dispersions (ASD) have become a well-established strategy to improve exposure for compounds with insufficient aqueous solubility. Of methods to generate ASDs, spray drying is a leading route due to its relative simplicity, availability of equipment, and commercial scale capacity. However, the broader industry adoption of spray drying has revealed potential limitations, including the inability to process compounds with low solubility in volatile solvents, inconsistent molecular uniformity of spray dried amorphous dispersions, variable physical properties across batches and scales, and challenges containing potent compounds. In contrast, generating ASDs via co-precipitation to yield co-precipitated amorphous dispersions (cPAD) offers solutions to many of those challenges and has been shown to achieve ASDs comparable to those manufactured via spray drying. This manuscript applies co-precipitation for early safety studies, developing a streamlined process to achieve material suitable for dosing as a suspension in conventional toxicity studies. Development targets involved achieving a rapid, safely contained process for generating ASDs with high recovery yields. Furthermore, a hierarchical particle approach was used to generate composite particles where the cPAD material is incorporated in a matrix of water-soluble excipients to allow for rapid re-dispersibility in the safety study vehicle to achieve a uniform suspension for consistent dosing. Adopting such an approach yielded a co-precipitated amorphous dispersion with comparable stability, thermal properties, and in vivo pharmacokinetics to spray dried amorphous materials of the same composition.

A differential equation based modelling approach to predict supersaturation and in vivo absorption from in vitro dissolution-absorption system (idas2) data

In vitro dissolution tests are widely used to monitor the quality and consistency of oral solid dosage forms, but to increase the physiological relevance of in vitro dissolution tests, newer systems combine dissolution and permeation measurements. Some of these use artificial membranes while others (e.g., in the in vitro dissolution absorption system 2; IDAS2), utilize cell monolayers to assess drug permeation. We determined the effect of the precipitation inhibitor Hypromellose Acetate Succinate (HPMCAS) on the supersaturation/permeation of Ketoconazole and Dipyridamole in IDAS2 and its effect on their absorption in rats. Thus the main objectives of this study were to determine: (1) whether dissolution and permeation data from IDAS2 could be used to predict rat plasma concentration using an absorption model and (2) whether the effect of the precipitation inhibitor HPMCAS on supersaturation and permeation in IDAS2 was correlated with its effect on systemic absorption in the rat. Predicted drug concentrations in rat plasma, generated using parameters estimated from IDAS2 dissolution/permeation data and a mathematical absorption model, showed good agreement with measured concentrations. While in IDAS2, the prolongation of Ketoconazole's supersaturation caused by HPMCAS led to higher permeation, which paralleled the higher systemic absorption in rats, Dipyridamole showed no supersaturation and, thus, no effect of HPMCAS in dissolution or permeation in IDAS2 and no effect on Dipyridamole absorption in rats. The ability of IDAS2 to detect supersaturation following a pH-shift supports the potential value of this system for studying approaches to enhance intestinal absorption through supersaturation and the accuracy of plasma concentration predictions in rats suggest the possibility of combining IDAS2 with absorption models to predict plasma concentration in different species.

Degrees of order: A comparison of nanocrystal and amorphous solids for poorly soluble drugs

Poor aqueous solubility is currently a prevalent issue in the development of small molecule pharmaceuticals. Several methods are possible for improving the solubility, dissolution rate and bioavailability of Biopharmaceutics Classification System (BCS) class II and class IV drugs. Two solid state approaches, which rely on reductions in order, and can theoretically be applied to all molecules without any specific chemical prerequisites (compared with e.g. ionizable or co-former groups, or sufficient lipophilicity), are the use of the amorphous form and nanocrystals. Research involving these two approaches is relatively extensive and commercial products are now available based on these technologies. Nevertheless, their formulation remains more challenging than with conventional dosage forms. This article describes these two technologies from both theoretical and practical perspectives by briefly discussing the physicochemical backgrounds behind these approaches, as well as the resulting practical implications, both positive and negative. Case studies demonstrating the benefits and challenges of these two techniques are presented.

An update on polymer-lipid hybrid systems for improving oral drug delivery

INTRODUCTION

A promising approach that has recently emerged to overcome the complex biobarriers and interrelated challenges associated with oral drug absorption is to combine the benefits of polymeric and lipid-based nanocarriers within one hybrid system. This multifaceted formulation strategy has given rise to a plethora of polymer-lipid hybrid (PLH) systems with varying nanostructures and biological activities, all of which have demonstrated the ability to improve the biopharmaceutical performance of a wide range of challenging therapeutics.

AREAS COVERED

The multitude of polymers that can be combined with lipids to exert a synergistic effect for oral drug delivery have been identified, reviewed and critically evaluated. Specific focus is attributed to preclinical studies performed within the past 5 years that have elucidated the role and mechanism of the polymer phase in altering the oral absorption of encapsulated therapeutics.

EXPERT OPINION

The potential of PLH systems has been clearly identified; however, improved understanding of the structure-activity relationship between PLH systems and oral absorption is fundamental for translating this promising delivery approach into a clinically relevant formulation. Advancing research within this field to identify optimal polymer, lipid combinations and engineering conditions for specific therapeutics are therefore encouraged.

Building a better particle: Leveraging physicochemical understanding of amorphous solid dispersions and a hierarchical particle approach for improved delivery at high drug loadings

Amorphous solid dispersions are a promising option for managing compounds with poor aqueous solubility. However, for compounds with high melting points, thermal stability limitations, or poor solubility in volatile solvents, conventional routes of hot melt extrusion or spray drying may not be viable. Co-precipitated amorphous dispersions (cPAD) can provide a solution. For the material studied in this paper, the cPAD material that was seemingly identical to spray dried material in terms of being single phase amorphous (as measured by DSC and XRD ) but showed slower dissolution behavior. It was identified that physical properties of the cPAD material could be improved to enhance wettability and improve dissolution performance. This was achieved by incorporating the cPAD material into a matrix of water soluble excipients generated via evaporative isolation routes. Importantly, this approach appears to offer another route to further increase the drug load in final dosage units and is significant as increased drug loading generally results in slower or incomplete release. Results showed successful proof of concept via in vitro biorelevant dissolution and confirmatory canine pharmacokinetic studies yielding comparable exposure for capsules comprised of conventional spray dried material as well as capsules with elevated drug load comprised of cPAD hierarchical particles.

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.