Effect of vinylpyrrolidone polymers on the solubility and supersaturation of drugs; a study using the Cheqsol method

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.

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.

Ionizable Drug Self-Associations and the Solubility Dependence on pH: Detection of Aggregates in Saturated Solutions Using Mass Spectrometry (ESI-Q-TOF-MS/MS)

It is widely accepted that solubility-pH profiles of ionizable compounds follow the Henderson-Hasselbalch equation. However, several studies point out that compounds often undergo additional processes in saturated solutions, such as sub-micellar oligomerization, micellar aggregation, or drug-buffer complexation among others, which make the experimental profiles deviate from the behavior predicted by the Henderson-Hasselbalch equation. Often, the presence of additional processes is supported by the analysis of experimental data through solubility computer programs. However, the purpose of this work is to experimentally prove the aggregation phenomena for a series of bases for which deviations from the theoretical profile have been observed. To this end, five monoprotic bases (lidocaine, maprotiline, cyproheptadine, bupivacaine, and mifepristone) susceptible to form ionic aggregates in solution have been selected, and mass spectrometry has been the technique of choice to prove the presence of aggregation. High declustering potentials have been applied to prevent aggregates from forming in the ionization source of the mass spectrometer. In addition, haloperidol has been used as a negative control since according to its profile, it is not suspected to form ionic aggregates. In all instances, except for haloperidol, the analysis of the saturated solutions revealed the presence of mixed-charged dimers (aggregates formed by a neutral molecule and a charged one) and even trimers in the case of mifepristone and bupivacaine. For lidocaine, the most soluble of the compounds, the presence of neutral aggregates was also detected. These experiments support the hypothesis that the simple Henderson-Hasselbalch equation may explain the solubility-pH behavior of certain compounds, but it can be somewhat inaccurate in describing the behavior of many other substances.

Polymer/lipid interplay in altering in vitro supersaturation and plasma concentration of a model poorly soluble drug

Supersaturation drug delivery system (SDDS) based on amorphous solid dispersion (ASD) is a widely used strategy to improve oral absorption of poorly water-soluble drugs by achieving a supersaturated state where drug concentration is significantly higher than drug solubility. However, dissolved drugs tend to recrystallize in gastrointestinal (GI) tract if without effective stabilizing excipients. In this paper, well-recognized polymer (polyvinylpyrrolidone, PVP) and lipid (phosphatidylcholine, PC) excipients are combined as ASD carrier, aiming at investigating the effects on evolution of in vitro supersaturation and in vivo plasma concentration of a model poorly soluble drug indomethacin (IND). Fundamental aspects including polymer/lipid composition ratio, drug loading (DL) degree and administration dose were investigated. The in vitro dissolution profiles of ASDs were assessed by supersaturation degree, duration, maximum achievable drug concentration and dose-normalized efficiency, and correlated with in vivo pharmacokinetic data. Results showed that both in vitro and in vivo concentration-time profiles of IND were significantly varying with abovementioned factors. Solution viscosity, solid-state properties and morphology of ASDs were related to the results. This study revealed fundamental mechanisms of PVP/PC mixture effect on IND supersaturation and oral bioavailability, demonstrating that polymer/lipid mixture could be used as a promising carrier to alter supersaturation profile and oral bioavailability of SDDS products.

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.

A review of methods for solubility determination in biopharmaceutical drug characterization

The significance of thermodynamic solubility in biopharmaceutical compound or drug characterization as well as the importance of having methods that accurately establish it have been extensively addressed. Nonetheless, its precise determination continues to remain a challenging task to accomplish. Even more so when the number of compounds to evaluate is high and the available amount of each compound is low, both of which are inevitable for the compound characterization during the drug development process. Except for the shake-flask method which is still considered as the 'gold standard' in obtaining thermodynamic data, it is currently difficult to say that another satisfactory model which is routinely used to determine thermodynamic solubility is being applied. Therefore, this review summarizes the various experimental approaches which are based on the classical shake flask method but have yet attempted to speed up the experimental process of obtaining such data more conveniently. The most important experimental features of these approaches are provided to the reader. Some advantages and disadvantages associated with each approach are also highlighted, consequently offering a resource to those looking for the most appropriate of the approaches that have already fared well at determining the biopharmaceutically relevant drug solubility.

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.