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

A review on design rules for formulating amorphous solid dispersions based on drug-polymer interactions in aqueous environment

Amorphous solid dispersions (ASDs) are multi-component formulations in which a drug is molecularly dispersed in a carrier. ASDs undergo complex dissolution mechanisms to generate and sustain a supersaturated state of poorly soluble drugs. The link between enhanced solubility, supersaturation stability and drug-polymer interaction (DPI) is critical for the rational design of ASDs. The key mechanism responsible for a high bioavailability is the evolution of supersaturation during the dissolution of ASDs which is also the driving force for drug precipitation. A critical determinant of robust supersaturation generation and stability during dissolution is the molecular interaction between the drug and polymer. Characterization of DPI in a solution state is, however, challenging because of the poor hydrodynamic resolution of the techniques, traditionally used in solid-state analysis. Further, the dissolution conditions, such as the choice of buffer, pH and ionic strength may complicate the analyses and predictions. The role of DPI is a poorly understood aspect of ASD dissolution and therefore is an active area of research. DPI is critical for understanding the design rules for formulating an optimal ASD formulation. The review focuses on different aspects of DPI to stabilize the supersaturated state of a drug during the dissolution of ASDs.

Influence of polymer and surfactant-based precipitation inhibitors on supersaturation-driven absorption of Ibrutinib from high-dose lipid-based formulations

There is a growing pharmaceutical interest in supersaturated lipid-based formulations (Super-LbF) as an innovative strategy to enhance drug loading capacities while simultaneously reducing pill burden. This approach involves increasing the drug concentration above its equilibrium solubility in a lipid solution, achieved through temperature-induced supersaturation or the dissolution of lipophilic ionic salts. However, the physical instability and potential drug precipitation upon the dispersion of LbF remain critical. The focus of this work was to assess the impact of polymer and surfactant as precipitation inhibitors (PIs) in Super-LbF and investigate whether PIs can effectively address the aforementioned challenges. Ibrutinib (Ibr) was selected as a model drug due to its limited solubility and dissolution characteristics. The optimized formulations were characterized with a focus on dispersibility, lipolysis-permeation, and physical stability during storage. The inclusion of PIs in Super-LbF significantly enhanced physical stability by increasing viscosity and reducing the degree of supersaturation through elevated equilibrium solubility. During the dispersion and digestion study, varying levels of transient supersaturation were observed for both Super-LbF and PI-loaded Super-LbF. A noteworthy 2.5 to 3-fold increase in the solubilization ratio was observed for PI-loaded Super-LbF in comparison to Super-LbF without PI. This increase indicates a significant rise in transient drug supersaturation through kinetic and thermodynamic precipitation inhibition mechanisms. Moreover, lipolysis-permeation studies revealed increased flux values with enhanced solubilization, except in the case of Pluronic® F68, which exhibited a reduced free drug concentration near the Permeapad® barrier. Further, the in vivo absorption study confirmed that prolonged supersaturation, facilitated by PIs, contributed to enhancement in drug exposure in rats. PI-loaded Super-LbFs demonstrated a significant improvement (5.1 to 8.9-fold) in the absorption profile compared to Super-LbF without PI (p < 0.001). The study results indicate that incorporating PIs into Super-LbF enhances physical stability and maintains transient drug supersaturation under digestive conditions. Overall, this formulation approach shows promise for expanding the application of LbF to enable the successful oral delivery of high-dose regimen drugs.

Photo-induced drug release at interfaces with arylazopyrazoles

Smart responsive materials have spurred the progress in high-precision drug delivery. Enormous attention has been given to characterizing drug release in bulk aqueous solutions, however, aqueous-hydrophobic interfaces are vital components of biological systems which serve as the point of entry into cells. These interfaces are involved in many key biomolecular interactions, and while the potential for drug molecules to adsorb to these interfaces is recognized, their specific role in the context of drug release remains largely unexplored. We present a fundamental investigation on the release of encapsulated drugs at the air-water interface as a representative model to mimic the organic/aqueous interface of cells. Combining the advantages of light as an external stimulus and the superiority of arylazopyrazoles (AAP) over conventional azobenzene photoswitches, we report a micellar nanocarrier for the capture and release of the chemotherapeutic drug doxorubicin. Using a powerful combination of interface-sensitive techniques such as the Langmuir-Blodgett technique, surface tensiometry, and the interface-specific vibrational sum-frequency generation spectroscopy, we demonstrate the photoresponsive release of doxorubicin encapsulated in the micelles of AAP photosurfactants to the air-water interface. Complementary fluorescence measurements corroborate additional drug release in bulk aqueous solutions.

Supersaturable diacyl phospholipid dispersion for improving oral bioavailability of brick dust molecule: A case study of Aprepitant

This study aims to investigate the potential use of polymer inclusion in the phospholipid-based solid dispersion approach for augmenting the biopharmaceutical performance of Aprepitant (APT). Initially, different polymers were screened using the microarray plate method to assess their ability to inhibit drug precipitation in the supersaturated solution and HPMCAS outperformed the others. Later, the binary (BD) and ternary (TD) phospholipid dispersions were prepared using the co-solvent evaporation method. Solid-state characterization was performed using SEM and PXRD to examine the physical properties, while molecular interactions were probed through FTIR and NMR analysis. In vitro dissolution studies were performed in both fasted and fed state biorelevant media. The results demonstrated a substantial increase in drug release from BD and TD, approximately 4.8 and 9.9 times higher compared to crystalline APT in FaSSIF. Notably, TD also showed a lowered dissolution difference between fed and fasted states in comparison to crystalline APT, indicating a reduction in the positive food effect of APT. Moreover, we assessed the impact of polymer inclusion on permeation under in vitro biomimetic conditions. In comparison with the crystalline APT suspension, both BD and TD demonstrated approximately 3.3 times and 14 times higher steady-state flux (Jss values), respectively. This can be ascribed to the supersaturation and presence of drug-rich submicron particles (nanodroplets) along with the multiple aggregates of drug with phospholipids and polymer in the donor compartment, consequently resulting in a more substantial driving force for passive diffusion. Lastly, in vivo pharmacokinetic evaluation demonstrated the enhanced absorption of both TD and BD over the free drug suspension in the fasted state. This enhancement was evident through a 2.1-fold and 1.3-fold increase in Cmax and a 2.3-fold and 1.4-fold increase in AUC0-t, respectively. Overall, these findings emphasize the potential of polymer-based phospholipid dispersion in enhancing the overall biopharmaceutical performance of APT.

Comparative analysis of drug-salt-polymer interactions by experiment and molecular simulation improves biopharmaceutical performance

The propensity of poorly water-soluble drugs to aggregate at supersaturation impedes their bioavailability. Supersaturated amorphous drug-salt-polymer systems provide an emergent approach to this problem. However, the effects of polymers on drug-drug interactions in aqueous phase are largely unexplored and it is unclear how to choose an optimal salt-polymer combination for a particular drug. Here, we describe a comparative experimental and computational characterization of amorphous solid dispersions containing the drug celecoxib, and a polymer, polyvinylpyrrolidone vinyl acetate (PVP-VA) or hydroxypropyl methylcellulose acetate succinate, with or without Na+/K+ salts. Classical models for drug-polymer interactions fail to identify the best drug-salt-polymer combination. In contrast, more stable drug-polymer interaction energies computed from molecular dynamics simulations correlate with prolonged stability of supersaturated amorphous drug-salt-polymer systems, along with better dissolution and pharmacokinetic profiles. The celecoxib-salt-PVP-VA formulations exhibit excellent biopharmaceutical performance, offering the prospect of a low-dosage regimen for this widely used anti-inflammatory, thereby increasing cost-effectiveness, and reducing side-effects.

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.