pH-Induced Precipitation Behavior of Weakly Basic Compounds: Determination of Extent and Duration of Supersaturation Using Potentiometric Titration and Correlation to Solid State Properties

Professor Lynne S. Taylor: Scientist, educator, and adventurer

This special edition of the Journal of Pharmaceutical Sciences is dedicated to Professor Lynne S. Taylor (Retter Distinguished Professor of Pharmacy, Department of Industrial and Molecular Pharmaceutics, Purdue University), to honor her distinguished career as a pharmaceutical scientist and educator. The goal of this commentary is to provide an overview of Professor Taylor's career path, summarize her key research contributions, and provide some insight into her personal and professional contributions as an educator, mentor, wife, mother, friend, and adventurer.

6-Carboxycellulose Acetate Butyrate: Effectiveness as an Amorphous Solid Dispersion Polymer

Amorphous solid dispersion (ASD) in a polymer matrix is a powerful method for enhancing the solubility and bioavailability of otherwise crystalline, poorly water-soluble drugs. 6-Carboxycellulose acetate butyrate (CCAB) is a relatively new commercial cellulose derivative that was introduced for use in waterborne coating applications. As CCAB is an amphiphilic, carboxyl-containing, high glass transition temperature (Tg) polymer, characteristics essential to excellent ASD polymer performance, we chose to explore its ASD potential. Structurally diverse drugs quercetin, ibuprofen, ritonavir, loratadine, and clarithromycin were dispersed in CCAB matrices. We evaluated the ability of CCAB to create ASDs with these drugs and its ability to provide solubility enhancement and effective drug release. CCAB/drug dispersions prepared by spray drying were amorphous up to 25 wt % drug, with loratadine remaining amorphous up to 50% drug. CCAB formulations with 10% drug proved effective at providing in vitro solubility enhancement for the crystalline flavonoid drug quercetin as well as ritonavir, but not for the more soluble APIs ibuprofen and clarithromycin and the more hydrophobic loratadine. CCAB did provide slow and controlled release of ibuprofen, offering a simple and promising Long-duration ibuprofen formulation. Formulation with clarithromycin showed the ability of the polymer to protect against degradation of the drug at stomach pH. Furthermore, CCAB ASDs with both loratadine and ibuprofen could be improved by the addition of the water-soluble polymer poly(vinylpyrrolidone) (PVP), with which CCAB shows good miscibility. CCAB provided solubility enhancement in some cases, and the slower drug release exhibited by CCAB, especially in the stomach, could be especially beneficial, for example, in formulations containing known stomach irritants like ibuprofen.

In vivo deposition of poorly soluble drugs

Administered drug molecules, whether dissolved or solubilized, have the potential to precipitate and accumulate as solid forms in tissues and cells within the body. This phase transition can significantly impact the pharmacokinetics of treatment. It is thus crucial to gain an understanding of how drug solubility/permeability, drug formulations and routes of administration affect in vivo behaviors of drug deposition. This review examines literature reports on the drug deposition in tissues and cells of poorly water-soluble drugs, as well as underlying physical mechanisms that lead to precipitation. Our work particularly highlights drug deposition in macrophages and the subcellular fate of precipitated drugs. We also propose a tissue permeability-based classification framework to evaluate precipitation potentials of poorly soluble drugs in major organs and tissues. The impact on pharmacokinetics is further discussed and needs to be considered in developing drug delivery systems. Finally, bioimaging techniques that are used to examine aggregated states and the intracellular trafficking of absorbed drugs are summarized.

Gastroretentive fibrous dosage forms for prolonged delivery of sparingly-soluble tyrosine kinase inhibitors. Part 1: Dosage form design, and models of expansion, post-expansion mechanical strength, and drug release

At present, the efficacy and safety of many sparingly-soluble tyrosine kinase inhibitors (TKIs) delivered by the prevalent oral dosage forms are compromised by excessive fluctuations in the drug concentration in blood. To mitigate this limitation, in this four-part study gastroretentive fibrous dosage forms that deliver drug into the gastric fluid (and into the blood) at a controlled rate for prolonged time are presented. The dosage form comprises a cross-ply structure of expandable, water-absorbing, high-molecular-weight hydroxypropyl methylcellulose (HPMC)-based fibers coated with a strengthening, enteric excipient. The intervening spaces between the coated fibers are solid annuli of drug particles, and low-molecular-weight HPMC and enteric excipients. The central regions of the annuli are open channels. In this part, models are developed for dosage form expansion, post-expansion mechanical strength, and drug release. The models suggest that upon immersing in a dissolution fluid, the fluid percolates the open channels, diffuses into the annuli and the coated fibers, and the dosage form expands. The expansion rate is inversely proportional, and the post-expansion mechanical strength proportional to the thickness of the strengthening coating. Drug particles are released from the annuli as the surrounding excipient dissolves. The drug release rate is proportional to the concentration of low-molecular-weight HPMC at the annulus/dissolution fluid interface. The dosage forms can be readily designed for expansion in a few hours, formation of a high-strength viscoelastic mass, and drug release at a constant rate over a day.

Drug Crystal Precipitation in Biorelevant Bicarbonate Buffer: A Well-Controlled Comparative Study with Phosphate Buffer

The purpose of the present study was to clarify whether the precipitation profile of a drug in bicarbonate buffer (BCB) may differ from that in phosphate buffer (PPB) by a well-controlled comparative study. The precipitation profiles of structurally diverse poorly soluble drugs in BCB and PPB were evaluated by a pH-shift precipitation test or a solvent-shift precipitation test (seven weak acid drugs (pKa: 4.2 to 7.5), six weak base drugs (pKa: 4.8 to 8.4), one unionizable drug, and one zwitterionic drug). To focus on crystal precipitation processes, each ionizable drug was first completely dissolved in an HCl (pH 3.0) or NaOH (pH 11.0) aqueous solution (450 mL, 50 rpm, 37 °C). A 10-fold concentrated buffer solution (50 mL) was then added to shift the pH value to 6.5 to initiate precipitation (final volume: 500 mL, buffer capacity (β): 4.4 mM/ΔpH (BCB: 10 mM or PPB: 8 mM), ionic strength (I): 0.14 M (adjusted by NaCl)). The pH, β, and I values were set to be relevant to the physiology of the small intestine. For an unionizable drug, a solvent-shift method was used (1/100 dilution). To maintain the pH value of BCB, a floating lid was used to avoid the loss of CO2. The floating lid was applied also to PPB to precisely align the experimental conditions between BCB and PPB. The solid form of the precipitants was identified by powder X-ray diffraction and differential scanning microscopy. The precipitation of weak acids (pKa ≤ 5.1) and weak bases (pKa ≥ 7.3) was found to be slower in BCB than in PPB. In contrast, the precipitation profiles in BCB and PPB were similar for less ionizable or nonionizable drugs at pH 6.5. The final pH values of the bulk phase were pH 6.5 ± 0.1 after the precipitation tests in all cases. All precipitates were in their respective free forms. The precipitation of ionizable weak acids and bases was slower in BCB than in PPB. The surface pH of precipitating particles may have differed between BCB and PPB due to the slow hydration process of CO2 specific to BCB. Since BCB is a physiological buffer in the small intestine, it should be considered as an option for precipitation studies of ionizable weak acids and bases.

Water-mediated phase transformations of posaconazole: An intricate jungle of crystal forms

Posaconazole is a broad-spectrum antifungal agent exhibiting rich polymorphism. Up to now, a total of fourteen different crystal forms have been reported, sometimes with an ambiguous nomenclature, but less is known about their properties and stability relationships. Investigating the solid-state of a drug compound is essential to identify the most stable form under working conditions and to prevent the risk of undesired solid-phase transformations under processing and storage. In this paper, we study posaconazole polymorphism by providing a description of its polymorphs, hydrates, and solvates. Powder X-ray diffraction (PXRD), dynamic vapor sorption (DVS), spectroscopic and thermal techniques were employed to characterize the different forms. In addition, the solid-phase transformations of posaconazole in aqueous suspensions were studied by means of Raman microscopy. Surprisingly, we found that Form S, the crystal form contained in the marketed oral suspension, is not the most stable form in water. Form S readily converts to a more stable hydrate, i.e. Form A, after storage in water for two weeks. In the commercial oral formulation the conversion between the two forms is prevented by the presence of polysorbate 80. Such insights into the stabilizing excipient effects beyond particle dispersion are critical to formulators.

Interplay of Drug-Polymer Interactions and Release Performance for HPMCAS-Based Amorphous Solid Dispersions

The interplay between drug and polymer chemistry and its impact on drug release from an amorphous solid dispersion (ASD) is a relatively underexplored area. Herein, the release rates of several drugs of diverse chemistry from hydroxypropyl methylcellulose acetate succinate (HPMCAS)-based ASDs were explored using surface area normalized dissolution. The tendency of the drug to form an insoluble complex with HPMCAS was determined through coprecipitation experiments. The role of pH and the extent of drug ionization were probed to evaluate the role of electrostatic interactions in complex formation. Relationships between the extent of complexation and the drug release rate from an ASD were observed, whereby the drugs could be divided into two groups. Drugs with a low extent of insoluble complex formation with HPMCAS tended to be neutral or anionic and showed reasonable release at pH 6.8 even at higher drug loadings. Cationic drugs formed insoluble complexes with HPMCAS and showed poor release when formulated as an ASD. Thus, and somewhat counterintuitively, a weakly basic drug showed a reduced release rate from an ASD at a bulk solution pH where it was ionized, relative to when unionized. The opposite trend was observed in the absence of polymer for the neat amorphous drug. In conclusion, electrostatic interactions between HPMCAS and lipophilic cationic drugs led to insoluble complex formation, which in turn resulted in ASDs with poor release performance.

Physicochemical interaction of rifampicin and ritonavir-lopinavir solid dispersion: an in-vitro and ex-vivo investigation

OBJECTIVE

To investigate the in-situ physicochemical interaction of Rifampicin and Ritonavir - Lopinavir Solid dispersion administered for the treatment of comorbid conditions i.e. Tuberculosis and HIV/AIDS.

METHODS

pH-shift dissolution of Rifampicin (RIF) in presence of Ritonavir-Lopinavir solid dispersion (RL-SD) was carried out in USP phosphate buffer 6.8 and FaSSIF. Equilibrium and amorphous solubility were determined for the drugs. Pure drugs, their physical mixtures, and pH-shifted co-precipitated samples were characterized using DSC, PXRD, and FTIR. Fluorescence spectroscopy was used to investigate drug-rich and drug-lean phases. In-vitro and ex-vivo flux studies were also carried out.

RESULTS

The results showed significant differences in the solubility and dissolution profiles of RTV and LOP in the presence of RIF, while RIF profile remained unchanged. Amorphicity, intermolecular interaction and aggregate formation in pH-shifted samples were revealed in DSC, XRD and FTIR analysis. Fluorescence spectroscopy confirmed the formation of drug-rich phase upon pH-shift. In-vitro and ex-vivo flux studies revealed significant reduction in the flux of all the drugs when studied in presence of second drug.

CONCLUSION

RIF, RTV and LOP in presence of each other on pH-shift, results in co-precipitation in the amorphous form (miscible) which leads to reduction in the highest attainable degree of supersaturation. This reduction corresponds to the mole fraction of the RIF, RTV and LOP within the studied system. These findings suggest that the concomitant administration of these drugs may lead to physicochemical interactions and possible ineffective therapy.

Effect of Buffer pH and Concentration on the Dissolution Rates of Sodium Indomethacin-Copovidone and Indomethacin-Copovidone Amorphous Solid Dispersions

The incorporation of counterions into amorphous solid dispersions (ASDs) has been proven to be effective for improving the dissolution rates of ionizable drugs in ASDs. In this work, the effect of dissolution buffer pH and concentration on the dissolution rate of indomethacin-copovidone 40:60 (IMC-PVPVA, w/w) ASD with or without incorporated sodium hydroxide (NaOH) was studied by surface area-normalized dissolution to provide further mechanistic understanding of this phenomenon. Buffer pH from 4.7 to 7.2 and concentration from 20 to 100 mM at pH 5.5 were investigated. As the buffer pH decreased, the IMC dissolution rate from both ASDs decreased. Compared to IMC-PVPVA ASD, the dissolution rate decrease from IMCNa-PVPVA ASD was more resistant to the decrease of buffer pH. In contrast, while buffer concentration had a negligible impact on the IMC dissolution rate from IMC-PVPVA ASD, the increase of buffer concentration significantly reduced the IMC dissolution rate from IMCNa-PVPVA ASD. Surrogate evaluation of microenvironment pH modification by the dissolution of IMCNa-PVPVA ASD demonstrated the successful elevation of buffer microenvironment pH and the suppression of such pH elevation by the increase of buffer concentration. These results are consistent with the hypothesis that the dissolution rate enhancement by the incorporation of counterions originates from the enhanced drug solubility by ionization and the modification of diffusion layer pH in favor of drug dissolution. At the studied drug loading (∼40%), relatively congruent release between IMC and PVPVA was observed when IMC was ionized in ASD or in solution, highlighting the importance of studying the ionization effect on the congruent release of ASDs, especially when drug ionization is expected in vivo. Overall, this work further supports the application of incorporating counterions into ASDs for improving the dissolution rates of ionizable drugs when enabling formulation development is needed.

Reliable and accurate prediction of basic pK[Formula: see text] values in nitrogen compounds: the pK[Formula: see text] shift in supramolecular systems as a case study

This article presents a quantitative structure-activity relationship (QSAR) approach for predicting the acid dissociation constant (pK[Formula: see text]) of nitrogenous compounds, including those within supramolecular complexes based on cucurbiturils. The model combines low-cost quantum mechanical calculations with QSAR methodology and linear regressions to achieve accurate predictions for a broad range of nitrogen-containing compounds. The model was developed using a diverse dataset of 130 nitrogenous compounds and exhibits excellent predictive performance, with a high coefficient of determination (R[Formula: see text]) of 0.9905, low standard error (s) of 0.3066, and high Fisher statistic (F) of 2142. The model outperforms existing methods, such as Chemaxon software and previous studies, in terms of accuracy and its ability to handle heterogeneous datasets. External validation on pharmaceutical ingredients, dyes, and supramolecular complexes based on cucurbiturils confirms the reliability of the model. To enhance usability, a script-like tool has been developed, providing a streamlined process for users to access the model. This study represents a significant advancement in pK[Formula: see text] prediction, offering valuable insights for drug design and supramolecular system optimization.

Harnessing Bile for Drug Absorption through Rational Excipient Selection

Bile solubilization and apparent solubility at resorption sites critically affect the bioavailability of orally administered and poorly water-soluble drugs. Therefore, identification of drug-bile interaction may critically determine the overall formulation success. For the case of the drug candidate naporafenib, drug in solution at phase separation onset significantly improved with polyethylene glycol-40 hydrogenated castor oil (RH40) and amino methacrylate copolymer (Eudragit E) but not with hydroxypropyl cellulose (HPC) in both phosphate-buffered saline (PBS) and PBS supplemented with bile components. Naporafenib interacted with bile as determined by 1H and 2D 1H-1H nuclear magnetic resonance spectroscopy and so did Eudragit E and RH40 but not HPC. Flux across artificial membranes was reduced in the presence of Eudragit E. RH40 reduced the naporafenib supersaturation duration. HPC on the other side stabilized naporafenib's supersaturation and did not substantially impact flux. These insights on bile interaction correlated with pharmacokinetics (PK) in beagle dogs. HPC preserved naporafenib bile solubilization in contrast to Eudragit E and RH40, resulting in favorable PK.

In vitro, in-vivo, and in-silico investigation of physicochemical interactions between pioglitazone and rifampicin

There is a possibility of in-situ physicochemical interactions between concomitantly administered drugs. This study aimed to investigate such physicochemical interactions between pioglitazone and rifampicin. Pioglitazone exhibited significantly higher dissolution in the presence of rifampicin, while the dissolution of rifampicin remained unaffected. The solid-state characterization of precipitates recovered after pH-shift dissolution experiments revealed the conversion of pioglitazone into an amorphous form in the presence of rifampicin. The Density Function Theory (DFT) calculations showed the intermolecular hydrogen bonding between rifampicin and pioglitazone. In-situ conversion of pioglitazone in amorphous form and subsequent supersaturation of GIT milieu translated into significantly higher in-vivo exposure of pioglitazone and its metabolites (M-III and M-IV) in Wistar rats. Therefore, it is advisable to consider the possibility of physicochemical interactions between concomitantly administered drugs. Our findings may be beneficial in tailoring the dose of concomitantly administered drugs, particularly for chronic conditions that entail polypharmacy.

Thermodynamic Correlation between Liquid-Liquid Phase Separation and Crystalline Solubility of Drug-Like Molecules

The purpose of the present study was to experimentally confirm the thermodynamic correlation between the intrinsic liquid−liquid phase separation (LLPS) concentration (S0LLPS) and crystalline solubility (S0c) of drug-like molecules. Based on the thermodynamic principles, the crystalline solubility LLPS concentration melting point (Tm) equation (CLME) was derived (log10S0C=log10S0LLPS−0.0095Tm−310 for 310 K). The S0LLPS values of 31 drugs were newly measured by simple bulk phase pH-shift or solvent-shift precipitation tests coupled with laser-assisted visual turbidity detection. To ensure the precipitant was not made crystalline at <10 s, the precipitation tests were also performed under the polarized light microscope. The calculated and observed log10S0C values showed a good correlation (root mean squared error: 0.40 log unit, absolute average error: 0.32 log unit).

Mechanisms and Extent of Enhanced Passive Permeation by Colloidal Drug Particles

Formulations containing nanosized drug particles such as nanocrystals and nanosized amorphous drug aggregates recently came into light as promising strategies to improve the bioavailability of poorly soluble drugs. However, the increased solubility due to the reduction in particle size cannot adequately explain the enhanced bioavailability. In this study, the mechanisms and extent of enhanced passive permeation by drug particles were investigated using atazanavir, lopinavir, and clotrimazole as model drugs. Franz diffusion cells with lipid-infused membranes were utilized to evaluate transmembrane flux. The impact of stirring rate, receiver buffer condition, and particle size was investigated, and mass transport analyses were conducted to calculate transmembrane flux. Flux enhancement by particles was found to be dependent on particle size as well as the partitioning behavior of the drug between the receiver solution and the membrane, which is determined by both the drug and buffer used. A flux plateau was observed at high particle concentrations above amorphous solubility, confirming that mass transfer of amorphous drug particles from the aqueous solution to the membrane occurs only through the molecularly dissolved drug. Mass transport models were used to calculate flux enhancement by particles for various drugs at different conditions. Good agreements were obtained between experimental and predicted values. These results should contribute to improved bioavailability prediction of nanosized drug particles and better design of formulations containing colloidal drug particles.

Study on the grain refinement mechanism of Mg-Al alloy based on carbon addition

In this study, a comprehensive treatment process based on the rotary injection of Ar+CO₂ Mg-Al alloy melt is proposed. The effect of carbon on the grain refinement of Mg-Al alloy is studied according to the proposed integrated treatment process. The regularity of carbon refinement in the Mg-Al alloy is examined by microstructural observation and theoretical calculation. The results show that carbon has no effect on the grain refinement of Mg-Al alloy when the Al content is less than 1wt.%. However, when the Al content reaches 2 wt.%, the refining effect is obvious, and the grain refinement efficiency is 62%. The refining effect increases with the increase in the Al content, and the refinement efficiency becomes 79% when the Al content reaches 9 wt.%. The size of Al-C-O in the matrix is approximately 5μm, which confirms the existence of Al₄C₃ phase exists as a heterogeneous nucleating agent. The theoretical calculations suggest that the Al₄C₃ heterogeneous nucleating agent cannot be formed when the Al content in the Mg alloy is less than 1.34%, so there is no thinning effect under such Al content. The crystallographic calculations reveal that the mismatch between the Al₄C₃ phase and Mg alloy matrix is only 4.05%, and Al₄C₃ can exist as a heterogeneous nucleating agent for α-Mg phase. Combining the measured solidification curves with the classical nucleation theory, the wetting angle of Mg-Al alloy on Al₄C₃ is calculated to be 24.3°.

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.

An Insight into Eudragit S100 Preserving Mechanism of Cinnarizine Supersaturation

Generally, supersaturation of weakly basic drug solution in the gastrointestinal tract can be followed by precipitation, and this can compromise the bioavailability of drugs. The purpose of this study was to evaluate the effect of Eudragit® S100 on the pH-induced supersaturation of cinnarizine and to examine the preserving mechanism of cinnarizine supersaturation by Eudragit®. Variables, including pH of media, ionic strength, and degree of supersaturation, were studied to investigate the effects of these parameters on cinnarizine supersaturation in the presence and absence of Eudragit®. The size of the Eudragit® aggregate in solution using dynamic light scattering was determined. The effect of Eudragit® on the transport of cinnarizine through the Caco-2 membrane was also investigated. The particle size study of Eudragit® aggregates showed that the size of these aggregates become large when the pH was lowered. Supersaturation experiments also demonstrated that Eudragit® preserved higher cinnarizine supersaturation with increasing ionic strength of the solution. The phase separation behavior of cinnarizine solution as a function of the degree of the supersaturation could be readily explained by considering the drug amorphous solubility. In vitro permeation studies revealed that the rate of cinnarizine permeation across Caco-2 cells increased in the presence of Eudragit®. According to the obtained results, the aggregation status of Eudragit® and nonspecific hydrophobic cinnarizine-Eudragit® interactions seemed to be essential in determining the effect of Eudragit® on cinnarizine supersaturation.

Characterizing the Physicochemical Properties of Two Weakly Basic Drugs and the Precipitates Obtained from Biorelevant Media

Generally, some weakly basic insoluble drugs will undergo precipitate and redissolution after emptying from the stomach to the small intestinal, resulting in the limited ability to predict the absorption characteristics of compounds in advance. Absorption is determined by the solubility and permeability of compounds, which are related to physicochemical properties, while knowledge about the absorption of redissolved precipitate is poorly documented. Considering that biorelevant media have been widely used to simulate gastrointestinal fluids, sufficient precipitates can be obtained in biorelevant media in vitro. Herein, the purpose of this manuscript is to evaluate the physicochemical properties of precipitates obtained from biorelevant media and active pharmaceutical ingredients (API), and then to explore the potential absorption difference between API and precipitates. Precipitates can be formed by the interaction between compounds and intestinal fluid contents, leading to changes in the crystal structure, melting point, and melting process. However, the newly formed crystals have some advantageous properties compared with the API, such as the improved dissolved rate and the increased intrinsic dissolution rate. Additionally, the permeability of some precipitates obtained from biorelevant media was different from API. Meanwhile, the permeability of rivaroxaban and Drug-A was decreased by 1.92-fold and 3.53-fold, respectively, when the experiments were performed in a biorelevant medium instead of a traditional medium. Therefore, the absorption of precipitate may differ from that of API, and the permeability assay in traditional medium may be overestimated. Based on the research results, it is crucial to understand the physicochemical properties of precipitates and API, which can be used as the departure point to improve the prediction performance of absorption.

Development of a gliclazide ionic liquid and its mesoporous silica particles: an effective formulation strategy to improve oral absorption properties

Ionic liquid (IL) technology provides a useful platform to enhance the oral absorption of therapeutic agents. In the present work, gliclazide (GLI), a second-generation sulfonylurea drug was transformed into an IL with tetrabutylphosphonium. The physicochemical properties of this IL were systematically characterized by DSC, TGA, FT-IR, NMR, and HPLC. For the further preparation development, a solution stability test was conducted. GLI-based IL could improve the solution stability in a neutral environment. To assess oral potential, the solubility characteristics including equilibrium solubility, 24 h kinetic saturation solubilities and supersaturation profiles were first explored. Significant enhancement of solubilities, supersaturation ratio and duration of supersaturation was found for the synthesized IL. Computational methodology was utilized to better understand the improved solubility results. From the simulated results, [TBP][GLI] showed a longer time period when the distance between cation and anion was far above the baseline and a higher deviation degree, indicating less stable ion pairs of [TBP][GLI] in an aqueous environment and it being easy for the cation and anion to tear apart and form interactions with water molecules. The prepared [TBP][GLI] exhibited intestinal transportation ability and safety as evidenced by the in vitro gastrointestinal tract artificial membrane permeability assays (GIT-PAMPA) and cytotoxicity experiments with Caco-2 cells. A mesoporous carrier, AEROPERL® 300 Pharma, was chosen to load the IL and then encapsuled into enteric capsules. The prepared oral capsules containing GLI-based IL loaded mesoporous silica particles released fast and could realize 100% release within 60 min.

pH-Dependent supersaturation from amorphous solid dispersions of weakly basic drugs

PURPOSE

In amorphous solid dispersions (ASDs), the chemical potential of a drug can be reduced due to mixing with the polymer in the solid matrix, and this can lead to reduced drug release when the polymer is insoluble in the dissolution media. If both the drug and the polymer composing an ASD are ionizable, drug release from the ASD becomes pH-dependent. The goal of this study was to gain insights into the pH-dependent solubility suppression from ASD formulations.

METHODS

The maximum release of clotrimazole, a weakly basic drug, from ASDs formulated with insoluble and pH-responsive polymers, was determined as a function of solution pH. Drug-polymer interactions in ASDs were probed using melting point depression, moisture sorption, and solid-state Nuclear Magnetic Resonance spectroscopy (SSNMR) measurements.

RESULTS

The extent of solubility suppression was dependent on polymer type and drug loading. The strength of drug-polymer interactions was found to correlate well with the degree of solubility suppression. For the same ASD, the degree of solubility suppression was nearly constant across the solution pH range studied, suggesting that polymer-drug interactions in residual ASD solids was independent of solution pH. The total drug release agrees with the Henderson-Hasselbalch relationship if the suppressed amorphous solubility of the free drug is independent of solution pH.

CONCLUSIONS

The mechanism of solubility suppression at different solution pHs appeared to be drug-polymer interactions in the solid-state, where the concentration of the free drug remains the same at variable pHs and the total drug concentration follows the Henderson-Hasselbalch relationship.

Implications of phase solubility/miscibility and drug-rich phase formation on the performance of co-amorphous materials: The case of Darunavir co-amorphous materials with Ritonavir and Indomethacin as co-formers

The present study was designed to investigate the contribution of solid-state and the impact of composite drug-rich phase generated as a consequence of pH shift on the maximum achievable supersaturation of co-amorphous formulations. The co-amorphous phases of weak base-weak base-pair i.e. Ritonavir and Darunavir were prepared in anticipation of studying the effect of drug-rich phase consequent to pH shift. While the co-amorphous phases of weak base-Weak acid pair i.e. Darunavir and Indomethacin were studied to understand the manifestation of the solid-state drug: co-former miscibility in the absence of drug rich phase. Thermodynamically, the lowering of the supersaturation was found commensurate with the mole fraction of the respective component (Drug/Co-former) within the co-amorphous materials for both Darunavir: Ritonavir and Darunavir: Indomethacin pair. Kinetically, for Darunavir: Ritonavir co-amorphous materials, the shift in the pH from acidic to the neutral side led to the generation of drug-rich phase and subsequent LLPS. The free drug concentration achieved in the bulk of the solution was found dependent upon the mole fraction of the respective component within the drug-rich phase. The relative mole fraction of each component within the composite drug-rich phase is dictated by pH-dependent solubility and molecular weight of the individual components.

Amorphous Solid Dispersions (ASDs): The Influence of Material Properties, Manufacturing Processes and Analytical Technologies in Drug Product Development

Poorly water-soluble drugs pose a significant challenge to developability due to poor oral absorption leading to poor bioavailability. Several approaches exist that improve the oral absorption of such compounds by enhancing the aqueous solubility and/or dissolution rate of the drug. These include chemical modifications such as salts, co-crystals or prodrugs and physical modifications such as complexation, nanocrystals or conversion to amorphous form. Among these formulation strategies, the conversion to amorphous form has been successfully deployed across the pharmaceutical industry, accounting for approximately 30% of the marketed products that require solubility enhancement and making it the most frequently used technology from 2000 to 2020. This article discusses the underlying scientific theory and influence of the active compound, the material properties and manufacturing processes on the selection and design of amorphous solid dispersion (ASD) products as marketed products. Recent advances in the analytical tools to characterize ASDs stability and ability to be processed into suitable, patient-centric dosage forms are also described. The unmet need and regulatory path for the development of novel ASD polymers is finally discussed, including a description of the experimental data that can be used to establish if a new polymer offers sufficient differentiation from the established polymers to warrant advancement.

Expandable, dual-excipient fibrous dosage forms for prolonged delivery of sparingly soluble drugs

In this work, the rates of expansion and drug release by fibrous dosage forms with two excipients are investigated for prolonged delivery of sparingly soluble drugs. The formulation consisted of ibuprofen drug, high-molecular-weight hydroxypropyl methyl cellulose (HPMC) excipient, and the enteric methacrylic acid-ethyl acrylate excipient. Upon immersion in a dissolution fluid, the single fibers and all dosage forms (fiber volume fractions, φ = 0.16, 0.39, and 0.56) expanded proportional to the square-root of time, a characteristic of diffusion-controlled processes. The size of the dosage forms doubled in ten minutes, and they were converted into a highly viscous gel that was stabilized by the enteric excipient for over two days. Eighty percent of the drug was released from single fibers in less than an hour, but in thirty-eight hours from the dosage form with φ = 0.56. Theoretical models suggest that if φ is small, drug release is limited by drug diffusion through the thin fibers. But if φ is very large, drug release is determined by diffusion through the thick, viscous dosage form gel. Between these extremes the drug release time increases exponentially with φ.

Towards more accurate solubility measurements with real time monitoring: a carvedilol case study

Study of factors like type of polymorphs, pH and buffer composition influencing the equilibrium time of carvedilol using in situ UV-probes.

Mechanisms for the Slowing of Desupersaturation of a Weak Acid at Elevated pH

Supersaturating drug delivery systems are used to achieve higher oral bioavailability for poorly soluble drugs. However, supersaturated solutions often decline to lower concentrations by precipitation and crystallization. The purpose of the current research is to provide a mechanistic understanding of drug crystallization as a function of pH, using indomethacin (IMC, pK_a 4.18) as a model compound. Desupersaturation kinetics to the γ-form of IMC was measured at pH 2.0, 3.0, 4.0, and 4.5 from an initial degree of supersaturation of 2.5-6. At equivalent levels of supersaturation, crystal growth rates decreased with an increase in solution pH. Two mechanisms for this phenomenon, reactive diffusion (resulting in a higher surface pH as compared to bulk pH) and inhibition of crystallization by structurally similar ionized IMC at higher pH, were explored. Non-steady-state models for reactive diffusion showed that the surface pH was only 0.01 units above that of the bulk solution pH. Mass transport models for reactive diffusion during crystallization could not explain the decrease in desupersaturation kinetics at higher pH. However, zeta potentials as high as -70 mV suggested that IMC^- is adsorbed on the surface of the particles. A mathematical model for inhibition of crystal growth by IMC^- accounted for the pH effect suggesting that ionized IMC acts as an effective crystallization inhibitor of IMC.

The Introduction of a New Flexible In Vivo Predictive Dissolution Apparatus, GIS-Alpha (GIS-α), to Study Dissolution Profiles of BCS Class IIb Drugs, Dipyridamole and Ketoconazole

The physiological pH changes and peristalsis activities in gastrointestinal (GI) tract have big impact on the dissolution of oral drug products, when those oral drug products include APIs with pH-dependent solubility. It is well documented that predicting the bioperformance of those oral drug products can be challenging using compendial methods. To overcome this limitation, in vivo predictive dissolution apparatuses, such as the transfer model, have been developed to predict bioperformance of oral formulation candidates and drug products. In this manuscript we utilize a new transfer-model dissolution apparatus, the gastrointestinal simulator-α (GIS-α), to characterize its behavior in terms of transfer kinetics and pH, assess its reproducibility and adaptability to mimic different transfer conditions, as well as study dissolution of ketoconazole and dipyridamole as model BCS class IIb compounds. Availability of commercially available dissolution transfer systems with similar configuration to compendial dissolution apparatus, may be helpful to simplify and standardize in vivo predictive dissolution methodologies for BCS class IIb compounds in the future.

Influence of Drug-Silica Electrostatic Interactions on Drug Release from Mesoporous Silica-Based Oral Delivery Systems

Mesoporous silica particles are attractive carriers for poorly soluble drugs whereby confinement of drugs in the mesopores leads to amorphization, which makes them potential carriers for enhanced oral delivery. However, interactions between the drug molecules and the silica surface can lead to incomplete drug release. The strength of the interaction depends on the silica surface chemistry, which varies as a function of pH, as well as on drug chemistry and ionization states. Herein, the adsorption and dissolution behavior of weakly basic drugs were evaluated as a function of pH to understand the impact of electrostatic interactions on the performance of mesoporous silica-based formulations. A higher adsorption was noted when the drug interacted with the silica surface via electrostatic interactions compared to hydrogen bonding. Higher adsorption, in turn, led to a lower extent of drug release. In two-stage release studies of drugs with pK_a values close to the intestinal pH, a shift from low to higher pH solutions resulted in a decrease in the solution concentration. Further investigations demonstrated that this was due to readsorption of the drug, initially released in the acidic medium when the pH was increased. Two-stage release studies were also coupled with mass transport measurements. Only a slight improvement in drug release due to simultaneous absorption across a membrane was observed, suggesting strong drug adsorption to the silica surface arising from favorable electrostatic interactions, which diminishes the effect of sink conditions provided by the absorptive environment. This study highlights that physiological parameters, such as solution pH, are important considerations when designing mesoporous silica-based formulations for poorly soluble drugs. It also underscores the importance of incorporating in vivo-relevant conditions in in vitro testing to better evaluate these complex formulations due to the notable effect of dissolution media on the release behavior.

Bioinspired Ion Pairs Transforming Papaverine into a Protic Ionic Liquid and Salts

Microbial, mammalian, and plant cells produce and contain secondary metabolites, which typically are soluble in water to prevent cell damage by crystallization. The formation of ion pairs, for example, with carboxylic acids or mineral acids, is a natural blueprint to maintain basic metabolites in solution. Here, we aim at showing whether the mostly large carboxylates form soluble protic ionic liquids (PILs) with the basic natural product papaverine resulting in enhanced aqueous solubility. The obtained PILs were characterized by 1H-15N HMBC nuclear magnetic resonance (NMR) and in the solid state using X-ray powder diffraction, differential scanning calorimetry, and dissolution measurements. Furthermore, their supramolecular pattern in aqueous solution was studied by means of potentiometric and photometrical solubility, NMR aggregation assay, dynamic light scattering, zeta potential, and viscosity measurements. Thereby, we identified the naturally occurring carboxylic acids, citric acid, malic acid, and tartaric acid, as being appropriate counterions for papaverine and which will facilitate the formation of PILs with their beneficial characteristics, like the improved dissolution rate and enhanced apparent solubility.

Application of the Gastrointestinal Simulator (GIS) Coupled with In Silico Modeling to Measure the Impact of Coca-Cola® on the Luminal and Systemic Behavior of Loratadine (BCS Class 2b)

In the present work, we explored if Coca-Cola^® had a beneficial impact on the systemic outcome of the weakly basic drug loratadine (Wal-itin^®, immediate-release formulation, 10 mg, generic drug product). To map the contribution of underlying physiological variables that may positively impact the intestinal absorption of loratadine, a multi-compartmental and dynamic dissolution device was built, namely the Gastrointestinal Simulator (GIS). The luminal behavior of one immediate-release (IR) tablet of 10 mg of loratadine was tested under four different fasted state test conditions in the GIS: (i) with 250 mL of water and applying a predetermined gastric half-life (t_1/2,G) of 15 min; (ii) with 250 mL of water and applying a t_1/2,G of 30 min; (iii) with 250 mL of Coca-Cola^® and a t_1/2,G of 15 min; (iv) with 250 mL of Coca-Cola^® and a t_1/2,G of 30 min. After initiating the experiments, solution concentrations and solubility were measured in the withdrawn samples, and pH was monitored. To address the impact of the present CO₂ in Coca-Cola^® on the disintegration time of the tablet, additional disintegration experiments were performed in a single-vessel applying tap water and sparkling water as dissolution media. These experiments demonstrated the faster disintegration of the tablet in the presence of sparkling water, as the present CO₂ facilitates the release of the drug. The buffer capacity of Coca-Cola^® in the presence of FaSSGF was 4-fold higher than the buffer capacity of tap water in the presence of FaSSGF. After performing the in vitro experiments, the obtained results were used as input for a two-compartmental pharmacokinetic (PK) modeling approach to predict the systemic concentrations. These simulations pointed out that (i) the present CO₂ in Coca-Cola^® is responsible for the enhancement in drug release and dissolution and that (ii) a delay in gastric emptying rate will sustain the supersaturated concentrations of loratadine in the intestinal regions of the GI tract, resulting in an enhanced driving force for intestinal absorption. Therefore, co-administration of loratadine with Coca-Cola^® will highly likely result in an increased systemic exposure compared to co-administration of loratadine with tap water. The mechanistic insights that were obtained from this work will serve as a scientific basis to evaluate the impact of Coca-Cola^® on the systemic exposure of weakly basic drugs for patients on acid-reducing agents in future work.

Orally ingestible medical devices for gut engineering

Orally ingestible medical devices provide significant advancement for diagnosis and treatment of gastrointestinal (GI) tract-related conditions. From micro- to macroscale devices, with designs ranging from very simple to complex, these medical devices can be used for site-directed drug delivery in the GI tract, real-time imaging and sensing of gut biomarkers. Equipped with uni-direction release, or self-propulsion, or origami design, these microdevices are breaking the barriers associated with drug delivery, including biologics, across the GI tract. Further, on-board microelectronics allow imaging and sensing of gut tissue and biomarkers, providing a more comprehensive understanding of underlying pathophysiological conditions. We provide an overview of recent advances in orally ingestible medical devices towards drug delivery, imaging and sensing. Challenges associated with gut microenvironment, together with various activation/actuation modalities of medical devices for micromanipulation of the gut are discussed. We have critically examined the relationship between materials–device design–pharmacological responses with respect to existing regulatory guidelines and provided a clear roadmap for the future.

Understanding the Oral Absorption of Irbesartan Using Biorelevant Dissolution Testing and PBPK Modeling

Poorly soluble weak bases form a significant proportion of the drugs available in the market thereby making it imperative to understand their absorption behavior. This work aims to mechanistically understand the oral absorption behavior for a weakly basic drug, Irbesartan (IRB), by investigating its pH dependent solubility, supersaturation, and precipitation behavior. Simulations performed using the equilibrium solubility could not accurately predict oral absorption. A multi-compartmental biorelevant dissolution testing model was used to evaluate dissolution in the stomach and duodenal compartment and mimic oral drug administration. This model exhibited sustained intestinal supersaturation (2-4-fold) even upon varying flow rates (4 mL/min, 7 mL/min, and mono-exponential transfer) from gastric to intestinal compartment. Simulation of oral absorption using GastroPlus™ and dissolution data collectively predicted plasma exposure with higher accuracy (% prediction error values within ± 15%), thereby indicating that multi-compartment dissolution testing enabled an improved prediction for oral pharmacokinetics of Irbesartan. Additionally, precipitates obtained in the intestinal compartment were characterized to determine the factors underlying intestinal supersaturation of Irbesartan. The solid form of these precipitates was amorphous with considerable particle size reduction. This indicated that following gastric transit, precipitate formation in the amorphous form coupled with an approximately 10 times particle size reduction could be potential factors leading to the generation and sustenance of intestinal drug supersaturation.

The Significance of Utilizing In Vitro Transfer Model and Media Selection to Study the Dissolution Performance of Weak Ionizable Bases: Investigation Using Saquinavir as a Model Drug

This study investigated the dissolution behavior of BCS class II ionizable weak base Saquinavir and its mesylate salt in the multi-compartment transfer setup employing different composition of dissolution media. The dissolution behavior of Saquinavir was studied by using a two-compartment transfer model representing the transfer of drug from the stomach (donor compartment) to the upper intestine (acceptor compartment). Various buffers like phosphate, bicarbonate, FaSSIF, and FeSSIF were employed. The dissolution was also studied in the concomitant presence of the additional solute, i.e., Quercetin. Further, the dissolution profiles of Saquinavir and its mesylate salt were simulated by GastroPlus^TM, and the simulated dissolution profiles were compared against the experimental ones. The formation of in situ HCl salt and water-soluble amorphous phosphate aggregates was confirmed in the donor and acceptor compartments of the transfer setup, respectively. As the consequence of the lower solubility product of HCl salt of Saquinavir, the solubility advantage of mesylate salt was vanished leading to the lower than the predicted dissolution in the acceptor compartment. However, the formation of water-soluble aggregates in the presence of the phosphate salts was observed leading to the higher than the predicted dissolution of the free base in the transfer setup. Interestingly, the formation of such water-soluble aggregates was found to be hindered in the concomitant presence of an ionic solute resulting in the lower dissolution rates. The in situ generation of salts and aggregates in the transfer model lead to the inconsistent prediction of dissolution profiles by GastroPlus^TM.

Formulation of Cinnarizine for Stabilization of Its Physiologically Generated Supersaturation

Physiologically generated supersaturation and subsequent crystallization of a weakly basic drug in the small intestine leads to compromised bioavailability. In this study, the pH-induced crystallization of cinnarizine (CNZ) in the presence of different polymers was investigated. Inhibitory effect of Eudragit L100 (Eu) on crystallization of CNZ at varying supersaturation ratios was examined. The effect of Eu on the dissolution behavior of CNZ from CNZ/Eu physical mixtures (PMs) and solid dispersions (SDs) was assessed. Results showed that both Eu and hydroxypropyl methylcellulose (HPMC) have a considerable maintenance effect on supersaturation of CNZ but Eu was more effective than HPMC. When Eudragit was used the phenomenon of liquid-liquid phase separation (formation of colloidal phase) was observed at supersaturation ratio of 20 times above the solubility of the drug. PMs showed a higher area under the dissolution curve (AUDC) compared with plain CNZ. In contrast, SDs showed a lower AUDC than plain CNZ. For SDs, the AUDC was limited by the slow release of the drug from Eu in acidic pH which in turn hindered the creation of CNZ supersaturation following the transition of acidic to neutral pH. From these findings, it can be concluded that the ability of the formulation to generate supersaturation state and also maintain the supersaturation is vital for improving the dissolution of CNZ.

Molecular Drivers of Crystallization Kinetics for Drugs in Supersaturated Aqueous Solutions

In this study, we explore molecular properties of importance in solution-mediated crystallization occurring in supersaturated aqueous drug solutions. Furthermore, we contrast the identified molecular properties with those of importance for crystallization occurring in the solid state. A literature data set of 54 structurally diverse compounds, for which crystallization kinetics from supersaturated aqueous solutions and in melt-quenched solids were reported, was used to identify molecular drivers for crystallization kinetics observed in solution and contrast these to those observed for solids. The compounds were divided into fast, moderate, and slow crystallizers, and in silico classification was developed using a molecular K-nearest neighbor model. The topological equivalent of Grav3 (related to molecular size and shape) was identified as the most important molecular descriptor for solution crystallization kinetics; the larger this descriptor, the slower the crystallization. Two electrotopological descriptors (the atom-type E-state index for -Caa groups and the sum of absolute values of pi Fukui(+) indices on C) were found to separate the moderate and slow crystallizers in the solution. The larger these descriptors, the slower the crystallization. With these 3 descriptors, the computational model correctly sorted the crystallization tendencies from solutions with an overall classification accuracy of 77% (test set).

Application of a Refined Developability Classification System

In 2010, the Developability Classification System was proposed as an extension of the Biopharmaceutics Classification System to align the classification system with the need for early evaluation of drug candidates according to their developability as oral formulations. Recent work on the Developability Classification System has resulted in the refined developability classification system (rDCS), consisting of standard investigations to estimate drug candidate solubility and permeability and offering customized investigations that are triggered when there is a potential for supersaturation/precipitation (e.g., salts of acids, weak bases) or to investigate permeation versus dissolution-limited absorption. In the present study, the rDCS concept was successfully applied to 6 marketed compounds (aciclovir, albendazole, danazol, dantrolene, dipyridamole, and piroxicam), for which there is a rich database of information. Furthermore, the rDCS was applied to 20 pipeline compounds from past and current research projects at Bayer AG. The rDCS was able to predict the results in humans correctly in 80% of cases. Overall, the results suggest that the rDCS is a highly useful tool for estimating the in vivo behavior of new drug candidates.

Evaluation and optimized selection of supersaturating drug delivery systems of posaconazole (BCS class 2b) in the gastrointestinal simulator (GIS): An in vitro-in silico-in vivo approach

Supersaturating drug delivery systems (SDDS) have been put forward in the recent decades in order to circumvent the issue of low aqueous solubility. Prior to the start of clinical trials, these enabling formulations should be adequately explored in in vitro/in silico studies in order to understand their in vivo performance and to select the most appropriate and effective formulation in terms of oral bioavailability and therapeutic outcome. The purpose of this work was to evaluate the in vivo performance of four different oral formulations of posaconazole (categorized as a biopharmaceutics classification system (BCS) class 2b compound) based on the in vitro concentrations in the gastrointestinal simulator (GIS), coupled with an in silico pharmacokinetic model to predict their systemic profiles. Recently published intraluminal and systemic concentrations of posaconazole for these formulations served as a reference to validate the in vitro and in silico results. Additionally, the morphology of the formed precipitate of posaconazole was visualized and characterized by optical microscopy studies and thermal analysis. This multidisciplinary work demonstrates an in vitro-in silico-in vivo approach that provides a scientific basis for screening SDDS by a user-friendly formulation predictive dissolution (fPD) device in order to rank these formulations towards their in vivo performance.

Influence of Polymers on the Physical and Chemical Stability of Spray-dried Amorphous Solid Dispersion: Dipyridamole Degradation Induced by Enteric Polymers

Amorphous solid dispersions (ASDs) are inherently unstable because of high internal energy. Evaluating physical and chemical stability during the process and storage is essential. Numerous researches have demonstrated how polymers influence the drug precipitation and physical stability of ASDs, while the influence of polymers on the chemical stability of ASDs is often overlooked. Therefore, this study aimed to investigate the effect of polymers on the physical and chemical stability of spray-dried ASDs using dipyridamole (DP) as a model drug. Proper polymers were selected by assessing their abilities to inhibit drug recrystallization in supersaturated solutions. HPMC E5, Soluplus®, HPMCP-55, and HPMCAS-LP were shown to be effective stabilizers. The optimized formulations were further stored at a high temperature (60 °C) and high humidity (40 °C, 75% RH) for 2 months, and their physical and chemical stability was evaluated using polarizing optical microscopy, FTIR, HPLC, and mass spectrometry (MS). In general, crystallization was observed in all samples, which indicated the physical instability under stressed storage conditions. Also, it was noted that the polymers in ASDs rather than physical mixtures, induced a dramatic drug degradation after being exposed to a high temperature (HPMCP-55 > 80% and HPMCAS-LP > 50%) and high humidity (HPMCP-55 > 40% and HPMCAS-LP > 10%). The MS analysis further confirmed the degradation products, which might be generated from the reaction between dipyridamole and phthalic anhydride decomposed from HPMCP-55 and HPMCAS-LP. Overall, the exposure of ASDs to stressed conditions resulted in recrystallization and even the chemical degradation induced by polymers.

The relevance of co-amorphous formulations to develop supersaturated dosage forms: In-vitro, and ex-vivo investigation of Ritonavir-Lopinavir co-amorphous materials

Ritonavir and Lopinavir have previously been demonstrated to decrease the maximum solubility advantage and flux in the presence of each other. The present study investigated the ability of Ritonavir and Lopinavir co-amorphous materials to generate a supersaturated state. Further, it explored the precipitation and flux behavior of co-amorphous materials. The co-amorphous materials of Ritonavir and Lopinavir were prepared by quench cool method and characterized in the solid state using XRPD, DSC, FTIR. The solubility studies were conducted in USP phosphate buffer (pH 6.8) for 12 h. The supersaturation potential and precipitation behavior were studied employing pH shift method. Further, the diffusion behavior was explored in vitro and ex-vivo using a semipermeable membrane and intestinal everted sac method, respectively. The results showed that the co-amorphous materials have the potential to generate a supersaturated state. However, the reduction in the amorphous solubility was observed for both the drug(s) and the degree of reduction was found proportionate with the mole fraction of the compound in the co-amorphous material. Interestingly, the flux of both the drugs from co-amorphous material of 2:1 M ratio (Ritonavir 2: Lopinavir 1) was found exceeding the flux of the individual drugs in the amorphous form. The significant increase in the flux was attributed to the improved drug release properties due to precipitation of drug rich phase of nano/micro dimensions.