Cocrystal Solubility Advantage Diagrams as a Means to Control Dissolution, Supersaturation, and Precipitation

DSPindex guides dose selection to extend drug supersaturation lifetime during cocrystal dissolution

Synchronising both cocrystal dissolution and drug precipitation processes is the key for the development of cocrystal systems with desired dissolution-supersaturation-precipitation (DSP) behaviours. Our findings with ketoconazole (KTZ) - p-aminobenzoic acid (PABA) 1:1 cocrystal show that this can be achieved by generating non-stoichiometric coformer concentrations that allow us to modulate the maximum theoretical cocrystal supersaturation SA (thermodynamic limit) below the drug critical supersaturation σcrit (kinetic limit). The application of our conceptual graphical approach combined with the two metrics SA and the DSPindex answer the question of how much additional coformer is needed to target optimal sustained drug supersaturation levels. Modulating SA < σcrit and DSPindex > 1 allowed for a stable and sustained KTZ release system with supersaturation levels of 6 by 24 h. Findings provide a direct approach for better early decisions regarding cocrystal dose design and/or coformer concentration to be added to formulations to ultimately fine-tune drug supersaturation by coupling dissolution and precipitation processes.

Going beyond the Ordered Bulk: A Perspective on the Use of the Cambridge Structural Database for Predictive Materials Design

When Olga Kennard founded the Cambridge Crystallographic Data Centre in 1965, the Cambridge Structural Database was a pioneering attempt to collect scientific data in a standard format. Since then, it has evolved into an indispensable resource in contemporary molecular materials science, with over 1.25 million structures and comprehensive software tools for searching, visualizing and analyzing the data. In this perspective, we discuss the use of the CSD and CCDC tools to address the multiscale challenge of predictive materials design. We provide an overview of the core capabilities of the CSD and CCDC software and demonstrate their application to a range of materials design problems with recent case studies drawn from topical research areas, focusing in particular on the use of data mining and machine learning techniques. We also identify several challenges that can be addressed with existing capabilities or through new capabilities with varying levels of development effort.

Revolutionizing Antiviral Therapeutics: Unveiling Innovative Approaches for Enhanced Drug Efficacy

Since the beginning of the coronavirus pandemic in late 2019, viral infections have become one of the top three causes of mortality worldwide. Immunization and the use of immunomodulatory drugs are effective ways to prevent and treat viral infections. However, the primary therapy for managing viral infections remains antiviral and antiretroviral medication. Unfortunately, these drugs are often limited by physicochemical constraints such as low target selectivity and poor aqueous solubility. Although several modifications have been made to enhance the physicochemical characteristics and efficacy of these drugs, there are few published studies that summarize and compare these modifications. Our review systematically synthesized and discussed antiviral drug modification reports from publications indexed in Scopus, PubMed, and Google Scholar databases. We examined various approaches that were investigated to address physicochemical issues and increase activity, including liposomes, cocrystals, solid dispersions, salt modifications, and nanoparticle drug delivery systems. We were impressed by how well each strategy addressed physicochemical issues and improved antiviral activity. In conclusion, these modifications represent a promising way to improve the physicochemical characteristics, functionality, and effectiveness of antivirals in clinical therapy.

Quabodepistat (OPC-167832), a Novel Antituberculosis Drug Candidate: Enhancing Oral Bioavailability via Cocrystallization and Mechanistic Analysis of Bioavailability in Two Cocrystals

Quabodepistat (code name OPC-167832) is a novel antituberculosis drug candidate. This study aimed to discover cocrystals that improve oral bioavailability and to elucidate the mechanistic differences underlying the bioavailability of different cocrystals. Screening yielded two cocrystals containing 2,5-dihydroxybenzoic acid (2,5DHBA) or 2-hydroxybenzoic acid (2HBA). In bioavailability studies in beagle dogs, both cocrystals exhibited better bioavailability than the free form; however, the extent of bioavailability of cocrystals with 2HBA (quabodepistat-2HBA) was 1.4-fold greater than that of cocrystals with 2,5DHBA (quabodepistat-2,5DHBA). Dissolution studies at pH 1.2 yielded similar profiles for both cocrystals, although the percent dissolution differed: quabodepistat-2HBA dissolved more slowly than quabodepistat-2,5DHBA. The poor solubility of quabodepistat-2HBA is likely the primary factor limiting dissolution at pH 1.2. To identify a dissolution method that maintains the bioavailability in beagle dogs, we performed pH-shift dissolution studies that mimic the dynamic pH change from the stomach to the small intestine. Quabodepistat-2HBA demonstrated supersaturation after the pH was increased to 6.8, while quabodepistat-2,5DHBA did not demonstrate supersaturation. This result was consistent with the results of bioavailability studies in beagle dogs. We conclude that a larger quantity of orally administered quabodepistat-2HBA remained in its cocrystal form while being transferred to the small intestine compared with quabodepistat-2,5DHBA.

An In Vitro Model for Cocrystal Dissolution with Simultaneous Surface and Bulk Precipitation

Cocrystals can be promising means of overcoming the poor aqueous solubility of many drugs. However, precipitation of the stable drug at the cocrystal surface or in the bulk medium is often provoked during cocrystal dissolution due to high drug supersaturation, which prevents sustaining high drug concentrations for enhanced bioavailability. There is a need for predictive in vitro models that can accurately describe this cocrystal dissolution-supersaturation-precipitation (DSP) process to aid drug development and formulation design. Consideration of surface precipitation is often essential for such models given the strong impact of surface precipitation on the drug concentration during cocrystal dissolution. However, DSP models that can explicitly account for the effect of surface precipitation are currently lacking. This work presents a population balance-based model to describe in vitro cocrystal DSP behavior, which accounts for cocrystal dissolution, surface precipitation, and bulk precipitation. Dissolution experiments with carbamazepine-succinic acid cocrystals are conducted for model development and validation. The developed model captures all of the principal experimental trends and predicts the dose-dependent DSP behavior outside the regression data set with reasonable accuracy. The results show that surface precipitation is an essential component of the model. Finally, the new model is integrated with numerical optimization to illustrate how it can be used to identify an optimal dose, particle size, and amount of predissolved coformer.

Optimisation of Pharmaceutical Cocrystal Dissolution Performance through a Synergistic Precipitation Inhibition

OBJECTIVES

Polymeric excipients play an important role in a cocrystal formulation to act as precipitation inhibitors to maximize the potential. Otherwise, a stable form of the parent drug will be recrystallized on the dissolving cocrystal surface and/or in the bulk solution during the cocrystal dissolution process, negating the solubility advantage. The objectives of this work were to investigate the potential of using combined polymers to maximise the dissolution performance of surface precipitation pharmaceutical cocrystals.

METHODS

The dissolution performance of a highly soluble flufenamic acid and nicotinamide (FFA-NIC) cocrystal has been systematically studied with predissolved or powder mixed with a single polymer, including a surface precipitation inhibitor [i.e., copolymer of vinylpyrrolidone (60%) /vinyl acetate (40%) (PVP-VA)] and two bulk precipitation inhibitors [i.e., polyethylene glycol (PEG) and Soluplus (SLP)], or binary polymers combinations.

RESULTS

A single polymer of PVP-VA prevented the FFA surface precipitation for an enhanced dissolution performance of FFA-NIC cocrystal. Unfortunately, it cannot sustain the supersaturated FFA concentration in the bulk solution. A combination of two polymers of PVP-VA and SLP has shown a synergistic inhibition effect to enhance the dissolution advantage of FFA-NIC cocrystal.

CONCLUSIONS

The dissolution of a cocrystal with surface precipitation of the parent drug can be described as: i) the cocrystal surface contacting the dissolution medium; ii) the cocrystal surface dissolving; iii) the parent drug precipitation on the dissolving surface; and iv) the parent drug particles redissolving. A combination of two types of polymers can be used to maximise the cocrystal performance in solution.

Exploring the Supramolecular Interactions and Thermal Stability of Dapsone:Bipyridine Cocrystals by Combining Computational Chemistry with Experimentation

The application of computational screening methodologies based on H-bond propensity scores, molecular complementarity, molecular electrostatic potentials, and crystal structure prediction has guided the discovery of novel cocrystals of dapsone and bipyridine (DDS:BIPY). The experimental screen, which included mechanochemical and slurry experiments as well as the contact preparation, resulted in four cocrystals, including the previously known DDS:4,4'-BIPY (2:1, CC₄₄-B) cocrystal. To understand the factors governing the formation of the DDS:2,2'-BIPY polymorphs (1:1, CC₂₂-A and CC₂₂-B) and the two DDS:4,4'-BIPY cocrystal stoichiometries (1:1 and 2:1), different experimental conditions (such as the influence of solvent, grinding/stirring time, etc.) were tested and compared with the virtual screening results. The computationally generated (1:1) crystal energy landscapes had the experimental cocrystals as the lowest energy structures, although distinct cocrystal packings were observed for the similar coformers. H-bonding scores and molecular electrostatic potential maps correctly indicated cocrystallization of DDS and the BIPY isomers, with a higher likelihood for 4,4'-BIPY. The molecular conformation influenced the molecular complementarity results, predicting no cocrystallization for 2,2'-BIPY with DDS. The crystal structures of CC₂₂-A and CC₄₄-A were solved from powder X-ray diffraction data. All four cocrystals were fully characterized by a range of analytical techniques, including powder X-ray diffraction, infrared spectroscopy, hot-stage microscopy, thermogravimetric analysis, and differential scanning calorimetry. The two DDS:2,2'-BIPY polymorphs are enantiotropically related, with form B being the stable polymorph at room temperature (RT) and form A being the higher temperature form. Form B is metastable but kinetically stable at RT. The two DDS:4,4'-BIPY cocrystals are stable at room conditions; however, at higher temperatures, CC₄₄-A transforms to CC₄₄-B. The cocrystal formation enthalpy order, derived from the lattice energies, was calculated as follows: CC₄₄-B > CC₄₄-A > CC₂₂-A.

Dissolution Profiles of Carbamazepine Cocrystals with Cis-Trans Isomeric Coformers

PURPOSE

The purpose of the present study was to investigate the dissolution profiles of cocrystals with cis-trans isomeric coformers. Previously, the carbamazepine (CBZ) cocrystals with even-carbon dicarboxylic acids showed higher supersaturation than those with odd-carbon ones, attributed to particle surface solution-mediated phase transformation (PS-SMPT) to CBZ dihydrate (CBZ DH). However, it has been unknown whether this odd-even pattern holds for cis-trans isomeric coformers.

METHOD

CBZ cocrystals with maleic acid (MLE) and fumaric acid (FUM) (CBZ-FUM anhydrate (CBZ-FUM AH) and monohydrate (CBZ-FUM H₂O)) were employed as model cocrystals. Hydroxypropyl　methylcellulose (HPMC), polyvinylpyrrolidone, and polyethylene glycol 6000 (PEG) were used as precipitation inhibitors. Dissolution tests were performed under a non-sink condition. Residual particles were analyzed by powder X-ray diffraction, differential scanning calorimetry, polarized light microscope, and scanning electron microscope.

RESULTS

All cocrystals showed little supersaturation in the absence of a polymer. In 0.1% HPMC, CBZ-FUM AH showed significant supersaturation, whereas CBZ-MLE and CBZ-FUM H₂O did not for the first two hours. HPMC reduced the initial dissolution rate of CBZ-MLE and CBZ-FUM H₂O while inducing the highest supersaturation among the polymers after 96 h. The particle surface changed from a smooth plane to a striped pattern, but little or no CBZ DH was detected.

CONCLUSION

The cocrystals with cis-trans isomeric coformers showed different dissolution profiles. HPMC increased the dissolution rate of CBZ-FUM AH by inhibiting PS-SMPT but reduced the dissolution rate of CBZ-MLE and CBZ-FUM H₂O without inducing PS-SMPT. The striped pattern was suggested to be due to surface etching rather than PS-SMPT.

Synchronization of Cocrystal Dissolution and Drug Precipitation to Sustain Drug Supersaturation

A graphical analysis of both drug and coformer concentrations contributed by dissolving cocrystals is presented in the context of a simplified cocrystal phase diagram. The conceptual basis and analysis identify parameters that control cocrystal dissolution-drug supersaturation-precipitation (DSP) behavior. The important effects of coformer concentration, cocrystal dose, and cocrystal solubility on drug supersaturation levels are demonstrated and quantified by the DSP_index. While the studies presented rely on high and nonstoichiometric coformer concentrations contributed by the dissolving cocrystals, the concepts and findings can answer the question of whether and how much coformer should be added to cocrystal dissolution media or formulations.

Hot Melt Extrusion-Triggered Amorphization as a Continuous Process for Inducing Extended Supersaturable Drug Immediate-Release from saSMSDs Systems

Hot melt extrusion (HME), a continuous manufacturing process for generating supersaturating amorphous self-micellizing solid dispersion systems (saSMSDs), holds promise for achieving amorphization of many pharmaceutical formulations. For saSMSDs generation, HME-triggered continuous processes offer advantages over traditional non-continuous processes such as fusion/quench cooling (FQC) and co-precipitation (CP). Here we employed HME, FQC, and CP to generate saSMSDs containing the water-insoluble BCS II drug nitrendipine (NIT) and self-micellizing polymer Soluplus^®. Scanning electron microscopy, powder X-ray diffraction, and differential scanning calorimetry results revealed that saSMSDs formed when NIT–Soluplus^® mixtures were subjected to the abovementioned amorphization methods. All saSMSDs outperformed crystalline NIT preparations and physical mixtures in achieving extended supersaturable immediate release states with superior solubility, “spring-parachute” process characteristics, and dissolution behaviors. Notably, Fourier transform-infrared spectroscopic results obtained for saSMSDs detected hydrogen bonding interactions between the drug and the carrier. Ultimately, our results revealed the advantages of HME-triggered amorphization as a continuous process for significantly improving drug dissolution, increasing solubility, and maintaining supersaturation as compared to traditional amorphization-based techniques.

Complexation with aromatic dicarboxylic acids expands the solid-state landscape of berberine

Two novel salt cocrystals of berberine chloride (BCl) with 4-aminobenzoic acid (BCl-4ABA) and 4-hydroxybenzoic acid (BCl-4HBA) and one new berberine salt with 2,6-dihydroxybenzoic acid (B)⁺(26DHBA)^- were prepared and characterized. The chloride anions form N-H···Cl^- hydrogen bonds in BCl-4ABA and O-H···Cl^- hydrogen bonds in BCl-4HBA. In (B)⁺(26DHBA)^-, the ionic interactions between 26DHBA^- and quaternary ammonium cation of berberine contribute to a stronger crystal lattice and a higher melting point. All three new crystal forms exhibit a lower hygroscopicity at 25 ℃ than BCl, which is the crystal form used in the commercial tablets. Compared to BCl, the dissolution rates of BCl-4ABA and BCl-4HBA in water are higher but that of (B)⁺(26DHBA)^- is lower. Among the three crystal forms, the form with a higher melting point also exhibits a lower dissolution rate, which is explained by the stronger intermolecular interactions in these crystals.

Polymorphs and Isostructural Cocrystals of Dexamethasone: Towards the improvement of aqueous solubility

Dexamethasone (DEX) is a corticosteroid drug used to treat arthritis, asthma, and considered as a promising drug for the treatment of Covid-19. The major drawback of DEX is its poor...

Mechanistic Investigation of Drug Supersaturation in the Presence of Polysorbates as Solubilizing Additives by Solution Nuclear Magnetic Resonance Spectroscopy

The introduction of solubilizing additives has historically been an attractive approach to address the ever-growing proportion of poorly water-soluble drug (PWSD) compounds within the modern drug discovery pipeline. Lipid-formulations, and more specifically micelle formulations, have garnered particular interest because of their simplicity, size, scalability, and avoidance of solid-state limitations. Although micelle formulations have been widely utilized, the molecular mechanism of drug solubilization in surfactant micelles is still poorly understood. In this study, a series of modern nuclear magnetic resonance (NMR) methods are utilized to gain a molecular-level understanding of intermolecular interactions and kinetics in a model system. This approach enabled the understanding of how a PWSD, 17β-Estradiol (E2), solubilizes within a nonionic micelle system composed of polysorbate 80 (PS80). Based on one-dimensional (1D) ¹H chemical shift differences of E2 in PS80 solutions, as well as intermolecular correlations established from 1D selective nuclear Overhauser effect (NOE) and two-dimensional NOE spectroscopy experiments, E2 was found to accumulate within the palisade layer of PS80 micelles. A potential hydrogen-bonding interaction between a hydroxyl group of E2 and a carbonyl group of PS80 alkane chains may allow for stabilizing E2-PS80 mixed micelles. Diffusion and relaxation NMR analysis and particle size measurements using dynamic light scattering indicate a slight increase in the micellar size with increasing degrees of supersaturation, resulting in slower mobility of the drug molecule. Based on these structural findings, a theoretical orientation model of E2 molecules with PS80 molecules was developed and validated by computational docking simulations.

Cocrystals, Salts, and Salt-Solvates of olanzapine; selection of coformers and improved solubility

Pharmaceutical cocrystals and salts are extensively researched in recent years due to their ability to tune the physicochemical properties of active pharmaceutical ingredients (APIs). A model API, olanzapine, an atypical antipsychotic drug classified as Biopharmaceutical Classification System class II, is used in this study. Cocrystals and salts of olanzapine are discovered using solvent drop grinding and ball milling. Appropriate coformers were selected based on a combination of hydrogen-bond propensity (HBP) and hydrogen-bond coordination (HBC) calculations. Eight new multicomponent phases of olanzapine, including one cocrystal hydrate with phenol; four anhydrous salts with salicylic acid, terephthalic acid, anthranilic acid, 3-hydroxybenzoic acid, and 2-aminoterephthalic acid; one salt dihydrate with terephthalic acid; and one salt solvate with 3-hydroxybenzoic acid and acetonitrile, have been discovered and characterized by PXRD and DSC. One reported cocrystal (olanzapine-resorcinol) has also been considered for the dissolution test. All these newly formed solid phases followed the "ΔpK_a rule of 3". The crystal structures of cocrystal/salts were determined by single-crystal X-ray (sc-XRD) diffraction. With the collected single-crystal data, the crystal packings were found to be primarily stabilized via strong hydrogen bonds between carboxyl, phenolic hydroxyl of co-formers/salt-formers with the piperazine and diazepine nitrogen of olanzapine, which confirmed the predicted result from the HBP and HBC calculations. HPLC coupled with UV-vis detector was used in the solubility and dissolution test instead of UV-vis spectroscopy, to avoid the peak overlap between olanzapine and co-formers/salt-formers. A threefold increase in the solubility was observed in olanzapinium 3-hydroxybenzoate and olanzapinium anthranilate, and an almost fivefold increase in solubility of olanzapinium 2-aminoterephthalate.

Effect of Surfactants and Polymers on the Dissolution Behavior of Supersaturable Tecovirimat-4-Hydroxybenzoic Acid Cocrystals

(1) Background: Pharmaceutical cocrystals have attracted remarkable interest and have been successfully used to enhance the absorption of poorly water-soluble drugs. However, supersaturable cocrystals are sometimes thermodynamically unstable, and the solubility advantages present a risk of precipitation because of the solution-mediated phase transformation (SMPT). Additives such as surfactants and polymers could sustain the supersaturation state successfully, but the effect needs insightful understanding. The aim of the present study was to investigate the roles of surfactants and polymers in the dissolution-supersaturation-precipitation (DSP) behavior of cocrystals. (2) Methods: Five surfactants (SDS, Poloxamer 188, Poloxamer 407, Cremophor RH 40, polysorbate 80) and five polymers (PVP K30, PVPVA 64, HPC, HPMC E5, CMC-Na) were selected as additives. Tecovirimat-4-hydroxybenzoic (TEC-HBA) cocrystals were chosen as a model cocrystal. The TEC-HBA cocrystals were first designed and verified by PXRD, DSC, SEM, and FTIR. The effects of surfactants and polymers on the solubility and dissolution of TEC-HBA cocrystals under sink and nonsink conditions were then investigated. (3) Results: Both the surfactants and polymers showed significant dissolution enhancement effects, and most of the polymers were more effective than the surfactants, according to the longer T_max and higher C_max. These results demonstrate that the dissolution behavior of cocrystals might be achieved by the maintained supersaturation effect of the additives. Interestingly, we found a linear relationship between the solubility and C_max of the dissolution curve for surfactants, while no similar phenomena were found in solutions with polymer. (4) Conclusions: The present study provides a basis for additive selection and a framework for understanding the behavior of supersaturable cocrystals in solution.

Fabrication of Carbamazepine Cocrystals: Characterization, In Vitro and Comparative In Vivo Evaluation

Carbamazepine (CBZ) is an antiepileptic drug having low bioavailability due to its hydrophobic nature. In the current study, efforts are made to investigate the effect of dicarboxylic acid coformer spacer groups (aliphatic chain length) on physicochemical properties, relative humidity (RH) stability, and oral bioavailability of CBZ cocrystals. Slurry crystallization technique was employed for the preparation of CBZ cocrystals with the following coformers: adipic (AA), glutaric (GA), succinic (SA), and malonic acid (MA). Powder X-ray diffractometry and Fourier-transform infrared spectroscopy confirmed cocrystal preparation. Physicochemical properties, RH stability, and oral bioavailability of cocrystals were investigated. Among the prepared cocrystals, CBZ-GA showed maximum solubility as well as improved dissolution profile (CBZ-GA > CBZ-MA > CBZ-AA > pure CBZ > CBZ-SA) in ethanol. Maximum RH stability was shown by CBZ-AA, CBZ-SA, and CBZ-MA. In vivo studies confirmed boosted oral bioavailability of cocrystals compared to pure CBZ. Furthermore, in vivo studies depicted the oral bioavailability order of cocrystals as CBZ-GA > CBZ-MA > Tegral® > CBZ-AA > CBZ-SA > pure CBZ. Thus, pharmaceutical scientists can effectively employ cocrystallization technique for tuning physicochemical properties of hydrophobic drugs to achieve the desired oral bioavailability. Overall, results reflect no consistent effect of spacer group on physicochemical properties, RH stability, and oral bioavailability of cocrystals.

Novel cocrystals of itraconazole: Insights from phase diagrams, formation thermodynamics and solubility

In this work, the cocrystallization approach was applied to itraconazole (ITR), a very slightly soluble triazole antifungal drug, which led to the formation of two new solid forms of ITR with 4-aminobenzoic acid (4AmBA) and 4-hydroxybenzamide (4OHBZA). A thermodynamic analysis of the solid-liquid binary phase diagrams for the (ITR + 4AmBA) and (ITR + 4OHBZA) systems provided conclusive evidence of the cocrystal stoichiometry: 1:1 for the cocrystal with 4-aminobenzoic acid, and 1:2 for the cocrystal with 4-hydroxybenzamide. Powder X-Ray diffraction analysis confirmed the formation of two different polymorphic forms of the [ITR + 4OHBZA] (1:2) cocrystal obtained either through solution or melt crystallization. Cocrystal formation and polymorphic transition processes were investigated in detail by the DSC and HSM methods. The thermodynamic functions of cocrystal formation were estimated from the solubility of the cocrystals and the corresponding solubility of the pure compounds at different temperatures. The combination of ITR and 4OHBZA was found to be more favorable than the reaction between ITR and 4AmBA in terms of both Gibbs energy and enthalpy. The pH-solubility behavior of the cocrystals was investigated at different pH values using eutectic concentrations of the components and the cocrystal solubility advantage was estimated. It was found that the cocrystallization of itraconazole with 4OHBZA and 4AmBA can potentially increase the drug solubility at pH1.2 and 37 °C by 225 and 64 times, respectively. The cocrystal dissolution behavior in biorelevant media was analyzed in terms of C_max, σ_max parameters (the maximum ITR concentration and supersaturation), and AUC (the concentration area under the curve during the dissolution - supersaturation - precipitation process). The cocrystals had similar σ_max values during the dissolution and sustained supersaturation for up to 6 h, which gave them an advantage in the AUC values (13-37 times higher) over the drug. The differences in the dissolution profiles of the cocrystals were rationalized in terms of their dissolution rate values.

Variable stoichiometry cocrystals: occurrence and significance

Stoichiometric variation in organic cocrystals, their synthesis, structure elucidation and properties are discussed. Accountable reasons for the occurrence of such cocrystals are emphasised.

Cocrystal engineering of pharmaceutical solids: therapeutic potential and challenges

This highlight presents an overview of pharmaceutical cocrystal production and its potential in reviving problematic properties of drugs in different dosage forms. The challenges and future outlook of its translational development are discussed.

Cocrystal Solubility Advantage and Dose/Solubility Ratio Diagrams: A Mechanistic Approach To Selecting Additives and Controlling Dissolution-Supersaturation-Precipitation Behavior

Two of the main questions regarding cocrystal selection and formulation development are whether the will be stable and how fast can it dissolve the drug dose. Dissolving the drug dose may require cocrystals with a high solubility advantage over drug (SA = S_CC/S_D), but these may have limited potential to sustain drug supersaturation. Thus, we propose a twofold approach to mitigate the risk of drug precipitation by optimizing thermodynamic (SA) and kinetic factors (nucleation inhibitors). This risk can be evaluated by considering the cocrystal SA and drug dose/solubility ratio (D_0D = C_dose/S_D), which in tandem represent the maximum theoretical supersaturation that a cocrystal may generate, the driving force for drug precipitation, and the potential for dose-/solubility-limited absorption. cocrystals with SA and D_0D values above critical supersaturation are prone to rapid precipitation, often negating their utility as a solubility enhancement tool. This work presents a mechanistic approach to controlling the dissolution-supersaturation-precipitation behavior of cocrystal systems, whereby relationships between SA, D_0D, and the drug-solubilizing power of surfactants (SP_D = S_D,T/S_D,aq) are used to fine-tune cocrystal-inherent supersaturation by rational additive selection. Experimental results with danazol-vanillin cocrystal demonstrate how SA, D_0D, and SP_D are key thermodynamic parameters to understanding the kinetic cocrystal behavior and how the risks of cocrystal development may be mitigated through the mechanistic formulation design.

Toward Developing Discriminating Dissolution Methods for Formulations Containing Nanoparticulates in Solution: The Impact of Particle Drift and Drug Activity in Solution

Enabling formulations are an attractive approach to increase the dissolution rate, solubility, and oral bioavailability of poorly soluble compounds. With the growing prevalence of poorly soluble drug compounds in the pharmaceutical pipeline, supersaturating drug delivery systems (SDDS), a subset of enabling formulations, have grown in popularity due to their properties allowing for drug concentrations greater than the corresponding crystalline solubility. However, the extent of supersaturation generated as the enabling formulation traverses the gastrointestinal (GI) tract is dynamic and poorly understood. The dynamic nature of supersaturation is a result of several competing kinetic processes such as dissolution, solubilization by formulation and endogenous surfactants, crystallization, and absorption. Ultimately, the free drug concentration, which is equivalent to the drug's inherent thermodynamic activity amid these kinetic processes, defines the true driving force for drug absorption. However, in cases where solubilizing agents are present (i.e., surfactants and bile salts), drug molecules may associate with colloidal nanoscale species, complicating drug activity determination. These nanoscale species can drift into the aqueous boundary layer (ABL), increasing the local API activity at the membrane surface, resulting in increased bioavailability. Herein, a novel approach was developed to accurately measure thermodynamic drug activity in complex media containing drug distributed in nanoparticulate species. This approach captures the influence of the ABL on the observed flux and, ultimately, the predicted unbound drug concentration. The results demonstrate that this approach can help to (1) measure the true extent of local supersaturation in complex systems containing solubilizing excipients and (2) elucidate the mechanisms by which colloidal aggregates can modulate the drug activity in solution and potentially enhance the flux observed across a membrane. The utilization of these techniques may provide development scientists with a strategy to evaluate formulation sensitivity to nanospeciation and allow formulators to maximize the driving force for absorption in a complex environment, perhaps enabling the development of dissolution methods with greater discrimination and correlation to pre-clinical and clinical data sets.

Improved Solubility and Oral Absorption of Emodin-Nicotinamide Cocrystal Over Emodin with PVP as a Solubility Enhancer and Crystallization Inhibitor

Emodin exerts anti-inflammatory and anti-cancer effects. However, its poor water solubility limits development into a pharmaceutical product. Although an emodin-nicotinamide cocrystal (ENC) with improved dissolution rate was proposed as a potential candidate, crystallization back to emodin after dissolution diminished the advantage of the cocrystal approach. The objectives of this study were to identify a crystallization inhibitor to maintain the emodin supersaturation generated by ENC dissolution, and to examine its effect on oral pharmacokinetics of ENC. Among various polymers, polyvinylpyrrolidone K30 (PVP) was the most effective solubilizer and crystallization inhibitor. The solubility of ENC in a simulated intestinal fluid containing 1.5% PVP was 2-fold higher than that of emodin. However, comparison of oral pharmacokinetics in rats between ENC and emodin did not reflect such improved solubility of ENC in vitro relative to emodin. Instead, the plasma concentrations of a major metabolite of emodin showed a positive correlation with in vitro dissolution results, suggesting rapid gastrointestinal metabolism of emodin during absorption. In conclusion, PVP contributes to enhanced dissolution rates of ENC and inhibits crystallization of emodin in vivo, so that more metabolites can be formed and absorbed. Therefore, a metabolism inhibitor would be necessary to improve the oral bioavailability of emodin further.

Effects of Coformer and Polymer on Particle Surface Solution-Mediated Phase Transformation of Cocrystals in Aqueous Media

The purpose of the present study was to investigate the effect of the coformer difference on particle surface solution-mediated phase transformation (PS-SMPT) during cocrystal particle dissolution in aqueous media in the absence and presence of polymers. SMPT can occur either in the bulk phase or at the particle surface because drug molecules can be supersaturated at the dissolving cocrystal surface, as well as in the bulk phase. Previously, bulk phase SMPT has been primarily investigated in formulation development. However, little is known about the effects of coformers and polymers on PS-SMPT of cocrystals. In this study, six carbamazepine (CBZ) cocrystals were used as model cocrystals (malonic acid (MAL), succinic acid (SUC), glutaric acid (GLA), adipic acid (ADP), saccharin (SAC), and nicotinamide (NCT); nonsink dissolution tests were performed with or without a precipitation inhibitor (hydroxypropyl methylcellulose (HPMC)) at pH 6.5. The residual particles were analyzed by powder X-ray diffraction, differential scanning calorimetry, polarized light microscopy (PLM), and scanning electron microscopy. Real-time PLM was used to directly observe rapid PS-SMPT. In the absence of HPMC, supersaturation was not observed in the bulk phase for all cocrystals. All cocrystals rapidly transformed to CBZ dihydrate aggregates via PS-SMPT (mostly within 1 min). In contrast, in the presence of 0.1% HPMC, supersaturation was observed for CBZ-SUC, CBZ-ADP, CBZ-SAC, and CBZ-NCT but not for CBZ-MAL and CBZ-GLA. The cocrystals with lower solubility coformers tended to induce higher supersaturation in the bulk phase. The PS-SMPT of CBZ-SUC, CBZ-ADP, and CBZ-SAC was slowed down by HPMC. By suppressing PS-SMPT, the cocrystals exhibited its supersaturation potential, depending on the properties of each coformer. To take advantage of the supersaturation potential of cocrystals to improve oral drug absorption, it is important to suppress particle surface SMPT in addition to bulk phase SMPT.

The role of pH and dose/solubility ratio on cocrystal dissolution, drug supersaturation and precipitation

Cocrystals that are more soluble than the constituent drug, generate supersaturation levels during dissolution and are predisposed to conversion to the less soluble drug. Drug release studies during cocrystal dissolution generally compare several cocrystals and their crystal structures. However, the influence of drug dose and solubility in different dissolution media has been scarcely reported. The present study aims to investigate how drug dose/solubility ratio (Do=C_dose/S_drug), cocrystal solubility advantage over drug (SA=S_cocrystal/S_drug), and dissolution media affect cocrystal dissolution-drug supersaturation and precipitation (DSP) behavior. SA and K_sp values of 1:1 cocrystals of meloxicam-salicylic acid (MLX-SLC) and meloxicam-maleic acid (MLX-MLE) were determined at cocrystal/drug eutectic points. Results demonstrate that both cocrystals enhance SA by orders of magnitude (20 to 100 times for the SLC and over 300 times for the MLE cocrystal) in the pH range of 1.6 to 6.5. It is shown that during dissolution, cocrystals regulate the interfacial pH (pH_int) to 1.6 for MLX-MLE and 4.5 for MLX-SLC, therefore diminishing the cocrystal dissolution rate dependence on bulk pH. Do values ranged from 2 (pH 6.5) to 410 (pH 1.6) and were mostly determined by the drug solubility dependence on pH. Drug release profiles show that maximum supersaturation (σ_max=C_max/S_drug)and AUC increased with increasing Do as pH decreased. When Do>>SA, the cocrystal solubility is not sufficient to dissolve the dose so that a dissolution-precipitation quasi-equilibrium state is able to sustain supersaturation for the extent of the experiment (24 h). When Do<<SA, cocrystal solubility is more than adequate to dissolve the dose. Low σ_max values (1.7 and 1.5) near the value of Do (2.3 and 2.4) were observed, where a large fraction of the cocrystal added is dissolved to reach σ_max. Two different cocrystal to drug conversion pathways were observed: (1) surface nucleation of the metastable MLX polymorph IV on the dissolving cocrystal preceeded formation of the stable MLX polymorph I in bulk solution (in all conditions without FeSSIF), and (2) bulk nucleation of the stable MLX polymorph (in FeSSIF). The interplay between cocrystal SA, Do_, and drug precipitation pathways provide a framework to interpret and understand the DSP behavior of cocrystals.

Dissolution Advantage of Nitazoxanide Cocrystals in the Presence of Cellulosic Polymers

The effect of hydroxypropyl methylcellulose (HPMC) and methylcellulose (Methocel^® 60 HG) on the dissolution behavior of two cocrystals derived from nitazoxanide (NTZ), viz., nitazoxanide-glutaric acid (NTZ-GLU, 1:1) and nitazoxanide-succinic acid (NTZ-SUC, 2:1), was explored. Powder dissolution experiments under non-sink conditions showed similar dissolution profiles for the cocrystals and pure NTZ. However, pre-dissolved cellulosic polymer in the phosphate dissolution medium (pH 7.5) modified the dissolution profile of NTZ when starting from the cocrystals, achieving transient drug supersaturation. Subsequent dissolution studies under sink conditions of polymer-based pharmaceutical powder formulations with NTZ-SUC cocrystals gave a significant improvement of the apparent solubility of NTZ when compared with analogous formulations of pure NTZ and the physical mixture of NTZ and SUC. Scanning electron microscopy and powder X-ray diffraction analysis of samples recovered after the powder dissolution studies showed that the cocrystals undergo fast dissolution, drug supersaturation and precipitation both in the absence and presence of polymer, suggesting that the solubilization enhancement is due to polymer-induced delay of nucleation and crystal growth of the less soluble NTZ form. The study demonstrates that the incorporation of an appropriate excipient in adequate concentration can be a key factor for inducing and maintaining the solubilization of poorly soluble drugs starting from co-crystallized solid forms. In such a way, cocrystals can be suitable for the development of solid dosage forms with improved bioavailability and efficacy in the treatment of important parasitic and viral diseases, among others.