Is Failure of Cocrystallization Actually a Failure? Eutectic Formation in Cocrystal Screening of Hesperetin

Diversity of Solid Forms Promoted by Ball Milling: Characterization and Intrinsic Dissolution Studies of Pioglitazone Hydrochloride and Fluvastatin Sodium Drug-Drug Systems

Coamorphous salt in a 1:1 ratio prepared by ball milling from Fluvastatin sodium (FLV) and Pioglitazone hydrochloride (PGZ·HCl) can be selectively formed by neat grinding (NG). Furthermore, the salt-cocrystal continuum was preferably formed by employing liquid-assisted grinding (LAG) using ethanol (EtOH). Attempts to prepare the coamorphous salt starting from the salt-cocrystal continuum by NG were unsuccessful. Interestingly, through ball milling by NG or LAG, a great diversity of solid forms (PGZ·HCl-FLV 1:1) could be accessed: NG and hexane (coamorphous); ethyl acetate (physical mixture); EtOH (salt-cocrystal continuum); and water (which presents two T_g, indicating immiscibility of the components). An exploration was performed at different drug-to-drug ratios by NG. By differential scanning calorimetry (DSC), the presence of two endothermic events was observed in this screening: incongruous melting point (solidus) and excess of one of the components (liquidus), except in the 1:1 solid form. From these results, eutectic behavior was observed. Through the construction of a binary phase diagram, it was determined that the 1:1 molar ratio gives rise to the formation of the most stable coamorphous composition. Dissolution profile studies of these solid forms were carried out, specifically on pure FLV and the solid forms of PGZ⋅HCl-FLV (1:2; 1:4; and 1:6), together with the coamorphous 1:1 salt. By itself, pure FLV presented the highest K_int (13.6270 ± 0.8127 mg/cm²⋅min). On the other hand, the coamorphous 1:1 showed a very low K_int (0.0220 ± 0.0014 mg/cm²·min), indicating very fast recrystallization by the FLV, which avoids observing a sudden release of this drug in the solution. This same behavior was observed in the eutectic composition 1:2. In the other solid forms, the value of K_int increases along with the %w of FLV. From the mechanochemical point of view, ball milling by NG or LAG became an important synthetic tool since it allows obtaining a great variety of solid forms to explore the solid-state reactivity of the drug-drug solid-form PGZ HCl-FLV.

Melting point depression for enhanced dissolution rate of eslicarbazepine acetate

BACKGROUND

Eslicarbazepine acetate (ESL) is antiepileptic agent which is approved for use as single therapy or in combination with other drugs. However, it suffers from poor oral bioavailability. Modulation of drug crystallinity can be utilized as an approach for enhancing drug dissolution.

OBJECTIVE

Accordingly, the aim of this study was to investigate possible eutectic system formation between eslicarbazepine with either tartaric acid or citric acid.

METHODOLOGY

Eslicarbazepine acetate was subjected to wet co-grinding with tartaric acid or citric acid at different molar ratios. The prepared formulations were assessed using Fourier-transform infrared (FTIR), X-ray powder diffraction (XRPD), differential scanning calorimetry in addition to dissolution studies.

RESULTS

The characterization techniques confirmed eutectic system formation with tartaric and citric acid with the optimum molar ratio for eutexia being 1:1 for both substances. Development of eutectic systems significantly enhanced the dissolution rate of ESL. Increasing the ratio of tartaric acid higher than the optimum ratio for eutexia resulted in additional increase in drug dissolution rate. This suggested the impact of pH modification on drug dissolution rate. The enhanced dissolution rate in case of the formulations containing ESL and citric acid was accredited to combined effect of eutaxia and pH modulation. These explanations were proven from investigating the dissolution rate of the physical mixtures which were inferior in their dissolution rate compared with the prepared formulations.

CONCLUSION

co-processing of ESL with either citric acid or tartaric acid resulted in hastened dissolution rate which was accredited to combined effect of eutexia with pH modification.

Development of ezetimibe eutectic with improved biopharmaceutical and mechanical properties to design an optimized oral solid dosage formulation

Eutectics are multicomponent systems which are an alternative to the conventional techniques for modulating the biopharmaceutical properties of a pharmaceutical. Ezetimibe (ETZ) is a hypocholesterolemic agent with limited dissolution, poor water solubility, and subsequently demonstrates low oral bioavailability. Additionally, ETZ exhibits poor mechanical properties, leading to difficulties in developing dosage forms through direct compression. The present work highlights the applicability of eutectics in the simultaneous improvement of physicochemical along with mechanical properties of ETZ. A pharmaceutical eutectic of ETZ with succinimide (SUC) was prepared by mechanochemical grinding and thoroughly characterized using thermoanalytical, X-ray diffraction, and spectroscopic methods. Intrinsic dissolution rate and pharmacokinetic analysis were also performed for ezetimibe-succinimide (ETZ-SUC) eutectic in contrast to pure ETZ. The eutectic demonstrated ∼2-fold increase in the solubility and dissolution rate. In pharmacokinetic studies, the area under the curve (AUC) for ETZ-SUC eutectic (28.03 ± 2.22 ng*h/mL) was found to be higher than ETZ (8.98 ± 0.36 ng*h/mL), indicating improved oral bioavailability for eutectics. Also, it was observed that enhanced material functionality aids in designing directly compressed tablets, where the eutectic formulation showed an improved dissolution profile over the ETZ formulation. The study demonstrates that eutectic conglomerates could be utilized to develop ideal oral solid dosage formulations.

Pharmaceutical Co-crystal of Antiviral Agent Efavirenz with Nicotinamide for the Enhancement of Solubility, Physicochemical Stability, and Oral Bioavailability

The present research work attempted to improve the oral bioavailability of the antiviral drug Efavirenz (EFV) using a pharmaceutical cocrystallization technique. EFV comes under BCS-II and has extremely low water solubility, and results in low oral bioavailability. EFV and nicotinamide (NICO) were selected in a (1:1) stoichiometric ratio and efavirenz nicotinamide cocrystal (ENCOC) was prepared through the liquid-assisted grinding method (LAG). The confirmation of the formation of a new solid phase was done through spectroscopic techniques like Fourier transmission infrared (FTIR), Raman, and ¹³C solid-state nuclear magnetic resonance (¹³C ssNMR). Thermal techniques like differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and hot stage microscopy (HSM) illustrated the thermal behavior and melting patterns of ENCOC, EFV, and NICO. The X-ray powder diffraction (XRPD) confirms the formation of a new crystalline phase in ENCOC. The Morphology was determined through scanning electron microscopy (FESEM). The results of saturated solubility studies and in vitro drug release studies exhibited 8.9-fold enhancement in solubility and 2.56-fold enhancement in percentage cumulative drug release. The percentage drug content of ENCOC was found higher than 97% and cocrystal exhibits excellent accelerated stability. The oral bioavailability of EFV (C_max, 799.08 ng/mL) exhibits significant enhancement after cocrystallization (C_max, 5597.09 ng/mL) than EFV and Efcure®-200 tablet (2896.21 ng/mL). The current work investigates the scalable and cost-effective method for enhancement of physicochemical stability, solubility, and oral bioavailability of an antiviral agent EFV.

A co-crystal berberine-ibuprofen improves obesity by inhibiting the protein kinases TBK1 and IKKɛ

Berberine (BBR) exerts specific therapeutic effects on various diseases such as diabetes, obesity, and other inflammation-associated diseases. However, the low oral bioavailability (below 1%) of berberine due to its poor solubility and membrane permeability limits its clinical use. In this paper, we have prepared a 1:1 co-crystal berberine-ibuprofen (BJ) using drug salt metathesis and co-crystal technology. Pharmacokinetic studies demonstrate a 3-fold increase in vivo bioavailability of BJ compared to that of BBR, and BJ is more effective in treating obesity and its related metabolism in vitro and in vivo. We also find that BJ promotes mitochondrial biogenesis by inhibiting TBK1 and inducing AMP-activated protein kinase (AMPK) phosphorylation, and BJ increases adipocyte sensitivity to catecholamine by inhibiting IKKε. Together, our findings support that co-crystal BJ is likely to be an effective agent for treating obesity and its related metabolic diseases targeting TBK1 and IKKε.

Bioavailability of Hesperidin and Its Aglycone Hesperetin—Compounds Found in Citrus Fruits as a Parameter Conditioning the Pro-Health Potential (Neuroprotective and Antidiabetic Activity)—Mini-Review

Hesperidin and hesperetin are polyphenols that can be found predominantly in citrus fruits. They possess a variety of pharmacological properties such as neuroprotective and antidiabetic activity. However, the bioavailability of these compounds is limited due to low solubility and restricts their use as pro-healthy agents. This paper described the limitations resulting from the low bioavailability of the presented compounds and gathered the methods aiming at its improvement. Moreover, this work reviewed studies providing pieces of evidence for neuroprotective and antidiabetic properties of hesperidin and hesperetin as well as providing a detailed look into the significance of reported modes of action in chronic diseases. On account of a well-documented pro-healthy activity, it is important to look for ways to overcome the problem of poor bioavailability.

Evaluation of Piperine as Natural Coformer for Eutectics Preparation of Drugs Used in the Treatment of Cardiovascular Diseases

Piperine (PIP) was evaluated as a natural coformer in the preparation of multicomponent organic materials for enhancing solubility and dissolution rate of the poorly water-soluble drugs: curcumin (CUR), lovastatin (LOV), and irbesartan (IBS). A screening based on liquid assisted grinding technique was performed using 1:1 drug-PIP molar ratio mixtures, followed by differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) analyses. Three eutectic mixtures (EMs) composed of CUR-PIP, LOV-PIP, and IBS-PIP were obtained. Therefore, binary phase and Tamman's diagrams were constructed for each system to obtain the exact eutectic composition, which was 0.41:0.59, 0.29:0.71, and 0.31:0.69 for CUR-PIP, LOV-PIP, and IBS-PIP, respectively. Further, bulk materials of each system were prepared to characterize them through DSC, PXRD fully, Fourier transform infrared spectroscopy (FT-IR), and solution-state nuclear magnetic resonance (NMR) spectroscopy. In addition, the contact angle, solubility, and dissolution rate of each system were evaluated. The preserved characteristic in the PXRD patterns and FT-IR spectra of the bulk material of each system confirmed the formation of EM mixture without molecular interaction in solid-state. The formation of EM resulted in improved aqueous solubility and dissolution rate associated with the increased wettability observed by the decrease in contact angle. In addition, solution NMR analyses of CUR-PIP, LOV-PIP, and IBS-PIP suggested no significant intermolecular interactions in solution between the components of the EM. Hence, this study concludes that PIP could be an effective coformer to improve the solubility and dissolution rate of CUR, LOV, and IBS.

Liquefying Flavonoids with Terpenoids through Deep Eutectic Solvent Formation

The formation of deep eutectic solvents (DES) is tied to negative deviations to ideality caused by the establishment of stronger interactions in the mixture than in the pure DES precursors. This work tested thymol and menthol as hydrogen bond donors when combined with different flavonoids. Negative deviations from ideality were observed upon mixing thymol with either flavone or flavanone, two parent flavonoids that only have hydrogen bond acceptor (HBA) groups, thus forming non-ionic DES (Type V). On the other hand, the menthol systems with the same compounds generally showed positive deviations from ideality. That was also the case with the mixtures containing the more complex hydroxylated flavonoid, hesperetin, which resulted in positive deviations when mixed with either thymol or menthol. COSMO-RS successfully predicted the behavior of the solid-liquid phase diagram of the studied systems, allowing for evaluation of the impact of the different contributions to the intermolecular interactions, and proving to be a good tool for the design of DES.

Synthesis, Characterization, and Intrinsic Dissolution Studies of Drug-Drug Eutectic Solid Forms of Metformin Hydrochloride and Thiazide Diuretics

The mechanochemical synthesis of drug–drug solid forms containing metformin hydrochloride (MET·HCl) and thiazide diuretics hydrochlorothiazide (HTZ) or chlorothiazide (CTZ) is reported. Characterization of these new systems indicates formation of binary eutectic conglomerates, i.e., drug–drug eutectic solids (DDESs). Further analysis by construction of binary diagrams (DSC screening) exhibited the characteristic V-shaped form indicating formation of DDESs in both cases. These new DDESs were further characterized by different techniques, including thermal analysis (DSC), solid state NMR spectroscopy (SSNMR), powder X-ray diffraction (PXRD) and scanning electron microscopy–energy dispersive X-ray spectroscopy analysis (SEM–EDS). In addition, intrinsic dissolution rate experiments and solubility assays were performed. In the case of MET·HCl-HTZ (χ_MET·HCl = 0.66), we observed a slight enhancement in the dissolution properties compared with pure HTZ (1.21-fold). The same analysis for the solid forms of MET·HCl-CTZ (χ_MET·HCl = 0.33 and 0.5) showed an enhancement in the dissolved amount of CTZ accompanied by a slight improvement in solubility. From these dissolution profiles and saturation solubility studies and by comparing the thermodynamic parameters (ΔH_fus and ΔS_fus) of the pure drugs with these new solid forms, it can be observed that there was a limited modification in these properties, not modifying the free energy of the solution (ΔG) and thus not allowing an improvement in the dissolution and solubility properties of these solid forms.

Microbial Phosphorylation Product of Hesperetin by Bacillus subtilis BCRC 80517 Improves Oral Bioavailability in Rats

The flavanoid hesperidin (Hsd) is one of the major polyphenols in citrus fruits. Hsd and its aglycone hesperetin (Hst) have a broad array of bioactivities; however, their low aqueous solubility and low intestinal permeability lead to their limited oral bioavailability. In the present study, we generated two water-soluble derivatives of Hst, namely, Hst 7-O-phosphate and Hst3'-O-phosphate, by a unique bioconversion process of Bacillus subtilis var. natto BCRC80517. The phosphorylated products showed superior aqueous solubility and distinct physicochemical properties compared with the original Hst. The Hst phosphate derivatives (HstPs) remained stable in simulated gastric and intestinal fluids for 240 min and could revert to the original Hst form by alkaline phosphatase treatment in Caco-2 cells, showing enhanced intestinal permeability in vitro. After oral administration in rats, HstPs greatly elevated plasma exposure to Hst and showed better bioavailability than did Hsd. HstPs may be a potential and efficient alternative to Hst.

Multicomponent crystalline solid forms of aripiprazole produced via hot melt extrusion techniques: An exploratory study

Multicomponent crystalline solid forms (salts, cocrystals and eutectics) are a promising means of enhancing the dissolution behavior of poorly soluble drugs. The present study demonstrates the development of multicomponent solid forms of aripiprazole (ARP) prepared with succinic acid (SA) and nicotinamide (NA) as coformers using the hot melt extrusion (HME) technique. The HME-processed samples were characterized and analyzed using differential scanning calorimetry (DSC), hot stage microscopy (HSM), Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). The DSC and HSM analyses revealed a characteristic single melting temperature in the solid forms, which differed from the melting points of the individual components. The discernible changes in the FTIR (amide C=O stretching) and PXRD results for ARP-SA confirm the formation of new crystalline solid forms. In the case of ARP-NA, these changes were less prominent, without the appearance or disappearance of peaks, suggesting no change in the crystal lattice. The SEM images demonstrated morphological differences between the HME-processed samples and the individual parent components. The in vitro dissolution and microenvironment pH measurement studies revealed that ARP-SA showed a higher dissolution rate, which could be due to the acidic microenvironment pH imparted by the coformer. The observations of the present study demonstrate the applicability of the HME technique for the development of ARP multicomponent solid forms.

Investigating Cocrystallization of Carbamazepine with Structurally Compatible Coformers: New Cocrystal and Eutectic Phases with Enhanced Dissolution

In this work, carbamazepine (CBZ), an anticonvulsant drug was cocrystallized with several structurally complement coformers (coformers with amide, acid and hydrazide functional groups) to enhance its dissolution. CBZ formed a cocrystal phase with acetamide (ACE) when mixtures of CBZ and ACE (containing CBZ mole fractions, X_CBZ of 0.25, 0.33, 0.5, and 0.67) were subjected to solid-state grinding (SSG), evaporative crystallization (EC), slurry conversion (SC), and slow cooling crystallization (SLC). Upon heating, the CBZ-ACE cocrystal phase formed from CBZ-ACE mixtures containing X_CBZ of 0.25, 0.33 and 0.67 underwent solid-state phase transition to CBZ form I and CBZ cocrytsal phase obtained from the CBZ-ACE mixture containing X_CBZ of 0.5 converted to CBZ form III. Interestingly, slow cooling cocrystallization experiments resulted in crystallization of a cocrystal as well as the CBZ dihydrate forms. The powder dissolution studies demonstrated that among the different CBZ-ACE-SSG cocrystal phases, CBZ-ACE-SSG-X_CBZ-0.33 cocrystal exhibited 7.47 times improved dissolution whereas the CBZ eutectic phase with nicotinic acid hydrazide (NAH) exhibited 4.93 times increased dissolution when compared to raw CBZ.

Eutectic mixtures as an approach to enhance solubility, dissolution rate and oral bioavailability of poorly water-soluble drugs

Eutectic mixtures have been known for a long time in the pharmaceutical field. However, its potential as a system to improve the solubility and dissolution of poorly water-soluble drugs remains little explored. Studies involving the microstructural characterization and the preparation of solid dosage forms containing eutectic mixtures are also an issue to be developed. Recently, the number of studies involving the preparation of eutectic mixtures to improve the solubility and oral bioavailability of poorly soluble drugs has increased considerably, including drug-carrier and drug-drug mixtures. In this review is discussed the potential of eutectic mixtures as an alternative pharmaceutical solid system to enhance drugs solubility, dissolution rate or oral bioavailability. Different aspects like history, physico-chemical, microstructural properties, preparation methods, mechanisms involved in solubility/dissolution enhancement, techniques for solid state characterization, in vivo studies, advantages, limitations and formulation perspective are also discussed.

What if Cocrystallization Fails for Neutral Molecules? Screening Offered Eutectics as Alternate Pharmaceutical Materials: Leflunomide-a Case Study

Background: The manuscript is aimed to optimize the biopharmaceutical parameters of a poorly soluble, neutral anti-rheumatic drug ‘leflunomide’ by preparing its non-covalent derivatives (NCDs). For this various monocarboxylic acids- (adipic acid, picolinic acid) and dicarboxylic acids (maleic acid, malonic acid, sorbic acid), as well as pyridine carboxamide derivatives (nicotinamide, isonicotinamide), are used as coformers. Methods: The novel solid forms were rationally prepared and systematically characterized. Further, these solid forms were subjected to equilibrium solubility and intrinsic dissolution rate (IDR) analysis in three aqueous media (pH 1.2, pH 4.5 and pH 6.8). In vivo plasma studies in male Wistar rats were done to assess the effect on area under the curve (AUC) and the maximum concentration (Cmax) of leflunomide in prepared solid forms. Results: These NCD were primarily characterized to be eutectics rather than cocrystals as expected. The stoichiometry was established by phase diagrams. The negative value of heat of mixing indicated them to be of cluster type. In addition, leflunomide in eutectics showed approximately 9 folds increase in solubility up to 4 hours. Besides this, approximately 4 folds enhancement in the in IDR was also observed. Maximum increase in bioavailability indicated by enhanced values of AUC and Cmax (490.29 μg h-1 mL-1 and 31.42 μg mL-1, respectively) for leflunomide-maleic acid eutectic in comparison to pure LEF (AUC: 193.20 μg h-1 mL-1 and Cmax: 12.09 μg mL-1). Conclusion: The unsuccessful cocrystallization experiments were found be the latent eutectics. The evaluation of these novel eutectics of poorly soluble drug exhibited possibility to further amplify the scope of accessible material phase options other than pure active pharmaceutical ingredient (API) without disturbing the structural integrity.

Drug Solubility Enhancement through the Preparation of Multicomponent Organic Materials: Eutectics of Lovastatin with Carboxylic Acids

Lovastatin (LOV) is a drug used to treat hypercholesterolemia. Recent studies have identified its antioxidant effects and potential use in the treatment of some types of cancer. However, the low bioavailability related to its poor water solubility limits its use in solid oral dosage forms. Therefore, to improve the solubility of LOV three eutectic systems of LOV with the carboxylic acids benzoic (BEN), salicylic (SAL) and cinnamic (CIN) were obtained. Both binary phase and Tammann diagrams were constructed using differential scanning calorimetry (DSC) data of mixtures prepared from 0.1 to 1.0 molar ratios. Binary mixtures and eutectics were prepared by liquid-assisted grinding. The eutectics were further characterized by DSC and powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The LOV-BEN, LOV-SAL and LOV-CIN system formed a eutectic at an LOV mole fraction of 0.19, 0.60 and 0.14, respectively. The systems exhibited improvements in LOV solubility, becoming more soluble by five-fold in the LOV-SAL system and approximately four-fold in the other two systems. Considering that the solubility enhancements and the carboxylic acids used are generally recognized as safe by the U.S. Food and Drug Administration (FDA), the LOV eutectic systems are promising materials to be used in a solubility enhancement strategy for pharmaceutical product formulation.

Engineering Cocrystals of PoorlyWater-Soluble Drugs to Enhance Dissolution in Aqueous Medium

Biopharmaceutics Classification System (BCS) Class II and IV drugs suffer from poor aqueous solubility and hence low bioavailability. Most of these drugs are hydrophobic and cannot be developed into a pharmaceutical formulation due to their poor aqueous solubility. One of the ways to enhance the aqueous solubility of poorlywater-soluble drugs is to use the principles of crystal engineering to formulate cocrystals of these molecules with water-soluble molecules (which are generally called coformers). Many researchers have shown that the cocrystals significantly enhance the aqueous solubility of poorly water-soluble drugs. In this review, we present a consolidated account of reports available in the literature related to the cocrystallization of poorly water-soluble drugs. The current practice to formulate new drug cocrystals with enhanced solubility involves a lot of empiricism. Therefore, in this work, attempts have been made to understand a general framework involved in successful (and unsuccessful) cocrystallization events which can yield different solid forms such as cocrystals, cocrystal polymorphs, cocrystal hydrates/solvates, salts, coamorphous solids, eutectics and solid solutions. The rationale behind screening suitable coformers for cocrystallization has been explained based on the rules of five i.e., hydrogen bonding, halogen bonding (and in general non-covalent bonding), length of carbon chain, molecular recognition points and coformer aqueous solubility. Different techniques to screen coformers for effective cocrystallization and methods to synthesize cocrystals have been discussed. Recent advances in technologies for continuous and solvent-free production of cocrystals have also been discussed. Furthermore, mechanisms involved in solubilization of these solid forms and the parameters influencing dissolution and stability of specific solid forms have been discussed. Overall, this review provides a consolidated account of the rationale for design of cocrystals, past efforts, recent developments and future perspectives for cocrystallization research which will be extremely useful for researchers working in pharmaceutical formulation development.

Antioxidant-Based Eutectics of Irbesartan: Viable Multicomponent Forms for the Management of Hypertension

The present research work highlights the development of multicomponent solid form of the antihypertensive drug irbesartan (IRB) to improve its biopharmaceutical attributes. Mechanochemical synthesis of a new solid form of IRB with coformers having antioxidant properties (syringic acid, nicotinic acid, and ascorbic acid) resulted into three eutectic mixtures (EMs). Formation of eutectic was ascertained by differential scanning calorimetry whereas exact stoichiometry (50/50% w/w) was established by phase diagram and Tamman's triangle. The strong homomeric interaction between individual components and steric hindrances is responsible for the eutectic formation. EMs exhibited superior apparent solubility (five- to nine fold) and significant enhancement in intrinsic dissolution rate (two- to three fold) as compared to the plain drug. In vivo pharmacokinetic and in vivo pharmacodynamic studies revealed a significant improvement in the biopharmaceutical performance of EMs. Marked protection against oxidative stress was observed in EMs over plain drug by controlling the level/activity of plasma H₂O₂ and antioxidant enzymes (superoxide dismutase and catalase) in the kidney matrix of dexamethasone (Dexa)-induced hypertensive rats. Thus, these solid forms of IRB can serve as viable multicomponent forms to be translated into product development for better therapeutic efficacy in the management of hypertension.