Compound selection for development - is salt formation the ultimate answer? Experiences with an extended concept of the "100mg approach"

Experimental and Machine-Learning-Assisted Design of Pharmaceutically Acceptable Deep Eutectic Solvents for the Solubility Improvement of Non-Selective COX Inhibitors Ibuprofen and Ketoprofen

Deep eutectic solvents (DESs) are commonly used in pharmaceutical applications as excellent solubilizers of active substances. This study investigated the tuning of ibuprofen and ketoprofen solubility utilizing DESs containing choline chloride or betaine as hydrogen bond acceptors and various polyols (ethylene glycol, diethylene glycol, triethylene glycol, glycerol, 1,2-propanediol, 1,3-butanediol) as hydrogen bond donors. Experimental solubility data were collected for all DES systems. A machine learning model was developed using COSMO-RS molecular descriptors to predict solubility. All studied DESs exhibited a cosolvency effect, increasing drug solubility at modest concentrations of water. The model accurately predicted solubility for ibuprofen, ketoprofen, and related analogs (flurbiprofen, felbinac, phenylacetic acid, diphenylacetic acid). A machine learning approach utilizing COSMO-RS descriptors enables the rational design and solubility prediction of DES formulations for improved pharmaceutical applications.

An empirical predictive model for determining the aqueous solubility of BCS class IV drugs in amorphous solid dispersions

CONTEXT

Determining solubility of drugs is laborious and time-consuming process that may not yield meaningful results. Amorphous solid dispersion (ASD) is a widely used solubility enhancement technique. Predictive models could streamline this process and accelerate the development of oral drugs with improved aqueous solubilities.

OBJECTIVE

This study aimed to develop a predictive model to estimate the solubility of a compound from the ASDs in polymer matrices.

METHODS

ASDs of model drugs (acetazolamide, chlorothiazide, furosemide, hydrochlorothiazide, sulfamethoxazole) with model polymers (PVP, PVPVA, HPMC E5, Soluplus) and a surfactant (TPGS) were prepared using hotmelt process. The prepared ASDs were characterized using DSC, FTIR, and XRD. The aqueous solubility of the model drugs was determined using shake-flask method. Multiple linear regression was used to develop a predictive model to determine aqueous solubility using the molecular descriptors of the drug and polymer as predictor variables. The model was validated using Leave-One-Out Cross-Validation.

RESULTS

The ASDs' drug components were identified as amorphous via DSC and XRD Studies. There were no significant chemical interactions between the model drugs and the polymers based on FTIR studies. The ASDs showed a significant (p < 0.05) improvement in solubility, ranging from a 3-fold to 118-fold, compared with the pure drug. The developed empirical model predicted the solubility of the model drugs from the ASDs containing model polymer matrices with an accuracy greater than 80%.

CONCLUSION

The developed empirical model demonstrated robustness and predicted the aqueous solubility of model drugs from the ASDs of model polymer matrices with an accuracy greater than 80%.

Evaluation of the antimalarial activity of SAM13-2HCl with morpholine amide (SKM13 derivative) against antimalarial drug-resistant Plasmodium falciparum and Plasmodium berghei infected ICR mice

Antimalarial drugs are an urgently need and crucial tool in the campaign against malaria, which can threaten public health. In this study, we examined the cytotoxicity of the 9 antimalarial compounds chemically synthesized using SKM13-2HCl. Except for SKM13-2HCl, the 5 newly synthesized compounds had a 50% cytotoxic concentration (CC50) > 100 µM, indicating that they would be less cytotoxic than SKM13-2HCl. Among the 5 compounds, only SAM13-2HCl outperformed SKM13-2HCl for antimalarial activity, showing a 3- and 1.3-fold greater selective index (SI) (CC50/IC50) than SKM13-2HCl in vitro against both chloroquine-sensitive (3D7) and chloroquine -resistant (K1) Plasmodium falciparum strains, respectively. Thus, the presence of morpholine amide may help to effectively suppress human-infectious P. falciparum parasites. However, the antimalarial activity of SAM13-2HCl was inferior to that of the SKM13-2HCl template compound in the P. berghei NK65-infected mouse model, possibly because SAM13-2HCl had a lower polarity and less efficient pharmacokinetics than SKM13-2HCl. SAM13-2HCl was more toxic in the rodent model. Consequently, SAM13-2HCl containing morpholine was selected from screening a combination of pharmacologically significant structures as being the most effective in vitro against human-infectious P. falciparum but was less efficient in vivo in a P. berghei-infected animal model when compared with SKM13-2HCl. Therefore, SAM13-2HCl containing morpholine could be considered a promising compound to treat chloroquine-resistant P. falciparum infections, although further optimization is crucial to maintain antimalarial activity while reducing toxicity in animals.

Amorphous solid dispersions in high-swelling, low-substituted hydroxypropyl cellulose for enhancing the delivery of poorly soluble drugs

Amorphous solid dispersions (ASDs) based on water-insoluble hydrophilic polymers can sustain supersaturation in their kinetic solubility profiles (KSPs) compared to soluble carriers. However, in the limit of very high swelling capacity, the achievable extent of drug supersaturation has not been fully examined. This study explores the limiting supersaturation behavior of ASDs of poorly soluble indomethacin (IND) and posaconazole (PCZ) based on a high-swelling excipient, low-substituted hydroxypropyl cellulose (L-HPC). Using IND as a reference, we showed that the rapid initial supersaturation buildup in the KSP of IND ASD can be simulated through sequential IND infusion steps, however at large times the KSP of IND release from ASD appears more sustained than direct IND infusion. This has been attributed to potential trapping of seed crystals generated in the L-HPC gel matrix thus limiting their growth and rate of desupersaturation. Similar result is also expected in PCZ ASD. Furthermore, the current drug loading process for ASD preparation resulted in the agglomeration of L-HPC based ASD particles, producing granules of up to 300-500µm (cf. 20µm individual particle), with distinct kinetic solubility profiles. This feature makes L-HPC particularly suitable as ASD carriers for fine tuning of supersaturation to achieve enhanced bioavailability for poorly soluble drugs.

Anti-malarial activity of HCl salt of SKM13 (SKM13-2HCl)

Malaria is among the most devastating and widespread tropical parasitic diseases in developing countries. To prevent a potential public health emergency, there is an urgent need for new antimalarial drugs, with single-dose cures, broad therapeutic potential, and novel mechanism of action. We synthesized HCl salt of SKM13 (SKM13-2HCl) based on the modification of SKM13 to improve solubility in water. The anti-malarial activity of the synthesized drug was evaluated in both in vitro and in vivo models. The selective index indicated that SKM13-2HCl showed the same effectiveness with SKM13 in Plasmodium falciparum in in-vitro. Even though, in vivo mouse study demonstrated that SKM13 (20 mg/kg) at single dose could not completely inhibit P. berghei growth in blood. The survival rate increased from 33 to 90% at 15 days after infection. However, SKM13-2HCl (20 mg/kg) at a single dose increased the survival rate up to 100% at the same duration. Ultra-High-Performance Liquid Chromatography (UHPLC) showed that solubility in water of SKM13 and SKM13-2HCL was 0.389 mg/mL and 417 mg/mL, respectively. Pharmacokinetics (PK) analysis corresponded to the increased solubility of SKM13-2HCl over SKM13. Haematological parameters [red blood cell (RBC) count, haemoglobin level, and haematocrit level] supported the comparable efficacy of SKM13 and SKM13-2HCl in a 4-day suppression test. One mode of these drugs was found to be activating phosphorylation of eIF2α, hallmark of ER-stress, to kill parasite. Novel salt derivative of SKM13 (SKM13-2HCl) have enhanced anti-malarial activity against P. falciparum with endoplasmic reticulum (ER)-stress and salt form of SKM13 is an excellent direction to develop anti-malarial drug candidate in mice model.

Complexation: An Interesting Pathway for Combining Two APIs at the Solid State

Combining different drugs into a single crystal form is one of the current challenges in crystal engineering, with the number of reported multi-drug solid forms remaining limited. This paper builds upon an efficient approach to combining Active Pharmaceutical Ingredients (APIs) containing carboxylic groups in their structure with APIs containing pyridine moieties. By transforming the former into their zinc salts, they can be successfully combined with the pyridine-containing APIs. This work highlights the successfulness of this approach, as well as the improvement in the physical properties of the obtained solid forms.

Quantification of Caffeine Interactions in Choline Chloride Natural Deep Eutectic Solvents: Solubility Measurements and COSMO-RS-DARE Interpretation

Solubility of active pharmaceutical ingredients is an important aspect of drug processing and formulation. Although caffeine was a subject of many studies aiming to quantify saturated solutions, many applied solvents suffer from not being environmentally friendly. This work fills this gap by presenting the results of solubility measurements in choline chloride natural deep eutectic solvents, ccNADES, comprising one of seven of the following polyalcohols: glycerol, sorbitol, xylitol, glucose, sucrose, maltose and fructose. The ratio of ccNADES components was optimized for maximizing caffeine solubility at room temperature. Additionally, temperature dependent solubility was measured for the first four systems exhibiting the highest solubility potential, both in their neat forms and in mixtures with water. Results were used for intermolecular interactions assessments using the COSMO-RS-DARE approach, which led to a perfect match between experimental and computed solubility values. An important methodological discussion was provided for an appropriate definition of the systems. Surprising linear trends were observed between the values of fitting parameters and water-ccNADES composition. In addition, comments on selection of the values of the fusion thermodynamic parameters were provided, which led to the conclusion that COSMO-RS-DARE solubility computations can effectively compensate for the inaccuracies of these important physicochemical properties.

Overcoming Bioavailability Challenges of Dasabuvir and Enabling a Triple-Combination Direct-Acting Antiviral HCV Regimen through a Salt of Very Weak Acid for Oral Delivery

Dasabuvir is a non-nucleoside polymerase inhibitor for the treatment of hepatitis C virus (HCV) infection. It is an extremely weak diacidic drug (pK_a = 8.2 and 9.2) and a prolific solvate former. Due to its exceedingly low aqueous solubility (≤0.127 μg/mL at pH 1-6.8, dose number of 1.31 × 10⁴), crystalline dasabuvir free acid exhibited poor oral bioavailability in initial animal pharmacokinetic (PK) assessment. This necessitated the development of enabling formulation for human clinical studies to achieve the required therapeutic in vivo concentration of dasabuvir. While salt formation has been widely used to enhance the solubility and dissolution rate of solids, this approach has rarely been applied to develop oral solid dosage forms for acidic drugs as weak as dasabuvir due to concerns of rapid disproportionation and crystallization of its free acid. In this contribution, we detail our efforts in identifying dasabuvir monosodium monohydrate as a drug substance that is stable, manufacturable, and, most importantly, significantly enhances the dissolution and oral absorption of this poorly soluble drug. The oral delivery of dasabuvir through the salt approach has enabled the commercialization of the triple-combination direct-acting antiviral HCV regimen, Viekira Pak. The methodologies and solutions identified in targeted studies to overcome technical challenges encountered along the way (i.e., incorporation of polymers to inhibit crystallization and disproportionation and species mapping to enable salt manufacturing process, etc.) can be applied to other insoluble compounds.

Application of the Solute-Solvent Intermolecular Interactions as Indicator of Caffeine Solubility in Aqueous Binary Aprotic and Proton Acceptor Solvents: Measurements and Quantum Chemistry Computations

The solubility of caffeine in aqueous binary mixtures was measured in five aprotic proton acceptor solvents (APAS) including dimethyl sulfoxide, dimethylformamide, 1,4-dioxane, acetonitrile, and acetone. The whole range of concentrations was studied in four temperatures between 25 °C and 40 °C. All systems exhibit a strong cosolvency effect resulting in non-monotonous solubility trends with changes of the mixture composition and showing the highest solubility at unimolar proportions of organic solvent and water. The observed solubility trends were interpreted based on the values of caffeine affinities toward homo- and hetero-molecular pairs formation, determined on an advanced quantum chemistry level including electron correlation and correction for vibrational zero-point energy. It was found that caffeine can act as a donor in pairs formation with all considered aprotic solvents using the hydrogen atom attached to the carbon in the imidazole ring. The computed values of Gibbs free energies of intermolecular pairs formation were further utilized for exploring the possibility of using them as potential solubility prognostics. A semi-quantitative relationship (R² = 0.78) between caffeine affinities and the measured solubility values was found, which was used for screening for new greener solvents. Based on the values of the environmental index (EI), four morpholine analogs were considered and corresponding caffeine affinities were computed. It was found that the same solute–solvent structural motif stabilizes hetero-molecular pairs suggesting their potential applicability as greener replacers of traditional aprotic proton acceptor solvents. This hypothesis was confirmed by additional caffeine solubility measurements in 4-formylmorpholine. This solvent happened to be even more efficient compared to DMSO and the obtained solubility profile follows the cosolvency pattern observed for other aprotic proton acceptor solvents.

Experimental and Theoretical Study on Theobromine Solubility Enhancement in Binary Aqueous Solutions and Ternary Designed Solvents

The solubility of theobromine was studied both experimentally and theoretically. The solubility was determined spectrophotometrically at 25 °C in neat organic solvents, aqueous binary mixtures, Natural Deep Eutectic Solvents (NADES) and ternary NADES mixtures with water. It was found that addition of water in unimolar proportions with some organic solvents increases theobromine solubility compared to neat solvents. Additionally, using NADES results in a solubility increase of the studied compound not only in relation to water but also DMSO. The addition of water (0.2 molar fraction) to NADES is responsible for an even larger increase of solubility. The measured solubilities were interpreted in terms of three theoretical frameworks. The first one-belonging to the set of data reduction techniques-proved to be very efficient in quantitative back-computations of excess solubility of theobromine in all studied systems. The default approach utilizing the well-recognized COSMO-RS (Conductor-like Screening Model for Real Solvents) framework offered at most a qualitative solubility description. The extended search for possible contacts provided evidence for the existence of many intermolecular complexes that alter the electron density of the solute molecule, thus influencing solubility computations. Taking into account such intermolecular contacts by using the COSMO-RS-DARE (Conductor-like Screening Model for Realistic Solvation-Dimerization, Aggregation, and Reaction Extension) framework seriously increased the accuracy of solubility computations.

Solvent Screening for Solubility Enhancement of Theophylline in Neat, Binary and Ternary NADES Solvents: New Measurements and Ensemble Machine Learning

Theophylline, a typical representative of active pharmaceutical ingredients, was selected to study the characteristics of experimental and theoretical solubility measured at 25 °C in a broad range of solvents, including neat, binary mixtures and ternary natural deep eutectics (NADES) prepared with choline chloride, polyols and water. There was a strong synergistic effect of organic solvents mixed with water, and among the experimentally studied binary systems, the one containing DMSO with water in unimolar proportions was found to be the most effective in theophylline dissolution. Likewise, for NADES, the addition of water (0.2 molar fraction) resulted in increased solubility compared to pure eutectics, with the highest solubilisation potential offered by the composition of choline chloride with glycerol. The ensemble of Statistica Automated Neural Networks (SANNs) developed using intermolecular interactions in pure systems has been found to be a very accurate model for solubility computations. This machine learning protocol was also applied as an extensive screening for potential solvents with higher solubility of theophylline. Such solvents were identified in all three subgroups, including neat solvents, binary mixtures and ternary NADES systems. Some methodological considerations of SANNs applications for future modelling were also provided. Although the developed protocol is focused exclusively on theophylline solubility, it also has general importance and can be used for the development of predictive models adequate for solvent screening of other compounds in a variety of systems. Formulation of such a model offers rational guidance for the selection of proper candidates as solubilisers in the designed solvents screening.

Preparation, Characterization, and Selection of Optimal Forms of (S)-Carvedilol Salts for the Development of Extended-Release Formulation

(S)-carvedilol (S-CAR) is the dominant pharmacodynamic conformation of carvedilol, but its further development for extended-release formulation is restricted by its poor solubility. This study aimed to prepare and screen S-CAR salts that could be used to improve solubility and allow extended release. Five salts of S-CAR with well-known acid counterions (i.e., phosphate, hydrochloride, sulfate, fumarate, and tartrate) were produced using similar processes. However, these salts were obtained with water contents of 1.60-12.28%, and their physicochemical properties differed. The melting points of phosphate, hydrochloride, and tartrate were 1.1-1.5 times higher than that of the free base. The solubility of S-CAR salts was promoted to approximately 3-32 times higher than that of the free base at pH 5.0-8.0. Typical pH-dependent solubilities were evidently observed in S-CAR salts, but considerable differences in solubility properties among these salts were observed. S-CAR phosphate and hydrochloride possessed high melting points, considerable solubility, and excellent chemical and crystallographic stabilities. Accordingly, S-CAR phosphate and hydrochloride were chosen for further pharmacokinetic experiments and pharmaceutical study. S-CAR phosphate and hydrochloride extended-release capsules were prepared using HPMC K15 as the matrix and presented extended release in in vitro and in vivo evaluations. Results implied that water molecules in the hydrated salt were a potential threat to the achievement of crystal stability and thermostability. S-CAR phosphate and hydrochloride are suitable for further development of the extended-release formulation.

Molecular Interactions in Solid Dispersions of Poorly Water-Soluble Drugs

Physicochemical characterization is a crucial step for the successful development of solid dispersions, including the determination of drug crystallinity and molecular interactions. Typically, the detection of molecular interactions will assist in the explanation of different drug performances (e.g., dissolution, solubility, stability) in solid dispersions. Various prominent reviews on solid dispersions have been reported recently. However, there is still no overview of recent techniques for evaluating the molecular interactions that occur within solid dispersions of poorly water-soluble drugs. In this review, we aim to overview common methods that have been used for solid dispersions to identify different bond formations and forces via the determination of interaction energy. In addition, a brief background on the important role of molecular interactions will also be described. The summary and discussion of methods used in the determination of molecular interactions will contribute to further developments in solid dispersions, especially for quick and potent drug delivery applications.

Mechanism and Improved Dissolution of Glycyrrhetinic Acid Solid Dispersion by Alkalizers

The purpose of this study was to increase the dissolution of glycyrrhetinic acid (GA) by preparing ternary solid dispersion (TSD) systems containing alkalizers, and to explore the modulating mechanism of alkalizers in solid dispersion systems. GA TSDs were prepared by hot melt extrusion (HME) with Kollidon^® VA64 as the carrier and L-arginine/meglumine as the alkalizers. The in vitro release of the TSD was investigated with a dissolution test, and the dissociation constant (pKa) was used to describe the ionization degree of the drug in different pH buffers. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), Fourier Transform Infrared Spectroscopy (FTIR), Raman spectra, X-ray photoelectron spectroscopy (XPS), and a molecular model were used for solid-state characterizations and to study the dissolution mechanism of the TSDs. It was evident that the dissolution of GA significantly increased as a result of the TSD compared to the pure drug and binary solid dispersion. SEM, DSC, and XPRD data showed that GA transformed into an amorphous form in TSD. As illustrated by FTIR, Raman, XPS, and molecular docking, high binding energy ion-pair complexes formed between GA and the alkalizers during the process of HME. These can destroy the H-bond between GA molecules. Further, intermolecular H-bonds formed between the alkalizers and Kollidon^® VA64, which can increase the wettability of the drug. Our results will significantly improve the solubility and dissolution of GA. In addition, the lower pKa value of TSD indicates that higher ionization is beneficial to the dissolution of the drug. This study should facilitate further developments of TSDs containing alkalizers to improve the dissolution of weakly acidic drugs and gain a richer understanding of the mechanism of dissolution.

Gold mediated sp3αC-H functionalization of steroidal diglycoside and their anti-cancer evaluation

C(sp³)-H alkylation at α-position of methyl-keto group on D-ring of Steroidal diglycoside (SG) with (i) C=N of Schiff base imines to form amine derivatives and (ii) C=C of acrylate Michael acceptors to form Markovnikov ester products using AuCl₃/NHC as pre-catalyst and Ag(I) salts as co-catalyst was described. The original form of SG (1) and its derivatives (3b-f & 5a-d) were screened for in vitro anti-cancer activity specifically on two breast cancer cell lines (i.e. MCF-7, MDA-MB-231) and deduced the structure-activity-relationship with the support of molecular docking studies. Among these compounds 3b, 3f, 5b & 5d have shown more potent anticancer activity than standard drug cisplatin with considerable IC50 values.

Optimization, thermodynamic characteristics and solubility predictions of natural deep eutectic solvents used for sulfonamide dissolution

The limited water solubility of sulfonamides provokes a search for new solvents offering not only increased solubility but also environmental and health safety. Therefore, six sulfonamides were studied in a series of natural deep eutectic solvents (NADES) comprising choline chloride with multi-hydroxyl compounds. Experimental screening aimed at finding the optimized NADES composition revealed that unimolar proportion of choline chloride and glycerol offers the highest solubility advantage, equal up to 43 times compared with water at 37 °C. Besides, quantum chemistry computations based on the COSMO-RS protocol were conducted in order to gain an insight into the thermodynamic characteristics of the systems and to explain the origin of the observed solubility increase. It was found that the factor responsible for the solubility gain in NADES are the interactions between choline chloride and sulfonamide drug molecules, having the highest affinities expressed in terms of Gibbs free energy of corresponding reactions. Finally, utilizing the obtained results together with artificial neural networks led to a perfect match between experimental and predicted solubility, documented by the mean absolute percentage error value below 2.5%. The developed protocol seems to be so general and accurate that screening of potential new API-NADES systems can be significantly simplified.

Successful oral delivery of poorly water-soluble drugs both depends on the intraluminal behavior of drugs and of appropriate advanced drug delivery systems

Poorly water-soluble drugs continue to be a problematic, yet important class of pharmaceutical compounds for treatment of a wide range of diseases. Their prevalence in discovery is still high, and their development is usually limited by our lack of a complete understanding of how the complex chemical, physiological and biochemical processes that occur between administration and absorption individually and together impact on bioavailability. This review defines the challenge presented by these drugs, outlines contemporary strategies to solve this challenge, and consequent in silico and in vitro evaluation of the delivery technologies for poorly water-soluble drugs. The next steps and unmet needs are proposed to present a roadmap for future studies for the field to consider enabling progress in delivery of poorly water-soluble compounds.

Natural Deep Eutectic Solvents as Agents for Improving Solubility, Stability and Delivery of Curcumin

Purpose

Study on curcumin dissolved in natural deep eutectic solvents (NADES) was aimed at exploiting their beneficial properties as drug carriers.

Methods

The concentration of dissolved curcumin in NADES was measured. Simulated gastrointestinal fluids were used to determine the concentration of curcumin and quantum chemistry computations were performed for clarifying the origin of curcumin solubility enhancement in NADES.

Results

NADES comprising choline chloride and glycerol had the highest potential for curcumin dissolution. This system was also successfully applied as an extraction medium for obtaining curcuminoids from natural sources, as well as an effective stabilizer preventing curcumin degradation from sunlight. The solubility of curcumin in simulated gastrointestinal fluids revealed that the significant increase of bioavailability takes place in the small intestinal fluid.

Conclusions

Suspension of curcumin in NADES offers beneficial properties of this new liquid drug formulation starting from excreting from natural sources, through safe storage and ending on the final administration route. Therefore, there is a possibility of using a one-step process with this medium. The performed quantum chemistry computations clearly indicated the origin of the enhanced solubility of curcumin in NADES in the presence of intestinal fluids. Direct intermolecular contacts leading to hetero-molecular pairs with choline chloride and glycerol are responsible for elevating the bulk concentration of curcumin. Choline chloride plays a dominant role in the system and the complexes formed with curcumin are the most stable among all possible homo- and hetero-molecular pairs that can be found in NADES-curcumin systems.

High-Throughput Dissolution/Permeation Screening -A 96-Well Two-Compartment Microplate Approach

Early formulation screening can alleviate development of advanced oral drug formulations, such as amorphous solid dispersions (ASDs). Traditionally, dissolution is used to predict ASD performance. Here, a high-throughput approach is described that simultaneously screens drug dissolution and permeation employing a two-compartment 96-well plate. Freeze-drying from hydro-alcoholic solutions was used to prepare amorphous formulations. The screening approach was tested on amorphous and crystalline tadalafil formulations with and without Soluplus^®. The workflow consisted of: 1) dispersion of the formulations; 2) incubation within the two-compartment plate, where a dialysis membrane separated donor (dispersed formulation) and acceptor; 3) sampling (donor and acceptor), where donor samples were centrifuged to remove non-dissolved material; and 4) quantification by UHPLC-UV. To identify optimal screening conditions, the following parameters were varied: dispersion medium (buffer / biomimetic media), acceptor medium (buffer / surfactant solutions), and incubation time (1, 3, and 6 h). Surfactants (acceptor) increased tadalafil permeation. Biomimetic medium (donor) enhanced dissolution, but not permeation, except for freeze-dried tadalafil, for which the permeated amount increased. The predictiveness was evaluated by comparing dissolution-/permeation-results with in vivo bioavailability. In general, both dissolution and permeation reflected bioavailability, whereof the latter was a better predictor. High-throughput dissolution/permeation is regarded promising for formulation screening.

Solubility advantage of sulfanilamide and sulfacetamide in natural deep eutectic systems: experimental and theoretical investigations

Objective: The aim of this study was to explore the possibility of using natural deep eutectic solvents (NADES) as solvation media for enhancement of solubility of sulfonamides, as well as gaining some thermodynamic characteristics of the analyzed systems. Significance: Low solubility of many active pharmaceutical ingredients is a well-recognized difficulty in pharmaceutical industry, hence the need for different strategies addressing this problem. Among such strategies, those that are environmentally and economically beneficial are of particular interest. Methods: The solubility of sulfanilamide and sulfacetamide in 21 different NADES compositions comprising choline chloride with sugars or sugar alcohols was measured spectrophotometrically. Thermodynamic parameters describing the studied systems were determined using the COSMO-RS computational protocol. Results: All of the considered NADES compositions gave an increase in solubility of the studied sulfonamides, with the highest solubilities obtained for the system comprising choline chloride and glycerol in unimolar proportions, which gave a solubility advantage of 83.7 and 73.8 for sulfanilamide and sulfacetamide, respectively. Theoretical studies indicated that the dissolution of both considered sulfonamides has a low endothermic character, with the lowest enthalpy values obtained for the most optimal, i.e. unimolar, proportions. The non-monotonous trend of enthalpy of dissolution was also discussed in terms of intermolecular interactions. Conclusions: The obtained results show the feasibility of using NADES as solubility enhancers for sulfonamides and encourage for further exploration in this field.

Combining amorphous solid dispersions for improved kinetic solubility of posaconazole simultaneously released from soluble PVP/VA64 and an insoluble ammonio methacrylate copolymer

The aim of this study was to evaluate the potential of combining multiple ASDs based on water soluble and insoluble polymers to reach and maintain poorly soluble posaconazole (PCZ) supersaturation over time. ASDs of PCZ were obtained with PVP/VA64 or an ammonio methacrylate copolymer by solvent evaporation method with a fixed 20% (wt/wt%) drug loading ratio and physical mixtures of these ASDs were prepared at various proportions. ASDs were characterized by Fourier transform infrared spectroscopy (FT-IR) and powder X-ray diffraction (PXRD) and compared to their respective physical mixture with crystalline PCZ. Crystalline PCZ equilibrium solubility was determined at pH 1.2-2 range. Dissolution profiles were constructed under non-sink condition with an adapted dissolution system. PXRD analysis demonstrated that both ASDs were at the amorphous state and FT-IR spectroscopy revealed that the analytical signal of PCZ was also absent in both ASDs. Equilibrium solubility of crystalline PCZ varied between 26.36 ± 0.32 (pH 2) to 609.33 ± 3.68 (pH 1.2) μg/mL. All ASDs reached higher concentrations than the equilibrium solubility of crystalline PCZ during dissolution. PVP/VA64 ASDs showed dominance over PCZ dissolution and recrystallization rates whereas Eudragit RS PO ASD alone did not cause PCZ recrystallization whatsoever. The combination containing 20 mg PVP/VA64 + 80 mg Eudragit RS PO as PCZ carriers obtained the highest AUC, suggesting that even after the PVP/VA64 part was completely dissolved, reaching a concentration above crystalline PC C_s, the insoluble polymer could still release PCZ slowly and maintain supersaturation over time. The research demonstrated a potential of combining multiple ASDs to achieve distinct dissolution profiles while increasing the kinetic solubility of poorly soluble drugs.

The crystalline salt form of a selected candidate drug showed photo-, thermal- and humidity induced form transitions

AZ3411 was selected as a lead compound for the treatment of Inflammatory Bowel Disease (IBD). The present research aimed to perform an early pharmaceutical assessment of this NK antagonist candidate focusing on the challenging solid-state part of the evaluation. X-ray powder diffraction (XRPD), hot stage XRPD and microscopy, differential scanning calorimetry, thermogravimetrical analysis measurements, nuclear magnetic resonance spectroscopy and liquid chromatographic analysis were used to characterize AZ3411. The amorphous, free base form of AZ3411 was transformed to a poorly crystalline material by salt formation using maleic acid. Suspensions of the poorly crystalline form (type A), prepared in various solvents, exhibited phase transformation on storage. Some precipitate was identified as a new, more crystalline form (type B) of the maleate salt of AZ3411. Also, a third crystalline form was observed at high temperatures (type C). AZ3411 maleate type A, maleate type B and amorphous, free base form was stored in 40 °C/75% relative humidity (RH), 60 °C and 80 °C for three months. Form B was found to be the most chemically stable at all conditions. After three months at 40 °C/75%RH, both type A and type B had transformed to the anhydrous type C. Moreover, type B was transformed to form C at 60 °C and 80 °C, while type A remained unchanged. These results, together with the loss of water with temperature, suggest that type B is a hydrate. The relative stability between the hydrate type B and anhydrous type C depend on humidity and temperature. Moreover, the photosensitivity of maleate type A, maleate type B and amorphous free base has been investigated under three different illumination conditions. In similarity to the previous study, Form B was the most chemically stable form. However, after completion the study, at the highest energy conditions (765 W/m², 250-800 nm), the crystalline type B had transformed to type C, while type A had lost in crystallinity. A similar photostability study was performed on solutions of pH 1 and pH 7. The degradation pattern was similar for the two pHs but appeared different from the unstressed solution stability study performed on different pHs between pH 1 and 7. Neither was there any obvious correlation between the degradation patterns obtained after the stressed thermal- and photostability studies performed on the drug substance in solid-state. The salt of AZ3411 fulfils basic requirements for further development of an oral immediate release (IR) dosage form, although the compound displays signs of light sensitivity and there may be a risk of solid-state transitions during formulation development and long-term storage.

A case study where pharmaceutical salts were used to address the issue of low in vivo exposure

The present active pharmaceutical ingredient (API) is a lipophilic compound with a significant risk of not achieving therapeutic plasma concentrations due to solubility-limited absorption. The aim of the presented studies was to investigate whether three novel salts of a new selected candidate in the cardiovascular therapy area could be applied to improve intestinal absorption and the subsequent in vivo exposure. Three salts (chloride, hydrogen sulfate, and hemi-1.5-naphtalenedisulphonate) of the compound were manufactured and investigated regarding solubility, dissolution rate, and in vivo exposure in rats. The chemical and physical stability of the salt forms (and the crystalline parent compound) were followed in solid state, when dissolved and when formulated as microsuspensions. All salts showed improved solubility in investigated media, increased dissolution rate, and elevated in vivo exposures compared to a nanocrystal formulation (top-down) of the parent free base of the compound. The chloride- and the hydrogen sulfate salts of the API showed similar patterns regarding the chemical stability in solid state as the crystalline free base, while the salt formed of the hemi-1.5-naphtalenedisulphonic acid showed significantly improved stability. In conclusion, this study showed that three salts of a new selected candidate drug could be used to improve solubility, increase dissolution rate, and enhance oral absorption compared with a more commonly used nanocrystal formulation of the API. However, the identity of the counter ion appeared to be of less importance. On the other hand, only the salt of the hemi-1.5-naphtalenedisulphonic acid seemed to improve chemical stability compared with the API.

Direct imaging of the dissolution of salt forms of a carboxylic acid drug

The optimisation of the pharmaceutical properties of carboxylic acid drugs is often conducted by salt formation. Often, the salt with the best solubility is not chosen due to other factors such as stability, solubility, dissolution and bioavailability that are taken into consideration during the preformulation stage. This work uses advanced imaging techniques to give insights into the preformulation properties that can aid in the empirical approach often used in industry for the selection of salts. Gemfibrozil (GEM) was used as a model poorly soluble drug. Four salts of GEM were made using cyclopropylamine (CPROP), cyclobutylamine (CBUT), cyclopentylamine (CPENT) and cyclohexylamine (CHEX) as counterions. DSC, XRD and SEM were used to confirm and characterise salt formation. IDR obtained using UV-imaging up to 10 min for all the salts showed that an increase in the chain length of the counterion caused a decrease in the IDR. Past the 10 min mark, there was an increase in the IDR value for the CPROP salt, which was visualised using UV-imaging. The developed interfacial (surface) area ratio (Sdr) showed significant surface gains for the compacts. Full dosage form (capsule) imaging showed an improvement over the GEM for all the salts with an increase in chain length of the counterion bringing about a decrease in dissolution which correlated with the obtained UV-imaging IDR data.

Fluorescence-Based High-Throughput Salt Screening

The present study reports a high-throughput screening method for the salt formation of amine-containing active pharmaceutical ingredients (APIs) based on fluorescence measurements. A free form amine API was alkynylated by a solid-vapor reaction using propargyl bromide, and a fluorescent compound was produced by a subsequent reaction using 9-azidomethylanthracene. In contrast, salts were inert to propargyl bromide; thus, no fluorescence was observed. Samples for salt screening were prepared by grinding haloperidol with various counter acids, and these mixtures were derivatized in a 96-well microplate to determine whether the salt formation had occurred between haloperidol and the counter acids. Samples that turned into fluorescent and nonfluorescent were confirmed to be free form and salt form, respectively, using powder X-ray diffraction and Raman spectroscopy. In conclusion, our method adequately functions as an indicator of the salt formation of amine APIs. Further, this method allows for the rapid evaluation of the salt formation of APIs using 96-well microplates without the need for special reagents or techniques; thus, it is valuable for the discovery of an optimal salt form of newly developed amine APIs in the pharmaceutical industry.

Novel strategies for the formulation and processing of poorly water-soluble drugs

Low aqueous solubility of active pharmaceutical ingredients presents a serious challenge in the development process of new drug products. This article provides an overview on some of the current approaches for the formulation of poorly water-soluble drugs with a special focus on strategies pursued at the Center of Pharmaceutical Engineering of the TU Braunschweig. These comprise formulation in lipid-based colloidal drug delivery systems and experimental as well as computational approaches towards the efficient identification of the most suitable carrier systems. For less lipophilic substances the preparation of drug nanoparticles by milling and precipitation is investigated for instance by means of microsystem-based manufacturing techniques and with special regard to the preparation of individualized dosage forms. Another option to overcome issues with poor drug solubility is the incorporation into nanospun fibers.

Measurement and Accurate Interpretation of the Solubility of Pharmaceutical Salts

Salt formation is one of the primary approaches to improve the developability of ionizable poorly water-soluble compounds. Solubility determination of the salt candidates in aqueous media or biorelevant fluids is a critical step in salt screening. Salt solubility measurements can be complicated due to dynamic changes in both solution and solid phases. Because of the early implementation of salt screening in research, solubility measurements often are performed using minimal amount of material. Some salts have transient high solubility on dissolution. Recognition of these transients can be critical in developing these salts into drug products. This minireview focuses on challenges in salt solubility measurements due to the changes in solution caused by self-buffering effects of dissolved species and the changes in solid phase due to solid-state phase transformations. Solubility measurements and their accurate interpretation are assessed in the context of dissolution monitoring and solid-phase analysis technologies. A harmonized method for reporting salt solubility measurements is recommended to reduce errors and to align with the U.S. Pharmacopeial policy and Food and Drug Administration recommendations for drug products containing pharmaceutical salts.

Comparison of 2 strategies to enhance pyridoclax solubility: Nanoemulsion delivery system versus salt synthesis

Pyridoclax is an original oligopyridine lead, very promising in treatment of chemoresistant cancers. However, from solubility measurement and permeability evaluation, it appeared that this compound can be considered as a BCS II drug, with a poor water solubility. To overcome this unfavorable property, two strategies were proposed and compared: pyridoclax di-hydrochloride salt synthesis and formulation of pyridoclax-loaded nanoemulsions (PNEs) efficiently performed by transposing the spontaneous emulsification process previously developed by our team. Whereas the salt improved the thermodynamic solubility of the drug by a factor 4, the apparent solubility of the encapsulated pyridoclax was 1000-fold higher. Their stability was assessed upon dilution in various complex biomimetic media relevant for oral administration (SGF, FaSSIF-V2, FeSSIF-V2) or for the intravenous route (PBS). The solubility of the salt was affected by the nature of the medium, indicating that it could precipitate after administration, negatively impacting its bioavailability and its efficiency in vivo. On the contrary, in all media, PNEs remained stable in terms of granulometric properties (determined by DLS), ζ-potential and encapsulation efficiency (measured by HPLC). Thus, such nanomedicines appear as a valuable option to perform preclinical studies on the promising pyridoclax.

The delivery of arbidol by salt engineering: synthesis, physicochemical properties and pharmacokinetics

The aim of the present study was to evaluate the feasibility of using the methanesulfonic salt of arbidol in order to improve its aqueous solubility and thus oral bioavailability. Arbidol mesylate (AM) was synthesized and then characterized using nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), and its apparent solubility and octanol-water partition coefficient were also studied. The results of NMR, IR, PXRD, SEM and DSC tests confirmed the salt formation. The apparent solubility of AM in water was 32-fold higher than that of the commercial product. A superior pH-dependent profile and an improved dissolution rate of AM were obtained in a variety of solutions with different pH values. In addition, AM exhibited a relatively higher peak plasma concentration (1460 versus 1297 ng/mL) and an increased AUC_0-t (2475 versus 1277 ng/mL × h) when comparing with the commercial product, indicating the improved bioavailability of the drug. This study suggests that AM may be able to improve the therapeutic efficacy of arbidol, which rendering it to be a promising candidate for further development.