Solubility and dissolution profile assessment in drug discovery

Mathematical Modeling of the Gastrointestinal System for Preliminary Drug Absorption Assessment

The objective of this study is to demonstrate the potential of a multicompartmental mathematical model to simulate the activity of the gastrointestinal system after the intake of drugs, with a limited number of parameters. The gastrointestinal system is divided into five compartments, modeled as both continuous systems with discrete events (stomach and duodenum) and systems with delay (jejunum, ileum, and colon). The dissolution of the drug tablet occurs in the stomach and is described through the Noyes-Whitney equation, with pH dependence expressed through the Henderson-Hasselbach relationship. The boluses resulting from duodenal activity enter the jejunum, ileum, and colon compartments, where drug absorption takes place as blood flows countercurrent. The model includes only three parameters with assigned physiological meanings. It was tested and validated using data from in vivo experiments. Specifically, the model was tested with the concentration profiles of nine different drugs and validated using data from two drugs with varying initial concentrations. Overall, the outputs of the model are in good agreement with experimental data, particularly with regard to the time of peak concentration. The primary sources of discrepancy were identified in the concentration decay. The model's main strength is its relatively low computational cost, making it a potentially excellent tool for in silico assessment and prediction of drug adsorption in the intestine.

A novel simulated media system for in vitro evaluation of bioequivalent intestinal drug solubility

Orally administered solid drug must dissolve in the gastrointestinal tract before absorption to provide a systemic response. Intestinal solubility is therefore crucial but difficult to measure since human intestinal fluid (HIF) is challenging to obtain, varies between fasted (Fa) and fed (Fe) states and exhibits inter and intra subject variability. A single simulated intestinal fluid (SIF) cannot reflect HIF variability, therefore current approaches are not optimal. In this study we have compared literature Fa/FeHIF drug solubilities to values measured in a novel in vitro simulated nine media system for either the fasted (Fa9SIF) or fed (Fe9SIF) state. The manuscript contains 129 literature sampled human intestinal fluid equilibrium solubility values and 387 simulated intestinal fluid equilibrium solubility values. Statistical comparison does not detect a difference (Fa/Fe9SIF vs Fa/FeHIF), a novel solubility correlation window enclosed 95% of an additional literature Fa/FeHIF data set and solubility behaviour is consistent with previous physicochemical studies. The Fa/Fe9SIF system therefore represents a novel in vitro methodology for bioequivalent intestinal solubility determination. Combined with intestinal permeability this provides an improved, population based, biopharmaceutical assessment that guides formulation development and indicates the presence of food based solubility effects. This transforms predictive ability during drug discovery and development and may represent a methodology applicable to other multicomponent fluids where no single component is responsible for performance.

Thermodynamic solubility measurement without chemical analysis

In this work, the optical imaging based single particle analysis (SPA) and the gold standard shake-flask (SF) solubility methods are compared. We show that to analyze pharmaceutical compounds spanning 7 log units in solubility and a diverse chemical space with limited resources, several analytical techniques are required (HPLC-UV, LC-MS, refractometry and UV-Vis spectrometry), whereas solely the SPA method is able to analyze all the same compounds. SPA experiments take only minutes, while for SF, it may take days to reach thermodynamic equilibration. This decreases the time span needed for the solubility experiment from initial preparations to obtaining the result from roughly three days to less than three hours. The optimal particle size for SPA ranges from approximately one to hundreds of microns. Challenges include measuring large particles, very fast dissolving compounds and handling small sample sizes. Inherent exclusion of density from the SPA measurement is a potential source of error for compounds with very low or high density values. The average relative difference of 37 % between the two methods is very good in the realm of solubility, where 400 % interlaboratory reproducibility can be expected.

Excipient Impact on Fenofibrate Equilibrium Solubility in Fasted and Fed Simulated Intestinal Fluids Assessed Using a Design of Experiment Protocol

Solubility is a critical parameter controlling drug absorption after oral administration. For poorly soluble drugs, solubility is influenced by the complex composition of intestinal media and the influence of dosage form excipients, which can cause bioavailability and bioequivalence issues. This study has applied a small scale design of experiment (DoE) equilibrium solubility approach in order to investigate the impact of excipients on fenofibrate solubility in simulated fasted and fed intestinal media. Seven media parameters (bile salt (BS), phospholipid (PL), fatty acid, monoglyceride, cholesterol, pH and BS/PL ratio) were assessed in the DoE and in excipient-free media, and only pH and sodium oleate in the fasted state had a significant impact on fenofibrate solubility. The impact of excipients were studied at two concentrations, and for polyvinylpyrrolidone (PVP, K12 and K29/32) and hydroxypropylmethylcellulose (HPMC, E3 and E50), two grades were studied. Mannitol had no solubility impact in any of the DoE media. PVP significantly increased solubility in a media-, grade- and concentration-dependent manner, with the biggest change in fasted media. HPMC and chitosan significantly reduced solubility in both fasted and fed states in a media-, grade- and concentration-dependent manner. The results indicate that the impact of excipients on fenofibrate solubility is a complex interplay of media composition in combination with their physicochemical properties and concentration. The results indicate that in vitro solubility studies combining the drug of interest, proposed excipients along with suitable simulated intestinal media recipes will provide interesting information with the potential to guide formulation development.

Impact of Silica Dry Coprocessing with API and Blend Mixing Time on Blend Flowability and Drug Content Uniformity

This paper considers two fine-sized (d50 ∼10 µm) model drugs, acetaminophen (mAPAP) and ibuprofen (Ibu), to examine the effect of API dry coprocessing on their multi-component medium DL (30 wt%) blends with fine excipients. The impact of blend mixing time on the bulk properties such as flowability, bulk density, and agglomeration was studied. The hypothesis tested is that blends with fine APIs at medium DL require good blend flowability to have good blend uniformity (BU). Moreover, the good flowability could be achieved through dry coating with hydrophobic (R972P) silica, which reduces agglomeration of not only fine API, but also of its blends while using fine excipients. For uncoated APIs, the blend flowability was poor, i.e. cohesive regime at all mixing times, and the blends failed to achieve acceptable BU. In contrast, for dry coated APIs, their blend flowability improved to easy-flow regime or better, improving with mixing time, and as hypothesized, all blends consequently achieved desired BU. All dry coated API blends exhibited improved bulk density and reduced agglomeration, attributed to mixing induced synergistic property enhancements, likely due to silica transfer. Despite coating with hydrophobic silica, tablet dissolution was improved, attributed to the reduced agglomeration of fine API.

Prediction of Liquid-Liquid Phase Separation at the Dissolving Drug Salt Particle Surface

During the dissolution of drug salt particles, liquid-liquid phase separation (LLPS) of a free form can occur within the unstirred water layer (UWL) of the particles (UWL-LLPS). Theoretically, UWL-LLPS occurs when the free form concentration at the salt particle surface (C₀) exceeds the intrinsic LLPS concentration (S₀^LLPS) of the free form. In the present study, we attempted to predict UWL-LLPS based on the intrinsic physicochemical properties of drugs. Cyproheptadine hydrochloride (CPH-HCl), diclofenac sodium (DCF-Na), papaverine hydrochloride (PAP-HCl), and propafenone hydrochloride (PRF-HCl) were selected as model drug salts. The pH₀ and C₀ values at pHs 4.0-9.5 (citric acid, phosphoric acid, and boric acid, buffer capacity = ca. 4 mM/ΔpH) were calculated using the pK_a, solubility product (K_sp), and diffusion coefficient (D) of a drug. S₀^LLPS was measured using the pH-shift method. UWL-LLPS was predicted to occur when C₀ ≥ S₀^LLPS. The prediction result was then compared with UWL-LLPS observed at each pH by polarized light microscopy (PLM). The pH-LLPS concentration (S_pH^LLPS) profile of each drug was also measured. UWL-LLPS was approximately correctly predicted for CPH-HCl, DCF-Na, and PRF-HCl. However, UWL-LLPS was not observable when C₀ was close to S₀^LLPS. Furthermore, UWL-LLPS was not accurately predicted in the case of PAP-HCl. The pH-S_pH^LLPS profile of PAP did not follow the Henderson-Hasselbalch equation, probably because of the formation of cationic aggregates. In conclusion, UWL-LLPS was approximately predictable for drug salts using their intrinsic physicochemical properties (K_sp, pK_a, D, and S₀^LLPS), except for PAP-HCl.

Dissolution Profiles of Poorly Soluble Drug Salts in Bicarbonate Buffer

PURPOSE

The purpose of the present study was to investigate the effect of buffer species on the dissolution profiles of poorly soluble drug salts, focusing on bicarbonate buffer (BCB).

METHODS

Pioglitazone HCl (PIO HCl) and dantrolene sodium (DNT Na) were used as model drugs. Non-sink dissolution tests were performed using phosphate buffer (PB) and BCB (pH 6.5, buffer capacity: 4.4 mM/pH, ionic strength: 0.14 M, with/ without bile micelles). The pH value of BCB was maintained using a floating lid that avoided the loss of CO₂. The particles collected at the early stage of dissolution (< 5 min) were analyzed by powder X-ray diffraction, polarized light microscopy, and scanning electron microscopy. A bulk-phase pH shift precipitation test was also performed.

RESULTS

The dissolution of PIO HCl was slower in BCB than in PB, whereas that of DNT Na was faster in BCB than in PB. The same trend was observed in the presence of bile micelles. Free-form precipitation on the surface of salt particles was observed early in their dissolution in both BCB and PB. However, the surface textures in BCB and PB were different. The bulk-phase precipitation of PIO was little affected by buffer species, whereas that of DNT was affected, but oppositely to the dissolution profile.

CONCLUSION

The dissolution profiles of PIO HCl and DNT Na in BCB were markedly different from those in PB. Free-form precipitation on the particle surface, rather than in the bulk phase, was affected by buffer species in the dissolution test.

Characterization of Mass Transfer within the Crystal-Solution Boundary Layer of l-Alanine {120} Faces Using Laser Interferometry during Growth and Dissolution

Crystallization and dissolution are important processes to consider in drug development as well as many other industrial processes. Many current growth and dissolution models are based on bulk solution properties and do not implicitly consider concentration variation close to the crystal surface-solution interface and how this is mediated by solute diffusive mass transfer. Solution boundary layer thickness and concentration distribution, for the {120} crystal habit face of single crystals of l-alanine in saturated aqueous solutions during both growth and dissolution processes, is measured as a function of super/undersaturation using a Mach-Zehnder optical interferometer system. Further analysis allows determination of the diffusion coefficient and mass flux within the boundary layer as well as whether the processes are controlled by mass transfer or crystal interfacial kinetics. The measurement of this study revealed that the {120} face was not saturated at its surface during growth or dissolution meaning both processes were somewhat limited by their crystal interfacial kinetics. Growth was limited by crystal interfacial kinetics at all supersaturations to the same degree, whereas dissolution had a mixed dependency on crystal interfacial kinetics and mass transfer at lower undersaturations becoming more limited by mass transfer at higher undersaturations. Boundary layer thickness increased with super/undersaturation but to a lesser degree than the increase in the concentration difference between the crystal surface and bulk solution leading to a higher mass flux of solute molecules through the boundary layer. At the same relative super/undersaturation mass flux of solute molecules was faster during dissolution which was concurrent with its increased surface to bulk solution concentration difference and boundary layer thickness.

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.

Pharmaceutical Methods for Enhancing the Dissolution of Poorly Water-Soluble Drugs

Low water solubility is the main hindrance in the growth of pharmaceutical industry. Approximately 90% of newer molecules under investigation for drugs and 40% of novel drugs have been reported to have low water solubility. The key and thought-provoking task for the formulation scientists is the development of novel techniques to overcome the solubility-related issues of these drugs. The main intention of present review is to depict the conventional and novel strategies to overcome the solubility-related problems of Biopharmaceutical Classification System Class-II drugs. More than 100 articles published in the last 5 years were reviewed to have a look at the strategies used for solubility enhancement. pH modification, salt forms, amorphous forms, surfactant solubilization, cosolvency, solid dispersions, inclusion complexation, polymeric micelles, crystals, size reduction, nanonization, proliposomes, liposomes, solid lipid nanoparticles, microemulsions, and self-emulsifying drug delivery systems are the various techniques to yield better bioavailability of poorly soluble drugs. The selection of solubility enhancement technique is based on the dosage form and physiochemical characteristics of drug molecules.

Celecoxib Nanoformulations with Enhanced Solubility, Dissolution Rate, and Oral Bioavailability: Experimental Approaches over In Vitro/In Vivo Evaluation

Celecoxib (CXB) is a Biopharmaceutical Classification System (BCS) Class II molecule with high permeability that is practically insoluble in water. Because of the poor water solubility, there is a wide range of absorption and limited bioavailability following oral administration. These unfavorable properties can be improved using dry co-milling technology, which is an industrial applicable technology. The purpose of this study was to develop and optimize CXB nanoformulations prepared by dry co-milling technology, with a quality by design approach to maintain enhanced solubility, dissolution rate, and oral bioavailability. The resulting co-milled CXB composition using povidone (PVP), mannitol (MAN) and sodium lauryl sulfate (SLS) showed the maximum solubility and dissolution rate in physiologically relevant media. Potential risk factors were determined with an Ishikawa diagram, important risk factors were selected with Plackett-Burman experimental design, and CXB compositions were optimized with Central Composite design (CCD) and Bayesian optimization (BO). Physical characterization, intrinsic dissolution rate, solubility, and stability experiments were used to evaluate the optimized co-milled CXB compositions. Dissolution and permeability studies were carried out for the resulting CXB nanoformulation. Oral pharmacokinetic studies of the CXB nanoformulation and reference product were performed in rats. The results of in vitro and in vivo studies show that the CXB nanoformulations have enhanced solubility (over 4.8-fold (8.6 ± 1.06 µg/mL vs. 1.8 ± 0.33 µg/mL) in water when compared with celecoxib pure powder), and dissolution rate (at least 85% of celecoxib is dissolved in 20 min), and improved oral pharmacokinetic profile (the relative bioavailability was 145.2%, compared to that of Celebrex^®, and faster t_max 3.80 ± 2.28 h vs. 6.00 ± 3.67 h, indicating a more rapid absorption rate).

Highly Potent and Oral Macrocyclic Peptides as a HIV-1 Protease Inhibitor: mRNA Display-Derived Hit-to-Lead Optimization

Human immunodeficiency virus type-1 (HIV-1) protease is essential for viral propagation, and its inhibitors are key anti-HIV-1 drug candidates. In this study, we discovered a novel HIV-1 protease inhibitor (compound 16) with potent antiviral activity and oral bioavailability using a structure-based drug design approach via X-ray crystal structure analysis and improved metabolic stability, starting from hit macrocyclic peptides identified by mRNA display against HIV-1 protease. We found that the improvement of the proteolytic stability of macrocyclic peptides by introducing a methyl group to the α-position of amino acid is crucial to exhibit strong antiviral activity. In addition, macrocyclic peptides, which have moderate metabolic stability and solubility in solutions containing taurocholic acid, exhibited desirable plasma total clearance and oral bioavailability. These approaches may contribute to the successful discovery and development of orally bioavailable peptide drugs.

Design, Synthesis, and Development of pyrazolo[1,5-a]pyrimidine Derivatives as a Novel Series of Selective PI3Kδ Inhibitors: Part I—Indole Derivatives

Phosphoinositide 3-kinase δ (PI3Kδ), a member of the class I PI3K family, is an essential signaling biomolecule that regulates the differentiation, proliferation, migration, and survival of immune cells. The overactivity of this protein causes cellular dysfunctions in many human disorders, for example, inflammatory and autoimmune diseases, including asthma or chronic obstructive pulmonary disease (COPD). In this work, we designed and synthesized a new library of small-molecule inhibitors based on indol-4-yl-pyrazolo[1,5-a]pyrimidine with IC50 values in the low nanomolar range and high selectivity against the PI3Kδ isoform. CPL302253 (54), the most potent compound of all the structures obtained, with IC50 = 2.8 nM, is a potential future candidate for clinical development as an inhaled drug to prevent asthma.

Design, Synthesis, and Development of Pyrazolo[1,5-a]pyrimidine Derivatives as a Novel Series of Selective PI3Kδ Inhibitors: Part II—Benzimidazole Derivatives

Phosphoinositide 3-kinase (PI3K) is the family of lipid kinases participating in vital cellular processes such as cell proliferation, growth, migration, or cytokines production. Due to the high expression of these proteins in many human cells and their involvement in metabolism regulation, normal embryogenesis, or maintaining glucose homeostasis, the inhibition of PI3K (especially the first class which contains four subunits: α, β, γ, δ) is considered to be a promising therapeutic strategy for the treatment of inflammatory and autoimmune diseases such as systemic lupus erythematosus (SLE) or multiple sclerosis. In this work, we synthesized a library of benzimidazole derivatives of pyrazolo[1,5-a]pyrimidine representing a collection of new, potent, active, and selective inhibitors of PI3Kδ, displaying IC50 values ranging from 1.892 to 0.018 μM. Among all compounds obtained, CPL302415 (6) showed the highest activity (IC50 value of 18 nM for PI3Kδ), good selectivity (for PI3Kδ relative to other PI3K isoforms: PI3Kα/δ = 79; PI3Kβ/δ = 1415; PI3Kγ/δ = 939), and promising physicochemical properties. As a lead compound synthesized on a relatively large scale, this structure is considered a potential future candidate for clinical trials in SLE treatment.

Another Move towards Bicalutamide Dissolution and Permeability Improvement with Acetylated β-Cyclodextrin Solid Dispersion

The complex formation of antiandrogen bicalutamide (BCL) with methylated (Me-β-CD) and acetylated (Ac-β-CD) β-cyclodextrins was investigated in buffer solution pH 6.8. A two-fold strongly binding of BCL to Ac-β-CD as compared to Me-β-CD was revealed. The solid dispersion of BCL with Ac-β-CD was prepared by the mechanical grinding procedure to obtain the complex in the solid state. The BCL/Ac-β-CD complex was characterized by DSC, XPRD, FTIR, and SEM techniques. The effect of Ac-β-CD in the BCL solid dispersions on the non-sink dissolution/permeation simultaneous processes was disclosed using the side-by-side diffusion cell with the help of the cellulose membrane. The elevated dissolution of the ground complex, as compared to the raw drug as well as the simple physical mixture, accompanied by the supersaturation was revealed. Two biopolymers—polyvinylpyrrolidone (PVP, M_n = 58,000) and hydroxypropylmethylcellulose (HPMC, M_n ~ 10,000)—were examined as the precipitation inhibitors and were shown to be useful in prolonging the supersaturation state. The BCL/Ac-β-CD complex has the fastest dissolution rate in the presence of HPMC. The maximal concentration of the complex was achieved at a time of 20, 30, and 90 min in the pure buffer, with PVP and with HPMC, respectively. The effectiveness of the BCL dissolution (release) processes (illustrated by the AUCC(t) parameter) was estimated to be 7.8-, 5.8-, 3.0-, and 1.8-fold higher for BCL/Ac-β-CD (HPMC), BCL/Ac-β-CD (PVP), BCL/Ac-β-CD (buffer), and the BCL/Ac-β-CD physical mixture, respectively, as compared to the BCL_raw sample. The excipient gain factor (EGF), calculated for the dissolution of the BCL complex, was shown to be 2.6 in the presence of HPMC, which is 1.3-fold greater as compared to PVP. From the experimental dissolution results, it can be concluded that the formation of BCL ground complex with Ac-β-CD enhances the dissolution rate of the compound. The permeation was also shown to be advantageous in the presence of the polymers, which was demonstrated by the elevated fluxes of BCL through the membrane. The comparison of the dissolution/permeation processes was illustrated and discussed. The conclusion was made that the presence of HPMC as a stabilizer of the supersaturation state is promising and seems to be a useful tool for the optimization of BCL pharmaceutical formulations manufacturing.

Small scale in vitro method to determine a potential bioequivalent equilibrium solubility range for fed human intestinal fluid

Intestinal drug solubility is a key parameter controlling oral absorption but varies both intra and inter individuals and between the fasted and fed states, with food intake known to alter the bioavailability of many compounds. Intestinal solubility can be measured in vitro either using sampled fed human intestinal fluid (FeHIF) or simulated fed intestinal fluid (SIF) but neither approach is optimal. FeHIF is difficult to obtain and variable, whilst for fed SIF multiple recipes are available with no consensus on the ideal version. A recent study characterised FeHIF aspirates using a multidimensional approach and calculated nine simulated media recipes that covered over ninety percent of FeHIF compositional variability. In this study the equilibrium solubility of thirteen drugs have been measured using the nine simulated media recipes and compared to multiple previous design of experiment (DoE) studies, which have examined the impact of fed SIF media components on solubility. The measured nine media solubility data set is only statistically equivalent to the large scale 92 media DoE in 4 out of 13 drug comparisons, but has improved equivalence against small scale DoEs (9 or 10 media) with 6 out of 9 or 10 out of 12 (9 and 10 media respectively) equivalent. Selective removal of non-biorelevant compositions from the 92 media DoE improves statistical equivalence to 9 out of 13 comparisons. The results indicate that solubility equivalence is linked to media component concentrations and compositions, the nine media system is measuring a similar solubility space to previous systems, with a narrower solubility range than the 92 point DoE but equivalent to smaller DoE systems. Phenytoin and tadalafil display a narrow solubility range, a behaviour consistent with previous studies in fed and fasted states and only revealed through the multiple media approach. Custom DoE analysis of the nine media results to determine the most statistically significant component influencing solubility does not detect significant components. Indicating that the approach has a low statistical resolution and is not appropriate if determination of media component significance is required. This study demonstrates that it is possible to assess the fed intestinal equilibrium solubility envelope using the nine media recipes obtained from a multi-dimensional analysis of fed HIF. The derivation of the nine media compositions coupled with the results in this study indicate that the solubility results are more likely to reflect the fed intestinal solubility envelope than previous DoE studies and highlight that the system is worthy of further investigation.

Structured solubility behaviour in bioequivalent fasted simulated intestinal fluids

Drug solubility in intestinal fluid is a key parameter controlling absorption after the administration of a solid oral dosage form. To measure solubility in vitro simulated intestinal fluids have been developed, but there are multiple recipes and the optimum is unknown. This situation creates difficulties during drug discovery and development research. A recent study characterised sampled fasted intestinal fluids using a multidimensional approach to derive nine bioequivalent fasted intestinal media that covered over 90% of the compositional variability. These media have been applied in this study to examine the equilibrium solubility of twenty one exemplar drugs (naproxen, indomethacin, phenytoin, zafirlukast, piroxicam, ibuprofen, mefenamic acid, furosemide, aprepitant, carvedilol, tadalafil, dipyridamole, posaconazole, atazanavir, fenofibrate, felodipine, griseofulvin, probucol, paracetamol, acyclovir and carbamazepine) to determine if consistent solubility behaviour was present. The bioequivalent media provide in the majority of cases structured solubility behaviour that is consistent with physicochemical properties and previous solubility studies. For the acidic drugs (pKa < 6.3) solubility is controlled by media pH, the profile is identical and consistent and the lowest and highest pH media identify the lowest and highest solubility in over 70% of cases. For weakly acidic (pKa > 8), basic and neutral drugs solubility is controlled by a combination of media pH and total amphiphile concentration (TAC), a consistent solubility behaviour is evident but with variation related to individual drug interactions within the media. The lowest and highest pH x TAC media identify the lowest and highest solubility in over 78% of cases. A subset of the latter category consisting of neutral and drugs non-ionised in the media pH range have been identified with a very narrow solubility range, indicating that the impact of the simulated intestinal media on their solubility is minimal. Two drugs probucol and atazanavir exhibit unusual behaviour. The study indicates that the use of two appropriate bioequivalent fasted intestinal media from the nine will identify in vitro the maximum and minimum solubility boundaries for drugs and due to the media derivation this is probably applicable in vivo. These media could be applied during discovery and development activities to provide a solubility range, which would assist placement of the drug within the BCS/DCS and rationalise drug and formulation decisions.

Synergistic Interaction and Binding Efficiency of Tetracaine Hydrochloride (Anesthetic Drug) with Anionic Surfactants in the Presence of NaCl Solution Using Surface Tension and UV–Visible Spectroscopic Methods

Surfactants are ubiquitous materials that are used in diverse formulations of various products. For instance, they improve the formulation of gel by improving its wetting and rheological properties. Here, we describe the effects of anionic surfactants on an anesthetic drug, tetracaine hydrochloride (TCH), in NaCl solution with tensiometry and UV–visible techniques. Various micellar, interfacial, and thermodynamic parameters were estimated. The outputs were examined by using different theoretical models to attain a profound knowledge of drug–surfactant mixtures. The presence of attractive interactions among drug and surfactant monomers (synergism) in mixed micelle was inferred. However, it was found that sodium dodecyl sulfate (SDS) showed greater interactions with the drug in comparison to sodium lauryl sarcosine (SLS). The binding of the drug with surfactants was monitored with a spectroscopic technique (UV–visible spectra). The results of this study could help optimize the compositions of these mixed aggregates and find the synergism between monomers of different used amphiphiles.

Using in vitro ADME data for lead compound selection: An emphasis on PAMPA pH 5 permeability and oral bioavailability

Membrane permeability plays an important role in oral drug absorption. Caco-2 and Madin-Darby Canine Kidney (MDCK) cell culture systems have been widely used for assessing intestinal permeability. Since most drugs are absorbed passively, Parallel Artificial Membrane Permeability Assay (PAMPA) has gained popularity as a low-cost and high-throughput method in early drug discovery when compared to high-cost, labor intensive cell-based assays. At the National Center for Advancing Translational Sciences (NCATS), PAMPA pH 5 is employed as one of the Tier I absorption, distribution, metabolism, and elimination (ADME) assays. In this study, we have developed a quantitative structure activity relationship (QSAR) model using our ∼6500 compound PAMPA pH 5 permeability dataset. Along with ensemble decision tree-based methods such as Random Forest and eXtreme Gradient Boosting, we employed deep neural network and a graph convolutional neural network to model PAMPA pH 5 permeability. The classification models trained on a balanced training set provided accuracies ranging from 71% to 78% on the external set. Of the four classifiers, the graph convolutional neural network that directly operates on molecular graphs offered the best classification performance. Additionally, an ∼85% correlation was obtained between PAMPA pH 5 permeability and in vivo oral bioavailability in mice and rats. These results suggest that data from this assay (experimental or predicted) can be used to rank-order compounds for preclinical in vivo testing with a high degree of confidence, reducing cost and attrition as well as accelerating the drug discovery process. Additionally, experimental data for 486 compounds (PubChem AID: 1645871) and the best models have been made publicly available (https://opendata.ncats.nih.gov/adme/).

Nanoconfinement of a Pharmaceutical Cocrystal with Praziquantel in Mesoporous Silica: The Influence of the Solid Form on Dissolution Enhancement

Nanoconfinement is a recent strategy to enhance solubility and dissolution of active pharmaceutical ingredients (APIs) with poor biopharmaceutical properties. In this work, we combine the advantage of cocrystals of racemic praziquantel (PZQ) containing a water-soluble coformer (i.e., increased solubility and supersaturation) and its confinement in a mesoporous silica material (i.e., increased dissolution rate). Among various potential cocrystalline phases of PZQ with dicarboxylic acid coformers, the cocrystal with glutaric acid (PZQ-GLU) was selected and successfully loaded by the melting method into nanopores of SBA-15 (experimental pore size of 5.6 nm) as suggested by physical and spectroscopic characterization using various complementary techniques like N₂ adsorption, powder X-ray diffraction (PXRD), infrared spectroscopy (IR), solid-state NMR (ss-NMR), differential scanning calorimetry (DSC), and field emission-scanning electron microscopy (FE-SEM) analysis. The PZQ-GLU phase confined in SBA-15 presents more mobility according to ss-NMR studies but still retains its cocrystal-like features in the IR spectra, and it also shows depression of the melting transition temperature in DSC. On the contrary, pristine PZQ loaded into SBA-15 was found only in the amorphous state, according to the aforementioned studies. This dissimilar behavior of the composites was attributed to the larger crystal lattice of PZQ over the PZQ-GLU cocrystal (3320.1 vs 1167.9 ų) and to stronger intermolecular interactions between PZQ and GLU, facilitating the confinement of a more mobile solid-like phase in the constrained channels. Powder dissolution studies under extremely nonsink conditions (SI = 0.014) of the confined PZQ-GLU and amorphous PZQ phases embedded in mesoporous silica showed transient supersaturation behavior when dissolving in simulated gastric fluid (HCl pH 1.2 at 37 ± 0.5 °C) in a similar fashion to the bare cocrystal PZQ-GLU. A comparison of the area under the curve (AUC_0-90 min) of the dissolution profiles afforded a dissolution advantage of 2-fold (p < 0.05) of the new solid phases over pristine racemic PZQ after 90 min; under these conditions, the solubilized API reprecipitated as the recently discovered PZQ hemihydrate (PZQ-HH). In the presence of a cellulosic polymer, sustained solubilization of PZQ from composites SBA-15/PZQ or SBA-15/PZQ-GLU was observed, increasing AUC_0-90 min up to 5.1-fold in comparison to pristine PZQ. The combination of a confined solid phase in mesoporous silica and a methylcellulose polymer in the dissolution medium effectively maintained the drug solubilized during times significant to promote absorption. Finally, powder dissolution studies under intermediate nonsink conditions (SI = 1.99) showed a fast release profile from the nanoconfined PZQ-GLU phase in SBA-15, which reached rapid saturation (95% drug dissolved at 30 min); the amorphous PZQ composite and bare PZQ-GLU also displayed an immediate release of the API but at a lower rate (69% drug dissolved at 30 min). In all of these cases, a large dissolution advantage was observed from any of the novel solid phases over PZQ.

Dissolution Kinetics of Nifedipine-Ionizable Polymer Amorphous Solid Dispersion: Comparison Between Bicarbonate and Phosphate Buffers

PURPOSE

The intestinal fluid pH is maintained by the bicarbonate buffer system that shows unique properties regarding drug dissolution. Nevertheless, current compendial dissolution tests use phosphate buffers. The purpose of the present study was to investigate the effect of bicarbonate and phosphate buffers on the dissolution profiles of amorphous solid dispersions (ASD) composed of ionizable polymers.

METHODS

Hydroxypropylmethylcellulose acetate succinate (HPMCAS), amino methacrylate copolymer (AMC), and hydroxypropylmethylcellulose (HPMC) were employed as acidic, basic, and neutral polymers, respectively. Nifedipine (NIF) was used as a model drug. Dissolution profiles were measured in pH 6.5 bicarbonate and phosphate buffers by a mini-scale paddle dissolution test. The pH of bicarbonate buffers was maintained by the floating lid method.

RESULTS

The pH change of the bicarbonate buffer was suppressed to less than + 0.25 pH for 3 h by the floating lid method. In all cases, the NIF concentration was supersaturated against the solubility of crystalline NIF. The dissolution rates of HPMCAS and AMC ASDs were 1.5 to 2.0-fold slower in the bicarbonate buffer than in the phosphate buffer when compared at the same buffer capacity. The dissolution profile of HPMC ASD was not affected by the buffer species. The higher the buffer capacity and ionic strength, the faster the dissolution rate of HPMCAS ASD.

CONCLUSION

The dissolution rate of ASDs with ionizable polymers would be overestimated by using unphysiological phosphate buffer solutions. It is important to use a biorelevant bicarbonate buffer solution for dissolution testing.

Simulate SubQ: The Methods and the Media

For decades, there has been a growing interest in injectable subcutaneous formulations to improve the absorption of drugs into the systemic circulation and to prolong their release over a longer period. However, fluctuations in the blood plasma levels together with bioavailability issues often limit their clinical success. This warrants a closer look at the performance of long-acting depots, for example, and their dependence on the complex interplay between the dosage form and the physiological microenvironment. For this, biopredictive performance testing is used for a thorough understanding of the biophysical processes affecting the absorption of compounds from the injection site in vivo and their simulation in vitro. In the present work, we discuss in vitro methodologies including methods and media developed for the subcutaneous route of administration on the background of the most relevant absorption mechanisms. Also, we highlight some important knowledge gaps and shortcomings of the existing methodologies to provide the reader with a better understanding of the scientific evidence underlying these models.

UNGAP best practice for improving solubility data quality of orally administered drugs

An important goal of the European Cooperation in Science and Technology (COST) Action UNGAP (UNderstanding Gastrointestinal Absorption-related Processes, www.ungap.eu) is to improve standardization of methods relating to the study of oral drug absorption. Solubility is a general term that refers to the maximum achievable concentration of a compound dissolved in a liquid medium. For orally administered drugs, relevant information on drug properties is crucial during drug (product) development and at the regulatory level. Collection of reliable and reproducible solubility data requires careful application and understanding of the limitations of the selected experimental method. In addition, the purity of a compound and its solid state form, as well as experimental parameters such as temperature of experimentation, media related factors, and sample handling procedures can affect data quality. In this paper, an international consensus developed by the COST UNGAP network on recommendations for collecting high quality solubility data for the development of orally administered drugs is proposed.

Is equilibrium slurry pH a good surrogate for solid surface pH during drug dissolution?

The purpose of the present study was to investigate the suitability of equilibrium slurry pH (pH_eq) as a surrogate of solid surface pH during drug dissolution (pH₀). A comprehensive calculation scheme for pH_eq and pH₀ was formalized based on the principle of charge neutrality (equilibrium charge neutrality for pH_eq and charge flux neutrality for pH₀). The formalized scheme was then used to investigate the validity of pH₀ ≈ pH_eq approximation. The approximation of pH₀ ≈ pH_eq was suggested to be accurate for small molecules (ca. MW = 150) in high concentration buffer media (ca. buffer capacity = 30 mM/ΔpH). In addition, it is valid provided no precipitation of its free form for salts (vice versa for free forms) in both the slurry pH measurement and at the dissolving drug surface. The formalized calculation scheme is simple and applicable to free and salt form drugs in unbuffered and buffered media including bicarbonate buffer. The computational expense is very small so that it is applicable to various computer simulations such as biopharmaceutics modeling and simulation.

Increasing the Robustness of Biopharmaceutical Precipitation Assays - Part II: Recommendations on the use of FaSSIF

Biopharmaceutical precipitation assays are an important in vitro tool to characterize the precipitation behavior of weakly basic drugs during their transit from the stomach into the small intestine. To mimic the intestinal fluids more closely, biorelevant media like Fasted State Simulated Intestinal Fluid (FaSSIF) and versions thereof are often applied. When applying UV analytics to measure the drug concentration during the transfer experiments, changes in the UV spectrum of the medium have been observed when FaSSIF was stored over a longer period of time or under accelerated conditions. Therefore, this study aimed at evaluating the stability of FaSSIF under various storage conditions. Furthermore, the impact of stressed FaSSIF on the supersaturation and precipitation behavior of ketoconazole was investigated. As a result of this study, it was demonstrated that the FaSSIF powder composition changes during storage, which, in turn, impacts the supersaturation and precipitation behavior of ketoconazole in in vitro transfer studies. Based on the results of this study, we provide recommendations on the application of FaSSIF in biopharmaceutical precipitation assays with the aim to increase reproducibility and enhance data reliability for those compounds where changing FaSSIF composition may impact the supersaturation and precipitation behavior.

Small scale in vitro method to determine a bioequivalent equilibrium solubility range for fasted human intestinal fluid

Drug solubility is a key parameter controlling oral absorption, but intestinal solubility is difficult to assess in vitro. Human intestinal fluid (HIF) aspirates can be applied but they are variable, difficult to obtain and expensive. Simulated intestinal fluids (SIF) are a useful surrogate but multiple recipes are available and the optimum is unknown. A recent study characterised fasted HIF aspirates using a multi-dimensional approach and determined nine bioequivalent SIF media recipes that represented over ninety percent of HIF compositional variability. In this study these recipes have been applied to determine the equilibrium solubility of twelve drugs (naproxen, indomethacin, phenytoin, piroxicam, aprepitant, carvedilol, zafirlukast, tadalafil, fenofibrate, griseofulvin, felodipine, probucol) previously investigated using a statistical design of experiment (DoE) approach. The bioequivalent solubility measurements are statistically equivalent to the previous DoE, enclose literature solubility values in both fasted HIF and SIF, and the solubility range is less than the previous DoE. These results indicate that the system is measuring the same solubility space as literature systems with the lower overall range suggesting improved equivalence to in vivo solubility, when compared to DoEs. Three drugs (phenytoin, tadalafil and griseofulvin) display a comparatively narrow solubility range, a behaviour that is consistent with previous studies and related to the drugs' molecular structure and properties. This solubility behaviour would not be evident with single point solubility measurements. The solubility results can be analysed using a custom DoE to determine the most statistically significant factor within the media influencing solubility. This approach has a lower statistical resolution than a formal DoE and is not appropriate if determination of media factor significance for solubilisation is required. This study demonstrates that it is possible to assess the fasted intestinal equilibrium solubility envelope using a small number of bioequivalent media recipes obtained from a multi-dimensional analysis of fasted HIF. The derivation of the nine bioequivalent SIF media coupled with the lower measured solubility range indicate that the solubility results are more likely to reflect the fasted intestinal solubility envelope than previous DoE studies and highlight that intestinal solubility is a range and not a single value.

Do Small Molecules Activate the TrkB Receptor in the Same Manner as BDNF? Limitations of Published TrkB Low Molecular Agonists and Screening for Novel TrkB Orthosteric Agonists

TrkB is a tyrosine kinase receptor that is activated upon binding to brain-derived neurotrophic factor (BDNF). To date, the search for low-molecular-weight molecules mimicking BDNF’s action has been unsuccessful. Several molecules exerting antidepressive effects in vivo, such as 7,8-DHF, have been suggested to be TrkB agonists. However, more recent publications question this hypothesis. In this study, we developed a set of experimental procedures including the evaluation of direct interactions, dimerization, downstream signaling, and cytoprotection in parallel with physicochemical and ADME methods to verify the pharmacology of 7,8-DHF and other potential reference compounds, and perform screening for novel TrkB agonists. 7,8 DHF bound to TrkB with K_d = 1.3 μM; however, we were not able to observe any other activity against the TrkB receptor in SN56 T48 and differentiated SH-SY5Y cell lines. Moreover, the pharmacokinetic and pharmacodynamic effects of 7,8-DHF at doses of 1 and 50 mg/kg were examined in mice after i.v and oral administration, respectively. The poor pharmacokinetic properties and lack of observed activation of TrkB-dependent signaling in the brain confirmed that 7,8-DHF is not a relevant tool for studying TrkB activation in vivo. The binding profile for 133 molecular targets revealed a significant lack of selectivity of 7,8-DHF, suggesting a distinct functional profile independent of interaction with TrkB. Additionally, a compound library was screened in search of novel low-molecular-weight orthosteric TrkB agonists; however, we were not able to identify reliable drug candidates. Our results suggest that published reference compounds including 7,8-DHF do not activate TrkB, consistent with canonical dogma, which indicates that the reported pharmacological activity of these compounds should be interpreted carefully in a broad functional context.

Effect of the physicochemical properties of zinc oxide sources on their bioavailability in broilers

1. The bioavailability of a trace mineral source is related to its intestinal solubility (bioaccessibility), which in turn is determined by its physicochemical properties. It is still not clear which characteristics are more relevant in affecting solubility and bioavailability of mineral sources. Zinc oxide (ZnO) is a common feed additive used to supplement zinc in the diet of monogastric animals. However, different sources have shown variable responses on animal bioavailability.2. This study hypothesised that different sources of feed grade ZnO have various physicochemical features that lead to distinct bioavailability values. Feed grade ZnO samples collected from the feed industry worldwide were characterised for their physicochemical features and tested in broilers to allow bioavailability determined.3. A total of 135 male Cobb broiler chickens were fed a standard starter diet from day 1 after hatching up to d 7. At d 8, animals were allocated in individual cages and fed one of the following dietary treatments during 15 days: a basal diet with 23.5 ppm of zinc and seven test diets with supplemented ZnO or zinc sulphate (ZnSO₄) at 6 or 12 ppm.4. Different sources of ZnO showed an effect of solubility in the stomach and supplementation influenced total Zn levels in the ileum. The bioavailability of the different sources varied from 49% to 160% in relation to ZnSO₄. Aggregate size of particles seems to explain most of the variability in the bioavailability of the different sources tested in broilers. In conclusion, physicochemical properties of ZnO can partly explain the variability observed in terms of biological value.

Fasted and fed state human duodenal fluids: Characterization, drug solubility, and comparison to simulated fluids and with human bioavailability

Accurate in vivo predictions of intestinal absorption of low solubility drugs require knowing their solubility in physiologically relevant dissolution media. Aspirated human intestinal fluids (HIF) are the gold standard, followed by simulated intestinal HIF in the fasted and fed state (FaSSIF/FeSSIF). However, current HIF characterization data vary, and there is also some controversy regarding the accuracy of FaSSIF and FeSSIF for predicting drug solubility in HIF. This study aimed at characterizing fasted and fed state duodenal HIF from 16 human volunteers with respect to pH, buffer capacity, osmolarity, surface tension, as well as protein, phospholipid, and bile salt content. The fasted and fed state HIF samples were further used to investigate the equilibrium solubility of 17 representative low-solubility small-molecule drugs, six of which were confidential industry compounds and 11 were known and characterized regarding chemical diversity. These solubility values were then compared to reported solubility values in fasted and fed state HIF, FaSSIF and FeSSIF, as well as with their human bioavailability for both states. The HIF compositions corresponded well to previously reported values and current FaSSIF and FeSSIF compositions. The drug solubility values in HIF (both fasted and fed states) were also well in line with reported solubility data for HIF, as well as simulated FaSSIF and FeSSIF. This indicates that the in vivo conditions in the proximal small intestine are well represented by simulated intestinal fluids in both composition and drug equilibrium solubility. However, increased drug solubility in the fed vs. fasted states in HIF did not correlate with the human bioavailability changes of the same drugs following oral administration in either state.

Investigating crystallization tendency, miscibility, and molecular interactions of drug-polymer systems for the development of amorphous solid dispersions

Crystallization tendencies, thermal analysis [i.e. glass transition temperature (T_g)], crystallinity, and melting point depression, along with theoretical calculations such as solubility parameter, of five different drugs [i.e. curcumin (CUR), indomethacin (IND), flutamide (FLU), dipyridamole (DIP), and griseofulvin (GRI)] in the absence and presence of four different polymers in various drug-polymer ratios were determined and analyzed. Physical states of the drug in the solid dispersions (SDs) and their stability were characterized by X-ray diffraction and modulated differential scanning calorimetry. Infrared (IR) and Raman were used in selected systems (i.e. CUR, DIP, and GRI systems) to explore the role of drug-polymer interactions in the amorphization of SDs. The crystallization tendencies of pure drugs were categorized as low (CUR, IND), moderate (FLU), and high (DIP, GRI). In the presence of selected polymers, the crystallization tendency of the drugs changed, though a high polymer concentration was required for high crystallization-tendency drugs [i.e. DIP and GRI (>50% w/w)]. Polymers showing a greater effect on the crystallization tendency of drugs were found to have higher drug-polymer miscibility and stronger molecular interactions. Drug-polymer systems selected from the investigation of physical mixtures formed stable amorphous solid dispersions (ASD). Furthermore, the rank order of the crystallization tendency of drug-polymer systems correlated well with those on miscibility and molecular interactions. Those rank orders also correlated well with the stability of prepared/reported SDs. Hence, the developed approach has significant potential to be a rational screening method for the development of amorphous SDs.

Drug-Induced Dynamics of Bile Colloids

Bile colloids containing taurocholate and lecithin are essential for the solubilization of hydrophobic molecules including poorly water-soluble drugs such as Perphenazine. We detail the impact of Perphenazine concentrations on taurocholate/lecithin colloids using analytical ultracentrifugation, dynamic light scattering, small-angle neutron scattering, nuclear magnetic resonance spectroscopy, coarse-grained molecular dynamics simulations, and isothermal titration calorimetry. Perphenazine impacted colloidal molecular arrangement, structure, and binding thermodynamics in a concentration-dependent manner. At low concentration, Perphenazine was integrated into stable and large taurocholate/lecithin colloids and close to lecithin. Integration of Perphenazine into these colloids was exothermic. At higher Perphenazine concentration, the taurocholate/lecithin colloids had an approximately 5-fold reduction in apparent hydrodynamic size, heat release was less exothermic upon drug integration into the colloids, and Perphenazine interacted with both lecithin and taurocholate. In addition, Perphenazine induced a morphological transition from vesicles to wormlike micelles as indicated by neutron scattering. Despite these surprising colloidal dynamics, these natural colloids successfully ensured stable relative amounts of free Perphenazine throughout the entire drug concentration range tested here. Future studies are required to further detail these findings both on a molecular structural basis and in terms of in vivo relevance.

Insights Into the Mechanism of Tyrosine Nitration in Preventing β-Amyloid Aggregation in Alzheimer's Disease

Nitration of tyrosine at the tenth residue (Tyr10) in amyloid-β (Aβ) has been reported to reduce its aggregation and neurotoxicity in our previous studies. However, the exact mechanism remains unclear. Here, we used Aβ_1-42 peptide with differently modified forms at Tyr10 to investigate the molecular mechanism to fill this gap. By using immunofluorescent assay, we confirmed that nitrated Aβ was found in the cortex of 10-month-old female triple transgenic mice of Alzheimer's disease (AD). And then, we used the surface-enhanced Raman scattering (SERS) method and circular dichroism (CD) to demonstrate that the modification and mutation of Tyr10 in Aβ have little impact on conformational changes. Then, with the aids of fluorescence assays of thioflavin T and 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid, transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS), we found that adding a large group to the phenolic ring of Tyr10 of Aβ could not inhibit Aβ fibrilization and aggregation. Nitration of Aβ reduces its aggregation mainly because it could induce the deprotonation of the phenolic hydroxyl group of Tyr10 of Aβ at physiological pH. We proposed that the negatively charged Tyr10 caused by nitration at physiological pH could interact with the salt bridge between Glu11 and His6 or His13 and block the kink around Tyr10, thereby preventing Aβ fibrilization and aggregation. These findings provide us new insights into the relationship between Tyr10 nitration and Aβ aggregation, which would help to further understand that keeping the balance of nitric oxide in vivo is important for preventing AD.

Interaction with biliary and pancreatic fluids drives supersaturation and drug absorption from lipid-based formulations of low (saquinavir) and high (fenofibrate) permeability poorly soluble drugs

Drug absorption from lipid-based formulations (LBFs) in the gastrointestinal (GI) tract is the result of a series of processes, including formulation dispersion, interaction with biliary and pancreatic secretions, drug solubilisation and supersaturation, and finally intestinal permeability. Optimal formulation design is dependent on a good understanding of the limitations to, and drivers of, absorption, but for LBFs the complexity of these processes makes data interpretation complex. The current study has re-examined a previous in vitro digestion-in situ perfusion model to increase physiological relevance and has used this model to examine drug absorption from LBFs. The composition of rat bile and jejunal fluid was also characterised to identify in vivo-relevant conditions. Digestion was initiated using rat bile/pancreatic fluid and the formulation and digestive enzymes mixed immediately prior to entry into the jejunum (allowing dilution/digestion to occur at the absorptive site). These conditions were employed to study drug absorption from LBFs of high (fenofibrate, FFB) and low (saquinavir, SQV) permeability compounds. The impact of polymeric precipitation inhibitors (PPIs) was also evaluated. For FFB, supersaturation, initiated by formulation interaction with biliary/pancreatic fluids, appeared to drive absorption and the addition of the PPIs poly(glycidyl methacrylate) (PPGAE) and hydroxypropylmethyl cellulose (HPMC), reduced drug precipitation, increased FFB supersaturation and increased absorption from a Type IV LBF of FFB. For a Type IIIB LBF however, PPIs were ineffective at increasing absorption. The impact of PPIs on the absorption of a less permeable drug, SQV, was similarly evaluated and again drug absorption appeared to be related to the extent of supersaturation, although in this case PPI were unable to promote absorption. For both FFB and SQV, drug absorption patterns obtained with the in vitro digestion-in situ perfusion mode, correlated well with in vitro supersaturation data and in vivo drug exposure data from oral bioavailability studies. The data are consistent with a mode of drug absorption where rapid dilution of LBFs with biliary and pancreatic secretions at the absorptive site in the upper small intestine drives transient supersaturation, that supersaturation is a significant driver of drug absorption for both low and high permeability drugs, and that PPIs delay drug precipitation, enhance supersaturation and promote drug absorption in a drug and formulation specific manner.

Prediction of negative food effect induced by bile micelle binding on oral absorption of hydrophilic cationic drugs

The purpose of the present study was to quantitatively predict the negative food effect induced by bile micelle binding on the oral absorption of hydrophilic cationic drugs. The intrinsic membrane permeability and bile micelle unbound fraction of 12 model drugs (7 tertiary amines, 3 quaternary ammoniums, and 2 neutral drugs) were calculated from the experimental Caco-2 permeability data (P_app) under fasted and fed conditions. From these input data, the fraction of a dose absorbed (Fa) was predicted using the gastrointestinal unified theoretical framework, a mechanism-based oral absorption model. The predicted Fa ratio (fed/fasted) was then compared with the in vivo fed/fasted area under the plasma concentration-time curve ratio (AUCr). The AUCr values of tertiary amines and neutral drugs were appropriately predicted (absolute average fold error (AAFE) = 1.19), whereas those of quaternary ammoniums were markedly underestimated (AAFE = 4.70). The P_app ratio (fed/fasted) predicted AUCr less quantitatively (AAFE = 1.30 for tertiary amines and neutral drugs). The results of the present study would lead to a better understanding of negative food effect on oral drug absorption.

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.

Bottom-Up Physiologically Based Oral Absorption Modeling of Free Weak Base Drugs

In this study, we systematically evaluated "bottom-up" physiologically based oral absorption modeling, focusing on free weak base drugs. The gastrointestinal unified theoretical framework (the GUT framework) was employed as a simple and transparent model. The oral absorption of poorly soluble free weak base drugs is affected by gastric pH. Alternation of bulk and solid surface pH by dissolving drug substances was considered in the model. Simple physicochemical properties such as pKa, the intrinsic solubility, and the bile micelle partition coefficient were used as input parameters. The fraction of a dose absorbed (Fa) in vivo was obtained by reanalyzing the pharmacokinetic data in the literature (15 drugs, a total of 85 Fa data). The AUC ratio with/without a gastric acid-reducing agent (AUCr) was collected from the literature (22 data). When gastric dissolution was neglected, Fa was underestimated (absolute average fold error (AAFE) = 1.85, average fold error (AFE) = 0.64). By considering gastric dissolution, predictability was improved (AAFE = 1.40, AFE = 1.04). AUCr was also appropriately predicted (AAFE = 1.54, AFE = 1.04). The Fa values of several drugs were slightly overestimated (less than 1.7-fold), probably due to neglecting particle growth in the small intestine. This modeling strategy will be of great importance for drug discovery and development.

Multidimensional analysis of human intestinal fluid composition

The oral administration of solid dosage forms is the commonest method to achieve systemic therapy and relies on the drug's solubility in human intestinal fluid (HIF), a key factor that influences bioavailability and biopharmaceutical classification. However, HIF is difficult to obtain and is known to be variable, which has led to the development of a range of simulated intestinal fluid (SIF) systems to determine drug solubility in vitro. In this study we have applied a novel multidimensional approach to analyse and characterise HIF composition using a published data set in both fasted and fed states with a view to refining the existing SIF approaches. The data set provided 152 and 172 measurements of five variables (total bile salt, phospholipid, total free fatty acid, cholesterol and pH) in time-dependent HIF samples from 20 volunteers in the fasted and fed state, respectively. The variable data sets for both fasted state and fed state are complex, do not follow normal distributions but the amphiphilic variable concentrations are correlated. When plotted 2-dimensionally a generally ellipsoid shaped data cloud with a positive slope is revealed with boundaries that enclose published fasted or fed HIF compositions. The data cloud also encloses the majority of fasted state and fed state SIF recipes and illustrates that the structured nature of design of experiment (DoE) approaches does not optimally cover the variable space and may examine media compositions that are not biorelevant. A principal component analysis in either fasted or fed state in combination with fitting an ellipsoid shape to enclose the data results in 8 points that capture over 95% of the compositional variability of HIF. The variable's average rate of concentration change in both fasted state and fed state over a short time scale (10 min) is zero and a Euclidean analysis highlights differences between the fasted and fed states and among individual volunteers. The results indicate that a 9-point DoE (8 + 1 central point) could be applied to investigate drug solubility in vitro and provide statistical solubility limits. In addition, a single point could provide a worst-case solubility measurement to define the lowest biopharmaceutical classification boundary or for use during drug development. This study has provided a novel description of HIF composition. The approach could be expanded in multiple ways by incorporation of further data sets to improve the statistical coverage or to cover specific patient groups (e.g., paediatric). Further development might also be possible to analyse information on the time dependent behaviour of HIF and to guide HIF sampling and analysis protocols.

Potentiometric Titration Method for the Determination of Solubility Limits and pKa Values of Weak Organic Acids in Water

The determination of solubility limits of compounds in water is unprecise and relies on certain prerequisites such as UV-vis absorption activity. In this study, we designed an experimental approach based on potentiometric titrations to determine solubility limits of various organic compounds by exploiting their pH-active carboxylic acid groups. By applying the law of mass action, utilizing a double-dosing method ensuring a constant compound concentration, it is possible to determine the intrinsic solubility limits, which are independent of the pH value. The derived equations enable the precise and fast determination of intrinsic solubility limits of organic compounds in aqueous solutions within 2-4 h. Moreover, it is shown how the pK_a value can be determined based on titrations carried out at two different compound concentrations.

Physiologically Based Absorption Modelling to Explore the Impact of Food and Gastric pH Changes on the Pharmacokinetics of Entrectinib

Entrectinib is a potent and selective tyrosine kinase inhibitor (TKI) of TRKA/B/C, ROS1, and ALK with both systemic and CNS activities, which has recently received FDA approval for ROS1 fusion-positive non-small cell lung cancer and NTRK fusion-positive solid tumors. This paper describes the application of a physiologically based biophamaceutics modeling (PBBM) during clinical development to understand the impact of food and gastric pH changes on absorption of this lipophilic, basic, molecule with reasonable permeability but strongly pH-dependent solubility. GastroPlus™ was used to develop a physiologically based pharmacokinetics (PBPK) model integrating in vitro and in silico data and dissolution studies and in silico modelling in DDDPlus™ were used to understand the role of self-buffering and acidulant on formulation performance. Models were verified by comparison of simulated pharmacokinetics for acidulant and non-acidulant containing formulations to clinical data from a food effect study and relative bioavailability studies with and without the gastric acid-reducing agent lansoprazole. A negligible food effect and minor pH-dependent drug-drug interaction for the market formulation were predicted based on biorelevant in vitro measurements, dissolution studies, and in silico modelling and were confirmed in clinical studies. These outcomes were explained as due to the acidulant counteracting entrectinib self-buffering and greatly reducing the effect of gastric pH changes. Finally, sensitivity analyses with the verified model were applied to support drug product quality. PBBM has great potential to streamline late-stage drug development and may have impact on regulatory questions.

An interlaboratory investigation of intrinsic dissolution rate determination using surface dissolution

The purpose of this study was to conduct an interlaboratory ring-study, with six partners (academic and industrial), investigating the measurement of intrinsic dissolution rate (IDR) using surface dissolution imaging (SDI) equipment. Measurement of IDR is important in pharmaceutical research as it provides characterising information on drugs and their formulations. This work allowed us to assess the SDI's interlaboratory performance for measuring IDR using a defined standard operating procedure (see supporting information) and six drugs assigned as low (tadalafil, bromocriptine mesylate), medium (carvedilol, indomethacin) and high (ibuprofen, valsartan) solubility compounds. Fasted State Simulated Intestinal Fluid (FaSSIF) and blank FaSSIF (without sodium taurocholate and lecithin) (pH 6.5) were used as media. Using the standardised protocol an IDR value was obtained for all compounds and the results show that the overall IDR rank order matched the solubility rank order. Interlaboratory variability was also examined and it was observed that the variability for lower solubility compounds was higher, coefficient of variation >50%, than for intermediate and high solubility compounds, with the exception of indomethacin in FaSSIF medium. Inter laboratory variability is a useful descriptor for understanding the robustness of the protocol and the system variability. On comparison to another published small-scale IDR study the rank ordering with respect to dissolution rate is identical except for the high solubility compounds. This results indicates that the SDI robustly measures IDR however, no recommendation on the use of one small scale method over the other is made.