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

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

Role of Permeability on the Biopredictive Dissolution of Amorphous Solid Dispersions

An ideal dissolution test for amorphous solid dispersions (ASDs) should reflect physicochemical, physiological, and hydrodynamic conditions which accurately represent in vivo dissolution. However, this is confounded by the evolution of different molecular and colloidal species during dissolution, generating a supersaturated state of the drug. The supersaturated state of a drug is thermodynamically unstable which drives the process of precipitation resulting in a loss of solubility advantage. Maintaining a supersaturated state of the drug with the help of precipitation inhibiting excipients is a key component in the design of ASDs. Therefore, a biopredictive dissolution test is critical for proper risk assessment during the development of an optimal ASD formulation. One of the overlooked components of biopredictive dissolution is the role of drug permeability. The kinetic changes in the phase behavior of a drug during dissolution of ASDs are influenced by drug permeability across a membrane. Conventionally, drug dissolution and permeation are analyzed separately although they occur simultaneously in vivo. The kinetic phase changes occurring during dissolution of ASDs can influence the thermodynamic activity and membrane flux of a drug. The present review evaluates the feasibility, predictability, and practicability of permeability/dissolution for the optimal development and risk assessment of ASD formulations.

Co-amorphization of atorvastatin by lisinopril as a co-former for solubility improvement

The co-amorphous (CAM) technology has attracted extensive attention in recent years because it can improve the solubility and provide a formulation strategy for fixed dose combination for poorly water-soluble drugs. Atorvastatin (ATR) is a poorly water-soluble drug and it has strong anti-hyperlipidemia activity, and it is usually used in combination with lisinopril (LNP), an anti-hypertension drug. The aim of this study is to test the feasibility to develop ATR/LNP co-amorphous formulation using a cryo-milling method. The solid-state behaviors of the CAM systems were characterized by polarizing light microscopy, differential scanning calorimetry and powder X-ray diffraction. The molecular interaction between ATR and LNP was confirmed by the analysis of glass transition temperature and Fourier transform infrared spectroscopy. Compared with crystalline ATR and neat amorphous ATR, the CAM systems showed significantly increased in vitro dissolution and intrinsic dissolution rate of ATR, because LNP enhanced the supersaturation maintenance of ATR and inhibited its solution-mediated recrystallization to a certain extent.

Supersaturating drug delivery systems containing fixed-dose combination of two antihypertensive drugs: Formulation, in vitro evaluation and molecular metadynamics simulations

The purpose of this study was to associate the poorly water-soluble antihypertensive drugs candesartan cilexetil (CC) and hydrochlorothiazide (HCTZ) as fixed-dose combination, in the form of ternary Amorphous Solid Dispersions (ASD), using hydroxypropylmethylcellulose acetate succinate (HPMCAS) type M as polymeric carrier. The potential of the system to generate and to maintain supersaturation of both drugs was also evaluated. The ASDs were prepared by ball milling technique and solid-state characterization was performed by differential scanning calorimetry (DSC), Fourier transformed infrared spectroscopy (FTIR) and X-ray powder diffraction (XRPD). Interaction between drugs and polymer in solid-state was evaluated by molecular metadynamics simulations. In vitro supersaturation profiles were determined in biorelevant medium. Physicochemical stability of ASDs was also evaluated under different storage conditions. Amorphization of both drugs was confirmed by solid-state characterization techniques. Molecular metadynamics simulations indicated that CC has stronger interaction with HMPCAS than HCTZ. In vitro supersaturation studies have shown that ternary ASDs could generate and maintain supersaturation of both drugs in biorelevant medium. The polymer reduced the desupersaturation of both drugs. Ternary ASDs also showed physicochemical stability over a period of 90 days, demonstrating the potential of the polymer in reducing the drugs recrystallization over the time. Ternary ASDs of CC, HCTZ and HPMCAS can be considered a promising system to associate the drugs as fixed-dose combinations. Also, these systems generate and maintain supersaturation of both drugs in biorelevant medium, with great storage stability. HPMCAS M was a good carrier for reducing the desupersaturation of associated HCTZ and CC.

The effect of some acrylic polymers on dissolution of celecoxib solid dispersion formulations

OBJECTIVE

The purpose of the present study was firstly to identify the effectiveness of Eudragit® polymers (Eudragit^® RL, RS, L100-55, L100, S100 and E100) in inhibition of celecoxib precipitation from buffer solutions (pH = 6.8). Furthermore, the influence of Eudragit^® polymers on non-sink dissolution behavior of celecoxib from solid dispersions was investigated.

METHODS

Solid dispersions were prepared by the rotary evaporation method. In vitro dissolution studies, FT-IR and differential scanning calorimetry were employed to characterize the formulations.

RESULTS

The results revealed that Eudragit^® E100, L100 and S100 inhibited precipitation of celecoxib efficiently. It is understood that crystallization during the dissolution of solid dispersions could happen through crystallization from solid matrix following contact with the dissolution medium or from the supersaturated solution produced following dissolution. The supersaturated drug concentrations attained from the dissolution of Eudragit^®-celecoxib solid dispersions were almost similar, suggesting that crystallization from solid matrix did not occur readily. However, only solid dispersions containing efficient crystallization inhibitor polymers were able to maintain the supersaturated solution up to the end of the dissolution run.

CONCLUSION

Results revealed that the principal mechanism of attaining supersaturated solution of celecoxib from solid dispersions was related to crystallization inhibition from solution not from solid matrix.

A Mechanistic Study of Drug Mass Transport from Supersaturated Solutions Across PAMPA Membranes

There is an increasing shift from dissolution testing to dissolution-permeation testing of formulations during formulation development and this has led increasing application of permeability measurements using parallel artificial membrane permeability assay (PAMPA) membranes. However, there is a lack of thorough analysis of the impact of variabilities in the PAMPA setup on the mass flow rate outcomes, particularly for complex solubility-enabling formulations. In this study, we investigated the impact of amorphous drug-rich nanodroplets, formed in supersaturated solutions by liquid-liquid phase separation, on membrane transport by measuring mass flow rate across PAMPA membranes. In addition, we explored the impact of PAMPA variants such as lipid composition, hydrophobicity and pore size of the filter support, as well as receiver sink properties on membrane mass flow rates of solutions containing amorphous nanodroplets. Filter properties and lipid composition did not show a notable influence on the mass flow rates for lipophilic molecules, while a marked impact was observed for hydrophilic molecules. High sink conditions in the receiver compartment, arising from addition of micellar surfactant, altered the membrane integrity for lipid-impregnated hydrophilic membranes. In contrast, no such effect was observed for a hydrophobic filter support. Membrane integrity tests also suggested that monitoring water transport may be an improved approach over using Lucifer yellow. Furthermore, high sink conditions in the receiver compartment resulted in an increase in the overall mass flow rate. This was due to the effect of asymmetric conditions, generated across the membrane, on mass transport kinetics. Linearity between mass flow rate and donor concentration was observed until the donor concentration reached the amorphous solubility. Above the amorphous solubility, a gradual increase in mass flow rate was observed i.e., with an increasing number of nanodroplets in the solution. This was attributed to decrease in the permeability barrier across unstirred water layer due to reduction of the concentration gradient as nanodroplets dissolved to replenish absorbed drug. Observations made in this study provide insights into the mechanisms associated with mass transport of supersaturated solutions across PAMPA membranes, which are critical for improved evaluation of enabling formulations.

Enabling formulations of aprepitant: in vitro and in vivo comparison of nanocrystalline, amorphous and deep eutectic solvent based formulations

A deep eutectic solvent (DES) is a eutectic system consisting of hydrogen bond donor and acceptor has been suggested as a promising formulation strategy for poorly soluble drugs. A DES consisting of choline chloride and levulinic acid in a 1:2  molar ratio was used to formulate a liquid solution of the model drug aprepitant. This formulation was tested in vitro (drug release and permeability) and in vivo (rat model) and compared with the performance of amorphous aprepitant and the commercial aprepitant nanocrystalline formulation. In this study a DES formulation is compared for the first time directly to other established enabling formulations. The in vitro drug release study demonstrated that the DES formulation and the amorphous form both were able to induce an apparent supersaturation followed by subsequent drug precipitation. To mitigate the risk of precipitation, HPMC was predissolved in the dissolution medium, which successfully reduced the degree of precipitation. In line with the results from the release study, an in vitro permeation study showed superior permeation of the drug from the DES formulation and from the amorphous form compared to the nanocrystalline formulation. However, the promising in vitro findings could not be directly translated into an increased in vivo performance in rats compared to the nanocrystalline formulation. Whilst the DES formulation (34 ± 4%) showed a higher oral bioavailability compared to amorphous aprepitant (20 ± 4%), it was on par with the oral bioavailability obtained from the nanocrystalline formulation (36 ± 2%).

Polymer-mediated drug supersaturation - A spotlight on the interplay between phase-separated amorphous drug colloids and dissolved molecules

HYPOTHESIS

Colloidal aggregation phenomena have been found responsible for the supersaturation of poorly water-soluble drugs, potentially leading to bioavailability enhancements. Unlike coarse precipitates, phase separation in the form of colloids, is expected to enhance drug supersaturation performance. Therefore, a high proportion of these colloids should correlate with the extent and the kinetics of supersaturation. The prime objective of the current study is to provide a mechanistic understanding on supersaturation for the model drug albendazole (ALB) in combination with twelve polymers.

EXPERIMENTS

Species separated after a pH-shift were characterized by dynamic light scattering (DLS), freeze-fracture electron microscopy (FF-EM) and transmission X-ray diffraction (XRD). Laser diffraction (LD) in a liquid cell was introduced for a relative quantification of the colloidally separated species, described as colloid fraction. The pH-dependent supersaturation was assessed online using a miniaturized dissolution assay.

FINDINGS

Here, a measure of the extent of amorphous colloidal phase separation was established, and its impact on supersaturation was evaluated. As a result, a correlation was found between the extent of supersaturation and the colloid fraction. This confirmed the dependence of polymer-mediated enabling and preservation of supersaturation on the ability of polymers to stabilize colloid fractions. Furthermore, a fixed ratio was suggested between the dissolved drug and colloidally separated drug as the kinetic profiles of both species showed similar trajectories. In conclusion, colloid fractions were identified to be responsible for dissolved and potentially bioavailable drug molecules.

Considerations for the selection of co-formers in the preparation of co-amorphous formulations

Co-amorphous drug delivery systems are evolving as a credible alternative to amorphous solid dispersions technology. In Co-amorphous systems (CAMs), a drug is stabilized in amorphous form using small molecular weight compounds called as co-formers. A wide variety of small molecular weight co-formers have been leveraged in the preparation of CAMs. The stability and supersaturation potential of prepared co-amorphous phases largely depend on the type of co-former employed in the CAMs. However, the rationality behind the co-former selection in co-amorphous systems is poorly understood and scarcely compiled in the literature. There are various facets to the rational selection of co-former for CAMs. In this context, the present review compiles various factors affecting the co-former selection. The factors have been broadly classified under Thermodynamic, Kinetic and Pharmacokinetic-Pharmacologically relevant parameters. In particular, the importance of Glass transition, Miscibility, Liquid-Liquid phase separation (LLPS), Crystallization inhibition has been deliberated in detail.

Precipitation from amorphous solid dispersions in biorelevant dissolution testing: The polymorphism of regorafenib

Amorphous Solid Dispersions (ASDs) are a major drug formulation technique to achieve higher bioavailability for poorly water-soluble active pharmaceutical ingredients. So far, dissolution tailoring and supersaturation enhancement have been studied in detail, whereas less is known about the importance of formed precipitates with amorphous or crystalline states at the site of drug absorption. Regorafenib monohydrate (RGF MH), a multikinase inhibitor drug categorized as Biopharmaceutics Classification System (BCS) class II compound, was formulated with povidone K25 and hypromellose acetate succinate (HPMCAS) as an ASD. Here, for the first time, the RGF precipitation process as well as the physicochemical properties of the arising precipitates are investigated. The formed precipitates from biorelevant dissolution showed varying drug content and were analyzed offline by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), confocal Raman microscopy (CRM), X-ray powder diffraction (XRPD), and small angle X-ray scattering (SAXS). In addition to different crystalline RGF precipitates, an amorphous co-precipitate of RGF and HPMCAS was identified, which was suppressed in the presence of PVP. Wide angle X-ray scattering (WAXS) and isothermal calorimetry (ITC) were used to track the precipitation process of RGF in-situ. From calorimetric data, the precipitation profile was calculated. RGF forms precipitates in multiple polymorphic states dependent on the environmental conditions, i.e., dissolution media composition and chosen excipients. The engineered formation of defined amorphous structures in-vivo may be a promising future drug formulation strategy.

Hydrophilic nanofibers as a supersaturating delivery system for carvedilol

Polymer nanofibers represent a promising delivery system for poorly water-soluble drugs; however, their supersaturating potential has not been explored yet. Here, carvedilol-loaded nanofibers based on poly(ethyleneoxide) and on amphiphilic block copolymer poloxamer 407 were produced by electrospinning. These nanofibers provided high carvedilol loading and improved dissolution of carvedilol. Their dissolution resulted in a supersaturated system that was not stable, and thus to avoid carvedilol precipitation, hydroxypropyl methylcelluloses or polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer (Soluplus) were additionally incorporated into the nanofibers. The morphology of the electrospun product was not affected by incorporation of carvedilol and the polymer precipitation inhibitors, as shown by scanning electron microscopy. The hydroxypropyl methylcelluloses were not effective polymer precipitation inhibitors for carvedilol. Incorporation of Soluplus significantly extended the duration of carvedilol supersaturation (>24 h) compared to the dissolution of nanofibers without Soluplus. Moreover, after 1 h of dissolution, incorporation of Soluplus into the nanofibers provided significantly higher carvedilol concentration (94.4 ± 2.5 μg/mL) compared to the nanofibers without Soluplus (32.7 ± 5.8 μg/mL), the polymer film (24.0 ± 2.2 μg/mL), and the physical mixture (3.3 ± 0.4 μg/mL). Thus, this study shows the great potential for hydrophilic nanofibers as a delivery system for sustained carvedilol supersaturation.

A differential equation based modelling approach to predict supersaturation and in vivo absorption from in vitro dissolution-absorption system (idas2) data

In vitro dissolution tests are widely used to monitor the quality and consistency of oral solid dosage forms, but to increase the physiological relevance of in vitro dissolution tests, newer systems combine dissolution and permeation measurements. Some of these use artificial membranes while others (e.g., in the in vitro dissolution absorption system 2; IDAS2), utilize cell monolayers to assess drug permeation. We determined the effect of the precipitation inhibitor Hypromellose Acetate Succinate (HPMCAS) on the supersaturation/permeation of Ketoconazole and Dipyridamole in IDAS2 and its effect on their absorption in rats. Thus the main objectives of this study were to determine: (1) whether dissolution and permeation data from IDAS2 could be used to predict rat plasma concentration using an absorption model and (2) whether the effect of the precipitation inhibitor HPMCAS on supersaturation and permeation in IDAS2 was correlated with its effect on systemic absorption in the rat. Predicted drug concentrations in rat plasma, generated using parameters estimated from IDAS2 dissolution/permeation data and a mathematical absorption model, showed good agreement with measured concentrations. While in IDAS2, the prolongation of Ketoconazole's supersaturation caused by HPMCAS led to higher permeation, which paralleled the higher systemic absorption in rats, Dipyridamole showed no supersaturation and, thus, no effect of HPMCAS in dissolution or permeation in IDAS2 and no effect on Dipyridamole absorption in rats. The ability of IDAS2 to detect supersaturation following a pH-shift supports the potential value of this system for studying approaches to enhance intestinal absorption through supersaturation and the accuracy of plasma concentration predictions in rats suggest the possibility of combining IDAS2 with absorption models to predict plasma concentration in different species.

Optimized sonoreactor for accelerative amyloid-fibril assays through enhancement of primary nucleation and fragmentation

Ultrasonication to supersaturated protein solutions forcibly forms amyloid fibrils, thereby allowing the early-stage diagnosis for amyloidoses. Previously, we constructed a high-throughput sonoreactor to investigate features of the amyloid-fibril nucleation. Although the instrument substantiated the ultrasonication efficacy, several challenges remain; the key is the precise control of the acoustic field in the reactor, which directly affects the fibril-formation reaction. In the present study, we develop the optimized sonoreactor for the amyloid-fibril assay, which improves the reproducibility and controllability of the fibril formation. Using β₂-microglobulin, we experimentally demonstrate that achieving identical acoustic conditions by controlling oscillation amplitude and frequency of each transducer results in identical fibril-formation behavior across 36 solutions. Moreover, we succeed in detecting the 100-fM seeds using the developed sonoreactor at an accelerated rate. Finally, we reveal that the acceleration of the fibril-formation reaction with the seeds is achieved by enhancing the primary nucleation and the fibril fragmentation through the analysis of the fibril-formation kinetics. These results demonstrate the efficacy of the developed sonoreactor for the diagnosis of amyloidoses owing to the accelerative seed detection and the possibility for further early-stage diagnosis even without seeds through the accelerated primary nucleation.

Chemical Structural Effects of Amphipathic and Water-soluble Phospholipid Polymers on Formulation of Solid Dispersions

For the polymeric carriers of solid dispersions, it is important that carriers themselves dissolve quickly and maintain the supersaturated state of amorphous drugs during their dissolution period to improve bioavailability. Amphipathic 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers can be dissolved in water, owing to the extremely high hydrophilicity of the MPC units, and are used as an ideal feeder for drug molecules to form aggregates in aqueous conditions. We synthesized amphipathic MPC copolymers with different hydrophobic side chains and molar ratios of MPC units, and evaluated the effect of the polymers on dissolution rate and supersaturation maintenance of solid dispersions of indomethacin. In most of the water-soluble amphipathic MPC copolymers, "spring-parachute"-like dissolution behavior was observed, where the drug initially became supersaturated followed by slow precipitation. In particular, MPC copolymers with aromatic rings in their side chains or polymers with a high percentage of hydrophobic units remained in a supersaturated state for a longer period. In contrast, urethane groups, which form hydrogen bonds with drug molecules, could also interact with water and were not conducive to maintaining supersaturation. In addition, water solubility of the polymer is important for rapid dissolution.

Mutarotation and solubility of lactose as affected by carrageenans

It has been reported that polysaccharides like carrageenan can change the crystallization of lactose. However, it is still unclear whether changes in lactose mutarotation, solubility, and super-solubility are involved in carrageenans' effect on lactose crystallization. It has been established that the conversion of α- to β-lactose forms (mutarotation) in an aqueous solution has a significant impact on lactose crystallization. Similarly, lactose solubility changes lead to changes in the metastable zone (MZ), a region between the solubility and super-solubility of lactose. The width of this MZ determines the temperature drop necessary to induce lactose nucleation. This work aimed to study the effect of carrageenans on lactose mutarotation and solubility. For this purpose, lactose solutions were added with ι and κ- carrageenan at two concentrations: 50 and 100 mg L^-1. Optical rotation measurements estimated the proportion of β/α isomers in lactose solutions. Besides, solubility and super- solubility was determined to build the MZ. The presence of carrageenans changed both the time to reach the mutarotation balance and the proportion of β/α isomers at mutarotation equilibrium. Carrageenans decreased the solubility of lactose in a range of temperatures between 10 and 60 °C and reduced the metastable zone width (MZW).

Prediction of in vivo supersaturation and precipitation of poorly water-soluble drugs: Achievements and aspirations

This review focuses on options available to a pharmaceutical scientist to predict in vivo supersaturation and precipitation of poorly water-soluble drugs. As no single device or system can simulate the complex gastrointestinal environment, a combination of appropriate in vitro tools may be utilized to get optimal predictive information. To address the empirical issues encountered during small-scale and full-scale in vitro predictive testing, theoretical background and relevant case studies are discussed. The practical considerations for selection of appropriate tools at various stages of drug development are recommended. Upcoming technologies that have potential to further reduce in vivo studies and expedite the drug development process are also discussed.

Composition of Urine Collected from Non-Stone-Forming Chinese Persons during Different Short-Term Periods of the Day

The purpose of this study in a small group of non-stone-forming Chinese persons was to measure the levels of supersaturation with calcium oxalate and calcium phosphate and pH with the aim of confirming if any of the different short-term urine samples were better for risk evaluation than a 24-h sample. Nine normal men and 1 woman collected urine during 4 periods of the day. Period 1 between 08 and 12 h, Period 2 between 12 and 18 h, Period 3 between 18 and 22 h, and Period 4 between 22 and 08 h. Each sample was analysed for calcium, oxalate, citrate, magnesium and phosphate, and estimates of supersaturation with calcium oxalate (CaOx) and calcium phosphate (CaP) were expressed in terms of AP(CaOx) and AP(CaP) index. An estimate of the solute load of CaOx was also calculated. Urine composition for 24-h urine (Period 24) was obtained mathematically from the analysed variables. Urine composition corresponding to 14-h urine portions 22-12 h (Period 14N) and 08-22 h (Period 14 D) were calculated. The lowest pH levels were recorded in Period 1 urine. The highest level of AP(CaOx) index was recorded during Period 1, and the product AP(CaOx) index × 107 × hydrogen ion concentration was significantly higher in Period 1 urine than in 24-h urine (p = 0.02). Also, the product SL(CaOx) × 107 × hydrogen ion concentration was significantly higher in Period 1 urine (p = 0.02). Low AP (CaP) index levels were recorded in Period 4, but also in all periods following dietary loads of calcium and phosphate. With the important reservation that the analytical results were obtained from non-stone-forming persons, the conclusion is that analysis of urine samples collected between 08 and 12 h might be an alternative to 24-h urine. The risk evaluation might advantageously be expressed either in terms of the product AP(CaOx) index × 107 × hydrogen ion concentration or the product SL(CaOx) × 107 × hydrogen ion concentration.

Effect of drug-coformer interactions on drug dissolution from a coamorphous in mesoporous silica

In this study, the molecular state of ritonavir (RTN)-saccharin (SAC) coamorphous incorporated into mesoporous silica by solvent evaporation and the effect of SAC on the RTN dissolution from mesopores were investigated. The amorphization of RTN-SAC was confirmed as a halo pattern in powder X-ray diffraction measurements and a single glass transition event in the modulated differential scanning calorimetry (MDSC) curve. ¹³C solid-state NMR spectroscopy revealed a hydrogen bond between the thiazole nitrogen of RTN and the amine proton of SAC. The glass transition of the RTN-SAC coamorphous in mesoporous silica was not found in the MDSC curve, indicating that RTN and SAC were monomolecularly incorporated into the mesopores. Solid-state NMR measurements suggested that the co-incorporation of SAC into the mesopores decreased the local mobility of the thiazole group of RTN via hydrogen bond formation. The RTN-SAC 1:1 coamorphous in mesoporous silica retained the X-ray halo-patterns after 30 d of storage, even under high temperature and humidity conditions. In the dissolution test, the RTN-SAC 1:1 coamorphous in mesoporous silica maintained RTN supersaturation for a longer time than the RTN amorphous in mesoporous silica. This study demonstrated that the drug-coformer interaction within mesoporous silica can significantly improve drug dissolution.

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

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

Polymeric Precipitation Inhibitor Based Supersaturable Self-microemulsifying Drug Delivery System of Canagliflozin: Optimization and Evaluation

BACKGROUND

The present investigation attempts to optimize Supersaturable lipid based formulation (SS SMEDDS) of Biopharmaceutical Classification System (BCS) class IV drug canagliflozin (CFZ) and evaluating the oral bioavailability of the formulation.

METHODS

Preliminary screening revealed Poloxamer 188 to most effectively inhibit precipitation of CFZ after dispersion during in vitro supersaturation studies. Box Behnken Design was employed for designing different formulations and various statistical analysis were done out to select an appropriate mathematical model. The optimized formulation (OSS 1) was evaluated for in vitro drug release and ex vivo permeation studies to evaluate drug release and permeation rate. Pharmacokinetic studies have been done according to standard methodologies.

RESULTS

The optimized formulation (OSS 1) containing 781.1 mg SS SMEDDS and 2.24 % w/w Poloxamer 188 was developed at a temperature of 60°C which revealed nano-globule size with negligible aggregation. Isothermal titration calorimetry revealed the thermodynamic state of formed microemulsion with negative ∆G. The optimized formulation was observed to possess physical stability under different stress conditions and acceptable drug content.. In vitro dissolution of optimized SS SMEDDS revealed higher dissolution rate of CFZ as compared with native forms of CFZ. The permeability of CFZ from optimized SS SMEDDS across various excised segments of rat intestine was observed to be multifold higher that manifested in 2.05-fold higher Cmax and 5.64-fold higher AUC0-36h following oral administration to Wistar rats.

CONCLUSION

The results could be attributed to substantial lymphatic uptake and P-glycoprotein substrate affinity of CFZ in SS SMEDDS investigated through chylomicron and P-glycoprotein inhibition approach, respectively.

Effects of Lipid Digestion and Drug Permeation/Re-Dissolution on Absorption of Orally Administered Ritonavir as Different Lipid-Based Formulations

The aim of this study is to clarify absorption mechanisms after oral administration of ritonavir (RTV) from different types of lipid-based formulations (LBFs) with particular emphasis on the effect of lipid digestion and drug permeation/re-dissolution on the oral absorption. Four LBFs were prepared; three contained either long-chain (LC) or medium-chain (MC) lipids [lipid formulation classification system (LFCS) Type II-LC, Type IIIA-MC, and Type IIIB-MC] and the fourth contained only surfactant and co-solvent (Type IV). The solubility of RTV in those LBFs was determined and drug subsequently loaded at 85% w/w of the saturated solubility in the formulations. Then, each LBF containing drug was added into a model rat intestinal fluid at approximately 2.5% w/v for evaluation using an in vitro digestion model. In vitro digestion study showed the ability of Type II-LC and Type IIIA-MC to support continued solubilization of RTV, and moderate supersaturation was observed in Type IIIA-MC. In contrast, RTV partly precipitated in the Type IIIB-MC during digestion, and the Type IV formulation lost its solubilization capacity rapidly upon dispersion, leading to drastic precipitation. Oral administration of RTV as Type IIIA-MC to rats showed significantly higher area under the plasma concentration-time curve compared to control suspension, whereas it was not improved with Type II-LC administration despite complete solubilization of RTV during digestion. From the results of in vitro permeation across dialysis membrane (a molecular weight cutoff of > 1000 Da), this may be attributed to the lowered free concentration in the gastrointestinal tract owing to incorporation of RTV into the undigested LC lipid. Oral absorption drastically increased with Type IIIB-MC and Type IV despite the observed moderate and drastic precipitation, respectively. Powder X-ray diffraction analysis revealed that the precipitate was amorphous. Therefore, improved re-solubilization may partly contribute to improved absorption. The present study revealed detailed absorption mechanisms from LBFs with different compositions. Our findings may be useful for selecting appropriate excipients to design optimal LBFs for poorly water-soluble drugs.

Improvement of lipid solubility and oral bioavailability of a poorly water- and poorly lipid-soluble drug, rebamipide, by utilizing its counter ion and SNEDDS preparation

Among drugs in development and/or in market, there are poorly water-soluble and poorly lipid-soluble compounds. Rebamipide, classified into BCS class IV, is one of those drugs which provide very low bioavailability and/or the difficulty of formulation for oral administration. Because of its low solubility in available lipoidal excipients, it was impossible to prepare an adequate SNEDDS formulation of rebamipide. Then, we tried to increase the solubility of rebamipide in lipoidal excipients for preparing a more practical SNEDDS formulation by making the complex with its counter ion, tetrabutylphosphonium hydroxide (TBPOH) or NaOH. Rebamipide concentration in ethanol was proportionally increased with the increment of TBPOH or NaOH added, indicating that the formation of complex with a counter ion should contribute to the solubilization of rebamipide in ethanol. Both Rebamipide-TBPOH complex (Reb-TBPOH) and Rebamipide-NaOH complex (Reb-NaOH) obtained by lyophilization showed no endothermic peak in DSC and no diffraction peak in XRPD, suggesting that the solid state of both complexes should be amorphous. Reb-TBPOH maintained the dissolution of rebamipide in SNEDDS vehicle (Capryol 90:Cremophor EL:Transcutol P = 4:3:3) at 20 mg/g at least for 28 days, while Reb-NaOH did it at 10 mg/g. In vitro dissolution study showed that Reb-TBPOH SNEDDS and Reb-NaOH SNEDDS containing rebamipide at 10 mg/g maintained the complete dissolution of rebamipide in FaSSIF (intestinal luminal condition). In the gastric luminal condition (pH3.9 acetate buffer), the high concentration, close to the complete dissolution, was transiently observed and quickly decreased to one-sixth of the maximum, but it was still around 70 times higher than that of the crystalline powder. The additional utilization of Eudragit EPO for SNEDDS preparations of both complexes successfully maintained the high concentrations of rebamipide in the gastric luminal condition. In vivo oral absorption studies clearly indicated that SNEDDS preparations utilizing Reb-counter ion complex successfully improved rebamipide absorption.

Influence of Particle Size and Drug Load on Amorphous Solid Dispersions Containing pH-Dependent Soluble Polymers and the Weak Base Ketoconazole

Among the great number of poorly soluble drugs in pharmaceutical development, most of them are weak bases. Typically, they readily dissolve in an acidic environment but are prone to precipitation at elevated pH. This was aimed to be counteracted by the preparation of amorphous solid dispersions (ASDs) using the pH-dependent soluble polymers methacrylic acid ethylacrylate copolymer (Eudragit L100-55) and hydroxypropylmethylcellulose acetate succinate (HPMCAS) via hot-melt extrusion. The hot-melt extruded ASDs were of amorphous nature and single phased with the presence of specific interactions between drug and polymer as revealed by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), and Fourier-transform infrared spectroscopy (FT-IR). The ASDs were milled and classified into six particle size fractions. We investigated the influence of particle size, drug load, and polymer type on the dissolution performance. The best dissolution performance was achieved for the ASD made from Eudragit L100-55 at a drug load of 10%, whereby the dissolution rate was inversely proportional to the particle size. Within a pH-shift dissolution experiment (from pH 1 to pH 6.8), amorphous-amorphous phase separation occurred as a result of exposure to acidic medium which caused markedly reduced dissolution rates at subsequent higher pH values. Phase separation could be prevented by using enteric capsules (Vcaps Enteric®), which provided optimal dissolution profiles for the Eudragit L100-55 ASD at a drug load of 10%.

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.

Exploring the Impact of Intestinal Fluid Components on the Solubility and Supersaturation of Danazol

Eleven simulated intestinal fluids (SIF) were designed using a Design of Experiment (DoE) approach. The DoE SIF covered a range of compositions of fasted state human intestinal fluid (FaHIF) with regard to pH, bile salt (BS), and phospholipid (PL). Using the model compound danazol, the apparent crystalline solubility (aCS) and apparent amorphous solubility (aAS), as well as the supersaturation propensity was determined in the DoE SIF media. The aCS of danazol was dependent on the composition of the SIF, with PL as the main factor, and a small effect from BS and an interaction between BS and PL. From the DoE solubility data a model was derived, which could predict aCS in commercially available SIF (FaSSIF-V1 and -V2) and in a range of FaHIF. The aAS of danazol was differently affected by the SIF composition than the aCS; PL was again the main factor influencing the aAS, but interactions between BS and pH, as well as pH and PL were also important. The supersaturation propensities of danazol in the DoE SIF media were affected by the same factors as the aCS. Hence, the supersaturation behaviour and aCS of danazol, were found to be closely related.