The impact of supersaturation level for oral absorption of BCS class IIb drugs, dipyridamole and ketoconazole, using in vivo predictive dissolution system: Gastrointestinal Simulator (GIS)

The development of formulations and the assessment of oral drug absorption for Biopharmaceutical Classification System (BCS) class IIb drugs is often a difficult issue due to the potential for supersaturation and precipitation in the gastrointestinal (GI) tract. The physiological environment in the GI tract largely influences in vivo drug dissolution rates of those drugs. Thus, those physiological factors should be incorporated into the in vitro system to better assess in vivo performance of BCS class IIb drugs. In order to predict oral bioperformance, an in vitro dissolution system with multiple compartments incorporating physiologically relevant factors would be expected to more accurately predict in vivo phenomena than a one-compartment dissolution system like USP Apparatus 2 because, for example, the pH change occurring in the human GI tract can be better replicated in a multi-compartmental platform. The Gastrointestinal Simulator (GIS) consists of three compartments, the gastric, duodenal and jejunal chambers, and is a practical in vitro dissolution apparatus to predict in vivo dissolution for oral dosage forms. This system can demonstrate supersaturation and precipitation and, therefore, has the potential to predict in vivo bioperformance of oral dosage forms where this phenomenon may occur. In this report, in vitro studies were performed with dipyridamole and ketoconazole to evaluate the precipitation rates and the relationship between the supersaturation levels and oral absorption of BCS class II weak base drugs. To evaluate the impact of observed supersaturation levels on oral absorption, a study utilizing the GIS in combination with mouse intestinal infusion was conducted. Supersaturation levels observed in the GIS enhanced dipyridamole and ketoconazole absorption in mouse, and a good correlation between their supersaturation levels and their concentration in plasma was observed. The GIS, therefore, appears to represent in vivo dissolution phenomena and demonstrate supersaturation and precipitation of dipyridamole and ketoconazole. We therefore conclude that the GIS has been shown to be a good biopredictive tool to predict in vivo bioperformance of BCS class IIb drugs that can be used to optimize oral formulations.

Amorphous is not always better-A dissolution study on solid state forms of carbamazepine

Poor aqueous solubility is a major concern for many new drugs. One possibility to overcome this issue is to formulate the drug as a high energy form, i.e. a metastable polymorph, an amorphous neat drug or a glass solution with polymers. In this study the dissolution properties of different solid state forms of carbamazepine, crystalline or amorphous drug, with or without either polyvinylpyrrolidone (PVP) or hydroxypropylmethylcellulose (HPMC) and glass solutions of the drug with both polymers (2:1, 4:1 and 10:1 (w/w) drug-to-polymer ratio) were tested with respect to their dissolution behaviour in a biorelevant gastric medium (for 30min) and subsequently in intestinal conditions (for 2h). Carbamazepine form III in the absence of polymer dissolved to a drug concentration of 540μg/ml, but the concentration decreased after around 70min due to precipitation of the dihydrate form, and reached 436μg/ml after 2.5h dissolution testing. The presence of PVP led to a similar dissolution profile with a slightly earlier onset of decrease in drug concentration, while in the presence of HPMC no decline in dissolved drug concentration was observed. Surprisingly, amorphous carbamazepine did not result in any supersaturation and the drug concentration was lower than that measured for crystalline carbamazepine. The addition of polymers further decreased the concentration of dissolved drug (290-310μg/ml, depending on polymer type and concentration). Amorphous drug converted quickly into the dihydrate form and thus no supersaturation was achieved. Glass solutions of carbamazepine with PVP reached drug concentrations between 348 and 408μg/ml after 2.5h, i.e. lower than for the crystalline drug, whilst glass solutions with HPMC reached concentrations similar to the crystalline drug.

Dual-mechanism gastroretentive drug delivery system loaded with an amorphous solid dispersion prepared by hot-melt extrusion

In the present study, we aimed to prepare a gastroretentive drug delivery system that would be both highly resistant to gastric emptying via multiple mechanisms and would also potentially induce in situ supersaturation. The bioadhesive floating pellets, loaded with an amorphous solid dispersion, were prepared in a single step of hot-melt extrusion technology. Hydroxypropyl cellulose (Klucel™ MF) and hypromellose (Benecel™ K15M) were used as matrix-forming polymers, and felodipine was used as the model drug. The foam pellets were fabricated based on the expansion of CO₂, which was generated from sodium bicarbonate during the melt-extrusion process. A 2ⁿ full factorial experimental design was utilized to investigate the effects of formulation compositions to the pellet properties. The melt-extrusion process transformed the crystalline felodipine into an amorphous state that was dispersed and "frozen" in the polymer matrix. All formulations showed high porosity and were able to float immediately, without lag time, on top of gastric fluid, and maintained their buoyancy over 12h. The pellet-specific floating force, which could be as high as 4800μN/g, increased significantly during the first hour, and was relatively stable until 9h. The sodium bicarbonate percentage was found to be most significantly effect to the floating force. The ex vivo bioadhesion force of the pellets to porcine stomach mucosa was approximately 5mN/pellet, which was more than five times higher than the gravitation force of the pellet saturated with water. Drug release was well controlled up to 12h in the sink condition of 0.5% sodium lauryl sulphate in 0.1N HCl. The dissolution at 1, 3, 5, and 8h were 5-12%, 25-45%, 55-80%, and ≥75% respectively for all 11 formulations. In biorelevant dissolution medium, a supersaturated solution was formed, and the concentration was maintained at around 2μg/mL, approximately 10-folds higher than that of the pure felodipine. All input factors significantly affected dissolution in the first 3h, but afterwards, only drug load and hypromellose (HPMC) content had significant effects. The prepared drug delivery system has great potential in overcoming low and fluctuating bioavailability of poorly soluble drugs.

CHEMICAL

Felodipine (PubChem CID: 3333); hypromellose (PubChem CID: 57503849), hydroxypropyl cellulose (PubChem CID: 71306830), sodium bicarbonate (PubChem CID: 516892); sodium carbonate (PubChem CID: 10340).

In vitro dissolution models for the prediction of in vivo performance of an oral mesoporous silica formulation

Drug release from mesoporous silica systems has been widely investigated in vitro using USP Type II (paddle) dissolution apparatus. However, it is not clear if the observed enhanced in vitro dissolution can forecast drug bioavailability in vivo. In this study, the ability of different in vitro dissolution models to predict in vivo oral bioavailability in a pig model was examined. The fenofibrate-loaded mesoporous silica formulation was compared directly to a commercial reference product, Lipantil Supra®. Three in vitro dissolution methods were considered; USP Type II (paddle) apparatus, USP Type IV (flow-through cell) apparatus and a USP IV Transfer model (incorporating a SGF to FaSSIF-V2 media transfer). In silico modelling, using a physiologically based pharmacokinetic modelling and simulation software package (Gastroplus™), to generate in vitro/in vivo relationships, was also investigated. The study demonstrates that the in vitro dissolution performance of a mesoporous silica formulation varies depending on the dissolution apparatus utilised and experimental design. The findings show that the USP IV transfer model was the best predictor of in vivo bioavailability. The USP Type II (paddle) apparatus was not effective at forecasting in vivo behaviour. This observation is likely due to hydrodynamic differences between the two apparatus and the ability of the transfer model to better simulate gastrointestinal transit. The transfer model is advantageous in forecasting in vivo behaviour for formulations which promote drug supersaturation and as a result are prone to precipitation to a more energetically favourable, less soluble form. The USP IV transfer model could prove useful in future mesoporous silica formulation development. In silico modelling has the potential to assist in this process. However, further investigation is required to overcome the limitations of the model for solubility enhancing formulations.

Protein Crystallization

Protein crystallization was discovered by chance nearly 200 years ago and was developed in the late nineteenth century as a powerful purification tool, and a demonstration of chemical purity. The crystallization of proteins, nucleic acids, and large biological complexes, such as viruses, depends on the creation of a solution that is supersaturated in the macromolecule, but exhibits conditions that do not significantly perturb its natural state. Supersaturation is produced through the addition of mild precipitating agents such as neutral salts or polymers, and by manipulation of various parameters that include temperature, ionic strength, and pH. Also important in the crystallization process are factors that can affect the structural state of the macromolecule, such as metal ions, inhibitors, cofactors, or other conventional small molecules. A variety of approaches have been developed that combine the spectrum of factors that effect and promote crystallization, and among the most widely used are vapor diffusion, dialysis, batch, and liquid-liquid diffusion. Successes in macromolecular crystallization have multiplied rapidly in recent years due to the advent of practical, easy-to-use screening kits, and the application of laboratory robotics.

First observations of saturopeaking: Characteristics and implications

During the monitoring of total dissolved gas (TDG) saturation in the Vetlefjordelva River in western Norway in 2014-2015, characteristic waves of supersaturated water were discovered. These waves were significantly correlated with hydropower operation, which was run by hydropeaking (R²=0.82, p<0.001). The TDG saturation varied between 99% and 108%, with a median of 105%. The term "saturopeaking" is introduced for these waves, defined as the artificial, rapid, periodic and frequent fluctuation of gas saturation caused by hydropeaking. Hydropeaking is recognized as hydropower operation that rapidly fluctuates according to the electricity market demand. Though the observed TDG saturation levels were moderate and not likely to cause acute effects on biota, we expect that the observed saturopeaking may have significant ecological impacts in general, especially in cases with TDG saturation levels >110^% which is considered as potentially lethal for fish in rivers.

Enhancement of physical stability and bioaccessibility of tangeretin by soy protein isolate addition

Soy protein isolate (SPI) was selected to fabricate supersaturated self-emulsifying nanoemulsions, aiming to enhance physical stability and bioaccessibility of hydrophobic tangeretin. Dissolution studies demonstrated that tangeretin had the highest solubility in Tween 80, followed by oil phase solutions, and polymer solutions. Supersaturated tangeretin in oil phases easily formed crystals. That metastable zone was found to vary with its initial concentrations. After encapsulation by nanoemulsions, the addition of glycerol compressed the retention amount of tangeretin from 76% to 53%, but benefited the transparency. Whereas, the combination of glycerol and SPI could not only maintain high-loading tangeretin (>85%), but also provide high transparency for nanoemulsions. When tangeretin concentration was 4.83mM, combination of 50% glycerol and 1% SPI could maintain around 88% tangeretin in the nanoemulsion within one month. Its bioaccessibility of different systems were at 60-65%. These findings can provide useful information for protein to be a potential precipitation inhibitor.

In vivo evaluation of supersaturation/precipitation/re-dissolution behavior of cinnarizine, a lipophilic weak base, in the gastrointestinal tract: the key process of oral absorption

The aim of this study is to evaluate how supersaturation, precipitation, and re-dissolution processes influence the intestinal absorption of cinnarizine (CNZ), a lipophilic weak base, by monitoring its plasma and luminal concentration-time profile, after oral administration as a HCl solution containing fluorescein isothiocyanate dextran (FD-4), a non-absorbable marker. In the in vitro pH shift experiment, the supersaturation stability was significantly lower when the higher-concentration solution of CNZ (pH1.5) was added to the simulated intestinal fluid. However, although the in vivo bioavailability after oral administration of high and low dose as HCl solutions was greatly improved compared to those as neutral suspensions, the difference in the supersaturation stability was not reflected in the improvement of the in vivo bioavailability. Analysis of CNZ and FD-4 concentrations in each segment of the gastrointestinal tract revealed that most of the CNZ precipitated in the duodenum after gastric emptying, and supersaturation was observed only in the duodenum. Thereafter, the precipitate was rapidly re-dissolved and absorbed in the upper and middle small intestine. The rapid re-dissolution may be caused by smaller particles of the precipitate. In this case, it is considered that the key process for the absorption of CNZ was re-dissolution, not supersaturation. Therefore, different supersaturation stabilities in different doses observed in in vitro precipitation experiment was not reflected to in vivo absorption. These findings may be useful to design efficient supersaturable formulations and to validate and improve current prediction methods.

In vitro evaluation of the impact of gastrointestinal transfer on luminal performance of commercially available products of posaconazole and itraconazole using BioGIT

Biorelevant Gastrointestinal Transfer system (BioGIT) has been shown to be useful in reproducing concentrations of drugs in the fasted upper small intestine after their administration in the stomach. In the present investigation, we evaluated the impact of gastrointestinal transfer on luminal performance of commercially available products of two highly lipophilic weak bases, posaconazole (Noxafil^® suspension) and itraconazole (Sporanox^® hard gelatin capsules and Sporanox^® oral solution) by comparing % solid fraction, concentrations and supersaturation in the duodenal compartment of BioGIT with recently reported data in the upper small intestine of healthy adults. BioGIT was useful for estimating the % solid fraction in the upper small intestine, in cases where dissolution during gastric residence was incomplete, i.e. after administration of Noxafil^® and Sporanox^® capsules, and the precipitated fraction of itraconazole in the upper small intestine after administration of Sporanox^® solution; median values in vitro were similar to the luminal values. Based on the values for the area under the concentration vs. time data estimated up to 45min post initiation of the experiment, concentrations in the duodenal compartment of BioGIT were similar to previously measured concentrations in the upper small intestine of healthy adults or they overestimated them by up to 2.5 times. In most cases, supersaturation of contents in the upper small intestine was overestimated, partly due to underestimation of luminal solubility.

Kinetics of the reversible reaction of struvite crystallisation

The crystallisation of struvite could be a sustainable and economical alternative for recovering phosphorus from wastewater streams with high phosphate concentrations. Knowledge regarding the kinetics and thermodynamics that are involved in the crystallisation of struvite is the key to determine the optimal conditions for obtaining an efficient process. This study was conducted in a continuous stirred batch reactor. Different sets of experiments were performed in which struvite was either dissolved (undersaturated) or precipitated (oversaturated). These experiments were conducted at different temperatures (25, 30 and 35 °C) and pH values (8.2, 8.5 and 8.8) to determine the kinetics of struvite precipitation and dissolution. Struvite crystallisation was modelled as a reversible reaction. The kinetic rate parameters of struvite precipitation were 1.03·10(-4), 1.25·10(-4) and 1.54·10(-4) mol m(-2) min(-1) at 25, 30 and 35 °C, respectively. Similar kinetic rate parameters were determined for struvite dissolution. Struvite heterogeneous crystallisation can be represented by a first-order kinetic model that fitted well the experimental data.

Supersaturation of Calcipotriene and Betamethasone Dipropionate in a Novel Aerosol Foam Formulation for Topical Treatment of Psoriasis Provides Enhanced Bioavailability of the Active Ingredients

Introduction

Previous studies have demonstrated the superior efficacy of a novel aerosol foam formulation of fixed combination calcipotriene 0.005% (Cal) and betamethasone dipropionate 0.064% (BD), compared with the ointment formulation. The aim of this study is to ascertain whether enhanced bioavailability of the active ingredients due to supersaturation and/or occlusive properties can explain the observed greater clinical efficacy.

Methods

Solubility and evaporation experiments were conducted to examine the abilities of Cal/BD aerosol foam ingredients to create a supersaturated environment. Optical microscopy, Raman imaging and X-ray powder diffraction were used to examine the physical state of Cal and BD in the formulations after application, and determine whether a supersaturated state remained stable for clinically relevant time periods. In vitro skin penetration and ex vivo biomarker assays were conducted to compare the skin penetration and bioavailability of Cal and BD from the aerosol foam and ointment formulations, respectively. Occlusive properties were examined via transepidermal water loss.

Results

Solubility studies showed that Cal and BD solubility increased with increasing dimethyl ether (DME) content. Both active ingredients are completely dissolved in the final aerosol foam formulation. DME rapidly evaporates after spraying, and the amount was reduced to 0.5% of the initial amount after 2 min. This led to the formation of a supersaturated environment, where Cal and BD crystals were absent for at least 26 h after application. Cal/BD aerosol foam had significantly greater in vitro skin penetration and had increased bioavailability compared with Cal/BD ointment. Both formulations effectively occluded the skin.

Conclusion

A stable supersaturated solution of Cal/BD in the aerosol foam leads to increased bioavailability and explains the improved clinical effect when compared to the Cal/BD ointment.

Funding

The studies included in the paper are all conducted by LEO Pharma A/S or CROs on behalf of LEO Pharma A/S.

Development of micro-fibrous solid dispersions of poorly water-soluble drugs in sucrose using temperature-controlled centrifugal spinning

Solid dispersion technology represents a successful approach to addressing the bioavailability issues caused by the low aqueous solubility of many Biopharmaceutics Classification System (BCS) Class II drugs. In this study, the use of high-yield manufacture of fiber-based dispersion is explored as an alternative approach to monolith production methods. A temperature-controlled solvent-free centrifugal spinning process was used to produce sucrose-based microfibers containing the poorly water-soluble drugs olanzapine and piroxicam (both BCS Class II); these were successfully incorporated into the microfibers and the basic characteristics of fiber diameter, glassy behavior, drug loading capacity and drug-sucrose interaction assessment were measured. Scanning electron microscopy revealed that bead-free drug-loaded microfibers with homogenous morphology and diameter in the range of a few micrometers were prepared using our process. Differential scanning calorimetric and X-ray diffraction analyses showed that both drug and carrier were present in the amorphous state in the microfibers, although in the case of piroxicam-loaded microfibers, the presence of small amounts of crystalline drug was observed under polarized light microscopy and in Fourier transform infrared spectra. Drug dissolution performance was evaluated under both sink and non-sink conditions and was found to be significantly enhanced compared to the corresponding crystalline physical mixtures and pure drugs, with evidence of supersaturation behavior noted under non-sink conditions. This study has demonstrated that microfiber-based dispersions may be manufactured by the centrifugal spinning process and may possess characteristics that are favorable for the enhanced dissolution and oral absorption of drugs.

Cocrystals to facilitate delivery of poorly soluble compounds beyond-rule-of-5

Besides enhancing aqueous solubilities, cocrystals have the ability to fine-tune solubility advantage over drug, supersaturation index, and bioavailability. This review presents important facts about cocrystals that set them apart from other solid-state forms of drugs, and a quantitative set of rules for the selection of additives and solution/formulation conditions that predict cocrystal solubility, supersaturation index, and transition points. Cocrystal eutectic constants are shown to be the most important cocrystal property that can be measured once a cocrystal is discovered, and simple relationships are presented that allow for prediction of cocrystal behavior as a function of pH and drug solubilizing agents. Cocrystal eutectic constant is a stability or supersatuation index that: (a) reflects how close or far from equilibrium a cocrystal is, (b) establishes transition points, and (c) provides a quantitative scale of cocrystal true solubility changes over drug. The benefit of this strategy is that a single measurement, that requires little material and time, provides a principled basis to tailor cocrystal supersaturation index by the rational selection of cocrystal formulation, dissolution, and processing conditions.

50years of oral lipid-based formulations: Provenance, progress and future perspectives

Lipid based formulations (LBF) provide well proven opportunities to enhance the oral absorption of drugs and drug candidates that sit close to, or beyond, the boundaries of Lipinski's 'rule-of-five' chemical space. Advantages in permeability, efflux and presystemic metabolism are evident; however, the primary benefit is in increases in dissolution and apparent intestinal solubility for lipophilic, poorly water soluble drugs. This review firstly details the inherent advantages of LBF, their general properties and classification, and provides a brief retrospective assessment of the development of LBF over the past fifty years. More detailed analysis of the ability of LBF to promote intestinal solubilisation, supersaturation and absorption is then provided alongside review of the methods employed to assess formulation performance. Critical review of the ability of simple dispersion and more complex in vitro digestion methods to predict formulation performance subsequently reveals marked differences in the correlative ability of in vitro tests, depending on the properties of the drug involved. Notably, for highly permeable low melting drugs e.g. fenofibrate, LBF appear to provide significant benefit in all cases, and sustained ongoing solubilisation may not be required. In other cases, and particularly for higher melting point drugs such as danazol, where re-dissolution of crystalline precipitate drug is likely to be slow, correlations with ongoing solubilisation and supersaturation are more evident. In spite of their potential benefits, one limitation to broader use of LBF is low drug solubility in the excipients employed to generate formulations. Techniques to increase drug lipophilicity and lipid solubility are therefore explored, and in particular those methods that provide for temporary enhancement including lipophilic ionic liquid and prodrug technologies. The transient nature of these lipophilicity increases enhances lipid solubility and LBF viability, but precludes enduring effects on receptor promiscuity and off target toxicity. Finally, recent efforts to generate solid LBF are briefly described as a means to circumvent the need to encapsulate in soft or hard gelatin capsules, although the latter remain popular with consumers and a proven means of LBF delivery.

Advanced topical formulations (ATF)

Topical formulations aim to target the skin for a variety of cosmetic, protective or therapeutic needs. Despite the use of creams and ointments over the millennia, the bioavailability of actives from topical preparations remains quite low, often not exceeding 1-2% of the applied dose. In this review we examine the reasons underlying the poor performance of topical preparations. We also outline a rational approach, based on Fick's laws of diffusion, to develop advanced topical formulations. Methodologies which are currently used in research and development are critically examined and the importance of understanding the fate of the vehicle as well as the active is emphasised. Advanced topical formulation development will also be facilitated by emerging and sophisticated analytical techniques that are able to probe real time delivery of actives to the skin. A good understanding of the underlying physical chemistry of both the formulation and the skin is crucial in the development of optimised topical products.

Selection of a discriminant and biorelevant in vitro dissolution test for the development of fenofibrate self-emulsifying lipid-based formulations

Fenofibrate, a BCS class II compound, has a low bioavailability especially when taken orally on an empty stomach. The challenge to find a new formulation for providing bioavailability, independent of food, is still ongoing. If the development of a suitable oral delivery formulation of BCS class II compounds is a frequent and great challenge to formulation scientists, the in vitro evaluation of these new formulations is also a great challenge. The purpose of this study was therefore to select an in vitro dissolution test that would be useful and as biorelevant as possible for the development of fenofibrate self-emulsifying lipid-based formulations. In this context, three different fenofibrate formulations, for which in vivo data are available in the literature, were tested using different dissolution tests until we found the one that was the most suitable. As part of this approach, we started with the simplest in vitro dissolution tests and progressed to tests that were increasingly more complex. The first tests were different single phase dissolution tests: a test under sink conditions based on the USP monograph, and different tests under non-sink conditions in non-biorelevant and biorelevant media. Given the inconclusive results obtained with these tests, biphasic dissolution systems were then tested: one with USP apparatus type II alone and another which combined USP apparatus types II and IV. This last combined test seemed the most suitable in vitro dissolution test for the development of the future fenofibrate lipid-based formulations we intend to develop in our own laboratory.

Compromised in vitro dissolution and membrane transport of multidrug amorphous formulations

Herein, the thermodynamic properties of solutions evolving from the non-sink dissolution of amorphous solid dispersions (ASDs) containing two or more drugs have been evaluated, focusing on the maximum achievable supersaturation and tendency of the system to undergo liquid-liquid phase separation (LLPS). Ritonavir (RTV) and atazanavir (ATV) were co-formulated with polyvinylpyrrolidone to produce ASDs with different molar ratios of each drug, and the dissolution profile of each drug was studied under non-sink conditions. The phase behavior of the supersaturated solutions generated by ASD dissolution was compared to that of supersaturated solutions generated by antisolvent addition. Dissolution of an ASD containing RTV, ATV and lopinavir (LPV) was also investigated. A thermodynamic model was used to predict the maximum achievable supersaturation for ASDs containing two and three drugs. In addition, a transport study with Caco-2 cells was conducted to evaluate the impact of co-addition of drugs on membrane transport. It was found that the formulation containing a 1:1 molar ratio of RTV and ATV achieved only 50% of the supersaturation attained by dissolution of the single drug systems. The maximum achievable concentration of ATV decreased linearly as the mole fraction of ATV in the formulation decreased and a similar trend was observed for RTV. For the dispersion containing a 1:1:1 molar ratio of RTV, ATV and LPV, the maximum concentration of each drug was only one third of that achieved for the single drug formulations. The decrease in the achievable supersaturation was well-predicted by the thermodynamic model for both the binary and ternary drug combinations. These observations can be explained by a decrease in the concentration at which the drugs undergo LLPS in the presence of other miscible drugs, thereby reducing the maximum achievable supersaturation of each drug. The reduced free drug concentration was reflected by a decreased flux across Caco-2 cells for the drug combinations compared to drug alone. This study sheds light on the complex dissolution and solution phase behavior of multicomponent amorphous dosage forms, in particular those containing poorly water soluble drugs, which may undergo supersaturation in vivo.

Metabolic risk-evaluation and prevention of recurrence in stone disease: does it make sense?

In this review, aspects on the importance of information on urine composition and selection of the most appropriate regimen for prevention of recurrence are discussed. For patients with urolithiasis the treatment is facilitated by urine analysis with estimates of supersaturation levels. Despite lack of strong scientific evidence for the benefit of selective versus non-selective prevention of recurrence in patients with calcium stone disease, there is currently both convincing and logical information in support of tailored/selective treatment regimens aiming at correction of abnormal target variables. Such an approach is also recommended in the EAU and AUA guidelines. It is important, however, that every preventive regimen is balanced between the effects on urine composition and patients' tolerance to the treatment in order to achieve satisfactory compliance. It is possible that future improved understanding of the causes of calcium stone formation might provide a different therapeutic approach.

The potential of at-home prediction of the formation of urolithiasis by simple multi-frequency electrical conductivity of the urine and the comparison of its performance with urine ion-related indices, color and specific gravity

It is important to control daily diet, water intake and life style as well as monitor the quality of urine for urolithiasis prevention. For decades, many ion-related indices have been developed for predicting the formation of urinary stones or urolithiasis, such as EQUILs, relative supersaturation (RSS), Tiselius indices (TI), Robertson risk factor algorithms (RRFA) and more recently, the Bonn risk index. However, they mostly demand robust laboratory analysis, are work-intensive, and even require complex computational programs to get the concentration patterns of several urine analytes. A simple and fast platform for measuring multi-frequency electrical conductivity (MFEC) of morning spot urine (random urine) to predict the onset of urolithiasis was implemented in this study. The performance thereof was compared to ion-related indices, urine color and specific gravity. The concentrations of relevant ions, color, specific gravity (SG) and MFEC (MFEC tested at 1, 10, 100, 5001 KHz and 1 MHz) of 80 random urine samples were examined after collection. Then, the urine samples were stored at 4 °C for 24 h to determine whether sedimentation would occur or not. Ion-activity product index of calcium oxalate (AP(CaOx) EQ2) was calculated. The correlation between AP(CaOx) EQ2, urine color, SG and MFEC were analyzed. AP(CaOx) EQ2, urine color and MFEC (at 5 frequencies) all demonstrated good prediction (p = 0.01, 0.01, 0.01, respectively) for stone formation. The positive correlation between AP(CaOx) EQ2 and MFEC is also significant (p = 0.01). MFEC provides a good metric for predicting the onset of urolithiasis, which is comparable to conventional ion-related indices and urine color. This technology can be implemented with much ease for objectively monitoring the quality of urine at points-of-care or at home.

Using Environment-Sensitive Fluorescent Probes to Characterize Liquid-Liquid Phase Separation in Supersaturated Solutions of Poorly Water Soluble Compounds

PURPOSE

Highly supersaturated aqueous solutions of poorly soluble compounds can undergo liquid-liquid phase separation (LLPS) when the concentration exceeds the "amorphous solubility". This phenomenon has been widely observed during high throughput screening of new molecular entities as well as during the dissolution of amorphous solid dispersions. In this study, we have evaluated the use of environment-sensitive fluorescence probes to investigate the formation and properties of the non-crystalline drug-rich aggregates formed in aqueous solutions as a result of LLPS.

METHODS

Six different environment-sensitive fluorophores were employed to study LLPS in highly supersaturated solutions of several model compounds, all dihydropyridine derivatives.

RESULTS

Each fluoroprobe exhibited a large hypsochromic shift with decreasing environment polarity. Upon drug aggregate formation, the probes partitioned into the drug-rich phase and exhibited changes in emission wavelength and intensity consistent with sensing a lower polarity environment. The LLPS onset concentrations determined using the fluorescence measurements were in good agreement with light scattering measurements as well as theoretically estimated amorphous solubility values.

CONCLUSIONS

Environment-sensitive fluorescence probes are useful to help understand the phase behavior of highly supersaturated aqueous solutions, which in turn is important in the context of developing enabling formulations for poorly soluble compounds.

Biophysical elucidation of the mechanism of enhanced drug release and topical delivery from polymeric film-forming systems

The effect of incorporating the lipidic medium-chain triglyceride (MCT) into polymeric film-forming systems (FFS) for topical drug delivery has been evaluated. First, the in vitro release of betamethasone-17-valerate (BMV), a representative dermatological drug, was determined from FFS comprising either hydrophobic polyacrylate co-polymers, or hydrophilic hydroxypropyl cellulose, with and without MCT. Release was enhanced from both polymers in the presence of MCT. Atomic force microscopy imaging and nanoindentation of FFS with MCT revealed two-phase structured films with softer inclusions (0.5 to 4μm in diameter) surrounded by a more rigid structure. Chemical mapping with Raman micro-spectroscopy showed that MCT was primarily confined to the inclusions within the polymer, which predominated in the surrounding film. BMV was distributed throughout the film but was more concentrated outside the inclusions. Furthermore, while BMV dissolved better into the hydrophobic films, it was more soluble in the MCT inclusions in hydrophilic films, suggesting its increased availability for diffusion from these softer regions of the polymer and explaining the release enhancement observed. Second, ex vivo skin penetration studies clearly revealed that uptake of BMV was higher from hydrophobic FFS than that from the more hydrophilic polymer due, at least in part, to the superior anti-nucleation efficiency of the former. Drug was quickly taken up into the SC from which it then diffused continuously over a sustained period into the lower, viable skin layers. In the presence of MCT, the overall uptake of BMV was increased and provides the basis for further optimisation of FFS as simple, convenient and sustained formulations for topical therapy.

'Pro et contra' ionic liquid drugs - Challenges and opportunities for pharmaceutical translation

Ionic liquids (ILs) are organic salts with a melting point below 100°C. Active pharmaceutical ingredients (APIs) are transformed into ILs by combining them with typically large yet charged counterions. ILs hold promise to build a large design space for relevant pharmaceutical parameters, particularly for poorly water soluble drugs. It is for this wide design space that ILs may be the entry into the fascinating vision of modifying physico-chemical properties without the need to structurally modify the active pharmaceutical ingredient itself. This extremely intriguing pharmaceutical option is critically discussed including its potential and limitations. The review is starting off with an introduction to the metathesis and characterization of ILs, and leads over to examples for pharmaceutical application, including enhancement of dissolution rate and kinetic solubility and hygroscopicity adaptation, respectively. Tuning biopharmaceutics and toxicology by proper IL design is another focus. The review connects the interrelated chemical, physical, pharmaceutical, and toxicological outcome of API-ILs, serving as guidance for the formulation scientist who aims at expanding ones armamentarium for poorly water soluble APIs while avoiding structural modification, thereof.

Probing the mechanisms of drug release from amorphous solid dispersions in medium-soluble and medium-insoluble carriers

The objective of the current study is to mechanistically differentiate the dissolution and supersaturation behaviors of amorphous drugs from amorphous solid dispersions (ASDs) based on medium-soluble versus medium-insoluble carriers under nonsink dissolution conditions through a direct head-to-head comparison. ASDs of indomethacin (IND) were prepared in several polymers which exhibit different solubility behaviors in acidic (pH1.2) and basic (pH7.4) dissolution media. The selected polymers range from water-soluble (e.g., PVP and Soluplus) and water-insoluble (e.g., ethylcellulose and Eudragit RL PO) to those only soluble in an acidic or basic dissolution medium (e.g., Eudragit E100, Eudragit L100, and HPMCAS). At 20wt.% drug loading, DSC and powder XRD analysis confirmed that the majority of incorporated IND was present in an amorphous state. Our nonsink dissolution results confirm that whether the carrier matrix is medium soluble determines the release mechanism of amorphous drugs from ASD systems which has a direct impact on the rate of supersaturation generation, thus in turn affecting the evolution of supersaturation in amorphous systems. For example, under nonsink dissolution conditions, the release of amorphous IND from medium-soluble carriers is governed by a dissolution-controlled mechanism leading to an initial surge of supersaturation followed by a sharp decline in drug concentration due to rapid nucleation and crystallization. In contrast, the dissolution of IND ASD from medium-insoluble carriers is more gradual as drug release is regulated by a diffusion-controlled mechanism by which drug supersaturation is built up gradually and sustained over an extended period of time without any apparent decline. Since several tested carrier polymers can be switched from soluble to insoluble by simply changing the pH of the dissolution medium, the results obtained here provide unequivocal evidence of the proposed transition of kinetic solubility profiles from the same ASD system induced by changes in the drug release mechanism in dissolution medium of a different pH.

Developing dissolution testing methodologies for extended-release oral dosage forms with supersaturating properties. Case example: Solid dispersion matrix of indomethacin

The objective of this study was to develop an in vitro dissolution test method with discrimination ability for an extended-release solid dispersion matrix of a lipophilic drug using the United States Pharmacopeia (USP) Apparatus 4, flow-through cell apparatus. In the open-loop configuration, the sink condition was maintained by manipulating the flow rate of the dissolution medium. To evaluate the testing conditions, the drug release mechanism from an extended-release solid dispersion matrix containing hydrophobic and hydrophilic polymers was investigated. As the hydroxypropyl methylcellulose (HPMC) maintained concentrations of indomethacin higher than the solubility in a dissolution medium, the release of HPMC into the dissolution medium was also quantified using size-exclusion chromatography. We concluded that the USP Apparatus 4 is suitable for application to an in vitro dissolution method for orally administered extended-release solid dispersion matrix formulations containing poorly water-soluble drugs.

Physicochemical properties of tadalafil solid dispersions - Impact of polymer on the apparent solubility and dissolution rate of tadalafil

To improve solubility of tadalafil (Td), a poorly soluble drug substance (3μg/ml) belonging to the II class of the Biopharmaceutical Classification System, its six different solid dispersions (1:1, w/w) in the following polymers: HPMC, MC, PVP, PVP-VA, Kollicoat IR and Soluplus were successfully produced by freeze-drying. Scanning electron microscopy showed a morphological structure of solid dispersions typical of lyophilisates. Apparent solubility and intrinsic dissolution rate studies revealed the greatest, a 16-fold, increase in drug solubility (50μg/ml) and a significant, 20-fold, dissolution rate enhancement for the Td/PVP-VA solid dispersion in comparison with crystalline Td. However, the longest duration of the supersaturation state in water (27μg/ml) over 24h was observed for the Td solid dispersion in HPMC. The improved dissolution of Td from Td/PVP-VA was confirmed in the standard dissolution test of capsules filled with solid dispersions. Powder X-ray diffraction and thermal analysis showed the amorphous nature of these binary systems and indicated the existence of dispersion at the molecular level and its supersaturated character, respectively. Nevertheless, as evidenced by film casting, the greatest ability to dissolve Td in polymer was determined for PVP-VA. The crystallization tendency of Td dispersed in Kollicoat IR could be explained by the low Tg (113°C) of the solid dispersion and the highest difference in Hansen solubility parameters (6.8MPa(0.5)) between Td and the polymer, although this relationship was not satisfied for the partially crystalline dispersion in PVP. Similarly, no correlation was found between the strength of hydrogen bonds investigated using infrared spectroscopy and the physical stability of solid dispersions or the level of supersaturation in aqueous solution.