Amorphous drug nanosuspensions. 3. Particle dissolution and crystal growth

Nanocrystal technologies in biomedical science: From the bench to the clinic

The pharmaceutical industry is grappling with a pressing crisis in drug development characterized by soaring R&D costs, setbacks in blockbuster drug development due to poor aqueous solubility, and patent-related limitations on newly approved molecules. To combat these challenges, diverse strategies have emerged to enhance the solubility and dissolution rates of Biopharmaceutics Classification System (BCS) II and IV drug molecules. Enter drug nanocrystals, a revolutionary nanotechnology-driven, carrier-free colloidal drug delivery system. This review provides a comprehensive insight into nanocrystal strategies, stabilizer selection criteria, preparation methods, advanced characterization techniques, the evolving nanocrystal technological landscape, current market options, and exciting clinical prospects for reshaping the future of pharmaceuticals.

Quercetin nanocrystals prepared using a microfluidic chip with improved in vitro dissolution

OBJECTIVE

In order to improve the dissolution property of quercetin (QCT), the quercetin nanocrystals (QNCs) were prepared in this study.

METHODS

QNCs were prepared by a 100 μm diameter Y-shape microfluidic channel. Some impact factors affecting the generation of QNCs such as concentration and flow rate were investigated. Furthermore, the fluid mixing in the microfluidic channel was simulated by fluid software.

RESULTS

XRPD and DSC analyses indicated that the prepared QNCs were amorphous. Stable QNCs with a particle size of 77.9 ± 3.63 nm and polydispersity index of 0.26 ± 0.02 were obtained. TEM showed that the as-prepared QNCs had a uniform spherical shape with an average particle size of about 100-300 nm. In the dissolution medium without cosolvent Tween -80, the dissolution of QCT was poor, its final accumulated dissolution was only 3.95%, while that of QNCs was 66%.

CONCLUSION

When QCT was changed to QNCs by microfluidic technology, its dissolution property could be obviously improved. Therefore, microfluidic technology as a new method to prepare nanocrystals has a good applying prospect in improving dissolution property for poorly water-soluble drugs.

The In Vivo Fate of Polycatecholamine Coated Nanoparticles Is Determined by a Fibrinogen Enriched Protein Corona

Polycatecholamine coatings have attracted significant attention in the past 10 years owing to their ability to functionalize a wide range of materials. Here we apply the use of such coatings to drug nanocrystals, made from a poorly soluble drug compound, to postfunctionalize the nanocrystal surface with the aim of providing steric stabilization and extending their circulation time after intravenous injection. We show that both polydopamine and polynorepinephrine can be used to successfully modify drug nanocrystals and subsequently incorporate end-functionalized PEG to the surface. Even though high grafting densities of PEG were achieved, we observed rapid clearance and increased liver uptake for polycatecholamine functionalized drug nanocrystals. Using both surface sensitive model systems and protein corona profiling, we determine that the rapid clearance was correlated with an increase in adsorption of proteins involved in coagulation to the polycatecholamine surface, with fibrinogen being the most abundant. Further analysis of the most abundant proteins revealed a significant increase in thiol-rich proteins on polycatecholamine coated surfaces. The observed interaction with coagulation proteins highlights one of the current challenges using polycatecholamines for drug delivery but might also provide insights to the growing use of these materials in hemostatic applications.

Leveraging the use of in vitro and computational methods to support the development of enabling oral drug products: An InPharma commentary

Due to the strong tendency towards poorly soluble drugs in modern development pipelines, enabling drug formulations such as amorphous solid dispersions, cyclodextrins, co-crystals and lipid-based formulations are frequently applied to solubilize or generate supersaturation in gastrointestinal fluids, thus enhancing oral drug absorption. Although many innovative in vitro and in silico tools have been introduced in recent years to aid development of enabling formulations, significant knowledge gaps still exist with respect to how best to implement them. As a result, the development strategy for enabling formulations varies considerably within the industry and many elements of empiricism remain. The InPharma network aims to advance a mechanistic, animal-free approach to the assessment of drug developability. This commentary focuses current status and next steps that will be taken in InPharma to identify and fully utilize 'best practice' in vitro and in silico tools for use in physiologically based biopharmaceutic models.

Characterization of Membrane-Type Dissolution Profiles of Clinically Available Orally Inhaled Products Using a Weibull Fit and a Mechanistic Model

Dissolution rate impacts the absorption rate of poorly soluble inhaled drugs. In vitro dissolution tests that can capture the impact of changes in critical quality attributes of the drug product on in vivo dissolution are important for the development of products containing poorly soluble drugs, as well as modified release formulations. In this study, an extended mathematical model allowing for dissolution of polydisperse powders and subsequent diffusion of dissolved drug across a membrane is described. In vitro dissolution profiles of budesonide, fluticasone propionate, and beclomethasone dipropionate delivered from three commercial drug products were determined using a membrane-type Transwell dissolution test, which consists of a donor and an acceptor compartment separated by a membrane. Subsequently, the profiles were analyzed using the developed mechanistic model and a semi-empirical model based on the Weibull distribution. The two mathematical models provided the same rank order of the performance of the three drug products in terms of dissolution rates, but the rates were significantly different. The faster rate extracted from the mechanistic model is expected to reflect the true dissolution rate of the drug; the Weibull model provides an effective and slower rate that represents not only drug dissolution but also diffusion across the Transwell membrane. In conclusion, the developed extended model provides superior understanding of the dissolution mechanisms in membrane-type (Transwell) dissolution tests.

Comparison of Paliperidone Palmitate from Different Crystallization Processes and Effect on Formulations In Vitro and In Vivo

The quality of active pharmaceutical ingredients (APIs) is an important factor which can affect the safety and efficacy of pharmaceuticals. This study was designed to investigate the nature of paliperidone palmitate (PP) obtained by different crystallization processes, then compare the characteristics between test formulations which prepared PP of different crystallization and reference formulations (Invega Sustenna^®) in vitro and in vivo. Two different PPs, namely PP-1 and PP-2, were prepared by different crystallization methods. Contact angle, morphology, and crystallinity of the PPs were characterized. Taking the particle sizes and distribution of Invega Sustenna^® as reference, test formulations were prepared by the wet milling method using either a PP-1 or PP-2 sample. Their release behavior, stability in vitro, and pharmacokinetics in vivo were subsequently investigated. The results indicated that PP-2 had a higher surface free energy (SFE). More small particles were attached to the PP-1 surface under the influence of crystallization temperature. Different crystallization processes did not change the crystal of PP, but changed the crystallinity of PP. There was no obvious difference in in vitro releases between test formulations. However, the stability and state of formulation containing PP-2 were better compared to formulations containing PP-1, indicated by differences in crystallinity and SFE. Meanwhile, pharmacokinetic in vivo results demonstrated that the pharmacokinetic profiles and parameters of formulation containing PP-2 and Invega Sustenna^® tended to be consistent, but those of formulations containing PP-1 were significantly different from those of formulations containing PP-2 or Invega Sustenna^®, and there was burst release phenomenon of formulations containing PP-1 in rats. PP made by different crystallization processes could induce changes in appearance, SFE, and crystallinity, and further affect the stability, state, and pharmacokinetic in vivo formulation.

Loading drugs into liposomes by temperature up-down cycle procedure with controllable results fitting prediction by mathematical and thermodynamic process

Liposomes are a useful carrier for delivering drugs but rarely make a poorly water-soluble drug (PWSD) realize its therapeutic potential. A key barrier lies in that, by conventional methods, PWSD is mainly loaded just in liposome bilayer membranes, which rarely provide sufficient room to accommodate drugs satisfying clinical therapy. In this investigation, a novel procedure of temperature up-down cycle (TUDC) was developed for loading PWSDs into the liposome interiors instead of bilayer membranes to hold enough agents. In particular, the TUDC procedure renders PWSDs such as curcumin (Cur) entrapment purposely controllable, as evidenced by the encapsulation efficiency (EE) of Cur varies nearly from 0% to 100% in response to changes the determinant factors of the procedure. In addition, several mathematical equations that could calculate the loading efficiency by TUDC were established and proved, when combined with thermodynamic process, able to successfully predict the loading results through including thermodynamic parameters, such as temperature and deduced drug solubility, thus remarkably cutting down the laborious experiments and enhancing liposome development efficiency. Cryo-TEM, SAXS, XRD and DSC tests proved that TUDC is feasible to load a PWSD into PEG-liposomes but rendering the drug in the amorphous state. Thus, the novel TUDC procedure and the established mathematical and thermodynamic process may provide a useful tool to promote the development of liposome products.

Progress in the development of stabilization strategies for nanocrystal preparations

In recent years, nanocrystal technology has been extensively investigated. Due to the submicron particle size and unique physicochemical properties of nanocrystals, they overcome the problems of low drug solubility and poor bioavailability. Although the structures of nanocrystals are simple, the further development of these materials is hindered by their stability. Drug nanocrystals with particle sizes of 1∼1000 nm usually require the addition of stabilizers such as polymers or surfactants to enhance their stability. The stability of nanocrystal suspensions and the redispersibility of solid nanocrystal drugs are the key factors for the large-scale production of nanocrystal preparations. In this paper, the factors that affect the stability of drug nanocrystal preparations are discussed, and related methods for solving the stability problem are put forward.

Milling of poorly soluble crystalline drug compounds to generate appropriate particle sizes for inhaled sustained drug delivery

One of the simplest design concepts of inhaled sustained drug delivery to the lung is to utilize the slow dissolution of drug crystals with poor aqueous solubility. An optimum dissolution rate, and thereby a delivery profile locally in the lung tissue, can be achieved in a reliable way by selecting a compound with an appropriate combination of solubility and particle size. It is in our experience relatively straightforward to manufacture monomodal particle size distributions of poorly soluble drug crystals in the mass median diameter range of either a few micrometers or a few hundred nanometers, but very challenging to manufacture a monomodal distribution in the range intermediate to these two. In this manuscript, we describe an investigation with the objective of generating desired particle sizes in the whole size range from a few micrometers to a few hundred nanometers for inhaled sustained drug delivery, by utilizing Adaptive Focused Acoustic (AFA) milling and planetary bead-milling. By combining the two different milling techniques it was possible to produce two to three distinctly different monomodal or almost monomodal particle size distributions in the desired particle size range of each of the model drug compounds in milligram scale. The dissolution kinetics of the different particle sizes of the model drugs were measured experimentally as well as predicted theoretically, showcasing that the dissolution kinetics can be characterized, predicted and significantly changed in a controlled way by modifying the particle size. For one of the model drugs, it was shown in an in vivo rat study that the inhaled sustained drug delivery profile in the lung tissue could be significantly changed by modifying the particle size of the drug.

The interplay of dissolution, solution crystallization and solid-state transformation of amorphous indomethacin in aqueous solution

Supersaturation profiles of amorphous indomethacin in aqueous solution containing 0.4 wt% and 4 wt% of isopropanol were predicted by combining separately-determined kinetics for dissolution, solution crystallization, and solid-state transformation. The kinetics of solid-state transformation were measured and compared to various data from the literature. The proposed kinetic model accounts for dissolution, solution crystallization and amorphous-to-crystalline solid-state transformation. It was validated for different initial amounts of amorphous and crystalline material and systems with different isopropanol contents. Furthermore, the influence of polyethylene glycol on the supersaturation behavior was investigated. The results clearly show the robustness of the model and give insight into the interplay of dissolution, solution crystallization, and solid-state transformation of. In particular, the influence of solid-state transformation on the overall supersaturation profile was elucidated in a quantitative manner. An amorphicity function φ(t) is proposed to account for the kinetics of the solid-state transformation. Its general form could be derived consistently from different sets of experimental data and seems to be independent of the particle size of the amorphous material and hydrodynamic conditions. This work is among the first of its kind to successfully integrate dissolution, crystallization from solution and solid-state transformation in a model that shows good predictability.

Slow Dissolution Kinetics of Model Peptide Fibrils

Understanding the kinetics of peptide self-assembly is important because of the involvement of peptide amyloid fibrils in several neurodegenerative diseases. In this paper, we have studied the dissolution kinetics of self-assembled model peptide fibrils after a dilution quench. Due to the low concentrations involved, the experimental method of choice was isothermal titration calorimetry (ITC). We show that the dissolution is a strikingly slow and reaction-limited process, that can be timescale separated from other rapid processes associated with dilution in the ITC experiment. We argue that the rate-limiting step of dissolution involves the breaking up of inter-peptide β–sheet hydrogen bonds, replacing them with peptide–water hydrogen bonds. Complementary pH experiments revealed that the self-assembly involves partial deprotonation of the peptide molecules.

A candidate drug administered subcutaneously to rodents as drug particles showing hepatic recirculation which influenced the sustained release process

The aim of the present study was to evaluate and interpret the pharmacokinetic profiles after subcutaneous (s.c.) administration of crystalline AZ'72 nano- and microsuspensions to rodents. Both formulations were injected at 1.5 and 150 mg/kg to rats. For the lower dose, the profiles were similar after s.c. injection but extended as compared to oral administration. The overall exposure was higher for nanoparticles compared with microparticles during the investigated period. For the higher dose, injection of both suspensions resulted in maintained plateaus caused by the drug depots but, unexpectedly, at similar exposure levels. After addition of a further stabilizer, pluronic F127, nanosuspensions showed improved exposure with dose and higher exposure compared to larger particles in mice. Obviously, a stabilizer mixture that suits one delivery route is not necessarily optimal for another one. The differences in peak concentration (C_max) between nano- and microparticles were mainly ascribed to differences in dissolution rate. Plasma profiles in mice showed curves with secondary absorption peaks after intravenous and oral administration, suggesting hepatic recirculation following both administration routes. This process, together with the depot formulation, complicates the analysis of absorption from s.c. administration, i.e. multiple processes were driving the plasma profile of AZ'72.

Engineering of siRNA loaded PLGA Nano-Particles for highly efficient silencing of GPR87 gene as a target for pancreatic cancer treatment

G protein-coupled receptor (GPCR) 87, is overexpressed in various cancer cells especially pancreatic cancer and plays a critical role in tumor cell survival. Nano-particles (NP) have become the essential vehicles for nucleotide internalization to the cell, due to the negative charge of nucleotides and their poor stability in blood circulation. In this study, the HEK293T cell linewas transfected with GPR87-plasmid after which the double-stranded RNA molecules targeting the GPR87 gene were prepared and purified. 1.1B4 cancer cell lines were used as model pancreatic cancer cells. Produced siRNA molecules were encapsulated in Poly(Lactic-Co-Glycolic Acid) (PLGA) nano-micelles using three different methods, two of which were according to literature with (siR-PLGA-S) or without (siR-PLGA-V) sonication. However, a new method was suggested to overcome problems such as poly-dispersity and large sizes of siR-PLGA-S and siR-PLGA-V. The new method consists of encapsulating siRNA using mild agitation to the pre-made PLGA NPs. The latter method provided mono-dispersed particles (siR-P-PLGA) with 92 nm size and desired Encapsulation Efficiency (EE%). siR-P-PLGA was able to silence the GPR-87 gene in a ratio of 83.9%, almost 41 times more effective than siR-PLGA-S and siR-PLGA-V in HEK 293 T cells. siR-P-PLGA was able to show a mild cytotoxic effect on 1.1B4 pancreatic cancer cells within 48 h.

Advanced modification of drug nanocrystals by using novel fabrication and downstream approaches for tailor-made drug delivery

Drug nanosuspensions/nanocrystals have been recognized as one useful and successful approach for drug delivery. Drug nanocrystals could be further decorated to possess extended functions (such as controlled release) and designed for special in vivo applications (such as drug tracking), which make best use of the advantages of drug nanocrystals. A lot of novel and advanced size reduction methods have been invented recently for special drug deliveries. In addition, some novel downstream processes have been combined with nanosuspensions, which have highly broadened its application areas (such as targeting) besides traditional routes. A large number of recent research publication regarding as nanocrystals focuses on above mentioned aspects, which have widely attracted attention. This review will focus on the recent development of nanocrystals and give an overview of regarding modification of nanocrystal by some new approaches for tailor-made drug delivery.

Formation of nanosuspensions in bottom-up approach: theories and optimization

BACKGROUND

Nanosuspensions, liquid dispersions with nanometer size distribution, are becoming trendy in pharmaceutical practice to formulate poorly water-soluble drugs and to enhance their bioavailability. Generally, nanosuspensions are produced in two main approaches; top-down or bottom-up. The former is based on size-reduction of large particles via milling or high pressure homogenization. The latter is focused on the mechanisms of nucleation and particle growth.

METHODS

In this review, the critical factors influencing the kinetics or dynamics of nucleation and growth are discussed. Subsequently, the mechanisms of nanosuspension instability as well as strategies for stabilization are elaborated. Furthermore, the effects of stabilizers on key parameters of instability as well as the process of choosing an appropriate stabilizer is discussed.

RESULTS

Steric and electrostatic stabilizations or combination of them is essential for nanosuspensions formulation to prevent coagulation. Accordingly, some characteristics of stabilizers play critical role on stability and optimization of nanosuspensions; i.e., HLB and concentration. Nevertheless, after reviewing various articles, it is ascertained that each formulation requires individual selection of surfactants according to the parameters of the particle surface and the medium.

CONCLUSIONS

Based on the results, application of excipients such as stabilizers requires proper optimization of type and concentration. This implies that each formulation requires its own optimization process. Graphical Abstract ᅟ.

Biorelevant intrinsic dissolution profiling in early drug development: Fundamental, methodological, and industrial aspects

Intrinsic dissolution rate (IDR) is the surface specific dissolution rate of a drug. In early drug development, this property (among other parameters) is measured in order to compare different polymorphs and salt forms, guide formulation decisions, and to provide a quality marker of the active pharmaceutical ingredient (API) during production. In this review, an update on different methods and small-scale techniques that have recently evolved for determination of IDR is provided. The importance of biorelevant media and the hydrodynamic conditions of dissolution are also discussed. Different preparation techniques for samples are presented with a focus on disc, particle- and crystal-based methods. A number of small-scale techniques are then described in detail, and their applicability domains are identified. Finally, an updated industrial perspective is provided about IDR's place in the early drug development process.

Search for the Source of an Apparent Interfacial Resistance To Mass Transfer of CnEm Surfactants To the Water/Oil Interface

Experiments have shown that relaxation of oil/water interfacial tension by adsorption of alkyl ethoxylate surfactants from water onto an oil droplet is delayed relative to diffusion-controlled adsorption. We examine possible causes of this delay, and we show that several are implausible. We find that redissolution of the surfactant in the oil droplet cannot explain the apparent interfacial resistance at short times because the interface will preferentially fill before any such redissolution occurs. We also perform umbrella sampling with molecular dynamics simulation and do not find any evidence of a free-energy barrier or low-diffusivity zone near the interface. Nor do we find evidence from the simulation that premicellar aggregation slows diffusion enough to cause the observed resistance to interfacial adsorption. We are therefore unable to pinpoint the cause of the resistance, but we suggest that "dead time" associated with the experimental method could be responsible-specifically a local depletion of surfactant by the ejected droplet when creating the fresh interface between the oil and water.

Fabrication and Evaluation of Lambda-Cyhalothrin Nanosuspension by One-Step Melt Emulsification Technique

Recent years have witnessed significant progress in nanotechnology and pesticide research in pest control and crop protection. There are more motivations to develop nanoformulations that are less harmful to environment than conventional formulations. The use of nanosuspension has been proposed as a novel formulation to process poorly soluble pesticides. In this study, the lambda-cyhalothrin nanosuspension (LCNS) was prepared in a melt emulsification method. The prepared nanosuspension had a mean particle size of 12.0 ± 0.1 nm and a polydispersity index of 0.279 ± 0.135. The smaller particle size and polydispersity confer better wettability, stability and bioavailability than conventional suspension concentrates. The excellent properties of the nanosuspension were attributed to the reduced particle size and the emulsification and dispersion of the surfactants. The LCNS eliminates the need for organic solvents and significantly reduces the amount of surfactant required. The simple production process of LCNS saves production and equipment costs. The results indicate that lambda-cyhalothrin nanosuspensions would have a broad application prospect in agricultural production systems.

Promoting intestinal lymphatic transport targets a liver-X receptor (LXR) agonist (WAY-252,623) to lymphocytes and enhances immunomodulation

Lymphocytes play a central role in the pathology of a range of chronic conditions such as autoimmune disease, transplant rejection, leukemia, lymphoma HIV/AIDs and cardiometabolic diseases such as atherosclerosis. Current treatments for lymphocyte-associated conditions are incompletely effective and/or complicated by a range of off-target toxicities. One major challenge is poor drug access to lymphocytes via the systemic blood and this may be attributed, at least in part, to the fact that lymphocytes are concentrated within lymph fluid and lymphoid tissues, particularly in gut-associated lymphatics. Here we demonstrate that promoting drug uptake into the intestinal lymphatics with a long chain fatty acid, thereby increasing lymphocyte access, enhances the pharmacodynamic effect of a highly lipophilic liver X receptor (LXR) agonist, WAY-252623, that has been suggested as a potential treatment for atherosclerosis. This has been exemplified by: (1) increased mRNA expression of key markers of LXR activation (ABCA1) and regulatory T cells (Foxp3) in local lymphatic lymphocytes and (2) enhanced numbers of CD4⁺CD25⁺Foxp3⁺ regulatory T cells in the systemic circulation, after administration of a 5-fold lower dose with a lymph directing lipid formulation when compared with a non-lipid containing formulation. These data suggest that combining lipophilic, lymphotropic drug candidates such as WAY-252,623, with lymph-directing long chain lipid based formulations can enhance drug targeting to, and activity on, lymphocytes in lymph and that this effect persists through to the systemic circulation. This presents a promising approach to achieve more selective and effective therapeutic outcomes for the treatment of lymphocyte associated diseases.

Ginsenoside Drug Nanocomposites Prepared by the Aerosol Solvent Extraction System for Enhancing Drug Solubility and Stability

Ginsenosides are the pharmacologically active constituents of ginseng. So far, more than 30 ginsenosides have been identified and widely used in pharmaceutical formulations. However, the therapeutic applications of ginsenosides are hampered by their poor solubility and low bioavailability. In this study, we selected two of the most important ginsenosides-Re and Rh₂ as model drugs to prepare ginsenoside drug nanocomposites (NanoGS) using the simple aerosol solvent extraction system (ASES) technique to address the poor solubility and bioavailability of these compounds. Compared with raw ginsenosides, NanoGS exhibited significantly enhanced dissolution rate owing to their low crystallinity and high surface area. Furthermore, in vitro cellular investigations showed that NanoGS-Rh₂ exhibited outstanding anticancer activity against MCF-7 cancer cells. Therefore, this study is expected to provide a promising strategy that could optimize and broaden the applications of ginsenosides, as well as other water-insoluble drugs in pharmaceutical formulations.

Design and characterization of loratadine nanosuspension prepared by ultrasonic-assisted precipitation

Nanoparticle engineering is a well-defined technique employed as a novel and effective method in drug design and delivery. It is widely used to control particle size, as well as the morphological and physicochemical properties of active pharmaceutical ingredients. Furthermore, it serves as a method of pre-dispersion preparation for various dosage form developments. Nanotechnology produces nanomaterials with enhanced properties in terms of solubility, dissolution and permeability. In this work, ultrasonic-assisted precipitation was employed to produce nanosuspensions of poorly water-soluble loratadine, using different stabilizers. The objective of our study was attempting to prepare solid nanoparticles of loratadine to be used as a possible intermediate for designing various dosage forms. The effects of the type(s) and concentration(s) of stabilizer(s) on mean particle size were assessed. Optimal process parameters required to produce homogeneous nanoparticles with particle size below 500 nm and polydispersity less than 0.3 were determined both for precipitation and ultrasonication. Pre-dispersions were evaluated for their particle size, polydispersity index and zeta potential. Freeze-drying was employed to produce dry nanoparticles. Particle size, particle size distribution and zeta potential of the dried nanoparticles were measured after reconstitution in water. Besides thermal analysis using DSC and structural analyses (XRPD and FT-IR), the morphological characteristics and dissolution behaviors were also investigated. The selected freeze-dried nanoparticles had a mean particle size range of 353-441 nm, a polydispersity index ranging between 0.167 and 0.229 and a zeta potential between -25.7 and -20.7 mV. These results suggest that material and process parameters were successfully optimized. DSC and XRPD spectra confirmed interactions between the formulation's components during freeze-drying. The solid nanoparticles showed 30-42% of cumulative release after 10 min compared to less than 1% of dissolution characterizing loratadine without pre-processing. This study demonstrates that preparing dried loratadine nanoparticles suitable for designing effective drug preparations is a feasible approach.

Colloidal aggregation: from screening nuisance to formulation nuance

It is well known that small molecule colloidal aggregation is a leading cause of false positives in early drug discovery. Colloid-formers are diverse and well represented among corporate and academic screening decks, and even among approved drugs. Less appreciated is how colloid formation by drug-like compounds fits into the wider understanding of colloid physical chemistry. Here we introduce the impact that colloidal aggregation has had on early drug discovery, and then turn to the physical and thermodynamic driving forces for small molecule colloidal aggregation, including the particulate nature of the colloids, their critical aggregation concentration-governed formation, their mechanism of protein adsorption and subsequent inhibition, and their sensitivity to detergent. We describe methods that have been used extensively to both identify aggregate-formers and to study and control their physical chemistry. While colloidal aggregation is widely recognized as a problem in early drug discovery, we highlight the opportunities for exploiting this phenomenon in biological milieus and for drug formulation.

Systematical Investigation of Different Drug Nanocrystal Technologies to Produce Fast Dissolving Meloxicam Tablets

Three different methods, i.e., high-pressure homogenization, wet bead milling, and a combination approach of freeze-drying and high-pressure homogenization, were used to produce meloxicam nanosuspensions, respectively. Wet bead milling led to the nanosuspensions with smallest particle size (88 nm) after 4 h and optimal dissolution performances. Freeze-dried meloxicam powder could highly improve the size reduction efficiency compared to the unmodified drug and particle size of the freeze-dried sample could be reduced to 342 nm after only one homogenization cycle at 1000 bar. The polymorphism transition and change of the particle morphology after the lyophilization might be important reasons to affect the nanosizing processes. Interestingly, the tablets prepared by using nanosuspensions from homogenizer and combination process showed faster dissolution in the first 20 min than the bead milling nanocrystal tablets.

Controlled Suspensions Enable Rapid Determinations of Intrinsic Dissolution Rate and Apparent Solubility of Poorly Water-Soluble Compounds

Purpose

To develop a small-scale set-up to rapidly and accurately determine the intrinsic dissolution rate (IDR) and apparent solubility of poorly water-soluble compounds.

Methods

The IDR and apparent solubility (S_app) were measured in fasted state simulated intestinal fluid (FaSSIF) for six model compounds using wet-milled controlled suspensions (1.0% (w/w) PVP and 0.2% (w/w) SDS) and the μDISS Profiler. Particle size distribution was measured using a Zetasizer and the total surface area was calculated making use of the density of the compound. Powder and disc dissolution were performed and compared to the IDR of the controlled suspensions.

Results

The IDR values obtained from the controlled suspensions were in excellent agreement with IDR from disc measurements. The method used low amount of compound (μg-scale) and the experiments were completed within a few minutes. The IDR values ranged from 0.2–70.6 μg/min/cm² and the IDR/S_app ratio ranged from 0.015 to 0.23. This ratio was used to indicate particle size sensitivity on intestinal concentrations reached for poorly water-soluble compounds.

Conclusions

The established method is a new, desirable tool that provides the means for rapid and highly accurate measurements of the IDR and apparent solubility in biorelevant dissolution media. The IDR/S_app is proposed as a measure of particle size sensitivity when significant solubilization may occur.

Nanocrystal formulations of a poorly soluble drug. 2. Evaluation of nanocrystal liver uptake and distribution after intravenous administration to mice

A stabilized high drug load intravenous formulation could allow compounds with less optimal pharmacokinetic profiles to be developed. Polyethylene glycol (PEG)-ylation is a frequently used strategy for particle delivery systems to avoid the liver, thereby extending blood circulation time. The present work reports the mouse in vivo distribution after i.v. administration of a series of nanocrystals prepared with the bead milling technique and PEG-ylated with DSPE-PEG2000 and Pluronic F127, with and without polyvinylpyrrolidone K30 (PVP)/Aerosol OT (AOT) as primary stabilizers. While all formulations were cleared significantly faster than expected from nanocrystal dissolution alone, purely DSPE-PEG2000 PEG-ylated particles displayed prolonged circulation time (particles elimination half-life of 9min) compared to DSPE-PEG2000/PVP/AOT formulation (half-life of 3min). The two Pluronic F127 stabilized formulations displayed similar half-lives (9min with and without PVP/AOT, respectively). Whole tissue kinetics shows that clearance of particles could be attributed to accumulation in the liver. A separate in vivo study addressed the liver cell distribution after administration. Dissolved compound accumulated in hepatocytes only, while particles were distributed between liver sinusoidal endothelial cells and Kupffer cells. More DSPE-PEG2000/PVP/AOT stabilized particles accumulated in the liver, preferably in Kupffer cells, compared to Pluronic F127/PVP/AOT stabilized particles. The present study extends the understanding of PEG-ylation and "stealth" behaviour to also include nanocrystals.

Nanocrystal formulations of a poorly soluble drug. 1. In vitro characterization of stability, stabilizer adsorption and uptake in liver cells

In the present work, milled nanocrystals of a poorly soluble compound using different stabilizers were prepared and characterized. The aim of the study was to evaluate a fundamental set of properties of the formulations prior to i.v. injection of the particles. Two polyethylene oxide containing stabilizers; (distearoyl phosphatidylethanol amine (DSPE)) -PEG2000 and the triblock copolymer Pluronic F127, were investigated, with and without polyvinylpyrrolidone K30/Aerosol OT (PVP/AOT) present. The solubility in water was around 10nM for the compound, measured from nanocrystals, but 1000 times higher in 4% human serum albumin. The particles were physically stable during the time investigated. The zeta potential was around -30 and -10mV for DSPE-PEG2000 and Pluronic F127 stabilized particles, respectively, at the conditions selected. The dissolution rate was similar for all four formulations and similar to the theoretically predicted rate. Critical micelle concentrations were determined as 56nM and 1.4μM for DSPE-PEG2000 and Pluronic F127, respectively. The adsorption isotherms for the PEG lipid showed a maximum adsorbed amount of about 1.3mg/m², with and without PVP/AOT. Pluronic F127 showed a higher maximum amount adsorbed, at around 3.1mg/m², and marginally lower with PVP/AOT present. Calculated data showed that the layer of Pluronic F127 was thicker than the corresponding DSPE-PEG2000 layer. The total amount of particles distributed mainly to the liver, and the hepatocellular distribution in vitro (Liver sinusoidal endothelial cells and Kupffer cells), differed depending on the stabilizing mixture on the particles. Overall, DSPE-PEG2000 stabilized nanocrystals (with PVP/AOT) accumulated to a larger degree in the liver compared to particles with Pluronic F127 on the surface. A theoretical model was developed to interpret in vivo pharmacokinetic profiles, explaining the balance between dissolution and liver uptake. With the present, fundamental data of the nanocrystal formulations, the platform for forthcoming in vivo studies was settled.

Optimization of ciprofloxacin complex loaded PLGA nanoparticles for pulmonary treatment of cystic fibrosis infections: Design of experiments approach

Design of Experiments (DoE) is a powerful tool for systematic evaluation of process parameters' effect on nanoparticle (NP) quality with minimum number of experiments. DoE was employed for optimization of ciprofloxacin loaded PLGA NPs for pulmonary delivery against Pseudomonas aeruginosa infections in cystic fibrosis (CF) lungs. Since the biofilm produced by bacteria was shown to be a complicated 3D barrier with heterogeneous meshes ranging from 100nm to 500nm, nanoformulations small enough to travel through those channels were assigned as target quality. Nanoprecipitation was realized utilizing MicroJet Reactor (MJR) technology based on impinging jets principle. Effect of MJR parameters flow rate, temperature and gas pressure on particle size and PDI was investigated using Box-Behnken design. The relationship between process parameters and particle quality was demonstrated by constructed fit functions (R²=0.9934 p<0.0001 and R²=0.9983 p<0.0001, for particle size and PDI, respectively). Prepared nanoformulations varied between 145.2 and 979.8nm with PDI ranging from 0.050 to 1.00 and showed encapsulation efficiencies >65%. Response surface plots provided experimental data-based understanding of MJR parameters' effect, thus NP quality. Presented work enables ciprofloxacin loaded PLGA nanoparticle preparations with pre-defined quality to fulfill the requirements of local drug delivery under CF disease conditions.

Super-cooled and amorphous lipid-based colloidal dispersions for the delivery of phytosterols

Super-cooled and amorphous lipid-based colloids are highly desirable delivery systems because of their ability to encapsulate compounds in a soluble or in a non-crystalline state. In this study, we demonstrate the preparation and characterization of super-cooled and amorphous lipid-based nanoscale colloidal dispersions containing high concentrations of phytosterols (PSs). PSs are highly hydrophobic natural bioactive compounds that are known to significantly reduce blood cholesterol levels in humans, but are insoluble in water and are poorly soluble in common lipids such as triacylglycerols (TAGs). Using the ultrahigh pressure homogenization of pre-heated dispersions, followed by temperature quenching, colloidal dispersions with varying concentrations of PSs in the lipid phase are prepared. Long and medium chain TAGs in combination with a non-ionic surfactant are used. The particle size, morphology and stability are analysed by dynamic and static light scattering, electron microscopy, and X-ray diffraction. Rapid temperature quenching enables the formation of stable colloidal dispersions of 10 wt% PSs, more than five times the equilibrium solubility at room temperature. Super-cooled emulsions are formed using liquid TAG, whereas amorphous particles are formed in the case of solid TAG. In both cases, the complete suppression of the crystallization of both PSs and lipids is observed due to the nanoscale confinement. The colloidal dispersions are stable for at least four months. The insights of this work will help understand the colloid formation and particle morphology control in the development of delivery systems for hydrophobic bio-actives such as drugs, cosmeceuticals, nutraceuticals, nutritional and agricultural nanoscale formulations.

Macromolecular Brushes as Stabilizers of Hydrophobic Solute Nanoparticles

Macromolecular brushes bearing poly(ethylene glycol) and poly(d,l-lactide) side chains were used to stabilize hydrophobic solute nanoparticles formed by a rapid change in solvent quality. Unlike linear diblock copolymers with the same hydrophilic and hydrophobic block chemistries, the brush copolymer enabled the formation of ellipsoidal β-carotene nanoparticles, which in cosolvent mixtures developed into rod-like structures, resulting from a combination of Ostwald ripening and particle aggregation. The stabilizing ability of the copolymer was highly dependent on the mobility of the hydrophobic component, influenced by its molecular weight. As shown here, asymmetric amphiphilic macromolecular brushes of this type may be used as hydrophobic drug stabilizers and potentially assist the shape control of nonspherical aggregate morphologies.

Recent advances in the engineering of nanosized active pharmaceutical ingredients: Promises and challenges

The advances in the field of nanotechnology have revolutionized the field of delivery of poorly soluble active pharmaceutical ingredients (APIs). Nanosized formulations have been extensively investigated to achieve a rapid dissolution and therefore pharmacokinetic properties similar to those observed in solutions. The present review outlines the recent advances, promises and challenges of the engineering nanosized APIs. The principles, merits, demerits and applications of the current 'bottom-up' and 'top-down' technologies by which the state of the art nanosized APIs can be produced were described. Although the number of research reports on the nanoparticle engineering topic has been growing in the last decade, the challenge is to take numerous research outcomes and convert them into strategies for the development of marketable products.

Size Control in the Nanoprecipitation Process of Stable Iodine (¹²⁷I) Using Microchannel Reactor-Optimization by Artificial Neural Networks

In this study, nanosuspension of stable iodine ((127)I) was prepared by nanoprecipitation process in microfluidic devices. Then, size of particles was optimized using artificial neural networks (ANNs) modeling. The size of prepared particles was evaluated by dynamic light scattering. The response surfaces obtained from ANNs model illustrated the determining effect of input variables (solvent and antisolvent flow rate, surfactant concentration, and solvent temperature) on the output variable (nanoparticle size). Comparing the 3D graphs revealed that solvent and antisolvent flow rate had reverse relation with size of nanoparticles. Also, those graphs indicated that the solvent temperature at low values had an indirect relation with size of stable iodine ((127)I) nanoparticles, while at the high values, a direct relation was observed. In addition, it was found that the effect of surfactant concentration on particle size in the nanosuspension of stable iodine ((127)I) was depended on the solvent temperature. Nanoprecipitation process of stable iodine (127I) and optimization of particle size using ANNs modeling.

Analysis of Diffusion-Controlled Dissolution from Polydisperse Collections of Drug Particles with an Assessed Mathematical Model

We introduce a "hierarchical" modeling strategy designed to be systematically extensible to increase the detail of dissolution predictions from polydisperse collections of drug particles and to be placed on firm mathematical and physical foundations with diffusion-dominated dissolution at its core to predict dissolution and the evolution of particle size distribution. We assess the model with experimental data and demonstrate higher accuracy by treating the polydisperse nature of dissolution. A level in the hierarchy is applied to study elements of diffusion-driven dissolution, in particular the role of particle-size distribution width with varying dose level and the influences of "confinement" on the process of dissolution. Confinement influences surface molecular flux, directly by the increase in bulk concentration and indirectly by the relative volume of particles to container. We find that the dissolution process can be broadly categorized within three "regimes" defined by the ratio of total concentration Ctot to solubility CS . Sink conditions apply in the first regime, when C tot /CS<∼0.1. When C tot /CS>∼5 (regime 3) dissolution is dominated by confinement and normalized saturation time follows a simple power law relationship. Regime 2 is characterized by a "saturation singularity" where dissolution is sensitive to both initial particle size distribution and confinement.

Hydrodynamic Effects on Drug Dissolution and Deaggregation in the Small Intestine-A Study with Felodipine as a Model Drug

The aim of this study was to understand and predict the influence of hydrodynamic effects in the small intestine on dissolution of primary and aggregated drug particles. Dissolution tests of suspensions with a low-solubility drug, felodipine, were performed in a Couette cell under hydrodynamic test conditions corresponding to the fed small intestine. Dissolution was also performed in the USP II apparatus at two paddle speeds of 25 and 200 rpm and at different surfactant concentrations below critical micelle concentration. The experimental dissolution rates were compared with theoretical calculations. The different levels of shear stress in the in vitro tests did not influence the dissolution of primary or aggregated particles and experimental dissolution rates corresponded very well to calculations. The dissolution rate for the aggregated drug particles increased after addition of surfactant because of deaggregation, but there were still no effect of hydrodynamics. In conclusion, hydrodynamics do not influence dissolution and deaggregation of micronized drug particles in the small intestine of this model drug. Surface tension has a strong effect on the deaggregation and subsequent dissolution. Addition of surfactants at in vivo relevant surface tension levels is thus critical for in vivo predictive in vitro dissolution testing.

Nanonization of curcumin by antisolvent precipitation: process development, characterization, freeze drying and stability performance

The present work aims to investigate applicability of antisolvent precipitation method for preparation of nanosized curcumin and to control their characteristics by determining the influence of process and solvents on solid-state properties of curcumin nanoparticles. Effects of different experimental parameters on particle size were investigated using dynamic light scattering. Particle morphology was studied using SEM. Drug content in stabilized nanoparticles was determined using HPLC. Residual moisture content after lyophilisation was determined using Karl Fischer method and solid state properties were investigated using DSC, TGA, FTIR and powder-XRD. The resulting product showed a high drug load and contained the drug in amorphous form. The particle diameters of prepared curcumin nanoparticles were found in the range of 100-200 nm. In vitro drug release studies indicated a sustained release profile of curcumin from the nanoparticles. Antisolvent precipitation produced amorphous curcumin nanoparticles whose size and morphology could be controlled using gelatine as stabilizer. Lyophilized curcumin nanoparticles with d-sorbitol as lyoprotectant possessed good redispersibility and showed up to 4 times faster in vitro curcumin release rate than that of unprocessed curcumin. Stability tests (at 2-8°C and ambient conditions) indicated that the product was stable for up to 6 months of storage.