In situ molecular elucidation of drug supersaturation achieved by nano-sizing and amorphization of poorly water-soluble drug

Hydroxypropyl-β-cyclodextrin Enhances Oral Absorption of Silymarin Nanoparticles Prepared Using PureNano™ Continuous Crystallizer

The oral bioavailability of drugs is limited by factors such as poor membrane permeability, low solubility, and low dissolution rate. Silymarin (SLM) is a health-food active ingredient that is good for immunosuppression and tumor suppression. However, obtaining a good oral bioavailability is difficult owing to its poor solubility and low dissolution ability. To overcome these concerns, we previously prepared SLM nanoparticles (NPs) using the high-pressure crystallization method (PureNano^TM) and freeze-dried them with erythritol (Ery) or hydroxypropyl-β-CyD (HP-β-CyD) as a water-soluble dispersion stabilizer. In the present study, we investigated the mechanism underlying the improved absorption of SLM/hypromellose (HPMC)/HP-β-CyD NPs after oral administration. The SLM/HPMC nano-suspension prepared using PureNano^TM exhibited a narrow size distribution. The size of the SLM/HPMC/HP-β-CyD NPs was approximately 250 nm after hydration. The SLM/HPMC/HP-β-CyD NPs were rapidly dissolved, and demonstrated a high solubility under supersaturated conditions. Additionally, they exhibited good wettability and their membrane permeability was improved compared with that of SLM original powder. These results suggest that the formulation of SLM NPs using PureNano^TM and freeze-drying with HP-β-CyD improves the absorption of SLM after oral administration by enhancing solubility, wettability, and membrane permeability.

Nanocrystals for Improving Oral Bioavailability of Drugs: Intestinal Transport Mechanisms and Influencing Factors

With the limitation of solubility and dissolution rate of insoluble drugs, following oral administration, they would rifely prove poor and volatile bioavailability, which may fail to realize its therapeutic value. The drug nanocrystals are perceived as effective tactic for oral administration of insoluble drugs attributes to possess many prominent properties such as elevating dissolution rate and saturation solubility, high drug loading capacity, and improving oral bioavailability. Based on these advantages, the application of nanocrystals in oral drug delivery has acquired significant achievement, and so far more than 20 products of drug nanocrystals have been confirmed in the market. However, the oral absorption of drug nanocrystals is still facing huge challenges due to the limitation of many factors. Intrinsic properties of the drugs and complex physiological environment of the intestinal tract are the two most important factors affecting the oral bioavailability of drugs. In addition, the research on the multi-aspect mechanisms of nanocrystals promoting gastrointestinal absorption and bioavailability has been gradually deepened. In this review, we summarized recent advances of the nanocrystals delivered orally, and provided an overview to the research progress for crossing the intestinal tract transport mechanisms of the nanocrystals by some new research techniques. Meanwhile, the factors relevant to the transport of drug nanocrystals were also elaborated in detail. Graphical Abstract.

Preparation and Evaluation of Rebamipide Colloidal Nanoparticles Obtained by Cogrinding in Ternary Ground Mixtures

Aphthous stomatitis is one of the side effects of chemotherapy and radiotherapy in cancer treatment. Rebamipide (RB) mouthwash for stomatitis acts as a radical scavenger. However, RB is poorly soluble in water, which leads to aggregation and precipitation of the dispersoid. The particle size of the drug needs to be less than 100 nm for the particles to reach the mucus layer in the oral cavity. In this study, we attempted to prepare nanoparticles of RB by cogrinding with polyvinylpyrrolidone (PVP) or hydroxypropyl cellulose (HPC) and sodium dodecyl sulfate (SDS) using a mixer ball mill, and evaluated the physicochemical properties of RB nanoparticles, the stability of dispersion in water, and permeation of the mucus layer in vitro. By cogrinding, the particle size decreased to around 110 nm, and powder X-ray diffraction (PXRD) of the particles showed totally broad halo patterns, which suggested a decreased crystalline region. Furthermore, the solubility of RB nanoparticles increased by approximately fourfold compared with RB crystals, and the water dispersibility and permeation of the mucus layer were improved. The results suggest that in a ternary ground mixture of RB, PVP or HPC, and SDS, the RB nanoparticles obtained can be applied as a formulation for stomatitis.

Oral formulation strategies to improve the bioavailability and mitigate the food effect of abiraterone acetate

Abiraterone acetate, marketed as Zytiga®, is an antiandrogen medication used in the treatment of prostate cancer. Abiraterone acetate is a BCS Class IV compound associated with several oral delivery challenges. Its low solubility and high lipophilicity lead to poor oral bioavailability (<10%) and a dramatic positive food effect (5-10-fold). Hence, a large dose of abiraterone acetate (1000 mg per day) is prescribed to patients who must fast for at least 1 h before and 2 h after administration. The recent expiry of Zytiga®s' patent has led to the emergence of publications describing improved oral formulation strategies for abiraterone acetate. This review aims to discuss the characteristics of abiraterone acetate that lead to its unfavorable oral delivery, examine the oral formulation strategies that have been applied, and to describe potential alternative oral formulation strategies that have been used for other BCS Class IV drugs, to determine the most valuable strategies to develop novel and improved alternatives to the current commercial product. Specific emphasis of this review is placed on enabling oral formulation strategies that can improve solubilization and bioavailability, reduce the clinical dose and remove the pharmaceutical food effect to ultimately provide prostate cancer patients with a more efficient formulation with greater patient compliance.

Polymeric precipitation inhibitor as an effective trigger to convert supersaturated into supersaturable state in vivo

The supersaturated state of the drug in vivo is thermodynamically unstable resulting in a delayed response and reduced efficacy. The use of polymeric precipitation inhibitor (PPI) has been demonstrated as an effective trigger for the conversion of supersaturated state to supersaturable state for improving solubilization, thermodynamic maintenance of drug concentration and oral absorption of poorly water-soluble compounds. PPI retards drug precipitation and provides a kinetically stabilized supersaturation state for an extended period in gastric and intestinal fluids. However, the selection of appropriate PPI and understanding its mechanism is a challenge for formulating a stable pharmaceutical formulation. The present review is aimed at understanding the intricacies of selecting PPIs and their applications in pharmaceutical formulations.

Investigating Permeation Behavior of Flufenamic Acid Cocrystals Using a Dissolution and Permeation System

The dissolution and permeation of the cocrystals, flufenamic acid-nicotinamide (FFA-NIC) and flufenamic acid-theophylline (FFA-TP), have been investigated in the presence of two polymers, polyvinylpyrrolidone (PVP) and copolymer of vinylpyrrolidone/vinyl acetate (PVP-VA), using a dissolution/permeation (D/P) system. It showed that the types and concentrations of the polymers and their interactions with the coformers had significant effects on the dissolution and permeation of the FFA cocrystals. The role of PVP as a stabilizing agent was not altered in spite of its interaction with the coformer of NIC or TP, which was supported by the proportional flux rate of FFA to the dissolution performance parameter (DPP). With an appropriate PVP concentration, the maximal flux rate of FFA could be obtained for a given FFA cocrystal. The situation was complicated in the presence of PVP-VA. The role of PVP-VA could change because of its association with the coformers, i.e., from a stabilizing agent to a solubilization agent. In addition, PVP-VA reduced the flux rate of FFA, in contrast to its DPP for FFA cocrystals. Finally, ¹H NMR provided evidence regarding the molecular interactions between FFA, coformers, and polymers at the atomic level and gave insight into the mechanism underlying the supersaturated solution and subsequent permeation behavior of the cocrystals.

Practical guidelines for the characterization and quality control of pure drug nanoparticles and nano-cocrystals in the pharmaceutical industry

The number of poorly soluble drug candidates is increasing, and this is also seen in the research interest towards drug nanoparticles and (nano-)cocrystals; improved solubility is the most important application of these nanosystems. In order to confirm the functionality of these nanoparticles throughout their lifecycle, repeatability of the formulation processes, functional performance of the formed systems in pre-determined way and system stability, a thorough physicochemical understanding with the aid of necessary analytical techniques is needed. Even very minor deviations in for example particle size or size deviation in nanoscale can alter the product bioavailability, and the effect is even more dramatic with the smallest particle size fractions. Also, small particle size sets special requirements for the analytical techniques. In this review most important physicochemical properties of drug nanocrystals and nano-cocrystals are presented, suitable analytical techniques, their pros and cons, are described with the extra input on practical point of view.

Drug nanocrystals - Versatile option for formulation of poorly soluble materials

Poor solubility of drug compounds is a great issue in drug industry today and decreasing particle size is one efficient and simple way to overcome this challenge. Drug nanocrystals are solid nanosized drug particles, which are covered by a stabilizer layer. In nanoscale many physical properties, like compound solubility, are different from the solubility of bulk material, and due to this drug nanocrystals can reach supersaturation as compared to thermodynamic solubility. The most important effect of the smaller particle size is that dissolution rate is highly enhanced mainly due to the increased surface area. In this review the most important properties of nanocrystalline drug compounds are presented, with multiple examples of the development and characterization of nanocrystalline drug formulations.

Recent strategies in spray drying for the enhanced bioavailability of poorly water-soluble drugs

Poorly water-soluble drugs are a significant and ongoing issue for the pharmaceutical industry. An overview of recent developments for the preparation of spray-dried delivery systems is presented. Examples include amorphous solid dispersions, spray dried dispersions, microparticles, nanoparticles, surfactant systems and self-emulsifying drug delivery systems. Several aspects of formulation are considered, such as pre-screening, choosing excipient(s), the effect of polymer structure on performance, formulation optimisation, ternary dispersions, fixed-dose combinations, solvent selection and component miscibility. Process optimisation techniques including nozzle selection are discussed. Comparisons are drawn with other preparation techniques such as hot melt extrusion, freeze drying, milling, electro spinning and film casting. Novel analytical and dissolution techniques for the characterization of amorphous solid dispersions are included. Progress in understanding of amorphous supersaturation or recrystallisation from solution gathered from mechanistic studies is discussed. Aspects of powder flow and compression are considered in a section on downstream processing. Overall, spray drying has a bright future due to its versatility, efficiency and the driving force of poorly soluble drugs.

Preliminary study of nanonized lamotrigine containing products for nasal powder formulation

The nasal delivery of drugs offers a great alternative route to avoid adverse events and to increase patient compliance due to its advantageous properties. Besides nasal application, topical, systemic and central effects are also available. Nasal powders (NPs) have better adhesion due to the additive polymers that may be, eg, gelling or good wettability agents; thus, their bioavailability is better compared to the liquid formulations. Using nanoparticles, innovative and more efficient products can be achieved, which may lead to the improvement of different therapies. The aim of this study was to produce NP formulations containing lamotrigine (LAM) as interactive physical mixtures and nanosized LAM-based formulations. After risk assessment of the preliminary tests, the micrometric properties (particle size and morphology) and the structural properties (differential scanning calorimetry [DSC], X-ray powder diffraction [XRPD]) were investigated; thereafter, physicochemical properties (solubility, polarity) and in vitro dissolution and diffusion profiles were also examined. These product samples showed an appropriate particle size ranging 10–25 µm, while the particle size of LAM in the products was between 120 and 230 nm and the dissolved amount of drug was >60% after 5 minutes in these cases.

Direct NMR Monitoring of Phase Separation Behavior of Highly Supersaturated Nifedipine Solution Stabilized with Hypromellose Derivatives

We investigated the phase separation behavior and maintenance mechanism of the supersaturated state of poorly water-soluble nifedipine (NIF) in hypromellose (HPMC) derivative solutions. Highly supersaturated NIF formed NIF-rich nanodroplets through phase separation from aqueous solution containing HPMC derivative. Dissolvable NIF concentration in the bulk water phase was limited by the phase separation of NIF from the aqueous solution. HPMC derivatives stabilized the NIF-rich nanodroplets and maintained the NIF supersaturation with phase-separated NIF for several hours. The size of the NIF-rich phase was different depending on the HPMC derivatives dissolved in aqueous solution, although the droplet size had no correlation with the time for which NIF supersaturation was maintained without NIF crystallization. HPMC acetate and HPMC acetate succinate (HPMC-AS) effectively maintained the NIF supersaturation containing phase-separated NIF compared with HPMC. Furthermore, HPMC-AS stabilized NIF supersaturation more effectively in acidic conditions. Solution ¹H NMR measurements of NIF-supersaturated solution revealed that HPMC derivatives distributed into the NIF-rich phase during the phase separation of NIF from the aqueous solution. The hydrophobicity of HPMC derivative strongly affected its distribution into the NIF-rich phase. Moreover, the distribution of HPMC-AS into the NIF-rich phase was promoted at lower pH due to the lower aqueous solubility of HPMC-AS. The distribution of a large amount of HPMC derivatives into NIF-rich phase induced the strong inhibition of NIF crystallization from the NIF-rich phase. Polymer distribution into the drug-rich phase directly monitored by solution NMR technique can be a useful index for the stabilization efficiency of drug-supersaturated solution containing a drug-rich phase.

The in vivo fate of nanocrystals

There has been significant research interest in, and development of, nanocrystals in recent years for the delivery of poorly water-soluble drugs via various routes. However, there is a common misinterpretation of nanocrystallization as an approach to modulate, and more specifically to enhance, the dissolution of drug crystals. Nevertheless, it is possible for nanocrystals to interact with biological tissues because nanocrystals can survive for a longer duration in vivo compared with solution counterparts. Therefore, understanding the in vivo fate of nanocrystals and determining its contribution to efficacy is of tremendous significance for optimizing the performance of nanocrystals. Here, we critically review the general hypotheses related to the in vivo fate of nanocrystals.

Performance Parameters and Characterizations of Nanocrystals: A Brief Review

Poor bioavailability of drugs associated with their poor solubility limits the clinical effectiveness of almost 40% of the newly discovered drug moieties. Low solubility, coupled with a high log p value, high melting point and high dose necessitates exploration of alternative formulation strategies for such drugs. One such novel approach is formulation of the drugs as “Nanocrystals”. Nanocrystals are primarily comprised of drug and surfactants/stabilizers and are manufactured by “top-down” or “bottom-up” methods. Nanocrystals aid the clinical efficacy of drugs by various means such as enhancement of bioavailability, lowering of dose requirement, and facilitating sustained release of the drug. This effect is dependent on the various characteristics of nanocrystals (particle size, saturation solubility, dissolution velocity), which have an impact on the improved performance of the nanocrystals. Various sophisticated techniques have been developed to evaluate these characteristics. This article describes in detail the various characterization techniques along with a brief review of the significance of the various parameters on the performance of nanocrystals.

Understanding Critical Quality Attributes for Nanocrystals from Preparation to Delivery

Poor solubility of active pharmaceutical ingredients (APIs) is a great challenge for the pharmaceutical industry and, hence, drug nanocrystals are widely studied as one solution to overcome these solubility problems. Drug nanocrystals have comparatively simple structures which make them attractive for the formulation for poorly soluble drugs, and their capability to improve the dissolution in vitro is easily demonstrated, but turning the in vitro superior properties of nanocrystals to success in vivo, is often demanding: controlled (including enhanced) drug dissolution followed by successful permeation is not guaranteed, if for example, the dissolved drug precipitates before it is absorbed. In this review critical quality attributes related to nanocrystal formulations from production to final product performance in vivo are considered. Many important parameters exist, but here physical stability (aggregation tendency and solid state form), solubility properties influencing dissolution and supersaturation, excipient use to promote the maintenance of supersaturation, and finally the fate of nanocrystals in vivo are the main subjects of our focus.