Ionic liquid form of donepezil: Preparation, characterization and formulation development

Ionic liquids as the effective technology for enhancing transdermal drug delivery: Design principles, roles, mechanisms, and future challenges

Ionic liquids (ILs) have been proven to be an effective technology for enhancing drug transdermal absorption. However, due to the unique structural components of ILs, the design of efficient ILs and elucidation of action mechanisms remain to be explored. In this review, basic design principles of ideal ILs for transdermal drug delivery system (TDDS) are discussed considering melting point, skin permeability, and toxicity, which depend on the molar ratios, types, functional groups of ions and inter-ionic interactions. Secondly, the contributions of ILs to the development of TDDS through different roles are described: as novel skin penetration enhancers for enhancing transdermal absorption of drugs; as novel solvents for improving the solubility of drugs in carriers; as novel active pharmaceutical ingredients (API-ILs) for regulating skin permeability, solubility, release, and pharmacokinetic behaviors of drugs; and as novel polymers for the development of smart medical materials. Moreover, diverse action mechanisms, mainly including the interactions among ILs, drugs, polymers, and skin components, are summarized. Finally, future challenges related to ILs are discussed, including underlying quantitative structure-activity relationships, complex interaction forces between anions, drugs, polymers and skin microenvironment, long-term stability, and in vivo safety issues. In summary, this article will promote the development of TDDS based on ILs.

Ionic Liquids: New Forms of Active Pharmaceutical Ingredients with Unique, Tunable Properties

This Review aims to summarize advances over the last 15 years in the development of active pharmaceutical ingredient ionic liquids (API-ILs), which make up a prospective game-changing strategy to overcome multiple problems with conventional solid-state drugs, for example, polymorphism. A critical part of the present Review is the collection of API-ILs and deep eutectic solvents (DESs) prepared to date. The Review covers rules for rational design of API-ILs and tools for API-IL formation, syntheses, and characterization. Nomenclature and ionic speciation, and the confusion that these may cause, are highlighted, particularly for speciation in both ILs and DESs of intermediate ionicity. We also highlight in vivo and in vitro pharmaceutical activity studies, with differences in pharmacokinetic/pharmacodynamic depending on ionicity of API-ILs. A brief overview is provided for the ILs used to deliver drugs, and the Review concludes with key prospects and roadblocks in translating API-ILs into pharmaceutical manufacturing.

Pharmaceutical Applications of Ionic Liquids: A Personal Account

Ionic liquids (ILs) have been extensively used in drug formulation and delivery as designer solvents and other components because of their inherent tunability and useful physicochemical and biopharmaceutical properties. ILs can be used to manage some of the operational and functional challenges of drug delivery, including drug solubility, permeability, formulation instability, and in vivo systemic toxicity, that are associated with conventional organic solvents/agents. Furthermore, ILs have been recognized as potential solvents to address the polymorphism, limited solubility, poor permeability, instability, and low bioavailability of crystalline drugs. In this account, we discuss the technological progress and strategies toward designing biocompatible ILs and explore potential biomedical applications, namely the solubilization of small and macromolecular drugs, the creation of active pharmaceutical ingredients, and the delivery of pharmaceuticals.

Improved Topical Drug Delivery: Role of Permeation Enhancers and Advanced Approaches

The delivery of drugs via transdermal routes is an attractive approach due to ease of administration, bypassing of the first-pass metabolism, and the large skin surface area. However, a major drawback is an inability to surmount the skin's stratum corneum (SC) layer. Therefore, techniques reversibly modifying the stratum corneum have been a classical approach. Surmounting the significant barrier properties of the skin in a well-organised, momentary, and harmless approach is still challenging. Chemical permeation enhancers (CPEs) with higher activity are associated with certain side effects restricting their advancement in transdermal drug delivery. Furthermore, complexity in the interaction of CPEs with the skin has led to difficulty in elucidating the mechanism of action. Nevertheless, CPEs-aided transdermal drug delivery will accomplish its full potential due to advancements in analytical techniques, synthetic chemistry, and combinatorial studies. This review focused on techniques such as drug-vehicle interaction, vesicles and their analogues, and novel CPEs such as lipid synthesis inhibitors (LSIs), cell-penetrating peptides (CPPs), and ionic liquids (ILs). In addition, different types of microneedles, including 3D-printed microneedles, have been focused on in this review.

Mechanistic Study of Release Characteristics of Two Active Ingredients in Transdermal Patch Containing Lidocaine-Flurbiprofen Ionic Liquid

Ionic liquids (ILs) have been proven to be an efficient technology for enhancing drug skin permeability. However, the question of whether the two components of ILs are released synchronously in transdermal preparations has remained unclear. Thus, this study aimed to investigate the release characteristics of two components of ILs and their underlying molecular mechanism. The ILs containing flurbiprofen (FLU) and lidocaine (LID) were synthesized and characterized. The four typical acrylates pressure sensitive adhesives (PSAs) with different functional groups were synthesized and characterized. The effects of PSAs on the release characteristics of two components of ILs were investigated by drug release tests and verified by skin permeation experiments. The action mechanisms were revealed by FTIR, Raman, dielectric spectrum, and molecular docking. The results showed that the average release amount of FLU (0.29 μmol/cm2) and LID (0.11 μmol/cm2) of ILs in the four PSAs was significantly different (p < 0.05), which illustrated that the two components did not release synchronously. The PSA−none and PSA−OH with low permittivity (7.37, 9.82) interacted with drugs mainly by dipole-dipole interactions and hydrogen bonds. The PSA−COOH and PSA−CONH2 with high permittivity (11.19, 15.32) interacted with drugs mainly by ionic bonds and ionic hydrogen bonds. Thus, this study provides scientific guidance for the application of ILs in transdermal preparations.

Transdermal Delivery of Metformin Utilizing Ionic Liquid Technology: Insight Into the Relationship Between Counterion Structures and Properties

PURPOSE

The purpose of the present study was to explore the feasibility of transdermal delivery of metformin, a commonly used oral antidiabetic drug, by ionic liquid (IL) technology.

METHODS

Metformin hydrochloride (MetHCl) was first transformed into three kinds of ILs with different counterions. The physicochemical properties of the obtained ILs were characterized in depth. The simulation of stable configuration and calculation of interaction energies were conducted based on density functional theory (DFT). Skin-PAMPA was used to evaluate the intrinsic transdermal permeation properties. The cytotoxicity assay of these ILs was conducted using HaCaT cells to evaluate the toxicity to skin. These metformin ILs were then formulated into transdermal patch, and the transdermal potential was further evaluated using in vitro dissolution test and skin permeation assay. Finally, the pharmacokinetic profiles of these metformin IL-containing patches were determined.

RESULTS

Among all the three Met ILs, metformin dihexyl sulfosuccinate (MetDH) with proper overall physiochemical and biological properties demonstrated the highest relative bioavailability. Metformin docusate (MetD) with the highest lipophilicity and intrinsic transdermal permeability exhibited the most significant sustained release profile in vivo. Both MetDH and MetD were the promising candidates for further clinical investigations.

CONCLUSIONS

Overall, the properties of ILs were closely related to the structures of counterion. IL technology provided the opportunities to finely tune the solid-state and biological properties of Metformin and facilitated the successful delivery by transdermal route.

Recent Developments in Ionic Liquid-Assisted Topical and Transdermal Drug Delivery

Ionic liquids (ILs) have attracted growing interest as designer solvents/materials for exploring unrealized functions in many areas of research including drug formulations and delivery owing to their inherent tunable physicochemical and biological properties. The use of ILs in the pharmaceutical industry can address challenges related to the use of conventional organic solvent-based chemical permeation enhancers. Their tunability in forming ion pairs with a diverse range of ions enables the task-specific optimization of ILs at the molecular level. In particular, ILs comprising second- and third-generation cations and anions have been extensively used to design biocompatible drug delivery systems to address the challenges related to conventional topical and transdermal drug delivery, including limited permeability, high cytotoxicity, and skin irritation. This review highlights the progress in IL-related research with particular emphasis on the very recent conceptual developments in transdermal drug delivery. Technological advancement and approaches for the formation of IL-based topical and transdermal delivery systems, as well as their promising application in drug delivery, are also discussed.

Comparative toxicity of [C8mim]Br and [C8py]Br in early developmental stages of zebrafish (Danio rerio) with focus on oxidative stress, apoptosis, and neurotoxicity

The increasing production and usage of ionic liquids (ILs) have raised global ecotoxicological concerns regarding their release into the environment. While the effects of side chains on the IL-induced toxicity in various aquatic organisms have been well-recognized, the role of cationic cores in determining their ecotoxicity remains to be elucidated. Herein, the comparative bioavailability and toxicity of two ILs with different cationic cores but the same anion and side chain in zebrafish embryos were determined. 1-octyl-3-methylimidazolium bromide ([C8mim]Br) has higher accumulation in zebrafish, and triggered developmental toxicity by inducing oxidative stress and apoptosis. Meanwhile, 1-octyl-1-methylpyridium bromide ([C8py]Br) enhanced SOD activity and upregulated anti-apoptotic bcl-2 gene expression, contributing to its much lower neurodevelopmental toxicity. Our study demonstrates the vital role of cationic core in determining the developmental toxicity of ILs and highlights the need for further investigations into the toxicity of imidazolium and pyridinium based ILs in aquatic ecosystems.

Formulation, Preparation, Characterization, and Evaluation of Dicarboxylic Ionic Liquid Donepezil Transdermal Patches

Donepezil (DPZ) is generally administered orally to treat Alzheimer’s disease (AD). However, oral administration can cause gastrointestinal side effects. Therefore, to enhance compliance, a new way to deliver DPZ from transdermal patch was developed. Ionic bonds were created by dissolving dicarboxylic acid and DPZ in ethanol, resulting in a stable ionic liquid (IL) state. The synthesized ILs were characterized by differential scanning calorimetry, optical microscope, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The DPZ ILs were then transformed to a suitable drug-in-adhesive patch for transdermal delivery of DPZ. The novel DPZ ILs patch inhibits crystallization of the IL, indicating coherent design. Moreover, DPZ ILs and DPZ IL patch formulations performed excellent skin permeability compared to that of the DPZ free-base patch in both in vitro and ex vivo skin permeability studies.

Salicylic Acid as Ionic Liquid Formulation May Have Enhanced Potency to Treat Some Chronic Skin Diseases

In recent years, numerous studies have shown that conversion of conventional drugs in ionic liquid (IL) formulation could be a successful strategy to improve their physicochemical properties or suggest a new route of administration. We report the synthesis and detailed characterization of eight salicylic acid-based ILs (SA-ILs) containing cation non-polar or aromatic amino acid esters. Using in vitro assays, we preliminary evaluated the therapeutic potency of the novel SA-ILs. We observed that conversion of the SA into ionic liquids led to a decrease in its cytotoxicity toward NIH/3T3 murine embryo fibroblasts and human HaCaT keratinocytes. It should be mentioned is that all amino acid alkyl ester salicylates [AAOR][SA] inhibit the production of the proinflammatory cytokine IL-6 in LPS-stimulated keratinocytes. Moreover, keratinocytes, pretreated with [PheOMe][SA] and [PheOPr][SA] seem to be protected from LPS-induced inflammation. Finally, the novel compounds exhibit a similar binding affinity to bovine serum albumin (BSA) as the parent SA, suggesting a similar pharmacokinetic profile. These preliminary results indicate that SA-ILs, especially those with [PheOMe], [PheOPr], and [ValOiPr] cation, have the potential to be further investigated as novel topical agents for chronic skin diseases such as psoriasis and acne vulgaris.

The Emerging Role of Ionic Liquid-Based Approaches for Enhanced Skin Permeation of Bioactive Molecules: A Snapshot of the Past Couple of Years

Topical and transdermal delivery systems are of undeniable significance and ubiquity in healthcare, to facilitate the delivery of active pharmaceutical ingredients, respectively, onto or across the skin to enter systemic circulation. From ancient ointments and potions to modern micro/nanotechnological devices, a variety of approaches has been explored over the ages to improve the skin permeation of diverse medicines and cosmetics. Amongst the latest investigational dermal permeation enhancers, ionic liquids have been gaining momentum, and recent years have been prolific in this regard. As such, this review offers an outline of current methods for enhancing percutaneous permeation, highlighting selected reports where ionic liquid-based approaches have been investigated for this purpose. Future perspectives on use of ionic liquids for topical delivery of bioactive peptides are also presented.

Development of gliclazide ionic liquid and the transdermal patches: An effective and noninvasive sustained release formulation to achieve hypoglycemic effects

Ionic liquids (IL) technology provides a useful platform to achieve the topical delivery of therapeutic agents, because of its capability to improve skin permeability. While the majority of the researches aimed to achieve local action by topical IL delivery, systemic action of therapeutic agents by local topical application has rarely been reported. In the present work, Gliclazide (GLI), a second-generation sulfonylurea drug was transformed into an IL with tributyl(tetradecyl)phosphonium for the first time. The physicochemical properties of this IL were systematically characterized by DSC, TGA, FT-IR, NMR, and HPLC. The transdermal patch based on this IL was further prepared using DURO-TAK®87-4098. The fabricated gliclazide based ionic liquid [P_6,6,6,14][GLI] transdermal patch displayed satisfactory in vitro and in vivo performance. The [P_6,6,6,14][GLI] patch released 88.17% of the loaded drug within a 3-day period in the in vitro dissolution test, confirming its sustained release property. Meanwhile, GLI effectively permeated through the artificial skin from [P_6,6,6,14][GLI] transdermal patch in the in vitro skin permeation test, with the permeation rate and lag time of 16.571 ± 0.328 μg/cm²/h and 3.027 ± 0.154 h respectively. The [P_6,6,6,14][GLI] transdermal patch showed favorable PK profile in rat as compared with GLI oral suspension. The relative bioavailability of GLI reached 92.06% of GLI oral suspension, while the C_max was significantly reduced. Most importantly, [P_6,6,6,14][GLI] transdermal patch demonstrated superior hypoglycemic effect to the oral suspension both in the fasted and fed condition, confirming the feasibility of systemic action by local topical delivery of IL. In addition, the [P_6,6,6,14][GLI] transdermal patch caused no skin irritation based on histopathological analysis.