Mechanistic study into the enhanced transdermal permeation of a model beta-blocker, propranolol, by fatty acids: a melting point depression effect

Towards a greater understanding of the deep eutectic phenomenon through examination of the lidocaine-NSAID therapeutic deep eutectic systems

Therapeutic deep eutectic solvents (THEDES) have been attracting increasing attention in the pharmaceutical literature as a promising enabling technology capable of improving physicochemical and biopharmaceutical properties for difficult-to-deliver drug compounds. The current literature has explored amide local anaesthetics and carboxylic acid nonsteroidal anti-inflammatories (NSAIDs) as commonly used THEDES formers for their active hydrogen-bonding functionality. However, little is known about what happens within the "deep eutectic" region where a range of binary compositions present simply as a liquid with no melting events detectable across experimentally achievable conditions. There is also very limited understanding of how parent compounds' physicochemical properties could impact upon the formation, interaction mechanism, and stability of the formed liquid systems, despite the significance of these information in dose adjustment, industrial handling, and scaling-up of these liquids. In the current work, we probed the "deep eutectic" phenomenon by investigating the formation and physicochemical behaviours of some chosen lidocaine-NSAID systems across a wide range of composition ratios. Our data revealed that successfully formed THEDES exhibited composition dependent Tg variations with strong positive deviations from predicted Tg values using the Gordon-Taylor theory, suggesting substantial interactions within the formed supramolecular structure. Interestingly, it was found that the parent compound's glass forming ability had a noticeable impact upon such profound interaction and hence could dictate the success of THEDES formation. It has also been confirmed that all successful systems were formed based on charge-assisted hydrogen bonding within their THEDES network, affirming the significant role of partial protonisation on achieving a profound melting point depression. More importantly, the work found that within the "deep eutectic" region there was still an ideal, or thermodynamically preferrable "THEDES point", which would exhibit excellent stability upon exposure to stress storage conditions. The discoveries of this study bring the literature one step closer to fully understanding the "therapeutic deep eutectic" phenomenon. Through correlation between parent reagents' physicochemical properties and the synthesised products' characteristics, we establish a more educated process for the prediction and engineering of THEDES.

Eutectic solutions for healing: a comprehensive review on therapeutic deep eutectic solvents (TheDES)

OBJECTIVE

TheDES are formed by mixing a Hydrogen Bond Donor (HBD) and a Hydrogen Bond Acceptor (HBA) in appropriate molar ratios. These solvents have been shown to enhance drug solubility, permeability, and delivery. The main objective of the present article is to review these advantages of TheDES.

SIGNIFICANCE

TheDES show unique properties, such as low toxicity, biodegradability, improved bioavailability and enhanced drug delivery of poorly soluble active pharmaceutical ingredients. They are also biocompatible in nature which makes them a promising candidate for various therapeutic applications, including drug formulations, drug delivery and other biomedical uses. The development and utilization of TheDES shows significant advancement in pharmaceutical research, providing new opportunities for improving drug delivery.

METHODS

The current study was carried out by conducting a systematic literature review that identified relevant papers from indexed databases. Numerous studies and research are cited and quoted in this article to demonstrate the effectiveness of TheDES in enhancing drug solubility, permeability, and delivery. All chosen articles were selected considering their significance, quality, and approach to addressing issues.

RESULT

As a result, various TheDES were identified that can be formulated in different ways: one component can act as a vehicle for an API, either HBD or HBA can be an API, both HBD and HBA can be APIs, or the individual components of DES are not therapeutically active but the resulting DES possesses therapeutic activity. Additionally, TheDES were also recognized to enhance drug delivery and solubility for different APIs, including NSAIDs, anesthetic drugs, antifungals, and others.

Therapeutic Deep Eutectic Solvents: A Comprehensive Review of Their Thermodynamics, Microstructure and Drug Delivery Applications

Deep eutectic solvents (DES) are multicomponent liquids that are usually formed by coupling a hydrogen bond donor and acceptor leading to strong non-covalent (NC) intermolecular networking and profound depression in the melting point of the system. Pharmaceutically, this phenomenon has been exploited to improve drugs' physicochemical properties, with an established DES therapeutic subcategory, therapeutic deep eutectic solvents (THEDES). THEDES preparation is usually via straightforward synthetic processes with little involvement of sophisticated techniques, which, in addition to its thermodynamic stability, make these multi-component molecular adducts a very attractive alternative for drug enabling purposes. Other NC bonded binary systems (e.g., co-crystals and ionic liquids) are utilized in the pharmaceutical field for enhancing drug's behaviours. However, a clear distinction between these systems and THEDES is scarcely discussed in the current literature. Accordingly, this review provides a structure-based categorization for DES formers, a discussion of its thermodynamic properties and phase behaviour, and it clarifies the physicochemical and microstructure boundaries between DES and other NC systems. Additionally, a summary of its preparation techniques and their experimental conditions preparation is supplied. Instrumental analysis techniques can be used to characterize and differentiate DES from other NC mixtures, hence this review draws a road map to for this purpose. Since this work mainly focuses on pharmaceutical applications of DES, all types of THEDES including the highly discussed types (conventional, drugs dissolved in DES and polymer based) in addition to the less discussed categories are covered. Finally, the regulatory status of THEDES was investigated despite the current unclear situation.

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.

Beneath the Skin: A Review of Current Trends and Future Prospects of Transdermal Drug Delivery Systems

The ideal drug delivery system has a bioavailability comparable to parenteral dosage forms but is as convenient and easy to use for the patient as oral solid dosage forms. In recent years, there has been increased interest in transdermal drug delivery (TDD) as a non-invasive delivery approach that is generally regarded as being easy to administer to more vulnerable age groups, such as paediatric and geriatric patients, while avoiding certain bioavailability concerns that arise from oral drug delivery due to poor absorbability and metabolism concerns. However, despite its many merits, TDD remains restricted to a select few drugs. The physiology of the skin poses a barrier against the feasible delivery of many drugs, limiting its applicability to only those drugs that possess physicochemical properties allowing them to be successfully delivered transdermally. Several techniques have been developed to enhance the transdermal permeability of drugs. Both chemical (e.g., thermal and mechanical) and passive (vesicle, nanoparticle, nanoemulsion, solid dispersion, and nanocrystal) techniques have been investigated to enhance the permeability of drug substances across the skin. Furthermore, hybrid approaches combining chemical penetration enhancement technologies with physical technologies are being intensively researched to improve the skin permeation of drug substances. This review aims to summarize recent trends in TDD approaches and discuss the merits and drawbacks of the various chemical, physical, and hybrid approaches currently being investigated for improving drug permeability across the skin.

Revisiting the Physicochemical Properties and Applications of Deep Eutectic Solvents

Recently, deep eutectic solvent (DES) or ionic liquid (IL) analogues have been considered as the newest green solvent, demonstrating the potential to replace harsh volatile organic solvents. DESs are mainly a combination of two compounds: hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD), which have the ability to interact through extensive hydrogen bonds. A thorough understanding of their physicochemical properties is essential, given their successful applications on an industrial scale. The appropriate blend of HBA to HBD can easily fine-tune DES properties for desired applications. In this context, we have reviewed the basic information related to DESs, the two most studied physicochemical properties (density and viscosity), and their performance as a solvent in (i) drug delivery and (ii) extraction of biomolecules. A broader approach of various factors affecting their performance has been considered, giving a detailed picture of the current status of DESs in research and development.

Submerged Eutectic-Assisted, Solvent-Free Mechanochemical Formation of a Propranolol Salt and Its Other Multicomponent Solids

Salt preparation via a solid-state reaction offers a solution to challenges posed by current pharmaceutical research, which include combining development of novel forms of active pharmaceutical ingredients with greener, sustainable synthesis. This work investigated in detail the mechanism of salt formation between propranolol (PRO) and capric acid (CAP) and explored the solid eutectic phases comprising this salt, propranolol caprate (PRC). The salt structure was solved by X-ray diffraction, and the properties in the crystalline and supercooled states were fully characterised using thermal analysis, nuclear magnetic resonance, Fourier-transform infrared spectroscopy and broadband dielectric spectroscopy (BDS). PRC forms via a submerged eutectic phase composed of PRO and CAP, below room temperature, by mechanochemistry without an extra input of energy. Two other solid eutectic phases are composed of PRC and either CAP or PRO, at 0.28 and 0.82 mol fraction of PRO, respectively. BDS indicated that the supercooled PRC has ionic character, whereas the supercooled PRC-PRO eutectic had predominantly non-ionic properties despite comprising the salt. In conclusion, knowledge of the mechanism of formation of multicomponent systems can help in designing more sustainable pharmaceutical processes.

Fabrication of Tizanidine Loaded Patches Using Flaxseed Oil and Coriander Oil as a Penetration Enhancer for Transdermal Delivery

Transdermal drug delivery is important to maintain plasma drug concentrations for therapeutic efficacy. The current study reports the design, formulation, and evaluation of tizanidine transdermal patches formulated using chitosan and thiolated chitosan, ethyl cellulose (EC), polyvinylpyrrolidone (PVP), and Eudragit RL100 in different ratios. The tizanidine patches were formulated using flaxseed oil and coriander oil in the concentrations of 1% v/w, 2% v/w, 3% v/w, 4% v/w, 5% v/w, and 10% v/w. The patches were subjected to characterization of physicochemical property (thickness, weight uniformity, drug content, efficiency, percentage moisture uptake/loss), in vitro drug release and drug permeation, skin irritation, in vivo application, pharmacokinetics analysis, and stability studies. The results indicate that the interaction of thiolated chitosan with the negative charges of the skin opens the tight junctions of the skin, whereas flaxseed and coriander oils change the conformational domain of the skin. The novelty of this study is in the use of flaxseed and coriander oils as skin permeation enhancers for the formulation of tizanidine transdermal patches. The formulations follow non-Fickian drug release kinetics. The FTZNE23, FTZNE36 and FTZNE54, with 5% v/w flaxseed oil loaded formulations, exhibited higher flux through rabbit skin compared with FTZNE30, FTZNE35, FTZNE42, and FTZNE47, formulations loaded with 10% v/w coriander oil. The study concludes that flaxseed oil is a better choice for formulating tizanidine patches, offering optimal plasma concentration and therapeutic efficacy, and recommends the use of flaxseed and coriander oil based patches as a novel transdermal delivery system for tizanidine and related classes of drugs.

Effect of the combination of permeation enhancer and ion-pairs strategies on transdermal delivery of tofacitinib

The aim of the present study was to develop a tofacitinib (TOF) transdermal patch by the combination of ion-pairs and chemical permeation enhancer strategies. And a theory of controlled release of chemical permeation enhancers by counterion was proposed on the basis of in vitro skin permeation and skin retention study. Through the in vitro skin permeation study, the formulation factors such as counterion, pressure sensitive adhesive (PSA), drug loading and patch thickness were investigated, and the optimized patch (6.5% LA-TOF, 15% POCC and thickness = 50 μm) was evaluated by the pharmacokinetic study. The AUC_0-t of the optimized patch was 529.89 ± 45 h ng/mL. Special attention has been paid to the molecular mechanism of the effects of counterion concentration on the release and permeation enhancement effect of penetration enhancer. FTIR study, ¹³C NMR, XPS and molecular modeling were conducted to investigate the molecular interaction between POCC and LA. Raman Imaging and ATR-FTIR were used to explore the POCC content in the skin and the interference degree to lipid. The results revealed that a strong hydrogen bond appeared between LA and the hydroxyl group of POCC, which inhibited the release of POCC, thus reducing the lipid disturbance and permeation enhancement effect of POCC. In conclusion, this TOF patch was successfully developed. The effect of counterion on permeation enhancers was clarified at molecular level, and these results provided references for the development of TOF patch.

Ionic liquids as a useful tool for tailoring active pharmaceutical ingredients

Ionic liquids (ILs) have been widely used in biomedical and pharmaceutical fields as solvents or permeation enhancers. Recently, more and more researchers focused on optimizing the physicochemical properties of active pharmaceutical ingredient (API) by ILs technology. Converting APIs into ILs (API-ILs) has shown great potential for drug delivery by eliminating polymorphism, tailoring solubility, improving thermal stability, increasing dissolution, controlling drug release, modulating the surfactant properties, enhancing permeability of APIs and modulating cytotoxicity on tumor cells. In addition, API-ILs are also used in various formulations as active ingredients, such as solutions, emulsions, even tablets or nanoparticles. This paper aims to review current status of API-ILs, including the rational and design, preparation and characterization, the improvement on the physicochemical characteristics of APIs, the compatibility of API-ILs with various formulations, and the future prospects of API-ILs in biomedical and pharmaceutical fields.

Characterisation and fundamental insight into the formation of new solid state, multicomponent systems of propranolol

The physiochemical properties of acidic or basic active pharmaceutical ingredients (APIs) can be optimised by forming salts with different counterions. The aim of this work was to synthesise a novel salt of propranolol (PRO) using sebacic acid (SEBA) as the counterion and to gain mechanistic understanding of not only the salt formation, but also its eutectic phase formation with SEBA. Thermal analysis showed a solid-state reaction occurring between PRO and SEBA leading to the formation of dipropranolol sebacate (DPS) melting at app. 170 °C and the eutectic composed of DPS and SEBA melting at app. 103 °C, comprising 0.33 mol fraction of PRO as determined by the Tammann plot. X-ray diffraction and Fourier-transform infrared spectroscopy (FTIR) confirmed the identity of the new multicomponent phases of PRO. DPS can be conveniently obtained by heat-induced crystallisation, grinding and conventional solvent crystallisation. Detailed analysis by FTIR revealed H-bond interactions between DPS and SEBA at the inter-phase in the eutectic. Bravais, Friedel, Donnay and Harker crystal morphology coupled with full interaction maps analysis allowed to understand further the nature of interactions which led to formation of the eutectic phase. This work contributes to furthering research on multicomponent pharmaceutical systems to harness their full potential.

Enhancement strategies for transdermal drug delivery systems: current trends and applications

Transdermal drug delivery systems have become an intriguing research topic in pharmaceutical technology area and one of the most frequently developed pharmaceutical products in global market. The use of these systems can overcome associated drawbacks of other delivery routes, such as oral and parenteral. The authors will review current trends, and future applications of transdermal technologies, with specific focus on providing a comprehensive understanding of transdermal drug delivery systems and enhancement strategies. This article will initially discuss each transdermal enhancement method used in the development of first-generation transdermal products. These methods include drug/vehicle interactions, vesicles and particles, stratum corneum modification, energy-driven methods and stratum corneum bypassing techniques. Through suitable design and implementation of active stratum corneum bypassing methods, notably microneedle technology, transdermal delivery systems have been shown to deliver both low and high molecular weight drugs. Microneedle technology platforms have proven themselves to be more versatile than other transdermal systems with opportunities for intradermal delivery of drugs/biotherapeutics and therapeutic drug monitoring. These have shown that microneedles have been a prospective strategy for improving transdermal delivery systems.

A Novel Eutectic-Based Transdermal Delivery System for Risperidone

This paper reports for the first time the possible formation of a novel room temperature therapeutic deep eutectic solvent (THEDES) of risperidone (RIS) with some fatty acids, namely capric acid (C10; CA), lauric acid (C12; LA), and myristic acid (C14; MA). All mixtures of RIS and MA yielded a solid or pasty-like solid and were readily discarded. Some of the prepared THEDESs from RIS and CA or LA have spontaneously transformed into a transparent liquid, without any precipitate at room temperature by simple physical mixing of the components. From the DSC thermograms, phase diagrams of the eutectic systems were constructed and the lowest obtained melting point for a RIS:CA mixture was 17°C at 40:60% w/w ratio. While 22°C was recorded as the lowest melting point for RIS:LA at a ratio of 30:70% w/w, solubility improvement of RIS was up to 70,000-fold compared with water. Freeze-drying microscopy provided valuable information regarding the phase change and transitions the drug undergoes as a function of temperature and it clarifies the interpretation of the DSC results and provides valuable evidence of drug crystals co-melting within the fatty acid base. The presence of natural fatty acid as one component of THEDES and the depression in the melting point significantly (P < 0.05) enhanced RIS skin permeation. Rheological studies showed a viscosity temperature dependency of the DES and well fitted to the Arrhenius equation. Application of the obtained THEDES on the shaved skin of rats revealed the absence of any irritation or edema effects.

Exploring the novel green eutectic solvent for the synthesis of 4-hydroxy-2-methyl-N-2-pyridinyl-2H-1,2,-benzothiazine-3-carboxamide 1,1-dioxide with benzoic acid cocrystal using a co-grinding technique

In the present study, the suitability of a green eutectic solvent, a mixture of menthol and camphor for cocrystal synthesis has been investigated to improve the biopharmaceutical properties of poorly water-soluble drugs.

Mechanistic insights into high permeation vesicle-mediated synergistic enhancement of transdermal drug permeation

Aim: To design a nanocarrier platform for enhanced transdermal drug permeation. Materials & methods: Gel-based high permeation vesicles (HPVs) were developed and their performance in terms of transdermal flux improvement, in vitro release and skin irritancy was assessed. The mechanistic insights of permeation enhancement were explored using confocal laser scanning microscopy, ATR-FTIR, DSC and P31 NMR. Results: HPVs exhibited as vesicles with uniform size (∼150 nm), extended drug-release profile (∼48 h) and improved transdermal flux. HPVs were also nontoxic and nonirritant to skin. Enhanced vesicle deformability, improved vesicle membrane fluidity and synergistic permeation enhancement action of synergistic combination of permeation enhancer components was found to be responsible for HPV-mediated permeation enhancement. Conclusion: Overall, the study established that HPVs demonstrate a promising therapeutic advantage over conventional transdermal drug carriers.

Evaporation Behavior and Characterization of Eutectic Solvent and Ibuprofen Eutectic Solution

Liquid eutectic system of menthol and camphor has been reported as solvent and co-solvent for some drug delivery systems. However, surprisingly, the phase diagram of menthol-camphor eutectic has not been reported previously. The evaporation behavior, physicochemical, and thermal properties of this liquid eutectic and ibuprofen eutectic solution were characterized in this study. Differential scanning calorimetry (DSC) analysis indicated that a eutectic point of this system was near to 1:1 menthol/camphor and its eutectic temperature was -1°C. The solubility of ibuprofen in this eutectic was 282.11 ± 6.67 mg mL(-1) and increased the drug aqueous solubility fourfold. The shift of wave number from Fourier transform infrared spectroscopy (FTIR) indicated the hydrogen bonding of each compound in eutectic mixture. The weight loss from thermogravimetric analysis of menthol and camphor related to the evaporation and sublimation, respectively. Menthol demonstrated a lower apparent sublimation rate than camphor, and the evaporation rate of eutectic solvent was lower than the sublimation rate of camphor but higher than the evaporation of menthol. The evaporation rate of the ibuprofen eutectic solution was lower than that of the eutectic solvent because ibuprofen did not sublimate. This eutectic solvent prolonged the ibuprofen release with diffusion control. Thus, the beneficial information for thermal behavior and related properties of eutectic solvent comprising menthol-camphor and ibuprofen eutectic solution was attained successfully. The rather low evaporation of eutectic mixture will be beneficial for investigation and tracking the mechanism of transformation from nanoemulsion into nanosuspension in the further study using eutectic as oil phase.

Transformation of eutectic emulsion to nanosuspension fabricating with solvent evaporation and ultrasonication technique

Eutectic solvent can solubilize high amount of some therapeutic compounds. Volatile eutectic solvent is interesting to be used as solvent in the preparation of nanosuspension with emulsion solvent evaporation technique. The mechanism of transformation from the eutectic emulsion to nanosuspension was investigated in this study. The 30% w/w ibuprofen eutectic solution was used as the internal phase, and the external phase is composed of Tween 80 as emulsifier. Ibuprofen nanosuspension was prepared by eutectic emulsion solvent evaporating method followed with ultrasonication. During evaporation process, the ibuprofen concentration in emulsion droplets was increased leading to a drug supersaturation but did not immediately recrystallize because of low glass transition temperature (T_g) of ibuprofen. The contact angle of the internal phase on ibuprofen was apparently lower than that of the external phase at all times of evaporation, indicating that the ibuprofen crystals were preferentially wetted by the internal phase than the external phase. From calculated dewetting value ibuprofen crystallization occurred in the droplet. Crystallization of the drug was initiated with external mechanical force, and the particle size of the drug was larger due to Ostwald ripening. Cavitation force from ultrasonication minimized the ibuprofen crystals to the nanoscale. Particle size and zeta potential of formulated ibuprofen nanosuspension were 330.87±51.49 nm and −31.1±1.6 mV, respectively, and exhibited a fast dissolution. Therefore, the combination of eutectic emulsion solvent evaporation method with ultrasonication was favorable for fabricating an ibuprofen nanosuspension, and the transformation mechanism was attained successfully.

Topical delivery of hexamidine

Hexamidine diisethionate (HEX D) has been used for its biocidal actions in topical preparations since the 1950s. Recent data also suggest that it plays a beneficial role in skin homeostasis. To date, the extent to which this compound penetrates the epidermis has not been reported nor how its topical delivery may be modulated. In the present work we set out to characterise the interaction of HEX D with the skin and to develop a range of simple formulations for topical targeting of the active. A further objective was to compare the skin penetration of HEX D with its corresponding dihydrochloride salt (HEX H) as the latter has more favourable physicochemical properties for skin uptake. Candidate vehicles were evaluated by in vitro Franz cell permeation studies using porcine skin. Initially, neat solvents were investigated and subsequently binary systems were examined. The solvents and chemical penetration enhancers investigated included glycerol, dimethyl isosorbide (DMI), isopropyl alcohol (IPA), 1,2-pentanol (1,2-PENT), polyethylene glycol (PEG) 200, propylene glycol (PG), propylene glycol monolaurate (PGML) and Transcutol(®)P (TC). Of a total of 30 binary solvent systems evaluated only 10 delivered higher amounts of active into the skin compared with the neat solvents. In terms of topical efficacy, formulations containing PGML far surpassed all other solvents or binary combinations. More than 70% of HEX H was extracted from the skin following application in PG:PGML (50:50). Interestingly, the same vehicle effectively promoted skin penetration of HEX D but demonstrated significantly lower uptake into and through the skin (30%). The findings confirm the unpredictable nature of excipients on delivery of actives with reference to skin even where there are minor differences in molecular structures. We also believe that they underline the ongoing necessity for fundamental studies on the interaction of topical excipients with the skin.

Removal of beta-blockers from aqueous media by adsorption onto graphene oxide

The aim of the present study is the evaluation of graphene oxide (GhO) as adsorbent material for the removal of beta-blockers (pharmaceutical compounds) in aqueous solutions. The composition and morphology of prepared materials were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Atenolol (ATL) and propranolol (PRO) were used as model drug molecules and their behavior were investigated in terms of GhO dosage, contact time, temperature and pH. Adsorption mechanisms were proposed and the pH-effect curves after adsorption were discussed. The kinetic behavior of GhO-drugs system was analyzed after fitting to pseudo-first and -second order equations. The adsorption equilibrium data were fitted to Langmuir, Freundlich and Langmuir-Freundlich model calculating the maximum adsorption capacity (67 and 116 mg/g for PRO and ATL (25 °C), respectively). The temperature effect on adsorption was tested carrying out the equilibrium adsorption experiments at three different temperatures (25, 45, 65 °C). Then, the thermodynamic parameters of enthalpy, free energy and entropy were calculated. Finally, the desorption of drugs from GhO was evaluated by using both aqueous eluants (pH2-10) and organic solvents.

Microneedle pretreatment enhances the percutaneous permeation of hydrophilic compounds with high melting points

Background

Two commercially available microneedle rollers with a needle length of 200 μm and 300 μm were selected to examine the influence of microneedle pretreatment on the percutaneous permeation of four non-steroidal anti-inflammatory drugs (diclofenac, ibuprofen, ketoprofen, paracetamol) with different physicochemical drug characteristics in Franz-type diffusion cells. Samples of the receptor fluids were taken at predefined times over 6 hours and were analysed by UV–VIS high-performance liquid-chromatography. Histological examinations after methylene blue application were additionally performed to gather information about barrier disruption.

Results

Despite no visible pores in the stratum corneum, the microneedle pretreatment resulted in a twofold (200 μm) and threefold higher (300 μm) flux through the pretreated skin samples compared to untreated skin samples for ibuprofen and ketoprofen (LogK_ow > 3, melting point < 100°C). The flux of the hydrophilic compounds diclofenac and paracetamol (logK_ow < 1, melting point > 100°C) increased their amount by four (200 μm) to eight (300 μm), respectively.

Conclusion

Commercially available microneedle rollers with 200–300 μm long needles enhance the drug delivery of topically applied non-steroidal anti-inflammatory drugs and represent a valuable tool for percutaneous permeation enhancement particularly for substances with poor permeability due to a hydrophilic nature and high melting points.

Polymeric Eutectic System

The liquid eutectic system comprising 1:1 menthol:camphor was selected to use as solvent due to it was lowest viscosity. Both menthol and camphor used in this eutectic system have been reported for their many pharmaceutical used. Various polymers were tested for their solubility in this eutectic system. Eudragit® EPO showed the highest solubility. Eudragit® EPO was the one of biocompatible polymer which could dissolve in this eutectic system up to 40% w/w with no chemical interaction of each compound. Viscosity of this system showed the exponential curve as a function of polymer concentration but all concentration showed the newtonian rheology. The pH and surface tension were slightly affected by type and amount of polymers. The obtained polymeric eutectic mixture should control the drug release for pharmaceutical applications.

Effect of fatty acids on the transdermal delivery of donepezil: in vitro and in vivo evaluation

The effect of fatty acids on the skin permeation of donepezil base (DPB) and its hydrochloride salt (DPH) were studied in vitro using hairless mouse and human cadaver skin. DPB and DPH were solubilized in propylene glycol (PG) containing 1% (w/v) fatty acid, after which the in vitro permeation through hairless mouse skin and human cadaver skin were evaluated using Keshary-Chien diffusion cells. The optimized formulation obtained from the in vitro study was then tested in rats for an in vivo pharmacokinetic study. The relative in vitro skin permeation rate of donepezil (DP) through the hairless mouse skin showed a parabolic relationship with increased carbon length of the fatty acid enhancers. Among the fatty acids tested, oleic acid for DPB and palmitoleic acid for DPH showed the highest enhancing effect, respectively. Both the permeation rates of DPB and DPH evaluated in human cadaver skin were in good correlation with those in hairless mouse skin, regardless of the presence of fatty acids. This suggests that the mouse skin model serves as a useful in vitro system that satisfactorily represents the characteristics of the human skin. Moreover, based on the in vitro results, the optimal formulation that could maintain the human plasma concentration of 50 ng/mL was determined to be 10mg DP with 1% (w/v) enhancer. When the DP transdermal formulations were applied to the abdominal skin of rats (2.14 cm(2)), the C(ss) was maintained for 48 h, among which the highest value of 52.21 ± 2.09 ng/mL was achieved with the DPB formulation using oleic acid. These results showed that fatty acids could enhance the transdermal delivery of DP and suggested the feasibility of developing a novel transdermal delivery system for clinical use.

Dynamic in-situ eutectic formation for topical drug delivery

Objectives

The relationship between the solution-state chemistry of eutectic systems and their transmembrane transport characteristics is difficult to define as these mixtures are sensitive to delivery vehicle-induced penetration enhancement. Through in-situ formation of a molten eutectic mixture using highly evaporative sprays this study aimed to gain an understanding of solution-state thermodynamic and chemical properties of eutectic combinations pertinent to transmembrane transport in the absence of a delivery vehicle.

Methods

In-situ molten lidocaine–prilocaine eutectics were formed using a hydroflouroalkane (HFA) propellant. Transport through silicone membranes and human skin in upright Franz diffusion cells was determined using in-house manufactured creams as controls.

Key findings

The application of the two drugs in an HFA spray produced a molten oil even when the melting point of the drug mixture was above the experimental temperature at the membrane surface. In the absence of vehicle effects, molecule presentation to the membrane interface was most effective using a lidocaine-rich mixture of 0.7% w/w lidocaine:prilocaine – 1985.06 ± 128.87 µg/h/cm2.

Conclusions

There appeared to be no link between melting point and transmembrane transport of lidocaine:prilocaine from a eutectic mixture. The rate of drug presentation to the membrane interface, which was highest in drug-rich, high-activity molten eutectic mixtures, was the driver for transmembrane transport in the absence of significant barrier interactions.

In vitro-in vivo study of CoQ10-loaded lipid nanoparticles in comparison with nanocrystals

The present work described the effect of CoQ10 dissolution characteristics in nanocrystals and lipid nanoparticles (LNs) on its oral absorption in rats. Nanocrystals and LNs were prepared by melt-high pressure homogenization and sucrose monolaurate was used as a stabilizer in all formulations. Witepsol(®)W35 and medium-chain triglycerides (MCT) were selected as lipid additives to form LN(CoQ10+W35) and LN(CoQ10+MCT), respectively. From the results obtained, the particle size of CoQ10 nanocrystals was 285 nm, while it was reduced to 150 nm by mixture with an equal amount of lipid additives due to their lower melting points. In vitro dissolution results indicated that the drug release from two LNs was delayed compared with that from nanocrystals, and LN(CoQ10+W35) exhibited the highest drug release over 4h. Finally, in vivo evaluation demonstrated that the oral absorption of CoQ10 was markedly increased by using nanocrystals and LNs compared with a coarse suspension. A good relationship was found between the in vitro dissolution and in vivo evaluation. The enhanced oral absorption of CoQ10 by nanocrystals and LNs was due to improved dissolution. In conclusion, Witepsol(®)W35 was shown to be a better lipid additive for the preparation of LNs to increase the oral absorption of CoQ10.

Enhancement of transdermal drug delivery via synergistic action of chemicals

Transdermal drug delivery is an attractive alternative to conventional techniques for administration of systemic therapeutics. One challenge in designing transdermal drug delivery systems is to overcome the natural transport barrier of the skin. Chemicals offer tremendous potential in overcoming the skin barrier to enhance transport of drug molecules. Individual chemicals are however limited in their efficacy in disrupting the skin barrier at low concentrations and usually cause skin irritation at high concentrations. Multicomponent mixtures of chemicals, however, have been shown to provide high skin permeabilization potency as compared to individual chemicals without necessarily causing irritation. Here we review systems employing synergistic mixtures of chemicals that offer superior skin permeation enhancement. These synergistic systems include solvent mixtures, microemulsions, eutectic mixtures, complex self-assembled vesicles and inclusion complexes. Methods for design and discovery of such synergistic systems are also discussed.

Interaction Study of Paracetamol with Saturated (Capric) and Unsaturated (Oleic) Fatty Acids

Interaction study of paracetamol with saturated and unsaturated fatty acids, namely, capric and oleic acid have been performed by using serial dilution method, release behavior, FT-IR, and DSC study. Preliminary investigations by release studies indicated the possibility of interaction between paracetamol and fatty acids. UV-studies failed to detect any interaction between paracetamol and fatty acids. The possibility of hydrogen bonding between amino group of paracetamol and carbonyl group of fatty acids was revealed by FT-IR study. Polymorphic transition of paracetamol in the binary sample of paracetamol-capric acid was identified by DSC studies. However, no such possibility was detected in paracetamol-oleic acid mixture.

Skin permeation enhancement of diclofenac by fatty acids

This study systematically investigated the enhancing effect of fatty acids on the skin permeation of diclofenac. The fatty acids were evaluated in terms of their carbon-chain length, the degree of unsaturation, and their functional groups. The rat-skin permeation rates of diclofenac, saturated in propylene glycol (PG) containing 1% (w/v) fatty acid, were determined using the Keshary-Chien diffusion cells at 37 degrees C. The effect of fatty acids on the saturated solubility of diclofenac in PG was also determined at 37 degrees C using high-performance liquid chromatography. Among the saturated fatty acids tested, palmitic acid (C16:0) showed the most potent skin permeation-enhancing effect. A parabolic correlation was observed between the enhancement effect and the fatty acid carbon-chain length among these saturated fatty acids of C12-C20 units. For the monounsaturated fatty acid series, an increase in permeation was observed as the carbon-chain length increased, and oleic acid (C18:1) showed the highest permeation-enhancing effect. Increasing the number of double bonds in the octadecanoic acids resulted in a parabolic effect in the permeation of diclofenac, revealing oleic acid as the most effective enhancer used in this study. When the carboxylic acid moiety of oleic acid was changed to an amide (oleamide) or hydroxyl (oleyl alcohol) group, a decrease in permeation activity was observed. These results, therefore, suggest that the cis-monounsaturated configuration and the carboxylic acid moiety of an 18-carbon unit fatty acid in PG are the optimum requirements for the effective skin permeation of diclofenac.

Skin permeation mechanism and bioavailability enhancement of celecoxib from transdermally applied nanoemulsion

BACKGROUND

Celecoxib, a selective cyclo-oxygenase-2 inhibitor has been recommended orally for the treatment of arthritis and osteoarthritis. Long term oral administration of celecoxib produces serious gastrointestinal side effects. It is a highly lipophilic, poorly soluble drug with oral bioavailability of around 40% (Capsule). Therefore the aim of the present investigation was to assess the skin permeation mechanism and bioavailability of celecoxib by transdermally applied nanoemulsion formulation. Optimized oil-in-water nanoemulsion of celecoxib was prepared by the aqueous phase titration method. Skin permeation mechanism of celecoxib from nanoemulsion was evaluated by FTIR spectral analysis, DSC thermogram, activation energy measurement and histopathological examination. The optimized nanoemulsion was subjected to pharmacokinetic (bioavailability) studies on Wistar male rats.

RESULTS

FTIR spectra and DSC thermogram of skin treated with nanoemulsion indicated that permeation occurred due to the disruption of lipid bilayers by nanoemulsion. The significant decrease in activation energy (2.373 kcal/mol) for celecoxib permeation across rat skin indicated that the stratum corneum lipid bilayers were significantly disrupted (p < 0.05). Photomicrograph of skin sample showed the disruption of lipid bilayers as distinct voids and empty spaces were visible in the epidermal region. The absorption of celecoxib through transdermally applied nanoemulsion and nanoemulsion gel resulted in 3.30 and 2.97 fold increase in bioavailability as compared to oral capsule formulation.

CONCLUSION

Results of skin permeation mechanism and pharmacokinetic studies indicated that the nanoemulsions can be successfully used as potential vehicles for enhancement of skin permeation and bioavailability of poorly soluble drugs.

Skin permeation of physostigmine from fatty acids-based formulations: evaluating the choice of solvent

This study was conducted to gain an understanding of the enhancement mechanism of fatty acids in skin permeation of physostigmine (PHY) by using a series of fatty acids and two solvents of opposing lipophilicity (propylene glycol (PG) and mineral oil (MO)). Interaction between fatty acid and drug was proven using NMR and conductivity measurements that showed a dependence on type of solvent used. Permeation flux of physostigmine from mineral oil-based formulations to skin was increased as solubility of physostigmine in mineral oil was enhanced in the presence of fatty acids having a longer chain. Thus, the dominant role of fatty acids in mineral oil was to increase solubility of physostigmine in the formulations that increased the driving force for physostigmine permeation through skin. As for propylene glycol, enhancement caused by fatty acids was attributed to their ability to increase the lipophilicity of formulation and to disrupt the lipid bilayers within the stratum corneum (SC). In conclusion, fatty acids enhancement for drug permeation across the skin was found to be dependent on the solvent used. Among various formulations here, oleic acid in mineral oil yielded fast permeation of PHY with a short lag time, which may be a good vehicle for transdermal delivery of PHY.

Ion Pair Formation as a Possible Mechanism for the Enhancement Effect of Lauric Acid on the Transdermal Permeation of Ondansetron

Transdermal application can be an alternative drug delivery route for ondansetron, an antiemetic drug. Previous studies found that fatty acids, namely oleic and lauric, were the most effective penetration enhancers. The aim of this study was to investigate the formation of an ion pair between ondansetron and lauric acid as a possible mechanism of its enhancing action. Several techniques were used to reveal the formation of an ion pair complex. Partitioning experiments, where the n-octanol/water coefficient was measured, showed an increase in the distribution coefficient in the presence of the acid, possibly as a result of the formation of more lipophilic ion pairs between the charged molecules of ondansetron and lauric acid. Further evidence of complex formation between ondansetron and lauric acid, was gained from the 13C-nuclear magnetic resonance (13C-NMR) spectra of ondansetron, lauric acid, and their mixture (molar ratio 1:1). The NMR spectra revealed alterations to the magnetic environment of the carbon atoms adjacent to the ionized group, which are the carbonyl group of the acid and the nitrogen of the imidazole ring of ondansetron. This evidence substantiates the theory of ion pair formation. Finally, thermal analysis of the binary mixtures of ondansetron and lauric acid revealed the formation of an additional compound, with different melting point from pure ondansetron and lauric acid, which is thermodynamically favored.

Effects of fatty acids and iontophoresis on the delivery of midodrine hydrochloride and the structure of human skin

PURPOSE

The purpose of this work was to investigate if fatty acids can increase the iontophoretic delivery of midodrine hydrochloride through human dermatomed skin and to observe the effects of iontophoresis and fatty acids on skin using SEM.

METHODS

After prehydration for 1 h, human dermatomed skin was treated with 0-0.3 M fatty acids (oleic acid, linoleic acid, decanoic acid, and lauric acid) in propylene glycol (PG) for 1 h. Then the fatty acid solution was replaced by 1% midodrine hydrochloride aqueous solution, and 0.1 mA/cm2 constant current was applied. Samples were taken over 24 h and analyzed by HPLC. After the treatments outlined above, the epidermis was separated, fixed with glutaraldehyde, and dehydrated for SEM.

RESULTS

SEM studies revealed that only 1 h of treatment with fatty acids opened up the tightly compact stratum corneum cell layer, and the permeation study showed a significant increase of the permeability of skin to midodrine hydrochloride after fatty acid treatment.

CONCLUSIONS

Using 5% oleic acid pretreatment, with the electrical current offset at 0.1 mA/cm2, the daily delivery of midodrine hydrochloride can provide an adequate clinical application. The enhancement of passive and iontophoretic delivery by fatty acids may be occurring through the same mechanism.