An In Vitro and In Vivo Comparison of Solid and Liquid–Oil Cores in Transdermal Aconitine Nanocarriers

This study compared transdermal aconitine delivery using solid lipid nanoparticles (SLN) and microemulsion (ME) vehicles. Aconitine‐loaded SLN and ME were formulated with the same surfactant, cosurfactant, and water content, with an equal amount of oil matrix (ATO 888 for SLN and ethyl oleate for ME). These nanosized formulations (70–90 nm) showed suitable pH values and satisfactory skin tissue biocompatibility. SLN contained a higher concentration of smaller nanoparticles, compared with that in ME. Neither of the nanocarriers penetrated across excised skin in their intact form. In vitro transdermal delivery studies found that transdermal aconitine flux was lower from SLN than from ME (p < 0.05), but skin aconitine deposition was higher using SLN (p < 0.05). Fluorescence‐activated cell sorting indicated that in vitro uptake of fluorescently labeled SLN by human immortalized keratinocyte (HaCaT) cells was greater than that of ME, indicating that a transcellular pathway may contribute to cutaneous drug absorption more effectively from SLN. In vivo studies found that these formulations could loosen stratum corneum layers and increase skin surface crannies, which may also enhance transdermal aconitine delivery. SLN produced a more sustained aconitine release, indicating that compared with ME, this transdermal delivery vehicle may reduce the toxicity of this drug. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:3602–3610, 2014     

Development and evaluation of niacinamide transdermal formulation by artificial membrane permeability

Despite many efforts to improve the transdermal permeability of drugs, most of them are blocked by the skin barrier. Niacinamide (NAC) is a Biopharmaceutics Classification System class I drug with high aqueous solubility and intestinal permeability. Due to the high solubility and intestinal permeability of NAC, the development of new formulations is insufficient as transdermal, injection etc. Thus, this study aimed to develop the novel NAC formulation with improved skin permeability and secured stability. The NAC formulation approach is to first select a solvent that improves skin permeability, and then select a second penetration enhancer to determine the final formulation. All formulations were evaluated for skin permeability using an artificial membrane (Strat-M®). The optimal formulation (non-ionic formulations (NF1) consisted of NAC/Tween®80 = 1:1 wt ratio in dipropylene glycol [DPG]) showed the highest permeability in all formulations in PBS buffer (pH 7.4). The thermal properties of NF1 were altered. Moreover, NF1 maintained a stable drug content, appearance, and pH value for 12 months. In conclusion, DPG had an excellent effect in increasing the NAC permeation, and Tween®80 played a boosting role. Through this study, an innovative NAC formulation was developed, and good results are expected for human transdermal research.     

Microemulsions as topical delivery vehicles for the anti-melanoma prodrug, temozolomide hexyl ester (TMZA-HE)

A prodrug, temozolomide acid hexyl ester (TMZA-HE), was identified as a skin-deliverable congener for temozolomide (TMZ) to treat skin cancers. Poor solubility and instability of TMZA-HE rendered a serious challenge for formulation of a topical preparation. Microemulsions (ME) were chosen as a potential vehicle for TMZA-HE topical preparations. ME systems were constructed with either oleic acid (OA) or isopropyl myristate (IPM) as the oil phase and tocopheryl (vitamin E) polyethylene glycol 1000 succinate (VE-TPGS) as a surfactant. Topical formulations of OA and IPM ME systems demonstrated beneficial solubilising ability and provided a stable environment for the prodrug, TMZA-HE. Significant differences between the microstructures of OA and IPM ME systems were revealed by freeze fracture electron microscopy (FFEM) and different loading abilities and permeation potencies between the two systems were also identified. In permeation studies, IPM ME systems, with inclusion of isopropyl alcohol (IPA) as a co-surfactant, significantly increased TMZA-HE permeation through silicon membranes and rat skin resulting in less drug retention within the skin, while OA ME systems demonstrated higher solubilising ability and a higher concentration of TMZA-HE retained within the skin. Therefore IPM ME systems are promising for transdermal delivery of TMZA-HE and OA ME systems may be a suitable choice for a topical formulation of TMZA-HE.     

In Vitro Permeation Screening of a New Formulation of Thiocolchicoside Containing Various Enhancers

Thiocolchicoside, a muscle relaxant agent with anti-inflammatory and analgesic actions, also is used topically for the treatment of muscular spasms and for rheumatologic, orthopedic, and traumatologic disorders. In this study, thiocolchicoside was formulated to use as foam to avoid contact with the afflicted area during the spreading phase. To enhance drug penetration, various enhancers were added to the base formulation. The tested enhancers were ethoxyethylendiglycol (Transcutol ®), highly purified phosphatidylcholine (Lipoid S20), capsaicin, propylene glycol dipelargonate (DPPG), and glycolysed ethoxylated glycerides (Labrafil M1944 CS). The transdermal absorption of the tested formulations containing enhancers, in comparison with base formulation, was evaluated in vitro through rat skin using standard Franz diffusion cells. Base formulation was found to have a higher permeation profile than the simple aqueous and hydroalcoholic solutions of the drug, meaning that the base formulation by itself enhances the drug permeation. Among the tested formulations, only the formulation containing DPPG/ethanol was found to be statistically different, showing an enhancement factor of 3.58. In the same experimental session, Muscoril ® ointment, the commercially available pharmaceutical product containing the same thiocolchicoside concentration (0.25%), also was tested. The formulation containing DPPG/ ethanol showed a 4.86 times increase of permeability constant in comparison with Muscoril ® ointment. The formulation containing DPPG/ethanol as an enhancer could be a good candidate for a new topical foam, considering its good characteristics of permeability and compliance.     

Development of water-in-oil microemulsions with the potential of prolonged release for oral delivery of L-glutathione

Oral delivery of L-L-glutathione is quite a challenge due to the enzymatic and physical barriers in the gastrointestinal tract (GIT). Colloidal delivery systems such as microemulsions (ME) can be valuable for oral delivery of L-glutathione, because they may protect L-glutathione from enzymatic degradation and enhance its permeability across the intestinal epithelium. The aim of this study was to identify ME systems capable of accommodating maximum amounts of L-glutathione in internal aqueous phase intended for oral delivery. Pseudoternary phase diagrams for the systems based on a single or a blend of two oily components, one or two nonionic surfactants and an aqueous phase loaded with L-glutathione were constructed, identified and characterized in terms of morphological, rheological and in vitro release studies. Among the tested formulations, the coarse emulsions resulted in the highest release rate, while the ME and liquid crystal systems provided sustained release of L-glutathione in vitro. There was a linear relationship between the cumulative amount of L-glutathione released from the ME and the liquid crystals, and the square root of time indicting a diffusion controlled process. The release of L-glutathione from the ME and the liquid crystal was related to the concentration of L-glutathione remaining in the formulations. In conclusion, two novel delivery colloidal systems of L-glutathione loaded water-in-oil ME and liquid crystal systems were developed and characterized. In addition, a simple isocratic HPLC analytic method was developed and validated, and was used for the qualitative and quantitative analysis of L-glutathione released from the selected formulations.     

Occlusive and Non-Occlusive Application of Microemulsion for Transdermal Delivery of Progesterone: Mechanistic Studies

This work evaluated the occlusive versus non-occlusive application of microemulsion (ME) for the transdermal delivery of progesterone. The mechanisms of enhanced skin penetration were investigated. ME comprised of oleic acid, Tween 80, propylene glycol, and water, was used neat or with ethanol as a volatile cosurfactant. The ME formulations enhanced progesterone transdermal flux compared to the saturated drug solution in 14% aqueous propylene glycol (control). Ethanol-containing ME (EME) was better than the ethanol-free system (EFME). Open application of EFME produced a marginal reduction in flux compared to occlusive application. For EME, open application reduced the flux by 26–28% with the flux remaining significantly higher than that obtained with EFME. The mechanistic studies revealed synergism between ethanol and EFME with EME, producing greater flux than the sum of fluxes obtained from 40% ethanol in water and EFME. Penetration enhancement and supersaturation played a role in enhanced transdermal delivery, but other mechanisms were also possible. This study thus introduced EME as a transdermal delivery system for progesterone with good potential for open application as a spray.     

Triamcinolone permeation from different liposome formulations through rat skin in vitro

The permeation of triamcinolone acetonide (TRMA) from various liposome formulations through rat skin was studied in vitro. The penetrated amount, permeability and intradermal retention of TRMA were compared among various lipid compositions, different vesicle sizes (0.2, 0.4 and 1 μm), charges (positive, negative and neutral), as well as between multilamellar vesicles (MLV) and small unilamellar vesicles (SUV). All of the liposome formulations resulted in significantly higher flux and permeability of TRMA than a commercial TRMA ointment. The ‘skin lipid’ liposome provided the most effective transdermal delivery of incorporated TRMA. Presence or absence of cholesterol in the lipid bilayers did not reveal any difference in transdermal delivery of the associated TRMA. The flux and permeability of TRMA through skin were not influenced by the vesicle size of MLV, but was significantly increased by negative SUV. Intradermal retention of TRMA from positive MLV was significantly higher, while that from neutral SUV was significantly lower, than from other formulations. Liposomal lipid was not detectable on the receptor compartment. These results suggest that liposome itself may not penetrate through the skin, but that it does enhance the transfer of incorporated TRMA. Liposomal lipid composition is the most important factor affecting the efficiency of transdermal delivery of incorporated drugs, but was not correlated with its phase transition temperature.     

Biomaterials as novel penetration enhancers for transdermal and dermal drug delivery systems

Abstract

The highly organized structure of the stratum corneum provides an effective barrier to the drug delivery into or across the skin. To overcome this barrier function, penetration enhancers are always used in the transdermal and dermal drug delivery systems. However, the conventional chemical enhancers are often limited by their inability to delivery large and hydrophilic molecules, and few to date have been routinely incorporated into the transdermal formulations due to their incompatibility and local irritation issues. Therefore, there has been a search for the compounds that exhibit broad enhancing activity for more drugs without producing much irritation. More recently, the use of biomaterials has emerged as a novel method to increase the skin permeability. In this paper, we present an overview of the investigations on the feasibility and application of biomaterials as penetration enhancers for transdermal or dermal drug delivery systems.     

Preparation and characterization of microemulsion formulations of nicotinic acid and its prodrugs for transdermal delivery

At pharmacological doses, nicotinic acid has a lipid-regulating effect and is in use clinically for that purpose. However, despite of all features, its utility is strongly limited by several disadvantages such as, extensive hepatic metabolism and flushing. Transdermal delivery of nicotinic acid may, therefore, be the solution to reducing side effects associated with oral administration, and to maintaining constant therapeutic blood levels for longer duration. The aim of this investigation was to develop a suitable formulation or select a suitable vehicle for the transdermal delivery of highly lipophilic prodrugs of nicotinic acid (dodecyl and myristyl nicotinate) designed to deliver nicotinic acid through skin without causing vasodilatation and flushing and optimizing its delivery to the blood stream. A microemulsion system and penetration enhancers have been attempted in this study. The microemulsion system was composed of isopropyl myristate (IPM), water and a 4:1 (w/w) mixture of Labrasol and Peceol where a pseudoternary phase diagram was constructed. Furthermore, the microemulsion formulations with different component ratios were characterized by determination of conductivity, pH, particle size, viscosity and refractive index. According to the particle size analysis, conductivity and viscosity measurements, the microemulsion formulations that formed were of oil-in-water type. The transdermal permeability of nicotinic acid and its prodrugs was evaluated in vitro using Franz diffusion cells fitted with mice skin and nicotinic acid concentration was analyzed by high performance liquid chromatography. A theoretical design of percutaneous penetration optimization in which prodrugs derivation and enhancer application are combined based on the skin diffusion model was experimentally verified. The selected formulations seemed promising for developing a transdermal drug delivery system of nicotinic acid from dodecyl nicotinate that would offer advantages like possible controlled drug release, reduced flushing, increased drug stability and ease of large-scale production.     

Microemulsion: a novel transdermal delivery system to facilitate skin penetration of indomethacin

In this study, we aimed to develop thermodynamically stable microemulsion formulations of indomethacin with lower surfactant and cosurfactant contents, to improve drug permeability. Formulations were based on the oil/water microemulsion region of pseudo-ternary phase diagrams. The characteristic parameters (viscosity, diameter, and polydispersity) of the microemulsion formulations were then determined. In vitro permeation studies were performed using Franz diffusion cells. Permeation through mouse skin and skin retention of indomethacin microemulsions and ointment were tested. The cumulative amount of permeated indomethacin and its skin retention were significantly higher in microemulsion formulations compared with ointment. Drug flux and skin retention improved with decreasing droplet diameter of the microemulsions. On the basis of these results, we suggest some possible mechanisms for the enhanced transdermal permeation of drugs in microemulsions, including high drug-loading capacity, permeation enhancement by surfactants and cosurfactants, and smaller droplet diameter. In conclusion, microemulsions represent a novel transdermal delivery vehicle for increasing the solubility and permeability of indomethacin.     

A combination of a microemulsion and a phospholipid complex for topical delivery of oxymatrine

Oxymatrine (OMT), a water-soluble drug, has a very low oral bioavailability because of its low membrane permeability and its biotransformation in the gastrointestinal tract. Formulated as an oxymatrine-phospholipid complex (OMT-PLC) can improve the lipid solubility and effectiveness of OMT. The purpose of this study was to explore the utility of the combination of a microemulsion and an OMT-PLC as a topical delivery vehicle for enhancing the absorption and efficacy of OMT. The solubility of OMT-PLC was determined and phase diagrams of microemulsions were constructed. Various microemulsion formulations were developed and characterized by their physicochemical properties, and their in vitro and in vivo permeability through skin. An optimal microemulsion (ME4), which presented as spherical droplets and consisted of 10.0% OMT-PLC, 8.0% isopropyl myristate, 30.0% Cremophor RH40/polyethylene glycol 400 (1:1) and 52.0% water, was selected. It possessed an average droplet size of 32.4 nm, a low viscosity of 113.7 mPa · s, and a high cloud point of 88°C. Compared to the control solution, ME4 provided better skin permeability in vitro and a higher retention ratio of OMT in skin in vivo. Moreover, ME4 significantly enhanced the antiproliferative activity of OMT on scar fibroblasts. These results indicate that the combination of a microemulsion and a phospholipid complex represents an effective vehicle for topical delivery of OMT.     

Topical delivery of different acyclovir palmitate liposome formulations through rat skin in vitro

The objective of this investigation was to examine the permeation of acyclovir palmitate from various liposome formulations through hairless rat skin in vitro. The penetrated amount, permeability and intradermal retention of ACV-C16 were compared among various lipid compositions and different vesicle charges. We found that all of the liposome formulations resulted in higher flux and permeability of ACV-C16 than a common ointment form. The 'skin lipid' liposome provided the most effective transdermal delivery of incorporated ACV-C16. Presence or absence of cholesterol in the lipid bilayers did not reveal any difference in transdermal delivery of the associated ACV-C16. Intradermal retention of ACV-C16 from positive liposomes was significantly higher than that from other formulations. These findings suggested that liposomes itself might not penetrate through the skin, but enhance the transfer of incorporated ACV-C16. Liposomal lipid composition was the most important factor affecting the efficiency of transdermal delivery of incorporated drugs, but was not correlated with its phase transition temperature.     

Novel Microemulsion Enhancer Formulation for Simultaneous Transdermal Delivery of Hydrophilic and Hydrophobic Drugs

Purpose. Microemulsion (ME) systems allow for the microscopic co-incorporation of aqueous and organic phase liquids. In this study, the phase diagrams of four novel ME systems were characterized. Methods. Water and IPM composed the aqueous and organic phases respectively, whereas Tween 80 served as a nonionic surfactant. Transdermal enhancers such as n-methyl pyrrolidone (NMP) and oleyl alcohol were incorporated into all systems without disruption of the stable emulsion. Results. A comparison of a W/O ME with an O/W ME of the same system for lidocaine delivery indicated that the O/W ME provides significantly greater flux (p < 0.025). The water phase was found to be a crucial component for flux of hydrophobic drugs (lidocaine free base, estradiol) as well as hydrophilic drugs (lidocaine HCl, diltiazem HCl). Furthermore, the simultaneous delivery of both a hydrophilic drug and a hydrophobic drug from the ME system is indistinguishable from either drug alone. Enhancement of drug permeability from the O/W ME system was 17-fold for lidocaine free base, 30-fold for lidocaine HCl, 58-fold for estradiol, and 520-fold for diltiazem HCl. Conclusions. The novel microemulsion systems in this study potentially offers many beneficial characteristics for transdermal drug delivery.     

Microemulsion and poloxamer microemulsion-based gel for sustained transdermal delivery of diclofenac epolamine using in-skin drug depot: In vitro/in vivo evaluation

Microemulsion (ME) and poloxamer microemulsion-based gel (PMBG) were developed and optimized to enhance transport of diclofenac epolamine (DE) into the skin forming in-skin drug depot for sustained transdermal delivery of drug. D-optimal mixture experimental design was applied to optimize ME that contains maximum amount of oil, minimum globule size and optimum drug solubility. Three formulation variables; the oil phase X₁ (Capryol^®), Smix X₂ (a mixture of Labrasol^®/Transcutol^®, 1:2 w/w) and water X₃ were included in the design. The systems were assessed for drug solubility, globule size and light absorbance. Following optimization, the values of formulation components (X₁, X₂, and X₃) were 30%, 50% and 20%, respectively. The optimized ME and PMBG were assessed for pH, drug content, skin irritation, stability studies and ex vivo transport in rat skin. Contrary to PMBG and Flector^® gel, the optimized ME showed the highest cumulative amount of DE permeated after 8 h and the in vivo anti-inflammatory efficacy in rat paw edema was sustained to 12 h after removal of ME applied to the skin confirming the formation of in-skin drug depot. Our results proposed that topical ME formulation, containing higher fraction of oil solubilized drug, could be promising for sustained transdermal delivery of drug.     

Synergistic enhancement of skin permeability by N-lauroylsarcosine and ethanol

To develop formulations for transdermal drug delivery, this study tested the hypothesis that the anionic surfactant, N-lauroylsarcosine (NLS), and ethanol synergistically increase skin permeability by increasing the fluidity of stratum corneum lipid structure. Skin permeability experiments showed that transdermal delivery of fluorescein across human cadaver epidermis was increased by up to 47-fold using formulations containing NLS in aqueous ethanol solutions. Skin permeability was increased by increasing NLS concentration in combination with 25-50% ethanol solutions. Skin permeability was shown to correlate with skin electrical conductivity measurements, changes in differential scanning calorimetry lipid transition peak temperature, and Fourier transform infrared spectroscopy CH stretching peak shifts indicative of stratum corneum lipid fluidization and changes in protein conformation. Evidence for lipid extraction was also evident, but did not appear to be responsible for the observed increases in skin permeability. We conclude that NLS in aqueous ethanol formulations can dramatically increase skin permeability by a mechanism involving synergistic lipid-fluidization activity in the stratum corneum.     

Drug delivery systems. 6. Transdermal drug delivery

Transdermal drug delivery system has been in existence for a long time. In the past, the most commonly applied systems were topically applied creams and ointments for dermatological disorders. The occurrence of systemic side-effects with some of these formulations is indicative of absorption through the skin. A number of drugs have been applied to the skin for systemic treatment. In a broad sense, the term transdermal delivery system includes all topically administered drug formulations intended to deliver the active ingredient into the general circulation. Transdermal therapeutic systems have been designed to provide controlled continuous delivery of drugs via the skin to the systemic circulation. The relative impermeability of skin is well known, and this is associated with its functions as a dual protective barrier against invasion by micro-organisms and the prevention of the loss of physiologically essential substances such as water. Elucidation of factors that contribute to this impermeability has made the use of skin as a route for controlled systemic drug delivery possible. Basically, four systems are available that allow for effective absorption of drugs across the skin. The microsealed system is a partition-controlled delivery system that contains a drug reservoir with a saturated suspension of drug in a water-miscible solvent homogeneously dispersed in a silicone elastomer matrix. A second system is the matrix-diffusion controlled system. The third and most widely used system for transdermal drug delivery is the membrane-permeation controlled system. A fourth system, recently made available, is the gradient-charged system. Additionally, advanced transdermal carriers include systems such as iontophoretic and sonophoretic systems, thermosetting gels, prodrugs, and liposomes. Many drugs have been formulated in transdermal systems, and others are being examined for the feasibility of their delivery in this manner (e.g., nicotine antihistamines, beta-blockers, calcium channel blockers, non-steroidal anti-inflammatory drugs, contraceptives, anti-arrhythmic drugs, insulin, antivirals, hormones, alpha-interferon, and cancer chemotherapeutic agents). Research also continues on various chemical penetration enhancers that may allow delivery of therapeutic substances. For example, penetration enhancers such as Azone may allow delivery of larger-sized molecules such as proteins and polypeptides.     

Formulation and evaluation of a testosterone transdermal spray

The long-term goal is to develop a spray formulation for transdermal testosterone delivery, and to optimize the drug's skin permeability. Testosterone transport from a series of ethanol/propylene glycol (PG)/water formulations was assessed in vitro across hairless rat skin, and the optimal composition determined. The formulation was then modified for delivery from a mechanical spray, and from an aerosol containing a high percentage of propellant. Drug transport was greatest from a saturated solution in 1:1:1 ethanol/PG/water (1.7 +/- 0.2 microg/cm(2) . h); five spray formulations were then tested, but only 1:1 ethanol/PG achieved a comparable flux. Increasing the % ethanol in the mixture increased evaporation rate but did not alter testosterone delivery. Formulation as an aerosol produced primarily unstable vehicles (phase separation, crystallization). Only 3:1 ethanol/PG remained stable, but no significant improvement in drug transport was observed (testosterone precipitated rapidly at the skin surface). The 1:1:1 ethanol/PG/water saturated solution suggested that some penetration enhancement was possible. Eliminating water to improve sprayability identified 1:1 ethanol/PG as a vehicle, which might allow transient supersaturation (and improved delivery). However, this effect was not improved by using a pressurized aerosol due to instability. Finally, testosterone fluxes were 5 to 10-fold lower than those required for useful transdermal therapy.     

Microemulsions for topical delivery of estradiol

Estradiol has been widely used for the treatment of hormonal insufficiencies. Due to its extensive first pass metabolism after oral administration, transdermal administration of estradiol in gels and emulsions has been used to improve its bioavailability, prolong activity and to optimize metabolic profile. The purpose of this study was to investigate microemulsions as delivery systems for estradiol. Various o/w microemulsions were used to deliver estradiol across human abdominal skin in vitro. Trasdermal flux of estradiol was determined using Franz-type diffusion cells and the samples were analyzed by high-performance liquid chromatography (HPLC). The permeation data showed that microemulsion formulations increased estradiol flux 200-700-fold over the control, but permeability coefficients were decreased by 5-18 times. The superior transdermal flux of estradiol was due to 1500-fold improvement in solubilization of estradiol by microemulsions. The results suggest that microemulsions are potential vehicles for improved topical delivery of estradiol.     

Design, development and evaluation of novel nanoemulsion formulations for transdermal potential of celecoxib

The aim of the present study was to investigate the potential of nanoemulsion formulations for transdermal delivery of celecoxib (CXB). The in vitro skin permeation profile of optimized formulations was compared with CXB gel and nanoemulsion gel. Significant increase in the steady state flux (Jss), permeability coefficient (Kp) and enhancement ratio (Er) was observed in nanoemulsion formulations T1 and T2 (p < 0.05). The highest value of these permeability parameters was obtained in formulation T2, which consisted of 2% (m/m) of CXB, 10% (m/m) of oil phase (Sefsol 218 and Triacetin), 50% (m/m) of surfactant mixture (Tween-80 and Transcutol-P) and 40% (m/m) water. The anti-inflammatory effects of formulation T2 showed a significant increase (p < 0.05) in inhibition after 24 h compared to CXB gel and nanoemulsion gel on carrageenan-induced paw edema in rats. These results suggested that nanoemulsions are potential vehicles for improved transdermal delivery of CXB.     

物理方法促进胰岛素经皮吸收的实验研究进展

目的胰岛素经皮吸收制剂是一种理想的胰岛素给药方式,但由于皮肤角质层的阻力、胰岛素分子在皮肤中的累积等因素限制了胰岛素的经皮给药。方法本文介绍了微针、电致孔、超声导入、离子导入等物理方法促进胰岛素经皮吸收实验研究进展。结果研究安全、有效、经济、方便的胰岛素透皮吸收物理促渗技术。结论随着对上述新技术、新方法实验研究的深入,物理促渗技术必将为胰岛素透皮吸收制剂的发展开辟更广阔的前景