Ethosomes: Novel Approach in Transdermal Drug Delivery System

 

Roge Ashish B*, Sakhare Ram S, Bakal RL, Channawar MA, Bakde BV, Gawande SR and Chandewar AV

P. Wadhwani College of Pharmacy, Yavatmal

 

ABSTRACT:

Transdermal drug delivery system is emerging system as compaired to oral and parentral.in TDDS, patch system was developed to control the release of drug .Conventional transdermal drug delivery system achieved advantages over the oral and parenteral. Consequently a number of vesicular drug delivery systems such as liposomes, niosomes were been developed as novel transdermal drug delivery system. Firstly, it delivers the drug at a rate directed by the needs of the body, over the period of treatment. Secondly, it channel the active entity to the site of action. However, TDDS has limited market success due to the barrier properties of the Stratum Corneum and stability of formulation. ethosomes is better achievement in vesicular drug delivery system, helpful to achieve  goal needed by NTDDS. Ethosomes are noninvasive delivery carriers that enable drugs to reach the deep skin layers and/or the systemic circulation. This review focus on introduction, mechanism of penetration, method of preparation, methods of characterization  and application in the field.

 

KEYWORDS: TDDS, CTDDS, NTDDS, Stratum  Corneum , Vesicular Drug Delivery System,  Ethosomes.

 

INTRODUCTION:

Development of Transdermal drug delivery is going on because of many advantages offered by it as compaired to traditional drug delivery systems, including oral and parenteral drug delivery system. Advantages claimed are increased patient acceptability (non invasiveness), avoidance of gastrointestinal disturbances and first pass metabolism of the drug ,relatively large and readily accessible surface area (1Š2 m2) for absorption, ease of application and termination of therapy.

 

SKIN AS SITE FOR TRANSDERMAL DRUG ADMINISTRATION:

The skin is one of the most extensive and readily accessible organs of the human body. The skin of an average adult body covers a surface area of approximately 2 m 2 and receives about one – third of the blood circulating through the body. It is elastic, rugged, and, under normal physiological conditions, self - regenerating. It serves as a barrier against physical and chemical attacks and shields the body from invasion by microorganisms. Microscopically the skin is a multilayered organ composed of, anatomically, many histological layers, but it is generally described in terms of three tissue layers: the epidermis, the dermis, and the subcutaneous fat tissue.

 

Microscopic sections of the epidermis show two main parts: the stratum corneum and the stratum germinativum. The stratum corneum (SC) represents the end product of the differentiation process initially started in the basal layer of the epidermis with the formation of keratinocytes by mitotic division. The stratum corneum forms the outermost layer of the epidermis and consists of many layers of compacted, . attened, dehydrated, keratinized cells in stratified layers. It is composed of dead cells (corneocytes)  interdispersed within a lipid rich matrix. It is the “brick and mortar” architecture and lipophilic nature of the SC, which primarily accounts for the barrier properties of the skin .


The intracellular space is dense offering little freedom of movement to orgnic molecule that may be dissolved within it. Morever because of its remarkable ionic character, the intracellular keratin mass borders on being thermodynamically impenetrable to organic molecules. The SC is also known to exhibit selective permeability and allows only relatively lipophilic compounds to diffuse into the lower layers. As a result of the dead nature of the SC, solute transport across this layer is primarily by passive diffusion  in accordance with Fick’s Law and no active transport processes have been identified. For a drug to be delivered passively via the skin it needs to have a suitable lipophilicity and a molecular weight < 500 Da.1,2.

 

APPROACHES TO TDDS:

Transdermal drug delivery system  has developed not only not only to bypass the hepatic Ist - pass elimination but also to maintain a constant, prolonged, and therapeutically effective drug level in the body. Recently there has been an increasing awareness that the benefits of intravenous drug infusion can be easily duplicated, without its potential hazards, by continuos transdermal drug administration through intact skin . The conventional transdermal drug delivery systems involve a patch, in which the drug permeates through various layers of skin, via a passive diffusion pathway.  However, this limits the basic potential of these systems, as stratum corneum is the most formidable barrier to the passage of most of the drugs, except for highly lipophilic, low molecular weight drugs. To overcome the stratum corneum barrier, various mechanisms were been investigated, including use of chemical or physical enhancers, such as iontophoresis, sonophoresis, etc. Consequently a number of vesicular drug delivery systems such as liposomes, niosomes were been developed as novel transdermal drug delivery system. Firstly, it delivers the drug at a rate directed by the needs of the body, over the period of treatment. Secondly, it channel the active entity to the site of action 3. Novel Transdermal Drug Delivery System (NTDDS) offers many advantages as compared to Conventional Transdermal drug delivery systems (CTDDS). The ability of the skin to impede the permeation of molecules means that, to date; only a small number of pharmaceutically active compounds have been suitable for conventional transdermal delivery. However, TDDS has limited market success due to the barrier properties of the Stratum Corneum. Drug delivery from liposomes in transdermal formulation has been studied for many purposes but unstable nature and poor skin permeation limits their use for topical delivery. In order to increase the stability of liposomes, the concept of proliposomes was proposed . This approach was extended to niosomes, which exhibited superior stability as compared to liposomes . However, due to poor skin permeability, liposomes and niosomes could not be successfully used for systemic drug delivery and their use was limited for topical use . To overcome problems of poor skin permeability Touitou et al  recently introduced  new vesicular carrier system  ethosomes, respectively for non-invasive delivery of drugs into or across the skin. Ethosomes incorporated penetration enhancers (alcohols and polyols), respectively, to influence the properties of vesicles and stratum corneum1.

 

ETHOSOMAL SYSTEMS:

Ethosomal systems, novel permeation-enhancing lipid carriers embodying ethanol, contain vesicles with interdigitated fluid bilayers. Ethosomes are noninvasive delivery carriers that enable drugs to reach the deep skin layers and/or the systemic circulation3. Ethosomes are soft, malleable vesicles tailored for enhanced delivery of active agents3.Ethosomes composed of mainly of phospholipids, ethanol (relatively high concentration) and water. These “soft vesicles” represents novel vesicular carrier for enhanced delivery to/through skin. Ethosomes have a negative charge that increases with increasing ethanol concentration 12. Ethosomes are sophisticated vesicular delivery carriers that are capable of delivering various chemical applications. The size of Ethosomes can be modulated to range anywhere from 30 nm to a few microns. Visualization by dynamic light scattering showed that Ethosomes could be unilamellar or multilamellar through to the core. Although ethosomal systems are conceptually sophisticated, they are characterized by simplicity in their preparation, safety, and efficacy--a combination that can highly expand their application3. Ethosomal systems were found to be significantly superior at delivering drugs through the skin in terms of both quantity and depth when compared to liposome sand to many commercial transdermal and dermal delivery systems4.

 

  Visualization of Ethosome          Visualization of Ethosome

(TEM magnification 315000)             (SEM x 100,000)

 

COMPOSITION6

The ethosomes are vesicular carrier comprise of hydroalcoholic or hydro/alcoholic/glycolic phospholipid in which the concentration of alcohols or their combination is relatively high. Typically, ethosomes may contain phospholipids with various chemical structures like phosphatidylcholine (PC), hydrogenated PC, phosphatidic acid (PA), phosphatidylserine (PS), phosphatidylethanolamine (PE), phosphatidylglycerol (PPG), phosphatidylinositol (PI), hydrogenated PC, alcohol (ethanol or isopropyl alcohol), water and propylene glycol (or other glycols) . Such a composition enables delivery of high concentration of active ingredients through skin. Drug delivery can be modulated by altering alcohol: water or alcohol-polyol: water ratio. Some preferred phospholipids are soya phospholipids such as Phospholipon 90 (PL-90). It is usually employed in a range of 0.5-10% w/w. Cholesterol at concentrations ranging between 0.1-1% can also be added to the preparation. Examples of alcohols, which can be used, include ethanol and isopropyl alcohol. Among glycols, propylene glycol and Transcutol are generally used. In addition, non-ionic surfactants (PEG-alkyl ethers) can be combined with the phospholipids in these preparations. Cationic lipids like cocoamide, POE alkyl amines, dodecylamine, cetrimide etc. can be added too. The concentration of alcohol in the final product may range from 20 to 50%. The concentration of the non-aqueous phase (alcohol and glycol combination) may range between 22 to 70% (Table 1).

 

 

Table 1: Different Additives Employed In Formulation of Ethosomes

Class
Example
Uses

Phospholipid

Soya phosphatidyl choline

Egg phosphatidyl choline

Dipalmityl phosphatidyl choline

Distearyl phosphatidyl choline

Vesicles forming component

Polyglycol

Propylene glycol

Transcutol RTM

As a skin penetration enhancer

 

Alcohol

Ethanol

Isopropyl alcohol

For providing the softness for vesicle membrane

As a penetration enhancer

Cholesterol

Cholesterol

For providing the stability to vesicle membrane

Dye

Rhodamine-123

Rhodamine red

Fluorescene Isothiocynate (FITC)

6- Carboxy fluorescence

For characterization study

Vehicle

Carbopol Š934

As a gel former

 

Fig. 1  Proposed mechanism for penetration of molecule from ethosomal system across the lipid domain of stratum corneum

 

 

MECHANISM OF DRUG PENETRATION:5

The enhanced delivery of actives using ethosomes over liposomes can be ascribed to an interaction between ethosomes and skin lipids. A possible mechanism for this interaction has been proposed. It is thought that the first part of the mechanism is due to the ‘ethanol effect’, whereby intercalation of the ethanol into intercellular lipids increasing lipid fluidity and decreases the density of the lipid multilayer.This is followed by the ‘ethosome effect’, which includes inter lipid penetration and permeation by the opening of new pathways due to the malleability and fusion of ethosomes with skin lipids, resulting in the release of the drug in deep layers of the skin, shown in Figure 1.

 

METHOD FOR PREPARING ETHOSOMES:1

Ethosomal formulation may be prepared by hot or cold method as described below. Both the methods are convenient, do not require any sophisticated equipment and are easy to scale up at industrial level.

 

1 Cold Method:

This is the most common method utilized for the preparation of ethosomal formulation. In this method phospholipid, drug and other lipid materials are dissolved in ethanol in a covered vessel at room temperature by vigorous stirring with the use of mixer. Propylene glycol or other polyol is added during stirring. This mixture is heated to 300C in a water bath. The water heated to 300C in a separate vessel is added to the mixture, which is then stirred for 5 min in a covered vessel. The vesicle size of ethosomal formulation can be decreased to desire extend using sonication  or extrusion  method. Finally, the formulation is stored under refrigeration .

 

2 Hot method:

In this method phospholipid is dispersed in water by heating in a water bath at 400C until a colloidal solution is obtained. In a separate vessel ethanol and propylene glycol are mixed and heated to 400C. Once both mixtures reach 400C, the organic phase is added to the aqueous one. The drug is dissolved in water or ethanol depending on its hydrophilic/ hydrophobic properties . The vesicle size of ethosomal formulation can be decreased to the desire extent using probe sonication or extrusion method.

 

METHODS OF CHARACTERIZATION:1,5

1.              Visualization: Visualization of ethosomes can be done using transmission electron microscopy (TEM) and by scanning electron microscopy (SEM) .

2.              Vesicle size and Zeta potential: Particle size and zeta potential can be determined by dynamic light scattering (DLS) using a computerized inspection system and photon correlation spectroscopy (PCS) .

3.              Entrapment Efficiency: The entrapment efficiency of drug by ethosomes can be measured by the ultracentrifugation technique  ,Mini column centrifugation method and Fluorescence spectrophotometry.

4.              Transition Temperature: The transition temperature of the vesicular lipid systems can be determined by using differential scanning calorimetry .

5.              Surface Tension Activity Measurement: The surface tension activity of drug in aqueous solution can be measured by the ring method in a Du Nouy ring tensiometer .

6.              Vesicle Stability : The stability of vesicles can be determined by assessing the size and structure of the vesicles over time. Mean size is measured by DLS and structure changes are observed by TEM .

7.              Drug Content : Drug can be quantified by a modified high performance liquid chromatographic method  .

8.              Penetration and Permeation Studies: Depth of penetration from ethosomes can be visualized by confocal laser scanning microscopy (CLSM)  .

9.              Turbidity  :Turbidity is determined by  Nephalometer.

10.           Phospholipid-ethanol interaction: Interaction between phospolipid and thanol is studied  by 31P NMR and Differential scanning calorimeter

11.           In vitro drug release study: In vitro drug release is studied by  Franz diffusion cell with artificial or biological membrane, Dialysis bag diffusion .

12.           Degree of deformability :  Deformability is dtermined by Extrusion method .

 

ADVANTAGES OF ETHOSOMAL DRUG DELIVERY:5

In comparison to other transdermal & dermal delivery systems,

1.                Ethosomes are enhanced permeation of drug through skin for transdermal and dermal delivery.

2.                Ethosomes are platform for the delivery of large and diverse group of drugs (peptides, protein molecules)

3.                Ethosome composition is safe and the components are approved for pharmaceutical and cosmetic use.

4.            Low risk profile- The technology has no large-scale drug development risk since the toxicological profiles of the ethosomal components are well documented in the scientific literature.

5.            High patient compliance- The Ethosomal drug is administrated in semisolid form (gel or cream), producing high patient compliance by is high. In contrast, Iontophoresis and Phonophoresis are relatively complicated to use which will affect patient compliance.

6.            High market attractiveness for products with proprietary technology. Relatively simple to manufacture with no complicated technical investments required for production of Ethosomes.

7.            The Ethosomal system is passive, non-invasive and is available for immediate commercialization.

8.            Various application in Pharmaceutical, Veterinary, Cosmetic field.

 

APPLICATION:

Ethosomes enhanced the intracellular delivery of molecules into 3T3 dermal fibroblasts and significantly improved the antiproliferative activity of 5-FU in human keratinocytes. These interesting results support further investigation of delivery of antiproliferative drugs from ethosomes into cancer cells located in deep layers of the skin6.

 

Complex lipid molecule, ethosomes can increase the transdermal flux, prolong the release and present an attractive route for the sustained delivery of zidovudine7.

 

Because of their unique structure, ethosomes are able to encapsulate and deliver through the skin highly lipophilic molecules such as cannabinoids, testosterone, and minoxidil, as well as cationic drugs such as propranolol and trihexyphenidil8.

 

Preliminary studies with plasmids and insulin revealed that the ethosomal carrier may be used for enhanced delivery of these agents8.

 

Horwitz et al. reported that a 5 % acyclovir ethosomal preparation compared to the 5 % acyclovir cream showed significant improvements in treatment of herpetic infections 9 Dayan et al. investigated the delivery of trihexyphenidyl HCl (THP) from ethosomes versus classic liposomes. As the THP concentration was increased from 0 to 3%, the size of the vesicles decreased from 154 to 90 nm. This is most likely due to the surface activity of THP (critical micelle concentration of 5.9 mg/ml), as measured in this work. In addition, the ethosome zeta potential value increased as a function of THP concentration, from -4.5 to +10.4 when the THP concentration was increased from 0 to 3%. In contrast, THP liposomes were much larger and their charge was not affected by THP. When compared with standard liposomes, ethosomes had a higher entrapment capacity and a greater ability to deliver entrapped fluorescent probe to the deeper layers of skin. The flux of THP through nude mouse skin from THP ethosomes (0.21 mg/cm2 h) was 87, 51 and 4.5 times higher than from liposomes10.

 

CONCLUSION:

From the above review , it is conclude that ethosomes posses great advantages over the liposomes. It may achieve the goal needed by novel vesicular drug delivery system. Because of its properties ,simplicity in method of preparation and characterization. It may improve the market demand of  transdermal  drug delivery system.

REFERENCES:

1.        Ethosomes  a recent approach in transdermal-topical delevery of bioactives.htm

2.        Marc.B.Brown,Mathew.J. Trayner,Gary.P. Martyyn, and Frankean.K.Akomeah. Transdermal drug delivery system,Skin perturbation device,Methods in molecular biology.437:119.

3.        Biju SS, Talegaonkar S, Mishra PR, Khar RK. Vesicular systems: An overview. Indian J Pharm Sci. 2006;68:141-53.

4.        Novel Therapeutic Technologies.Htm.

5.        Sanjay Patel. Ethosomes: A Promising Tool For Transdermal Delivery Of Drug. Pharmainfo net. 2007; 5: 2.

6.        E. Touitou, D. Ainbinder, B. Godin.Ethosomes for enhanced antiproliferative effect of anticancer drugs . School of Pharmacy, Hebrew University of Jerusalem.

7.        S Jain, RB Umamaheshwari, D Bhadra, NK Jain.Ethosomes  a novel vesicular carries for enhanced transdermal delivery of an  anti HIV agent .Indian J Pharm Sci. 2004; 66: 72-81.

8.        Godin B, Touitou E.Ethosomes: new prospects in transdermal delivery. Crit Rev Ther Drug Carrier Syst. 2003;20(1):63-102.

9.        Horwitz E, Pisanty S, Czerninski R, Helser M, Eliav E, and Touitou E, A clinical evaluation of a novel liposomal carrier for acyclovir in the topical treatment of recurrent herpes labialis, Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod., 1999;88:700-705.

10.     Dayan N, and Touitou E, Carrier for skin delivery of trihexyphenidyl HCl: Ethosomes vs liposomes. Biomaterials, 2002;21:1879-1885.

 

Received on 11.11.2009

Accepted on 05.01.2010        

© A&V Publication all right reserved

Research Journal of Pharmaceutical Dosage Forms and Technology. 2(1): Jan. –Feb. 2010, 23-27