The ethosomal systems gained a great attention for the researchers to overcome problems associated with liposomal vesicles. These systems are best alternative for conventional oral and parenteral dosage forms. These systems are very successful in crossing the barrier and overcoming the problems associated with stratum corneum by encapsulating the drugs in these vesicles, ethosomes are noninvasive drug delivery vesicle carriers where these enable drugs to penetrate or permeate in to deeper layers of skin or into systemic circulation. The preparation is very easy, convenient and one of the most gullible methods for drug transport across the skin use of vesicle formulations as drug delivery systems. As the formulation application mode itself saying that which is very suitable for the drugs which are unfavorable to administer orally, as well as these formulations are suitable for the drugs which are having gastrointestinal toxicity and pain free administration is added advantage. The mini-review aims to reveal the different noteworthy drugs which are formulated form year 2000 to mid 2024, what are the different kinds of methods adopted in preparing the ethosomes and future prospects. 

The human body is covered by a layer which is known as skin. It receives about one third blood that circulates throughout the body. The drug absorption is higher as the surface of the skin contains sweat pores and hair follicles per each centimeter square, by mean of this components more surface area is possible, which enables grater rate of drug absorption [1-3]. Transdermal formulation have gained the great importance over conventional dosage forms in recent few years such as, circumvention of fluctuation which appears at gastrointestinal absorption, improving the bioavailability of drug by transporting them via systemic circulation by neglecting the hepatic metabolism [4-5]. In order to enhance the permeation of molecules when administered as transdermal applications various passive and active approaches are proposed like penetration enhancers, supersaturated systems, iontophoresis, phonophoresis, use of micro needles and jet injections, among all these techniques penetration enhancement is concentrated mostly [6-8]. Only few bioactive agents are administered transdermally in current scenario [9-12]. Drug delivery research entered a new era with the discovery of liposomes, and since then, numerous vesicular systems have been developed [13]. A liposome is a tiny synthetic vesicle with at least one lipid bilayer that is spherical in shape [14]. Liposomal delivery vehicles for the administration of pharmaceutical medications and nutrients, such as lipid nanoparticles in mRNA vaccines and DNA vaccines, can be employed as drug delivery vehicles due to their hydrophobicity and/or hydrophilicity, biocompatibility, particle size, and many other features [15]. 

Figure 1: Ethosomes

In 1992, Cevc and Blume also developed transferosomes, which are elastic or pliable liposomes [16]. After transferosomes, Touitou et al.'s groundbreaking research led to the identification of ethosomes, a distinct kind of lipid vesicular system [17].  Because of their smaller size, reduced entrapment effectiveness, and negative zeta potential, modified liposomes were developed. Ethosomes are novel modified lipid carriers composed of phospholipids, water, and ethanol [18-20]. Ethosomes include relatively large concentrations of ethanol in addition to phospholipids and water, which have been proposed to have enhanced vesicular characteristics and skin penetration [21-23] (Figure 1). Ethosomes have rapidly become a distinctive drug delivery mechanism. They are classified as binary, classical, and transethosomes depending on their contents, such as alcohol [24-26]. The mini review contains the information of different drugs which were designed as ethosomes and types/ methods adopted to process them.

Due to the requirement of controlled or sustained delivery of molecules vesicular systems had been adopted from past few years [27]. Vesicles are 

nothing but a colloidal moieties which is composed of aqueous core where it is bounded by amphiphilic bodies in a dual layer pattern, single layered (unilamellar) or multilayered (multilamellar) concentric are possible in case of overindulgence of water [28-29]. The behaviour of vesicle is directed by physicochemical properties such as charge, size, lamellarity and thermodynamic phase and bilayer elasticity and the following are influenced by formulation considerations and vesicles play several roles in dermal and transdermal options [30]. It was evidenced from the past recent research reports not the how effectively vesicles work and focused on the development from conventional studies in 1980s to mid 2024 [31-36].

2.1. Composition of ethosomes

The ethosomal vesicles are comprised in a way such alcohol content is grater and the different ingredients employed in manufacturing the ethosomes in general they are likely vesicle forming agents, penetration enhancers, stabilizer, gel formers, and dyes and few examples are in below Table 1.

Table 1: Formulation considerations

2.2. Methods employed to prepare ethosomes of various drugs 

There are different methods to process the ethosomal preparations as enlisted in below Table 2.

Table 2: Ethosomal preparation methods

2.3. Description of different methods to prepare ethosomal vesicles

2.3.1. Thin film hydration 

Thin film hydration was employed in the ethosomal research bench as procedural technique to carry drug molecules, however evaporation is required in this method. The ethosomes can be achieved by mixing of drug with soy lecithin, phosphatidylcholine, cholesterol in methanol at required concentrations. The organic layer can be evaporated by using rotary evaporation method under lipid transition temperature under the subjection of vacuum [41, 43, 47, 52]. 

2.3.2. Cold method 

Firstly the drug is dispersed in ethanol followed by solubilizing the soylecithins, phospholipids either both are any one of the excipients under magnetic stirring. A small quantity propylene glycol can be added for promoting the sooth penetration. The formed solution is covered to prevent the evaporation of ethanol from the ethosomal formulation, stirring should be continued for 30 minutes at room temperature. The final preparation should undergo centrifugation under 20x103 revolutions per minute for not less than three hours. The formulation can be considered for further investigations if phase separation was not found after centrifugation because the step reveals the stability of the product. Refrigeration recommended to store the vesicles [18, 37, 40, 42, 44-46, 48, 50-51, 53-54, 58, 60-61, 64-65, 69, 72, 75-76, 78-79, 81].

2.3.3. Hot method 

This method follows as such lecithin, cholesterol solubilized in ethanol with drug under mixing with help of magnetic stirrer for 30 minutes by maintaining 40 oC heat to boil the lipid mixture the opening of the round bottomed flask should be closed in order to retain ethanol content water for injection (distilled water) can be added slowly on maintain continuous stirring which results the colloidal ethosomal suspension. The obtained suspension can be sonicated for size reduction [53, 55-57, 59, 63, 65].

2.3.4. Ethanol injection/sonication method

In the method, organic media which holds solubilized phospholipid in ethanol where it should be injected into aqueous media by employing a syringe system under the flow rate of 200 µL/min, can be sonicated using probe sonicator for homogenizing the mixture [39, 49, 62, 73-74, 77].

2.3.5. Trans menbrane pH-gradient method 

The process is done two steps: which involves in making binary ethosomes and active loading of drug. Initially, the phospholipid dissolved in alcoholic phase which comprises both ethanol and propylene glycol. Upon constant stirring under 700 rpm slowly a citrate buffer solution can be added and system is approximately maintained 30±10C while running this process later on cooled at room temperature then blank binary ethosomes are formed. Upon formation blank binary ethosomes drug loading can done actively into ethosomes under 700 rpm constatnt stirring to obtain effective dispersion drug can be solubilized. The pH gradient alkaline layer (external) and the in the internal layer (acid) of ethosomal system can be attained by addition 0.5 molar sodium hydroxide solution to adjust external pH. Later on the system is incubated under suitable temperature for a certain time period. Where this facilitates unionized drug can pass actively via ethosomal lipid bilayer and gets entrapped or encapsulates into vesicles [82].

This phase is very important for any type of pharmaceutical formulation and there are various parameters which are implemented on ethosomal systems to optimize them to provide a safe and effective formulation. The various parameters are explained below.

Morphology

The morphology is majorly considered in the field of nanomaterials and vesicular drug delivery systems. This parameter can be assessed by employing the microscopic techniques like scanning electron and transmission electron microscopic studies are useful in determining the architecture of the vesicles. The mean size of the vesicle can be determined by adopting photon correlation spectroscopy [9, 77]. Dynamic light scattering would be an added advantage on applying this technique in morphological studies which results about the size and zeta potential of the vesicle [40]. 

Dialysis method can be employed for determining the entrapment efficiency. In this method cellulose acetate membrane plays a major role in this procedure so it should be soaked in suitable solution to moisten the membrane. The required sample should be taken in dialysis bag furtherly the bag is transferred in to the receiver media on magnetic stirrer. Then sample to be withdrawn at respective time points and replace the same media (suitable buffer). Upon the separation of free drug lysing agent triton X can be added in the required amount (for example 0.1% v/v) and then subject it for drug content analysis [40].  The entrapment efficiency reveals about the amount of drug entrapped in to the vesicles and it can be calculated by applying the following equation which is written below [55].

5. Permeation Studies 

In vitro permeation study using synthetic membranes and skin 

The study can be carried out by using Franz diffusion cell apparatus with synthetic membranes. The prepared formulation can be placed on the superior portion on donor compartment and as well as by maintaining the temperature 370 ± 2 0C. Samples should be collected at appropriate time interval meanwhile, the same amount dissolution solution to be replaced freshly prepared receptor media. Then collected sample should undergo further analysis [51]. The synthetic membranes are replaced skin of any experimental subjects for conducting the permeation analysis of drug which permeated through skin or natural membranes by maintaining all the above conditions [76].

Ex vivo permeation study

The studies can conducted by using animals skin (Wister rats, Guinea pig, Goat, and Rabbit) can be used in while conducting experimental studies. The transdermal preparations like patch or gels can be conducted by assessing in between control formulation and optimized formulation, finding can be finalized upon acquired data of steady state flux (Jss), Permeability coefficient (P) diffusion coefficient (D) and further it is important find out whether it follows fickian or non fickian release [81].

Confocal laser microscopic studies 

The confocal laser microscopic technique can be employed to study the penetration ethosomal drug formulations. During the permeation analysis any type of dyes can be entrapped into the ethosomal vesicles. The dye which is present in the deeper layers of the skin signifies the extent of distribution of drug. This technique helps a researcher to find about penetration capacity of drug for proving the ethosomal vesicles might be best due high penetration of drug which is possible due to ethanol which is affecting the intracellular portion of stratum corneum [80].

The stratum coreneum does not permit most drug and other therapeutic moieties to pass through. The ethosomal vesicles are specially designed with high amount of ethanol which hammers, the strong lipid layer of stratum coreneum which can escape the damage of the vesicles finally which attains the delivery of drug in to deeper layers of the skin. Along with the non-invasive drug delivery of  small and larger drug molecules it also provide good patient compliance and cost effective acyclovir ethosomal formulation supports and bench marks this statement.   

However ethosomes need more concentration in preventing the evaporation by describing closure techniques clearly, reporting the skin irritation studies of the formulation is required, the proper stability assessment is recommended to be carried out for the drug which are used in the treatment of hair transplantation therapy like finasteride this technique might give commercial importance over problems associated with marketed finasteride formulation.  This topic has enormous scope for the young researchers to design and apply new strategies for effective drug delivery.

Not applicable

Yes

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Dr. RV is grateful to Dr. Ch. V. Rajasekhar for his kind support and encouragement.