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Current Trends in Biotechnology and PharmacyVol. 5 (1) 972-981 January 2011. ISSN 0973-8916 (Print), 2230-7303 (Online)973to liposomes produced in the presence of ethanolcomprise of hydroalcoholic or hydro/alcoholic/glycolic phospholipids with high concentration ofalcohol may be upto 50 % (2, 6, 12, 13, 14).The ethosomal system consists ofphospholipids, ethanol and water (15) Thephospholipids with various chemical structureincludes phosphatidylcoholine (PC), hydrogenatedPC, phosphatidylethanolamine (PE), phosphatidylglycerol (PPG), phosphatidylinositol (PI),hydrogenated PC etc (16). The nonaqueous phaserange between 22 % to 70 %. The alcohol maybe ethanol or isopropyl alcohol. Dyes oramphiphilic fluorescent probe such as D – 289,Rhodamine – 123 , fluorescence isothiocynate(FITC), 6 – carboxy fluorescence are often addedto ethosomes for characterization study (3, 17,18).Effect of high alcohol concentration: Ethanolis an established permeation enhancer and isproposed that it fluidizes the ethosomal lipids andstratum corneum bilayer thus allowing the soft,malleable vesicles to penetrate the disorganizedlipid bilayer (8). The relatively high concentrationof ethanol (20 – 50 %) is the main reason forbetter skin permeation ability and is packed lesstightly than conventional vesicles but hasequivalent stability and better solubility of manydrugs (3,19). Moreover the vesicular nature ofethosomal formulation could be modified byvarying the components ratio and phospholipids(20). Ethanol confers a surface negative netcharge to the ethosome which causes the size ofvesicles to decrease. The size of ethosomalvesicles increase with decreasing ethanolconcentration (3).Advantages of ethosomes1. Enhanced permeation of drug molecules toand through the skin to the systemiccirculation (3, 14).2. Contrary to deformation liposomes,ethosomes improve skin delivery of drugsboth under occlusive and non-occlusiveconditions (22).3. Since composition and components ofethosomes are safe, they have variousapplications in pharmaceutical, veterinaryand cosmetic field.4. Better patient compliance.5. Better stability and solubility of many drugsas compared to conventional vesicles.7. Relatively smaller size as compared toconventional vesicles.Limitations of ethosomes1. Poor yield (23).2. In case if shell locking is ineffective thenthe ethosomes may coalescence and fallapart on transfer into water.3. Loss of product during transfer form organicto water media (24)Methods of preparation ethosomes: Ethosomescan be prepared by two very simple and convenientmethods that is hot method (Fig 1 and Fig 2) andcold method (Fig 3) (16, 17, 18, 25)Fig.1. General method for the preparation of ethosomesAbdul Wahid et al
Current Trends in Biotechnology and PharmacyVol. 5 (1) 972-981 January 2011. ISSN 0973-8916 (Print), 2230-7303 (Online)9742. Vesicle size and size distribution: Ethosomesize and size distribution can be done by dynamiclight scattering method (DLS) using computerizedinspection system (27, 28).Fig.2. Hot method for the preparation of ethosomes3. Entrapment efficiency: The ability ofethosomes to efficiently entrap lipophilic andhydrophilic drugs can be measured byultracentrifugation technique, mini columncentrifugation method and fluorescencespectrophotometry (20, 29, 30).4. Glass transition temperature: The glasstransition temperature of the vesicular lipidsystems can be determined by using differentialscanning calorimetry (DSC) (31).5. Interfacial tension activity measurement:Interfacial Surface tension activity of ethosomescan be measured in aqueous solution by Du Nouyring tensiometer (32).6. Turbidity: It can be measured by nephalometer(14).Fig.3. Cold method for the preparation of ethosomesVarious methods of characterization ofethosomes1. Surface morphology: Transmission electronmicroscope (TEM) and Scanning electronmicroscope (SEM) can be used for vesicularshape and surface morphology studies. TEM canbe performed using phosphotungstic acid asnegative stain (26)7. Vesicle skin interaction study: Vesicle skininteraction study can be done by examining undertransmission electron microscopy or confocallaser scanning microscope (CSLM) orfluorescence microscope or eosin – hematoxylinstaining. For fluorescence microscopy ethosomesshould be loaded with fluorescence marker likerhodamine 123 (20, 27).7. Degree of deformability or Elasticitymeasurement: The elasticity of ethosome vesiclemembrane can be determined by extrusionmethod. The ethsomal formulation are extrudedthrough filter membrane (pore diameter 50 nm)using stainless steel filter holder of diameter 25nm, by applying a pressure of 2.5 bar (32).8. Zeta potential: zeta potential can be measuredby zeto meter or dynamic light scattering method(DLS) (20).Ethosomes: A Tool for Transdermal Drug Delivery
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