TRANSDERMAL DRUG DELIVERY THROUGH

VESICLES

Jolly R. ParikhAssistant ProfessorA. R. College of PharmacyVallabh Vidhyanagar

TRANSDERMAL DELIVERY

• It is the delivery of drugs by topical application of drugs on skin.

•Drug is delivered from the outside of the skin through its various layers into the bloodstream.

ADVANTAGES OF TRANSDERMAL DELIVERY• The system avoids the chemically hostile GI environme

nt.• No GI distress or other physiological contraindications

of the oral route.• Can provide adequate absorption of certain drugs.• Increased patient compliance.• Avoids first-pass effect.• Allows effective use of drugs with short biological half-

life.• Allow administration of drugs with narrow therapeutic

windows.• Provides controlled plasma levels of very potent drugs.• Drug input can be promptly interrupted when toxicity o

ccurs.

Disadvantages of transdermal delivery

•Drug that require high blood levels cannot be administered.

•Drug or drug formulation may cause skin irritation or sensitization.

•Low permeability of drugs through stratum corneum the outermost layer of the skin.

Structure of human skin

• Human skin– The stratified avascular cellular epidermi

s– An underlying dermis of connective tissu

e– Subcutaneous layer

• Possible pathways for a penetrant to cross the skin barrier. (1) across the intact horny layer, (2) through the hair follicles with the associated sebaceous glands, or (3) via the sweat glands

Routes of penetration through skin

• There are three potential pathways to deliver the drugs through skin:

1. Through hair follicles2. Through sweat ducts3. Through stratum corneum- Transcellular route

• Fractional appendageal area available for transport is 0.1%. Therefore this route contributes negligibly to steady state drug flux.

• This pathway is important for ions and large polar molecules as well as polymers and colloidal particles which target follicles.

• The intact stratum corneum provides the main barrier to skin delivery.

Factors influencing the permeation of drugs through skin

• Skin structure and its properties: Integrity and thickness of stratum corneum.

• The penetrating molecule and its physical-chemical relationship to skin and the delivery platform: Physicochemical properties of penetrant (pKa, molecular size, stability, binding affinity, solubility, partition coefficient.

• The platform or delivery system carrying the penetrant.

• The combination of skin, penetrant, and delivery system.

• Density of sweat glands and folicles.• Skin hydration.• Vehicle effects.

Barriers to Transdermal delivery

• Structure of stratum corneum is compared with that of a brick wall of- with the coeneocytes acting as bricks surrounded by a mortar of intercellular lipid lamallae.

• The highly organized lipid lamallae plays an essential role in the barrier properties of stratum corneum.

• Most techniques are aimed to disrupt and weaken the highly organized intercellular lipids in an attempt to enhance drug transport across the skin barriers.

STRATEGIES FOR TRANSDERMAL DELIVERY

Drug/ vehicle interaction

Vesicles and particles

Stratum corneumbypassed

Electrically assisted methods

Drug / prodrug

Chemicalpotential

Ion paircoacervates

Eutectic systems

Liposomes &Analogues

High velocity particles

Micro needle array

Ablation

Follicular delivery

Ultrasound

Iontophoresis

Magnetophoresis

Photomechanical thermal wave

Stratum corneummodified

Hydration

Chemical Enhancers

STRATEGIES FOR TRANSDERMAL DELIVERY

Drug/ vehicle interaction:• Selection of drug with correct physicochemical properties to

translocate barrier at an acceptable rate.• Drug should be at its highest thermodynamic activity for

maximum penetration.• Charged molecules do not penetrate SC but forming ion pair

complex increases permeation into SC lipids.• Eutectics of drug with terpenes or menthol increases

permeation.Vesicles and particles• Powder jet systems fires solid particles through SC into lower

skin layers.Modification of SC:• Hydration of stratum corneum increases penetration as water

opens up the compact structure of horny layer.• Penetration enhancers like surfactants, sulphoxides,

pyrrolidones, fatty acid esters improves penetration.• Solvents enter SC and change its solution properties by

altering chemical environment and thus increasing partitioning of drug into horny layer.

STRATEGIES FOR TRANSDERMAL DELIVERY

Stratum corneum bypassed: Micro needle array• Use of solid silicone microneedles[400]/hollow metal needles

filled with drug solution which insert drug below the barrier• Laser ablation using high powered pulses to vaporize a section

of horny layer so as to produce permeable skin regions or chemical peeling is also employed

• Follicular delivery: the poly sebaceous unit hair follicle, hair shaft and sebaceous gland provides a route that bypasses intact SC.

• Electrically assisted methods:• Application of a preparation topically and massaging with

ultrasound source. Ultrasound energy disrupts lipid packing in SC by cavitations.

• Iontophoresis is electrical delivery of charged molecules into tissues by passing electric current through a drug containing electrode in contact with the skin.

• Skin electroporation is creation of transient aqueous pores in the lipid bilayers of skin by applying short electrical pulses for mili or microseconds.

• Magnetophoresis is application of magnetic fields to move diamagnetic materials through skin

• Photomechanical waves: A drug solution is placed on the skin covered by a black polystyrene target which is irradiated with laser pulse. The resultant photomechanical wave stresses the horny layer and enhances drug delivery.

INTRODUCTION TO VESICULAR SYSTEMS

• Vesicles are water filled colloidal particles• The walls of these capsules consist of amphiphilic

molecules in bilayer conformation.• In excess of water these amphiphiles can form

one(unilamellar) or more (multilamellar) concentric layers.

• Hydrophilic drugs can be incorporated into the internal aqueous compartment, whereas amphiphilic, lipophilic and charged drugs can be associated with the vesicle bilayer by hydrophobic or electrostatic attractions

• A wide variety of lipids and surfactants can be used to prepare vesicles.

• The basic structure of vesicles is shown in the following figure:

GLOSSARY OF VESICULAR SYSTEMS• Vesicles: water-filled colloidal particles. The walls of these

particles consist of amphiphilic molecules in a bilayer conformation.

• Liposomes: vesicles prepared from mainly phospholipids

• Liquid-state vesicles: the amphiphiles in the bilayers of these vesicles form a liquid phase.

• Non-ionic surfactant vesicles or niosomes: vesicles prepared from mainly non-ionic surfactants.

• Deformable non-ionic surfactant vesicles: vesicles prepared from mainly non-ionic surfactants using a surfactant composition that results in deformable bilayers.

• Transfersomes1: the walls of these vesicles consist of phospholipids and an edge activator, which results in deformable bilayers.

• Gel-state vesicles: the amphiphiles in the bilayers of these vesicles form a gel-phase.

Rationale for using vesicles in dermal and transdermal delivery

Vesicles act as• Act as drug carriers to deliver entrapped drug

molecules into or across the skin.• Act as penetration enhancers owing to the

penetration of the individual lipid components into the stratum corneum and subsequently alteration of intercellular lipid lamellae.

• Vesicles can penetrate the outer layer of the stratum corneum where desosomal linkages become disrupted and keratinocytes are less tightly bound.

• Lipid vesicles may fuse with endogenous lipids on the surface or in outermost layers of stratum corneum. This fusion is followed by structural changes in the deeper layers of stratum corneum which are presumed to be the result of intercellular diffusion of vesicle lipid components to the deeper layersas well as intercation with and disruption of endogenous lipid lamallae. This will lead to increased permeation rates.

ROLE OF LIPOSOMES IN TRANSDERMAL DELIVERY

• Liposomes are simple microscopic vesicles in which lipid bilayer structures are present with an aqueous volume entirely enclosed by a membrane composed of lipids.

• Liposomes can enhance drug delivery through skin routes by various mechanisms:

Liposomes

Permeation enhancer effect

Direct transfer of drug between Liposomes and skin

Flexible vesicles

Disruption of SC lipids

High partitioning

Drug solubility

Affinity betweenLiposomes & Skin

Introduction of liposomes into skin

Transdermal osmotic ingredient

Hydration force

Role of Liposomes• Liposomes may act as permeation enhancers by

penetration of individual lipid components.• Phospholipids are able to diffuse into SC and interaction

and enhancer effects are based on lipid mixing of Liposomal phospholipids with lipid bilayers of skin.

• Phospholipids can disrupt the bilayer fluidity in the SC decreasing barrier properties of skin.

• Phospholipids in Liposomes may mix with SC lipids creating a lipid rich environment. This lipid depot in skin is preferred by lipophilic drugs resulting in enhanced skin uptake. Phospholipids may also act as solubilizers to increase solubility of lipophilic drugs such as indomethacin & miconazole.

• The type of phospholipids also play an important role in transdermal flux of drugs. Egg PC, soybean PC, Dioleylphosphatidyl ethanolamine increase drug permeation through skin while distearoyl PC does not. EPC,SPC and DOPE have low value of gel liquid crystalline phase transition temperature and they are in a fluid state at skin temp of 32oC.The fluid state phospholipids disturb the rigid bilayer structure of skin lipids leading to increased drug partitioning.

Role of Liposomes• The mechanism of SC liposome interaction have been

studied using DSC, x-ray diffraction, electro paramagnetic resonance, pluoro micrography, & con focal laser scanning microscopy.

• Most of the investigators have suggested that direct transfer of drug between phospholipid bilayers of Liposomes and lipid content of skin causes enhancement of drug delivery via skin.

• Liposomes do not act as permeation enhancers but provide the necessary physicochemical environment for transfer of drugs into the skin.

• Liposome penetration into skin largely depends on lipid composition, thermodynamic state of bilayers and liquid or gel state of vesicles.

• Liquid state vesicles may act not only on in superficial skin layers but may also modify intercellular lipid lamallae in deeper layers of Sc while gel state vesicles interact with outer most layers in SC.

• Liquid state vesicles are more effective in transporting drugs across the skin.

Applications of liposomes in transdermal delivery

Drug Application

Triamcinolone acetonide The application of the liposomal preparations was associated with greater steroid concentrations in the epidermis and dermis

- Retinoic acid- Caffeine- Lignocaine

Enhanced delivery into the skin has been reported by liposome encapsulation. Liposomal delivery results in the formation of a large drug reservoir in the skin which can be used for local treatment.

Hydrocortisone,fluocinolone acetonide,inulin (cyclosporine

Increased uptake form liposomes into the cornified layer of hairless mice and/or guinea pigs.

Liposomal entrapmentof calcein ,melanin & DNA

Specific delivery into the hair follicles of histocultured mouse skin while aqueous control solutions of these molecules showed no drug localization within the follicle.

•Tretinoin for the treatment of acne •Glucocorticoids for the treatment of atopic eczema.•Lignocaine and Tetracaine as anesthetics

Liposomal carriers have been successful in enhancing the clinical efficacy of all these drugs.

Applications of liposomes in transdermal delivery

• The first marketed topical liposomal drug, Pevaryl Lipogel, produced by Cilag AG, became available in Switzerland in 1988. The product contains 1% econazole in a liposomal gel form.

Role of Niosomes in transdermal delivery

• Niosomes are vesicular systems composed of nonionic surfactants instead of phospholipids.

• They are capable of entrapping hydrophobic and hydrophilic drugs.

Recently niosomes are gaining popularity in the field of topical and transdermal delivery due to their following characteristics:

• They increase skin penetration of drugs.• They can act as a local depot for sustained

release of dermally active compounds.• They can serve as solubilizing matrix for

hydrophilic and lipophilic type of drugs.

Mechanism of skin penetration by niosomes

• Adsorption and fusion of niosomes onto the surface of the skin leading to high thermodynamic activity gradient at the interface, which is the driving force for permeation of lipophilic drugs.

• The effect of vesicles as penetration enhancer reduces barrier properties of stratum corneum. As surfactants are the components of niosomes, they increase transdermal permeation and Percutaneous absorption by decreasing surface tension, improving wetting of skin and enhance distribution of drugs.

• The lipid bilayers of niosomes act as a rate limiting membrane barrier for drugs.

Proniosomes

• Proniosomes offer a versatile vesicle drug delivery concept with potential for delivery of drugs via transdermal route.

• This would be possible if Proniosomes form niosomes upon hydration with water from skin following topical application under occlusive conditions.

• Proniosomes minimizes problems of niosomes physical stability such as aggregation, fusion and leaking and provide additional convenience in transportation, storage and dosing.

Applications of niosomes/ Proniosomes in

transdermal delivery Drug Application

Nimesulide Better anti-inflammatory effect when entrapped in niosomes

Methotrexate Niosomal Methotrexate gel is more efficacious in the treatment of localized psoriasis

Levonorgestrel Proniosomal transdermal patch bearing Levonorgestrel produces more effective contraception.

Ammonium glycyrrhizinate

Niosome formulation shows efficacious anti-inflammatory activity

Ketorolac Increased Permeation form ProniosomesCaptopril Transdermal delivery through niosomes

Celecoxib Niosomal gel formulation possess great potential for enhanced skin accumulation, prolonging drug release and improving the site specificity of celecoxib

Elastic Vs Rigid vesicles• Rigid vesicles consist of double chain nonionic

surfactants or lipids.• Elastic vesicles consist of double chain nonionic

surfactants or lipids and an edge activator.• Elastic vesicles have superior characteristics as

compared to rigid conventional vesicles both in terms of skin permeation and skin interaction.

• Elastic vesicles can be produced by incorporation of surfactants or ethanol into bilayers.

ETHOSOMES

• The ethosomes are vesicular carrier comprising of hydro alcoholic or hydro/alcoholic/glycolic phospholipid in which the concentration of alcohols or their combination is relatively high.

Different Additives Employed In Formulation of Ethosomes : 

Class Example Uses

Phospholipid

- Soya phosphatidyl choline- Egg phosphatidyl choline- Dipalmitylphosphatidyl Choline- Distearyl phosphatidyl choline

Vesicles forming component

Polyglycol Propylene glycolTranscutol RTM

As a skinPenetrationenhancer

Alcohol EthanolIsopropyl alcohol

For providing the softness for vesicle membraneAs a penetration enhancer

Cholesterol Cholesterol For providing the stability to vesicle membrane

Morphological characterizations of ethosomal formulation by Transmission Electron Microscopy (TEM). Magnification (x 80, 000)

ROLE OF ETHOSOMES IN SKIN PENETRATION

• Touitou discovered and investigated lipid vesicular systems embodying ethanol in relatively high concentration and named them ethosomes.

• The basic difference between liposomes and ethosomes lies in their composition.

• The synergistic effect of combination of relatively high concentration of ethanol (20-50%) in vesicular form in ethosomes was suggested to be the main reason for their better skin permeation ability.

• The high concentration of ethanol (20-50%) in ethosomal formulation can disturb the skin lipid bilayer organization. Therefore, when integrated into a vesicle membrane, it can give an ability to the vesicles to penetrate the SC.

• Furthermore, due to high ethanol concentration the ethosomal lipid membrane is packed less tightly than conventional vesicles but possesses equivalent stability. This allows a softer and malleable structure giving more freedom and stability to its membrane, which could squeeze through small openings created in the disturbed SC lipids.

• In addition, the vesicular nature of ethosomal formulations can be modified by varying the ratio of components and chemical structure of the phospholipids. The versatility of ethosomes for systemic delivery is evident from the reports of enhanced delivery of quite a few drugs like acyclovir, minoxidil, triphexyphenidyl, testosterone , cannabidol and zidovudine.

Proposed Mechanism of Skin Permeation of Ethosomes

• The figure shows the schematic representation of mechanism of skin permeation of ethosomes.

• The stratum corneum lipid multilayers at physiological temperature are densely packed and highly conformationally ordered.

• Ethosomal formulations contain ethanol in their composition that interacts with lipid molecules in the polar headgroup regions, resulting in an increased fluidity of the SC lipids.

• The high alcohol content is also expected to partial extract the SC lipids. These processes are responsible for increasing inter and intracellular permeability of ethosomes.

• In addition, ethanol imparts flexibility to the ethosomal membrane that shall facilitate their skin permeation. The interdigitated, malleable ethosome vesicles can forge paths in the disordered SC and finally release drug in the deep layers of skin.

• The transdermal absorption of drugs could then result from fusion of ethosomes with skin lipids. This is expected to result in drug release at various points along the penetration pathway.

Fluorescence photomicrograph of rat skin after application of hydrophilic fluorescence probe 6-carboxyfluorescein from (A) Liposomal formulation (x

100); (B) Ethosomal formulation (x100) and Rhodamine 123 from (C) Liposomal formulation; (x 100) (D) Ethosomal formulation (x100). SC = Stratum corneum, E = Epidermis, D = Dermis; FL = Fibrous layer, Ad =

Adipose tissue, Ve = Vesicular stacks 

Applications of ethosomes in transdermal delivery

Drug Application of ethosomes

NSAIDS (Diclofenac) Selective delivery of drug to desired side for prolong period of time

Acyclovir Increase skin permeation

Trihexyphenidyl hydrochloride

Improved transdermal flux

AntibioticCannabidolErythromycin

Improved skin deposition

Bacitracin Improved dermal deposition

Anti-HIV agentsZidovudineLamivudine

Improved transdermal flux

Ammonium glycyrrhizinate    Improved dermal deposition exhibiting sustained release¯     Improved biological anti-inflammatory activity

Tranferosomes

• Tranferosomes are modified Liposomes developed to increase transdermal permeation of drugs.

• They are more deformable than standard Liposomes and thus well suited for skin penetration.

• Deformability is achieved by including surface active agents in the formula in an appropriate ratio.

• They consist of phospholipids and an edge activator which is a surfactant that destabilizes lipid bilayers of the vesicles and increases deformability.

• Not only the physicochemical characteristics of vesicles but also the mode of application of Tranferosomes play a crucial role in vesicle skin interactions.

Mechanism of skin penetration by Tranferosomes

• The passage of Tranferosomes across the skin is a function of vesicle membrane flexibility, hydrophilicity and ability of vesicle to retain its integrity.

• When Tranferosomes in suspension are applied on the skin surface the water evaporates from the skin surface and vesicles begin to dry out.

• Due to high polarity of Tranferosomes ingredients vesicles get attracted towards areas of higher water content in the narrow gaps between the adjoining cells in the skin

• This process along with vesicle membrane’s deformability, enables the Tranferosomes aggregates to open the tiny pores temporarily through which water normally gets evaporated between the cells.

• Such newly activated intercellular channels can accommodate sufficiently deformable vesicles, maintaining their integrity and changing their shape to fit the channels and reach regions of higher water content in the deeper layers of skin in which the vesicles get distributed between the cells.

• Tranferosomes bypass the cutaneous capillary bed because they are too large to enter the blood vessels locally and reach the subcutaneous tissue.

• Ultimately the vesicles arrive into the systemic circulation via the lymphatic system. The presence of large number of hydrophilic molecules in tranferosomes enhances aggregate sensitivity to the driving force which results from a water concentration across the skin.

• This process explains the ability of highly deformable Tranferosomes to cross the skin barrier.

• The difference in skin condition between occlusive and non-occlusive conditions is of importance for Tranferosomes penetration.

• Cevc et al suggested that the transport of Tranferosomes is driven by the osmotic gradient across the skin. Occlusion would eliminate this osmotic ingredient and prevent skin penetration.

Protransferosome gels• The provesicular approach has been

extended to the tranferosomes, which are reported to have superior skin penetration ability.

• Liquid crystalline protransfersome gel (PTG) will be converted into the ultra flexible vesicles, tranferosomes also known as elastic liposomes, in situ by absorbing water.

Protransferosome gel

Lamellar liquid crystalline structure of protransfersomal gel (Photomicrograph A, X 400), Scale bar = 500 μm and vesicular structure of tranferosomes formed upon hydration of protransfersomal gel (photomicrograph ×1000). Scale bar = 1 μm.

Figure 2. TEM photomicrograph of PTG formulation after hydration (×1,20,000). Scale bar = 500 nm.

Protransferosome gels• For optimum drug delivery, a high degree of drug-vesicle

association is essential so that appreciable quantity of drug could be carried by elastic vesicles across the stratum corneum.

• Subsequently, larger quantities of drugs will be released from the vesicles, thereby increasing the amount of free drug available for diffusion into the deeper skin layers. High entrapment efficiency of protransfersome gel is probably the reason for its better skin permeation.

• Furthermore, higher skin permeation of PTG could be a result of better partitioning across the stratum corneum and to deeper layers of skin under the influence of transepidermal osmotic gradients.

• The osmotic gradient is developed because skin penetration barrier prevents water loss through the skin and maintains a water activity difference in viable parts of the epidermis (75% water content) and nearly completely dry stratum corneum near the surface (15% water content).

• PTG consists of polar lipids (PC) that have a tendency to attract water because of the energetically favorable interaction between the hydrophilic lipid residues and proximal water molecules. Hence, when PTG is applied on skin surface that is partly dehydrated by water loss due to evaporation, the lipid vesicles feel this osmotic gradient and try to escape complete drying by moving along this gradient resulting in faster partitioning of vesicles into the stratum corneum and other deeper layers of the skin.

Applications of Transferosomes in transdermal delivery

• Transferosomes have been widely used as a carrier for the transport of proteins and peptides. Proteins and peptide are large biogenic molecules which are very difficult to transport into the body, when given orally they are completely degraded in the GI tract.

• These are the reasons why these peptides and proteins are still have to be introduced into the body through injections. Various approaches have been developed to improve these situations. The bioavaibility obtained from Transferosomes is some what similar to that resulting from subcutaneous injection of the same protein suspension.

• Delivery of insulin by transferosomes is the successful means of non invasive therapeutic use of such large molecular weight drugs on the skin (Cevc et al, 1990). Insulin is generally administered by subcutaneous route that is inconvenient. Encapsulation of insulin into transferosomes (transfersulin) overcomes these entire problems. After transfersulin application on the intact skin, the first sign of systemic hypoglycemia are observed after 90 to 180 min, depending on the specific carrier composition3.

• Transferosomes have also been used as a carrier for interferons, for example leukocytic derived interferone-α (INF-α) is a naturally occurring protein having antiviral, antiproliferive and some immunomodulatory effects. Transferosomes as drug delivery systems have the potential for providing controlled release of the administered drug and increasing the stability of labile drugs.

Applications of Transferosomes in transdermal delivery

• Another most important application of transferosomes is transdermal immunization using transferosomes loaded with soluble protein like integral membrane protein, human serum albumin, gap junction protein. These approach offers at least two advantages, first they are applicable without injection and second, they give rise to rather high titer and possibly, to relatively high IgA levels.

• Transferosomes have also used for the delivery of corticosteroids. Transferosomes improves the site specificity and overall drug safety of corticosteroid delivery into skin by optimizing the epicutaneously administered drug dose Transferosomes based cortiosteroids are biologically active at dose several times lower than the currently used formulation for the treatment of skin diseases (Cevc et al, 1997).

• Application of anesthetics in the suspension of highly deformable vesicles, transferosomes, induces a topical anesthesia, under appropriate conditions, with less than 10 min. Maximum resulting pain insensitivity is nearly as strong (80%) as that of a comparable subcutaneous bolus injection, but the effect of transferosomal anesthetics last longer.

• Transferosomes have also been used for the topical analgesics, anesthetics agents, NSAIDS and anti-cancer agents. 

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