Penetration Enhancers in Transdermal Drug Delivery System

Penetration Enhancers in Transdermal Drug Delivery System
Permeation enhancers are substances that reduce the skin barrier's ability to make skin more permeable and allow drug molecules to cross the skin at a faster rate
advantages and disadvantages
types of penetration enhancers
techniques
physical and chemical enhancers

1. Penetration Enhancers in Transdermal Drug Delivery System Presented by Simran M. Pharmacy 1 st year GGSCOP, YNR

2. TRANSDERMAL DRUG DELIVERY SYSTEM Transdermal drug delivery has been accepted as a potential non-invasive route of drug administration, with advantages of prolonged therapeutic action, decreased side effect, easy use and better patient compliance. Transdermal drug delivery system (TDDS) also known as “patches” are dosage form design to deliver a therapeutically effective amount of drug across a patient skin. Transdermal delivery not only provides controlled, constant administration of the drug, but also allows continuous input of drugs with short biological half-lives and eliminates pulsed entry into systemic circulation, which often causes undesirable side effects.

3. The principal barrier to most transdermal drug delivery is the stratum corneum, the outermost layer of the skin comprising keratin-rich cells embedded in multiple lipid bilayers. Many strategies have been suggested in order to overcome the low permeability of drugs through the skin. A popular approach is the use of penetration enhancers , which enhance the permeability of the stratum corneum. These agents partition into, and interact with, the stratum corneum constituents to induce reversible increase in skin permeability. Permeation enhancers are the substances that reduce the skin barrier ability make skin more permeable and allow drug molecules to cross the skin at a faster rate.

4. PENETRATION ENHANCERS Permeation enhancers are defined as substances that are capable of promoting penetration of drugs into skin and transdermal therapeutic systems offers a more reliable mean of administering drug through the skin. Ideal properties of penetration enhancers 1. They should have no pharmacological activity within the body. i.e. should not bind to receptor sites. 2. It should be nontoxic, non-irritating, and non-allergenic. 3. Onset of action should be rapid, and duration of activity should be predictable and suitable for the drug used. 4. Upon removal of the enhancer, the horny layer should be immediately and fully recover its normal barrier property.

5. 5. When removed from the skin, barrier properties should return both rapidly and fully. 6. The accelerant should be chemically and physically compatible with all drugs and adjuvants to be formulated in topical preparations and devices. 7. If liquid and to be used at high volume fractions, it should be suitable solvent for drugs. 8. It should spread well on the skin, with a suitable skin “feel”. 9. It should readily formulate into dermatological preparations, transdermal devices, and skin adhesives.

6. ADVANTAGES 1. Penetration rate of drug sufficiently high for therapeutic efficiency by using penetration enhancers. 2. It is useful for unabsorbable drugs to facilitate their absorption through skin. 3. It can improve transdermal absorption of topical preparation. 4. It is penetration rate determining factor in transdermal drug delivery system. 5. The terpenes like limonene in propylene glycol solution are effective penetration enhancer for cytotoxic drugs. 6. It also acts as rate limiting factor.

7. DISADVANTAGES 1. The effective concentration varies from drug to drug. 2. The uses of different penetration enhancer with various concentrations are restricted completely. 3. Physicochemical properties of enhancers are also affecting the side effects in the body.

8. BASIC PRINCIPLE OF TRANSDERMAL PERMEATION Transdermal permeation is based on passive diffusion. Skin is the most intensive and readily accessible organ of the body as only a fraction of millimeter of tissue separates its surface from the underlying capillary  network. The release of a therapeutic agent from a formulation applied  to the skin surface and its transport to the systemic circulation is a multistep process, which includes: 1) Diffusion of drug from drug to the rate controlling membrane. 2) Dissolution within and release from the formulation. 3) Sorption by stratum corneum and penetration through viable epidermis. 4) Uptake of drug by capillary network in the dermal papillary layer. 5) Effect on the target organ. 6) Partitioning into the skin’s outermost layer, the stratum corneum. 7) Diffusion through the stratum corneum, principal via a lipidic intercellular pathway.

9. CLASSIFICATION OF PENETRATION ENHANCERS AND TECHNIQUES Types/Techniques of penetration enhancers Mechanism of action Examples 1. Chemical enhancers They act by three mechanisms By disruption of the highly ordered structure of stratum corneum lipid. By interaction with intercellular protein. By improved partition of the drug or solvent into stratum corneum. Sulphoxides -dimethyl sulphoxide (DMSO),dimethyl formamide(DMF) Azones Pyrrolidones Fattyacids –Lauric acid, Myristic acid oxizolidinones Amine and Amides –Urea Surface active agents–sodium lauryl sulphate, Benzalkonium chloride 8. cyclodextrins

10. Types/Techniques of penetration enhancers Mechanism of action Examples 2. Drug Vehicle Based Interaction of enhancers with stratum corneum and development of SAR for enhances with optimal characteristics and minimal toxicity. Ion pairs and complex Coacervates chemical potential adjustment 3. Natural Penetration enhancers Mechanism for Terpenes It may increase one or more of following effects: 1. Partition coefficient 2. Diffusion coefficient 3. Lipid Extraction 4. Drug Solubility 5. Macroscopic Barrier Perturbation Terpenes-Menthol, Linalool, Limonene, Carvacrol. Essential oil-Basil oil, Neem oil, Eucalyptus, 4. Physical Enhancers These are variable techniques available for increasing the penetration by physical separation and magnetic and ultrasonic. Iontophoresis Sonophoresis Phonophoresis Magnetophoresis Electroporation Thermophoresis Radiofrequency

11. CHEMICAL PENETRATION ENHANCERS Water - a) Free water with in the tissue can alter the permeant solubility in the stratum corneum thereby modifying partitioning from the permeant vehicle into the membrane. b) Hydration causes an increased permeability by aqueous solvation of the intercellular lipids, in particular the glycosphingolipids and ceramides. c) Increased hydration causes an increase in water binding to keratin in the cells thereby swelling the corneocytes. Sulphoxides and similar chemicals - Dimethyl sulfoxide (DMSO) is an effective penetration enhancer that promotes permeation by reducing skin resistance to drug molecules or by promotion of drug partitioning from the dosage form. In addition, DMSO may alter the physical structure of the skin by elution of lipid, lipoprotein and nucleoprotein structures of the stratum corneum.

12. Azones - Azone enhances the skin transport of a wide variety of drugs including steroids, antibiotics and antiviral agents. Azone partitions into a bilayer lipid to disrupt their packing arrangement but integration into the lipid is unlikely to be homogeneous. Azone molecules may exist dispersed within the barrier lipoid or separate domains within the bilayer. Pyrrolidones - Pyrrolidones are able to promote both the penetration of hydrophilic drugs ( eg mannitol) and 5- fluorouracil) and the penetration of lipophilic drug substances ( eg progesterone). N-Methyl-2- pyrrolidone (NMP) and 2-pyrrolidone (2P) as well as 2-pyrrolidone-5-carboxylic acid are the most widely used enhancers of this group. Fatty Acids - A large number of fatty acids and their esters have been used as permeation enhancers. Fatty acids, alcohols, sulphoxides , surfactants, and amides are enhancers for Naloxone.

13. Urea - Urea promotes transdermal permeation by facilitating hydration of the stratum corneum and by the formation of hydrophilic diffusion channels within the barrier. Cyclic urea permeation enhancers are biodegradable and non-toxic molecules consisting of a polar parent moiety and a long chain alkyl ester group. As a result, enhancement mechanism may be a consequence of both hydrophilic activity and lipid disruption mechanism. Oxazolidinones - Oxazolidinones are a new class of chemical agents which have the potential for use in many cosmetic and personal care product formulations. This is due to their ability to localize co-administered drug in skin layers, resulting in low systemic permeation. Oxazolidinones such as 4-decyloxazolidin-2-one has been reported to localize the delivery of many active ingredients such as retinoic acid and diclofenac sodium in skin layers. Cyclodextrins - These compound can form inclusion complexes with lipophilic drugs with a resultant increase in their solubility, particularly in aqueous solutions.

14. Essential oils, Terpenes, and Terpenoids - They have been used as medicines, flavoring, and fragrance agents. The essential oils of eucalyptus, Chenopodium, Ylang have been found to be effective enhancers for 5-fluorouracil. Modifying the solvent nature of stratum corneum improves drug partitioning. L-methanol has been used to facilitate in vitro permeation of HCL. Surfactants – Usually surfactants are added to formulations in order to solubilize lipophilic active ingredients. They have the potential to solubilize lipids within the stratum corneum. Anionic Surfactants – include cetry trimethyl ammonium bromide Non-ionic Surfactants and Zwitterionic surfactants include dodecyl betaine

15. PHYSICAL PENETRATION ENHANCERS Physical Enhancers Definition Characteristics Sonophoresis Sonophoresis is the application of ultrasonic energy that temporarily improves skin permeability. Sonophoresis functions at frequencies of 20 kHz-16 MHz and intensities up to 14 W/cm2 (spatial average pulse average intensity, ISAPA) to enhance skin permeability. Iontophoresis Iontophoresis is the use of slight electric current in order to improve the transport of drugs, which consists of an anode and a cathode deposited on a surface (e.g. skin). Iontophoresis uses an electric current of ~ 0.5 A/cm). A drug can pass through the surface by electromigration, electroosmosis or passive diffusion.

16. Physical Enhancers Definition Characteristics Electroporation The electroporation technique consists of the application of a high electrical field pulses with the purpose to create nanosized pores in a cell membrane and thus, increase the passage of ions and macromolecules through the skin. Electroporation can be reversible and irreversible. Microneedles Microneedles are used to open holes into the skin to create a pathway for the following delivery of drugs. Generally, microneedles have a length of 100-500 µm. Radiofrequency Radiofrequency ablation (RF) is a simple, safe, and effective therapy for chronic radiation proctopathy . The frequency is between 10 kHz and 900 MHz.