Topical Gel: A Novel approach for drug delivery - Journal of ...

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Formulation...Sudhir Bharadwaj et al.through the body. An average human skin surface is known to contain, on the average 40-70 hair folliclesand 200-300 sweat ducts on every square centimeter of the skin 1 . Although skin has been dividedhistologically into the stratum corneum, the living epidermis and the dermis, collectively it can beconsidered a laminate of barrier, permeation of this laminate can occur by diffusion via:a. Transcellular penetration (across the cells)b. Intracellular penetration (between the cells)c. Transappendageal penetration (via hair follicles, sweat and sebum glands) 2, 3A myriad of medicated product are applied to the skin or readily accessible mucous membrane that insome way either augment or restore a fundamental function of a skin or pharmacologically modulate anaction in the underlined tissues. Such products are referred as topical or dermatological product 4 .1.RATIONAL APPROACH TO TOPICAL FORMULATIONS 5Topical formulation can be used to:• Manipulate the barrier function of the skin, e.g., topical antibiotics and antibacterial help a damagedbarrier to ward off infection, sun screening agents and the horny layer protect the viable tissues fromU.V. radiation.• Direct drugs to the viable skin tissues without using oral, systemic or other routes of therapy, e.g.,anaesthetic, anti-inflammatory, antipruritic and antihistaminics drugs are to be delivered to viableepidermis and dermis.• For skin appendage treatment, e.g., antiperspirants, exfolients and depilatories are to be delivered tothe skin appendages.• Deliver drugs for systemic treatment, e.g., transdermal therapeutic systems provide systemic therapyfor motion sickness, angina and hypertension.1.1. TOPICAL GELSThe term ‘Gel’ was introduced in the late 1800 to name some semisolid material according to theirphysiological characteristics rather than molecular composition.Gels are semisolid systems in which a liquid phase is constrained within a three dimensional polymericmatrix of natural or synthetic gums in which a high degree of physical or chemical cross linking has beenestablished 6 .The U.S.P. defines gels 7 as a semisolid system consisting of dispersion made up of either small inorganicparticle or large organic molecule enclosing and interpenetrated by liquid. The inorganic particles form athree-dimensional ‘house of cards’ structure. Gels consist of two-phase system in which inorganicparticles are not dissolved but merely dispersed throughout the continuous phase and large organicparticles are dissolved in the continuous phase, randomly coiled in the flexible chains. These chains areentangled with each other and shown as a single phase. The interaction between the colloidal phase,(inorganic or organic) set up the ‘structural viscosity’.Most topical gels are prepared with organic polymers, such as carbomers, that impart an aestheticallypleasing, clear, sparkling appearance to the products and are easily washed off from the skin with water.The type of base used in formulating a topical dermatological product greatly influences its effectiveness.Bases containing large amounts of oleaginous substances provide an emollient effect to dry irritated skin.More importantly, bases made up of non-volatile oleaginous substances (e.g. hydrocarbon bases) can form857 J. Chem. Bio. Phy. Sci. Sec.B, 2012, Vol.2, No.2,856-867
Formulation...Sudhir Bharadwaj et al.an occlusive barrier on the skin that prevents escape of moisture from the skin into the environment. As aresult, moisture accumulates between the skin and the ointment layer that cause hydration of the stratumcorneum. Hydration of stratum corneum all ‘opening up’ of intra and inter-cellular channels and pathwayfor easier passage of drug molecules. Additionally, the moisture layer provides a medium for dissolutionof the drug that is otherwise dispersed as fine particles in the ointment base. Since only the dissolved drugpresented to the skin, as an individual molecular entity is able to enter the stratum corneum, skinocclusion generally results in enhanced percutaneous drug absorption 8 .1.1.1. ClassificationGels are classified mainly by two methods based on 9 :a. Nature of colloid phasei. Inorganic gelsii.Organic gelsb. Based on nature of solventi. Aqueous gelsii.Non aqueous gels1.1.2. Gel forming substances 10Polymers are used to give the structural network, which is essential for the preparation of gels. Gelforming polymers are classified as follows:1. Natural polymera. Proteinsi. Collagenii. Gelatinb. Polysaccharidesi. Agarii. Alginic acidiii. Sodium or Potassium carrageenaniv. Tragacanthv. Pectinvi. Guar Gumvii. Cassia toraviii. Xanthinix. Gellum Gum2. Semisynthetic polymersa. Cellulose derivativesi. Carboxymethyl cellulose858 J. Chem. Bio. Phy. Sci. Sec.B, 2012, Vol.2, No.2,856-867
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