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

Formulation...Sudhir Bharadwaj et al.b. Biological properties:• The drug should not be directly irritated to the skin.• The drug should not stimulate an immune reaction in the skin.• Drugs, which degrade in gastrointestinal tract or are inactivated by hepatic first pass effect, aresuitable for topical delivery.• Tolerance to the drug must not develop under the near zero order release profile of topicaldelivery.• Drugs which have to be administered for a long time or which cause adverse effects to non-targettissue can also be formulated for topical delivery.(C)Penetration Enhancers: These are the compounds, which promote skin permeability by altering theskin as a barrier to the flux of a desired penetrant and are considered as an integral part of most topicalformulations. To achieve and maintain therapeutic concentration of drug in the blood, the resistance ofskin (stratum corneum) to diffusion of drugs has to be reduced in order to allow drug molecules to crossskin and to maintain therapeutic levels in blood. They can modify the skin’s barrier to penetration eitherby interacting with the formulation that applied or with the skin itself.Various criteria that ideal penetration enhancers must meet are:• Ability to act specifically, reversibly and for predictable duration.• Pharmacological inertness.• Non-toxic, non-allergenic, non-irritating.• Controlled and reverse enhancing action.• Should not cause loss of body fluids, electrolytes or other endogeneous materials.• Chemical and physical compatibility with drugs and other pharmaceutical excipients with which itis used.• Following removal of the enhancer, the stratum corneum should immediately and fully recover itsnormal barrier property.• Odourless, colorless and economical and cosmetically acceptable.Enhancers increase the penetration of permeants by disrupting the structure of skin’s outer layer‘stratum corneum’ and increasing penetrant solubility. Disruption either by chemical means, may affectboth intracellular and extracellular structure. Disruption may be due to protein denaturation, fluidizationand randomization of intercellular lipids or intercellular delamination and expansion. The accelerantscause keratin to swell and leach out essential structural material from the stratum corneum, thusreducing the diffusional resistance and increasing the permeation of drugs through skin.In hydrophilic topical penetration enhancer, the miscibility and solution properties of solvent are usedfor the enhanced topical permeation of a water-soluble drug.Lipophilic enhancers assist the percutaneous absorption of both water soluble and oil soluble drugs. Theenhancement in the absorption of oil soluble drugs is apparently due to the partial leaching of theepidermal lipids by the enhancer, resulting in the improvement of the skin condition for wetting and fortopical and transfollicular penetration.The effect of surfactant action upon the skin may change the physical stage of water in the skin in such865 J. Chem. Bio. Phy. Sci. Sec.B, 2012, Vol.2, No.2,856-867