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

Formulation...Sudhir Bharadwaj et al.c. Uptake of the drug by the capillary network in the dermal papillary layerThis permeation can be possible if the drug possesses certain physico-chemical properties. The rate ofpermeation across the skin (dQ/ dt) is given by:dQ / dt = P s (C d – C r ) Eq. 1Where,C d = Concentration of skin penetrant in the donar compartment (e.g., on thesurface of stratum corneum)C r = Concentration in the receptor compartment (e.g., body) respectivelyP s = Overall permeability constant of the skin tissue to the penetrantWhere,P s = ( K s D ss ) / h s Eq. 2K s is the partition coefficient for the interfacial partitioning of the penetrant molecule from a solutionmediumD ss is the apparent diffusivity for the steady state diffusion of the penetrant molecule through a thicknessof skin tissuesh s is the overall thickness of skin tissues.As K s , D ss and h s are constant under given conditions, the permeability coefficient (P s ) for a skinpenetrant can be considered to be constant.From Eq.1 it is clear that a constant rate of drug permeation can be obtained only when C d >>C r i.e., thedrug concentration at the surface of the stratum corneum (C d ) is consistently and substantially greaterthan the drug concentration in the body (C r ), then Eq. 1 becomes:dQ / dt = P s C s Eq. 3Permeability coefficient = (KsDss) / hs = 1 / resistance1.2.3. Physiological Factors in Percutaneous AbsorptionPhysiological factors are those that involve the properties of the barrier itself. Some important factorsare:1. Skin integrity2. Hydration3. Temperature4. Anatomic location5. Age6. Disease862 J. Chem. Bio. Phy. Sci. Sec.B, 2012, Vol.2, No.2,856-867