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• Lipophilic drugs permeate by Intracellular (Transcellular) mechanism (lipid-rich
amorphous materials)

Drug transport through the skin (Kinetics of transdermal permeation)

Fick’s first law
• The mechanism of drug absorption through the skin involves passive diffusion
• Fick’s law of diffusion postulates that the diffusing molecules go from regions of high

concentration to regions of low concentration.
• The rate of diffusion, the amount of material (M) flowing through a unit cross-section (S)

of a barrier in unit time (t) is defined as the flux (J).
• J= x 1

• where:
• J is the flux, in g/(cm2 s)
• S is the cross-section of the barrier, in cm2
• dm/dt = rate of diffusion, in g/s (m = mass in g; t = time in s)
• Flux is related to the concentration gradient (dC = C1−C2) between the donor region at a

higher
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