Authored by the Simon group - Providing more effective and affordable health care

Laboratory Online is a series of educational and interactive modules offered by the Simon group. The purpose of the project is to enhance knowledge in drug-delivery technologies and underlying engineering principles. Within this user-friendly environment, practitioners and researchers can enter their own process parameter values in corresponding boxes (or use the default quantities provided). The findings of the simulation study are monitored in real-time by pressing the red-shaded button near the bottom of the page.

Transdermal drug-delivery model: Edipermal turnover

This contribution focuses on the influence of the epidermal turnover rate on percutaneous drug absorption (Fig. 1). The process of desquamation bears important implications for controlled-release technologies as it affects the rate at which dissolved molecules are delivered to the systemic circulation. The mathematical model is based on a two-layer representation of the skin (i.e., stratum corneum and viable epidermis). An infinite reservoir, sink condition and mass flux continuity at the interface between the stratum corneum and viable epidermis are assumed. Dimensionless variables are used in the simulation. The parameters of the model are [1, 2]:

a	stratum corneum thickness
b	viable epidermis thickness
D1	drug diffusivity in the stratum corneum
u1	velocity of the cells in the stratum corneum
D2	drug diffusivity in the viable epidermis
u2	velocity of the cells in the viable epidermis
K1/v	equilibrium partition coefficient of the drug between the stratum corneum and the vehicle
K2/v	equilibrium partition coefficient of the drug between the viable epidermis and the vehicle
K2/1	parameter defined as K2/v/K1/v
ω1	parameter defined as u1a/D1
ω2	parameter defined as u2a/D1
ψ	parameter defined as D2/D1
ξ	parameter defined as b/a

Fig. 1. Drug transport across the stratum corneum and the viable epidermis.

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ENTER DATA HERE

K_2/1 :     ω₁ :     ω₂ :

ψ :     ξ :    

Cumulative amount of drug released per unit area



Drug flux out of the skin and into the bloodstream

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References

[1] Reddy MB, Guy RH and Bunge AL. (2000), Does epidermial turnover reduce percutaneous penetration? Pharmaceutical Research, 17, 1414-1419.

[2] Simon, L. and Goyal, A. (2009), Dynamics and control of percutaneous drug absorption in the presence of epidermal turnover, Journal of Pharmaceutical Sciences, 98, 187-204.