Which site would you expect to have the highest penetration for a transdermal system if the stratum corneum is very thin?

Which site would you expect to have the highest penetration for a transdermal system if the stratum corneum is very thin?

• A. Forearm
• B. Palm
• C. Scrotum
• D. Back

Answer: (C)

Penetration through the skin is driven mainly by the stratum corneum, the outer barrier. When that layer is very thin, the diffusion path is shorter and there is less barrier to drug passage, so a transdermal system delivers more drug into the body. Among the sites listed, the scrotum has the thinnest stratum corneum, giving it the highest permeability. The palm has a thick stratum corneum, and the forearm and back are thicker still than the scrotum, so they show lower permeability. Thus, with a very thin stratum corneum, the scrotum would allow the greatest penetration.

Penetration through the skin is driven mainly by the stratum corneum, the outer barrier. When that layer is very thin, the diffusion path is shorter and there is less barrier to drug passage, so a transdermal system delivers more drug into the body. Among the sites listed, the scrotum has the thinnest stratum corneum, giving it the highest permeability. The palm has a thick stratum corneum, and the forearm and back are thicker still than the scrotum, so they show lower permeability. Thus, with a very thin stratum corneum, the scrotum would allow the greatest penetration.