Is the relationship between penetration ratio and skin thickness first-order (proportional) or inverse?

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Study for the Pharmaceutics Xenobiotics Across Bio Membrane Test. Prepare with flashcards and multiple-choice questions, each providing hints and explanations. Get ready for your pharmacy exam!

Multiple Choice

Is the relationship between penetration ratio and skin thickness first-order (proportional) or inverse?

Explanation:
The effect comes from diffusion through a barrier. For a membrane like skin, steady-state flux follows Fick’s law: J ≈ D ΔC / h, where h is the thickness. If you look at the permeability (the flux per unit driving concentration), P ≈ D/h (times the partition coefficient, if you include it). This shows the penetration ratio is inversely proportional to thickness: doubling the skin thickness cuts the penetration by about half, assuming D and other factors stay the same. The other shapes—proportional to thickness, constant regardless of thickness, or logarithmic—don’t match this diffusion-driven behavior.

The effect comes from diffusion through a barrier. For a membrane like skin, steady-state flux follows Fick’s law: J ≈ D ΔC / h, where h is the thickness. If you look at the permeability (the flux per unit driving concentration), P ≈ D/h (times the partition coefficient, if you include it). This shows the penetration ratio is inversely proportional to thickness: doubling the skin thickness cuts the penetration by about half, assuming D and other factors stay the same. The other shapes—proportional to thickness, constant regardless of thickness, or logarithmic—don’t match this diffusion-driven behavior.

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