Mechanism of drug transport across the skin

There are primarily three mechanisms by which drugs can transport across the skin:

1. Passive Diffusion:

• This is the most common mechanism.

• Drugs diffuse from a region of higher concentration (in the drug delivery system) to a region of lower concentration (in the skin and subsequently in the blood).

• This process does not require energy.

  1. Transcellular Route: The drug penetrates the corneocytes of the stratum corneum. This route is more common for small, lipophilic molecules.

  2. Intercellular Route: The drug diffuses through the lipid matrix between the corneocytes. This is the primary pathway for most drugs.
     

2. Active Transport:

• This is less common in TDDS and requires cellular energy.

• It usually involves carrier proteins or pumps that help move the drug against its concentration gradient.

3. Electrotransport:

1. Iontophoresis: Uses a small electric current to drive charged molecules into the skin.

2. Electroporation: Brief high-voltage pulses increase skin permeability temporarily.

Flowchart of Mechanism of drug transport across the skin

Flowchart of skin surface