Dermal penetration refers to the process by which drugs or active substances traverse the layers of the skin to reach systemic circulation or exert their therapeutic effects locally. The skin is a barrier that protects the body, and dermal penetration involves overcoming this barrier for effective drug delivery.
Classification
Dermal penetration can be classified into two main categories:
1. Transcellular Penetration:
Involves drug penetration through the cellular components of the skin, passing through both the lipid-rich stratum corneum and the underlying epidermis and dermis.
2. Intercellular Penetration:
Involves drug penetration between the cells of the stratum corneum. This route exploits the lipid-rich intercellular spaces.
Mechanisms
Several mechanisms contribute to the dermal penetration of drugs:
1. Passive Diffusion:
The most common mechanism is where drugs move from an area of higher concentration (applied formulation) to an area of lower concentration (skin layers). Lipid-soluble drugs generally penetrate more easily.
2. Active Transport:
Involves the use of carrier proteins or transporters to facilitate the movement of drugs across the skin.
3. Follicular Penetration:
Some drugs can penetrate the skin through hair follicles, the infundibulum or the follicular epithelium.
4. Iontophoresis:
Utilizes an electric current to enhance the penetration of charged molecules through the skin.
5. Microneedle Technology:
Involves the use of tiny needles to create micropores in the stratum corneum, facilitating drug penetration.
Factors Influencing Dermal Penetration
Several factors affect the ability of drugs to penetrate the skin:
1. Physicochemical Properties of the Drug:
Lipophilicity, molecular weight, and water solubility influence a drug’s ability to penetrate the skin.
2. Formulation Factors:
The composition of the drug formulation, including excipients, penetration enhancers, and delivery systems, plays a crucial role.
3. Skin Factors:
Skin thickness, hydration, integrity, and the presence of hair follicles impact dermal penetration.
4. Environmental Factors:
Temperature, humidity, and exposure to sunlight can influence the skin’s condition and affect drug penetration.
5. Application Site:
Different anatomical sites on the body have skin thickness and permeability variations, influencing dermal drug absorption.
6. Duration of Contact:
The time the drug formulation remains in contact with the skin affects penetration.
