Passive skin penetration enhancement and its quantification in vitro

Area of Science:

• Pharmacology
• Materials Science
• Biomedical Engineering

Background:

• Poor drug penetration through the skin, particularly the stratum corneum, often compromises topical formulation efficacy.
• Key strategies to improve skin penetration include enhancing drug diffusivity, increasing drug solubility within the skin, and elevating the drug's saturation level in the formulation.

Purpose of the Study:

• To review literature on chemical penetration enhancers and supersaturated formulations for improving topical drug delivery.
• To discuss the application of in vitro methods for quantifying skin transport parameters and differentiating kinetic/thermodynamic effects of enhancement strategies.

Main Methods:

• Literature review focusing on chemical penetration enhancers and supersaturated formulations.
• Evaluation of in vitro methods: classic diffusion cell studies, attenuated total-reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and tape stripping combined with analytical techniques.

Main Results:

• Chemical penetration enhancers can modulate drug diffusivity and/or solubility in the skin.
• Supersaturated formulations increase the drug's degree of saturation compared to conventional ones.
• In vitro methods provide quantitative data on skin transport parameters and allow separation of kinetic and thermodynamic effects.

Conclusions:

• Chemical enhancers and supersaturated formulations are viable strategies to overcome poor skin penetration.
• In vitro techniques are crucial for characterizing the mechanisms and effectiveness of drug delivery enhancement strategies.
• Quantitative analysis of skin transport parameters aids in optimizing topical formulation design and efficacy.