Lateral drug diffusion in human nails

Area of Science:

• Pharmacology
• Biophysics
• Dermatology

Background:

• Transungual drug delivery is crucial for treating nail fungal infections.
• Understanding drug diffusion within the nail plate is essential for optimizing treatment efficacy.
• Passive lateral diffusion within the nail plate can impact drug permeation rates.

Purpose of the Study:

• To demonstrate passive lateral diffusion of ciclopirox olamine (CPO) in the human nail plate.
• To investigate the effect of this lateral diffusion on the passive transungual permeation of CPO.
• To establish optimal experimental conditions for in vitro transungual permeation studies.

Main Methods:

• Utilized a novel suspended nail experiment to visualize lateral diffusion using methyl red sodium salt (MR) as a tracer dye.
• Assessed the in vitro transungual permeation of CPO across human toenails with varying surface areas (25 mm², 49 mm², 81 mm²).
• Correlated the concentrations of CPO and MR in application and peripheral areas to confirm diffusion patterns.

Main Results:

• Demonstrated significant passive lateral diffusion of CPO within the human nail plate.
• Observed a decrease in CPO permeation flux with increasing toenail surface area.
• Found a positive correlation between CPO and MR concentrations, confirming lateral diffusion.
• Noted that lateral diffusion reduces in vitro transungual drug permeation and prolongs lag-time.

Conclusions:

• Passive lateral diffusion of CPO profoundly impacts its transungual permeation in human toenails.
• Experimental designs for in vitro transungual permeation studies should minimize the peripheral nail area around the application site.
• This optimization is necessary to obtain reliable data that accurately mimics in vivo drug behavior.