Skin permeation and stability studies of 5-aminolevulinic acid in a new gel and patch preparation.

A new cubic gel as well as a patch system containing additional carrageenan as matrix were used as vehicles for 5-aminolevulinic acid (5-ALA). Standard diffusion experiments of 5-ALA using Franz-type diffusion cells and porcine skin were performed. Drug stability was monitored by analysing the 5-ALA content in the formulations. The analysis of 5-ALA as non-fluorescent probe was performed after chemical reaction leading to a fluorescent derivative. The 5-ALA permeation through porcine skin after 48 h was the highest from the patch formulation with 80.3% and the second highest from the cubic gel with 66.4%, however only about 40% of 5-ALA were chemical stable after 14 days storage in the patch formulation, whereas no degradation of 5-ALA was measured in the cubic gel over 90 days of observation.