Microemulsions development and characterization for ALA topical photodynamic therapy

Abstract

Photodynamic therapy is a new tool for the treatment of certain cancerous and pre-cancerous conditions in dermatology. 5-aminolevulinic acid and simple derivatives thereof are the principal active agents used for this purpose. For optimal efficacy, the drug must be released at an appropriate rate from the formulation and penetrate the skin, ideally to reach the target tissue at a sufficiently high concentration. Because ALA is a polar, zwitterionic compound, its formulation in conventional topical vehicles, and its inherently poor skin permeability, pose important challenges for the pharmaceutical scientist. The synthesis of more lipophilic (e.g. ester) prodrugs of ALA resolves, in part, these issues but their retention in the stratum corneum can increase the lag time. Microemulsions are a modern drug delivery system that can facilitate skin penetration of hidro and lipophilic drugs. Therefore, the goal of this work is to obtain and to characterize microemulsions containing a hidrophilic (ALA) and a lipophilic (h-ALA) PpIX precursor to understanding and optimizing their in vitro and in vivo cutaneous penetration. (AU)