New directions in ALA-PDT

Certain types of cells may accumulate relatively high concentrations of protoporphyrin IX (PpIX) when exposed to 5-aminolevulinic acid or certain of its derivatives. PpIX is a photosensitizing agent which can be photoactivated in vivo by ultraviolet and/or visible light, thereby initiating a photodynamic reaction that may lead to the destruction of cells and tissues containing high concentrations of PpIX. This process is referred to as ALA-induced PpIX photodynamic thereapy (ALA-PDT), a, rapidly growing field of research. ALA is effective when administered topically, orally, by intravenous, subcutaneous, or intradermal injection, or by infusion into accessible body cavities. PpIX is the main photosensitizer produced under most conditions, although others may be present also, especially during split dose therapy. Multiple wavelength excitation sources are required to produce and subsequently activate the far red absorbing chlorin type photoproducts that are produced under certain conditions.