Fluorescence induced by aminolevulinic acid and methyl aminolevulinate on normal skin

PDT is a treatment modality, which uses a combination of a photosensitising drug, oxygen and light to selectively destroy pre-malignant and malignant tissue. The most commonly used PDT photosensitiser precursor is 5-aminolevulinic acid (ALA). However recently the introduction of methyl aminolevulinate (MAL) another topical photosensitiser has posed the question of which may be of greater clinical advantage when used in PDT.

The characteristics of PpIX fluorescence following the application of different quantities of both ALA and MAL were investigated in normal skin.

PpIX fluorescence was detected using a non-invasive spectroscopy system. A total of 17 healthy volunteers were recruited, and varying quantities of both ALA and MAL were applied to the inner forearm.

Topical application (within the range of 0.01-0.09ml) of both ALA and MAL to normal human skin-induced PpIX fluorescence. This induced fluorescence was not dose dependent within the range investigated. However, the time course and intensity of fluorescence was significantly different for ALA and MAL. PpIX-induced fluorescence peaked at 7h following the application of MAL, compared to 24h following the application of ALA. At all time points, ALA-induced fluorescence was significantly greater than that induced by MAL. These results help define some of the characteristics of ALA- and MAL-induced PpIX fluorescence in normal skin.