A time course investigation of the fluorescence induced by topical application of 5‐aminolevulinic acid and methyl aminolevulinate on normal human skin

Abstract

Treatment of non-melanoma skin cancers (NMSC) with topical photodynamic therapy (PDT) is a treatment of choice for many clinicians. The two most commonly used PDT photosensitizer precursors are 5-aminolevulinic acid (ALA) and methyl aminolevulinate (MAL). Current PDT treatment regimes advise longer (4-6 h) application times for ALA and shorter times (3 h) for MAL. To establish the time course characteristics of protoporphyrin IX (PpIX) fluorescence following the application of ALA and MAL in normal skin. A total of 17 healthy volunteers were recruited, and both ALA and MAL were applied to the inner forearm for varying times (1-6 h). PpIX fluorescence was detected using a non-invasive spectroscopy system. PpIX fluorescence (following the application of either ALA or MAL) is dependent on duration of application. Following the application of ALA for 1-3 h peak fluorescence was noted at 7 h. Longer duration times (4-6 h) resulted in sustained fluorescence, which peaked at 24 h. MAL-induced fluorescence peaked at 7 h and was significantly decreased by 24 h for all application times. ALA induced fluorescence was shown to be significantly greater than MAL. The findings from this study have shown that potentially it would be more beneficial to apply ALA for shorter periods of time and MAL for longer than current practice.