Excretion measurement of porphyrins and their precursors after topical administration of 5-aminolaevulinic acid for fluorescence endoscopy in head and neck cancer.

5-Aminolevulinic acid (5-ALA) is a useful agent to enhance the detection of early epithelial lesions in head and neck cancers. It is applied either topically or systemically and converted intracellular into photosensitive protoporphyrin IX (PpIX). By ultraviolet light illumination malignant and fast proliferating lesions are detected by a characteristic red fluorescence and delineated by the bluish fluorescence of healthy tissue. To assess the elimination patterns 5-ALA, porphobilinogen (PBG) and porphyrin were measured 12h and 36h after administration in urine, 12h and 24h after examination in blood and in feces 12h after endoscopy. 5-ALA was applied either by inhalation (250 mg) or mouth rinse (200 mg). After both administration routes, excretion levels in urine returned to background levels within 12 hours after administration and only in feces values are slightly increased for PpIX and total porphyrin. Concentrations in erythrocytes were elevated, but not in plasma. No side effects were observed. According to our results the topical administration of 5-ALA is a useful method with satisfying fluorescence imaging results. Levels of metabolites in urine and plasma return to normal within 12 hours so that skin photosensitization can be neglected.