Are photosensitizers toxic or harmful?
Because many photosensitizers are derivatives of naturally occurring hemoglobin or chlorophyll the toxicity usually is low and the margin of safety between the therapeutic dosage and toxic levels us great. Many agents however, have a long residual period in the skin and normal tissue and long periods of sunlight photosensitivity are typical of first Generation agents: in the case of Photofrin 6-8 weeks is not unusual. Also with Photofrin selectivity for cancer cells is not very great so light applied to the area of tumor also results in swelling of adjacent normal tissue. Earlier agents such as Foscan are not naturally soluble in blood and there have been reports of damage to veins at the site of injection as well as prolonged sunlight photosensitivity. Additionally, Foscan is so light sensitive much care has to be taken to shield adjacent normal tissue from light exposure.
