Meso-tetra(hydroxyphenyl)chlorin: an in vivo photodegradation study

摘要

Abstract: This in vivo study was carried out to determine to what extent meso-tetra(hydroxyphenyl)chlorin (mTHPC), a chemically very stable second generation photosensitizer, can be 'photobleached'. Experiments were designed to determine if the degradation was dependent on the light dose and if clearance of drug could be achieved in an exposed skin area after a single exposure. Rabbits were injected with 0.3 mg/kg mTHPC and, utilizing injection to exposure intervals of 2 and 6 days, multiple skin areas were exposed to nonhyperthermic light at the absorption maximum (652 mn) for this drug. The exposed areas and control areas were excised immediately (or after an interval) and analyzed for drug content by chemical extraction and spectrofluorometry. Blood was taken prior to and again immediately after light exposure (or after 4 hours) to determine the drug levels circulating in the plasma. The drug content in skin could be reduced by half using light doses of 10 to 320 J/cm$+2$/ independently of the fluence. Our findings indicate that 'bleaching' is dependent on the drug concentration in plasma. The concept of intentional 'bleaching' designed to reduce skin photosensitivity either prior to or after treatment is discussed with respect to these findings. !14