The structure of the active component of hematoporphyrin derivative.

Photoradiation therapy (PRT) for local treatment of malignant tumors utilizing hematoporphyrin derivative (Hpd) as photosensitizing drug is undergoing clinical trials in several centers in the U. S. and abroad. This therapy is based on the localization and retention of Hpd in most tumors, as well as its photodynamic action which likely generates singlet oxygen at least as a first step. The only drug toxicity encountered to date in over 1500 patients receiving Hpd has been a generalized photosensitivity which requires patients to avoid bright light, especially sunlight, for 30 days or more. While this toxicity is avoidable it presents a drawback to utilizing PRT for early stage disease in ambulatory and active patients.