Induction of drug photosensitization in man after parenteral exposure to hematoporphyrin.

Two patients had acute phototoxic reactions after intravenous injections of hematoporphyrin (7 mg/kg) and exposure to light. These reactions were characterized by pain, redness, and swelling of affected sites. Controlled clinical studies were instituted using known types and amounts of light to ascertain the degree of photosensitivity at various time intervals after drug administration. In addition, action spectrum studies elicited a peak response at 405 nm (+/- 5 nm). Plasma hematoporphyrin concentration was approximately 520 microgram/100 ml one hour after hematoporphyrin infusion and it gradually declined during a period of 42 days with a biphasic diminution that suggested the existence of at least two pools of hematoporphyrin with half-life decay times of 16 hours and 12 days. beta-carotene was administered to ascertain whether or not the phototoxic response could be modified. It is suggested that a degree of protection was obtained that was insufficient to protect the patient.