Acute normal skin toxicity induced by porphyrin photosensitization has been examined using albino mice. Oxic and anoxic (clamped) skin was exposed to red light (630 nm) 24 h following administration of hematoporphyrin derivative (HpD) or Photofrin II (the active component of HpD). Experiments were also performed to determine the effect of sodium pentobarbital anesthesia on HpD and Photofrin II photosensitization of normal skin. Results from this study demonstrated that comparable levels of acute skin damage were induced by HpD and Photofrin II under oxic conditions but neither porphyrin produced any apparent phototoxicity under anoxic conditions. In addition, the level of skin damage induced by porphyrin photosensitization was not affected by sodium pentobarbital anesthesia.

In this pilot study, the duration and degree of skin photosensitivity after intravenous injection of HpD or DHE was tested sequentially once a week, using a solar simulator delivering 19.5 ± 1.5 J cm−2 to an area of skin 1.4 cm diameter. The longest duration of skin photosensitivity was 7 weeks amongst the 12 patients studied. In 180 other patients, the incidence of sunburn following PDT was less than 10% over a period of 7 y. Sunburn was always minimal (mild redness and swelling–no blisters), and required no systemic therapy or hospitalization. The reaction subsided within 2‐3 days. The low incidence was attributed to good verbal and written instructions in methods of prevention delivered to not only patients, but spouse, family members and friends by the investigator.

Cytotoxicity induced by hematoporphyrin derivative (HpD) photoradiation in both normal and experimental tumor tissue of pigmented rabbit eyes has been examined. In addition, documentation of HpD induced fluorescence in ocular structures has also been obtained. Acute normal ocular tissue toxicity studies demonstrated that HpD (1-10 mg HpD/kg) followed 48 hours later by a transpupil irradiation of red light (635 nm, 36-90 J/cm2) resulted in demarcated areas of retinal damage. Long term (chronic) toxicity studies have shown that the initial damage to the retina was permanent but that no damage to the cornea, lens or vitreous could be observed during a 16 month follow-up. Visual and histological documentation have been obtained, following HpD photoradiation therapy (PRT), in rabbit eyes having heterotransplanted single nodule amelanotic melanomas. A toxic effect characterized by tumor blanching, edema and hemorrhage was observed within 24 hours of treatment. Histological examination obtained 24 hours following HpD PRT illustrated massive tumor tissue necrosis and vascular disruption. HpD PRT at clinically relevant doses was also shown to be effective in selectively curing the highly malignant amelanotic iris melanoma. It is concluded that HpD PRT may prove to be an effective modality for treating certain ocular tumors.