Porfimer

Porfimer, typically referred to as porfimer sodium, is a photosensitizing agent used in photodynamic therapy (PDT). It is a purified mixture of hematoporphyrin derivatives that is administered intravenously and preferentially accumulates in malignant tissue, enabling targeted light-activated treatment.

Mechanism and light activation: After IV infusion, porfimer sodium localizes to tumor tissue more than to normal tissue. When illuminated with light in the red spectrum around 630 nanometers, the drug transfers energy to molecular oxygen to generate reactive oxygen species, causing tumor cell damage and vascular injury. The treatment effect depends on the presence of oxygen and the light dose delivered to the target area.

Administration and dosing: Porfimer sodium is given as an intravenous infusion, often at a dose near 2 mg/kg. The therapeutic light exposure is scheduled typically 24 to 72 hours after administration, with the specific timing and light dose tailored to the treated site and cancer type. Light delivery can be endoluminal, endobronchial, or other targeted forms of illumination.

Indications and usage: It is used in photodynamic therapy for certain cancers and precancerous conditions, including cancers of the esophagus, bronchi, and other regions, as well as high-grade dysplasia and selected premalignant lesions. PDT with porfimer sodium is also used for palliation of obstructive tumors to relieve symptoms and improve function in some patients.

Safety and precautions: A major and distinctive risk is prolonged photosensitivity, requiring avoidance of direct sunlight and intense indoor lighting for several weeks after treatment. Other potential adverse effects include light-related skin and eye reactions, nausea, vomiting, fatigue, and transient liver function changes. Patients with porphyrias or who are pregnant or breastfeeding generally require special caution.

History and status: Porfimer sodium, marketed under brand names such as Photofrin, was one of the first agents approved for cancer-related PDT and remains in use in various countries within approved indications.