Photofrin (porfimer sodium) is a specialized medication used in medical treatments. It functions as a photosensitizing agent, meaning it makes tissues more sensitive to light. This property allows Photofrin to be activated by specific wavelengths of laser light, leading to therapeutic effects within photodynamic therapy (PDT), a treatment approach that combines light-sensitive drugs with light to target specific cells or tissues.
What is Photofrin?
Photofrin (porfimer sodium) is a photosensitizer derived from porphyrins. This drug is designed to be administered intravenously. Once in the body, Photofrin exhibits a tendency to accumulate in rapidly growing cells, such as those found in tumors, more so than in healthy tissues. It also possesses a particular sensitivity to red light, specifically at a wavelength of 630 nanometers. This selective accumulation and light sensitivity are central to its use in targeted therapies.
How Photofrin Works
Photofrin’s action involves a two-step process. After intravenous administration, the drug circulates throughout the body and is selectively retained by certain cells, including cancerous or precancerous cells. It takes approximately 40 to 50 hours for most of the Photofrin to clear from healthy tissues, allowing for a differential concentration in target areas.
Following this accumulation period, the second step involves exposing the targeted area to laser light, typically 630 nanometers. This light activates the Photofrin within the cells, initiating a photochemical reaction. The activated Photofrin then interacts with molecular oxygen present in the tissues, producing highly reactive forms of oxygen, such as singlet oxygen. These reactive oxygen species are cytotoxic, meaning they can damage or destroy the targeted cells.
Conditions Treated with Photofrin
Photofrin, as a component of photodynamic therapy (PDT), is approved for treating several medical conditions. It is indicated for the palliation of patients with completely or partially obstructing esophageal cancer, helping to relieve symptoms by reducing the size of tumors that block the esophagus.
The drug is also used for the treatment of microinvasive endobronchial non-small cell lung cancer (NSCLC) in patients who are not candidates for surgery or radiotherapy. Furthermore, Photofrin is indicated for the ablation of high-grade dysplasia in patients with Barrett’s esophagus.
The Photodynamic Therapy Procedure
Undergoing Photodynamic Therapy with Photofrin begins with the intravenous administration of the drug. After this initial step, there is a waiting period of 40 to 50 hours, allowing the Photofrin to accumulate in the target cells and clear from healthy tissues.
Once the waiting period is complete, laser light is applied to the affected area. For internal conditions like esophageal or lung cancers, a fiber optic is guided through an endoscope to deliver the red laser light directly to the tumor. The light dose for esophageal cancer treatment is typically 300 Joules per centimeter (J/cm) of diffuser length, delivered over approximately 12 minutes and 30 seconds. Patients may receive additional light treatments or courses of PDT, usually separated by a minimum of 30 days.
Safety and Potential Side Effects
A primary safety concern with Photofrin is photosensitivity, which is an extreme sensitivity to light. Because Photofrin remains in the body for an extended period, patients must take precautions to avoid exposure to natural sunlight and bright indoor lights for at least 30 days after treatment. This includes wearing protective clothing, wide-brimmed hats, and dark sunglasses when outdoors, and avoiding direct exposure to bright lamps or unshaded bulbs indoors.
Other potential side effects can include fever, chills, or chest pain. Patients should also be monitored for signs of anemia. It is also important to avoid concomitant use of Photofrin with other photosensitizing agents, as this may increase the risk of a photosensitivity reaction.