Porfimer

Porfimer is a medication and a complex mixture of oligomers used primarily in photodynamic therapy (PDT). It is marketed under the name Photofrin and is primarily used for the treatment of certain types of cancer, including esophageal cancer and non-small cell lung cancer. Porfimer is administered intravenously and works by accumulating in cancer cells. When these cells are exposed to a specific wavelength of light, the porfimer is activated, producing a form of oxygen that kills the cells.

Mechanism of Action

Porfimer sodium, upon activation by light, induces a series of complex biochemical reactions leading to the destruction of cancer cells. The drug absorbs light at a specific wavelength (around 630 nm), which excites the porfimer molecules. This excitation state allows the transfer of energy to molecular oxygen present in the tissues, generating singlet oxygen, a highly reactive form of oxygen. Singlet oxygen can cause direct damage to cellular components, including membranes, proteins, and nucleic acids, leading to cell death. The selectivity of porfimer for cancer cells over normal cells is not fully understood but is believed to be due to the preferential retention of the drug in rapidly dividing cells.

Clinical Uses

Porfimer is used in the treatment of:

• Esophageal cancer: For palliative treatment to relieve symptoms or for curative intent in early stages.
• Non-small cell lung cancer (NSCLC): Particularly for endobronchial lesions that are not amenable to surgical resection or radiotherapy.
• Barrett's esophagus: To ablate high-grade dysplasia and reduce the risk of progression to esophageal adenocarcinoma.

Administration and Dosage

Porfimer is administered intravenously, usually 48 hours before the light exposure. The dosage and the timing of light exposure after administration depend on the condition being treated. It is crucial for patients to avoid direct sunlight and bright indoor light for a certain period after receiving porfimer to prevent photosensitivity reactions.

Side Effects

Common side effects of porfimer include:

• Photosensitivity reactions
• Nausea and vomiting
• Localized swelling at the injection site
• Fever and chills

Serious side effects can include:

• Severe photosensitivity leading to burns if exposed to light
• Respiratory distress in cases where the airway is compromised
• Esophageal stricture following treatment for esophageal cancer

Precautions

Patients treated with porfimer should take precautions to avoid exposure to direct sunlight and bright indoor light for at least 4 to 6 weeks post-treatment to minimize the risk of photosensitivity reactions. Protective clothing and sunglasses may be necessary when going outdoors.

Conclusion

Porfimer represents a significant advancement in the field of photodynamic therapy, offering a treatment option for certain cancers that may not be suitable for traditional therapies. Its ability to selectively target cancer cells while sparing surrounding healthy tissue makes it a valuable tool in the oncologist's arsenal. However, the risk of photosensitivity requires careful patient management and education.