Porfimer sodium (trade name PHOTOFIN) is a photosensitizing agent that belongs to a group of medicines known as antineoplastics.
Purpose
Porfimer is used in a treatment called photodynamic therapy (PDT). This form of cancer treatment is for patients presenting with obstructing esophageal and endobronchial non-small cell lung cancers (NSCLC) and early stage radiologically occult endobronchial cancer.
Description
The FDA granted approval in December 1995 to porfimer sodium. Porfimer is a chemical mixture of up to eight porphyrin units. The freeze-dried compound exists as a dark red to reddish-brown cake or powder and is typically reconstituted with 5% dextrose or 0.9% sodium chloride. Porfimer sodium's antitumor effects are dependent upon its activation by a specific wavelength of light that results in the subsequent release of highly toxic oxygen-free radicals. Additionally, PDT using porfimer produces a significant decrease in blood flow to the treatment area that enhances necrosis in certain tumor cells. Clinical test results suggest that use of porfimer sodium for the palliative management of esophageal cancer, and NSCLC yields a statistically significant improvement after a single course of therapy. Porfimer sodium and the associated laser treatment have not been formally tested in conjunction with other photosensitizing compounds. However, it may be speculated that an increase in the photosensitive reaction would result.
Recommended dosage
The dose of porfimer sodium will vary among patients. The oncologist will make a final dose determination based on a number of factors, including body weight. An appropriate starting regimen for adults would be:
2mg porfimer per kg of body weight injected into a vein.
Approximately 48 hours post injection, tumor illumination with a laser light source set at 630nm wavelength.
Two to three days post tumor illumination, the physician will remove the destroyed cancer cells.
If prescribed, a second laser treatment may be given 96-120 hours after the initial porfimer injection followed by subsequent removal of destroyed cancer cells.
Patients may receive a second dose of porfimer at a minimum of 30 days from the initial treatment for up to three cycles, each 30 days apart.
Precautions
All patients who have received PDT must avoid exposure of the skin and eyes to direct sunlight and bright indoor lighting for a minimum of 30 days. Some patients may still present photosensitivity for 90 days or more. Sensitivity is produced from the residual porfimer that has not cleared the patient's system; therefore, ambient indoor lighting will help to gradually quench the photosensitive effect. Intermittent exposure trials of a small patch of skin to direct sunlight should be conducted in 10-minute segments beginning 30 days after PDT, and before returning to normal outdoor activities. If no photosensitive reaction (redness, edema, blistering) is apparent 24 hours after exposure, cautious and gradually increased exposure may continue. If the test results are positive, patients should continue precautions for an additional two weeks before repeating the exposure test. Over-the-counter sunscreens are of no use because the photo activation of porfimer occurs in the visible light range. Patient eye sensitivity should be guarded for a minimum of 30 days by wearing dark sunglasses that allow for no greater than 4% of available white light to pass through the lenses. PDT treatment scheduling before or after radiation therapy should be properly spaced to avoid any cumulative inflammatory response from one treatment regimen to the next. A two-to four-week recovery phase between treatment types is recommended. Careful monitoring of endobronchial lesion patients is required to reduce the risk of respiratory distress caused by necrotic tissue obstructing the airway. These patients are also at risk from bleeding problems associated with erosion into a major blood vessel. As with all antineoplastic agents, pregnancy should be avoided. If the patient is pregnant,
PDT should only be used if the potential benefits outweigh the risks to the fetus.
Side effects
Side effects are associated with all antineoplastic drugs, and patients should be instructed to discuss any concerns. Side effects produced with porfimer that may engender patient concern, but do not typically require medical attention, may include mild diarrhea or constipation, mild nausea and vomiting, blistering, redness or swelling of the skin, difficulty sleeping, weakness, and vision changes. These conditions usually subside as the body adjusts to the porfimer. Side effects associated with porfimer sodium that do require immediate medical attention include:
There have been no formal interaction studies between porfimer and other drugs. One may speculate on the possible synergistic effects of porfimer in conjunction with other photosensitizing agents, such as phenothiazines, chlorpropramide, demeclocycline, doxycycline, and tetracycline. Animal research studies suggest certain compounds decrease the effectiveness of porfimer used in PDT. These inhibitors include drug compounds such as dimethyl sulfoxide (DMSO) and ethanol that act by inhibiting the formation of free radicals. Other drug groups, such as thromboxane A 2 inhibitors, inhibit by decreasing clotting, vasoconstriction, or platelet aggregation. Other pre-clinical trial data suggests a decrease in porfimer efficacy in PDT in response to glucocorticoids hormones, calcium channel blockers, and prostagladin synthesis inhibitors. As with any course of treatment,
patients should first notify their doctor of any medications they are taking.
Jane Taylor-Jones, Research Associate, M.S.
Antineoplastic
—An agent that inhibits or prevents the maturation and proliferation of malignant cells.
Free radicals
—Highly reactive molecules that act as agents of tissue damage.
Necrosis
—The sum of all the morphological changes that are indicative of cell death.
Oncologist
—A physician who specializes in the diagnosis and treatment of cancer patients.
Photodynamic therapy
—Cancer treatment that uses the interaction between laser light and an agent that makes cells more sensitive to light.
Photosensitizing agents
—Ultraviolet or sunlight-activated drugs used in the treatment of certain cancer types.
Porphyrin
—Pigments found in the body that have an active affinity for metals.
