Photodynamic Therapy (cont.)

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What photosensitizer drugs are available?

FDA-approved photosensitizers include porfimer sodium (Photofrin), 5-aminolevulinic acid or ALA (Levulan), and methyl aminolevulinate [MAOP] (Metvix). More drugs may become available in the near future. Photofrin is used intravenously for internal cancers while Levulan and Metvix are applied topically for skin therapy.

What light sources are available, and how are they applied?

PDT light sources include laser, intense pulsed light, light-emitting diodes (LEDs), blue light, red light, and many other visible lights (including natural sunlight). Photosensitizer drugs may become activated by one or several types of light. The optimal light depends on the ideal wavelength for the particular drug used and target tissue.

The light source needs to be directly applied to the target tissue for a specific amount of time. For surface skin treatments, the light is easily directly applied to the area of the skin where the photosensitizer drug has been applied (such as face, scalp, arms, etc.). For internal cancers, delivering the light to the desired area is more challenging. The light may be delivered through small fiber-optic cables into the body cavity or area being treated. Sometimes, endoscopes (a thin, lighted, elongated tube that is inserted into a body space) are used to deliver the light into the lungs, stomach, or bladder.

How does photodynamic therapy work?

PDT works by direct injury to the target cells and tissues. This involves an activated oxygen molecule that can injure or destroy nearby cells. Because the normal skin barrier is not present at the sites of the actinic keratoses, it is preferentially absorbed there and activated by light. Then, the activated oxygen destroys the adjacent abnormal tissue. Once the areas have healed following PDT, the areas are reexamined to see if additional treatments or biopsies are needed.

With traditional cryosurgery (freezing with liquid nitrogen), only the visible actinic keratoses can be treated. Since many actinic keratoses are often not evident, this PDT might be preferable since it presumably would destroy these "subclinical" lesions. PDT allows for treatment of an entire area of sun damage simultaneously, but subsequent treatments may be necessary.

Medically Reviewed by a Doctor on 5/5/2014

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