The use of 5-ALA for Photodynamic Therapy
Photodynamic therapy (PDT) is a treatment that uses a drug, called a photosensitiser or photosensitising agent, and a particular type of light. When photosensitisers are exposed to a specific wavelength of light, they produce a form of oxygen that kills nearby cells.
Each photosensitiser is activated by a specific wavelength of light. This wavelength determines how far the light can penetrate the body. Thus, doctors use specific photosensitisers and wavelengths of light to treat different areas of the body with PDT.
Photodynamic therapy also describes the application of a photosensitising chemical to a specific cutaneous lesion which, when followed by exposure to visible light, results in an excitation of the photosensitiser.
Once this photosensitiser is irradiated and activated, reactive oxygen species are produced affecting subcellular structures, which leads to cytotoxicity. Due to this phototoxic effect, malignant and non-malignant hyperproliferative tissue can be destroyed or decreased in size, and eventually be eradicated.
PDT can be used to treat solar damage.
- A photosensitiser precursor (aminolevulinic acid (ALA) ) is applied.
- A waiting period of a few hours is allowed to elapse, during which time:
- ALA will be taken up by cells, and
- ALA will be converted by the cells to Protoporphyrin IX, a photosensitiser
- The physician applies a red/blue light on the area to be treated. The light exposure lasts between 5 – 15 minutes.
- Within a few days, the exposed skin and carcinoma scabs over and flakes away.
- In a few weeks, the treated area has healed, leaving healthy skin behind. For extensive malignancies, repeat treatments may be required.
- After the treatment the patient will need to avoid excessive exposure to sunlight for approximately two days
Specificity of treatment is achieved in three ways. First, light is delivered only to tissues that a physician wishes to treat. In the absence of light, there is no activation of the photosensitiser and no cell destruction. Second, photosensitisers may be administered in ways that restrict their mobility.
Finally, photosensitisers may be chosen which are selectively absorbed at a greater rate by targeted cells. ALA is taken up much more rapidly by metabolically active cells. Since malignant cells tend to be growing and dividing much more quickly than healthy cells, the ALA targets the unhealthy cells.
Contra-indications and side effects of the use of ALA with Photodynamic Therapy
- Slight tingling or burning at the therapy site
- Scaling, itching, changes in skin colour
- Mild swelling for two to three days after therapy
- Generalised photosensitivity lasting up to three to four days
- Skin sensitivity to blue light
- Allergies to chemicals called porphyrins
- Treated lesions are sensitive to light therefore, people being treated will need to avoid sunlight and sources of bright light for at least 40 hours after 5-ALA is applied
Medicines that are contra-indications for the use of ALA include:
- Thiazides (used to treat high blood pressure)
- Tetracyclines, fluoroquinolones, griseofulvin, or sulfonamides (used to treat infection)
- Sulfonylureas (used to treat diabetes)
- Phenothiazines (used to treat serious emotional problems)
The ACPHARM ALA formulation
There are no registered products containing ALA on the Australian Market.
The new ALA formula is a stable single phase solution which eliminates the prior need for mixing compounded ALA. The preparation is packaged in a multi-use spray.
It can be sprayed on the area directly or sprayed on paintbrush/cotton bud for targeted application. It has to be shipped in an esky and is stable for six months with refrigeration.