Painless PDT: The next stage in the evolution
Fast, in-office photodynamic therapy with no patient pain
For nearly two decades, dermatologists have been able to offer their patients a highly effective treatment for AKs thanks to Levulan, a liquid containing 5 aminolevulinic acid (5-ALA), to treat actinic keratoses (AKs) using photodynamic therapy (PDT). The FDA approved Levulan (5-ALA) based on a 14 to 18 hour incubation period following its application to the face or scalp.
Two significant factors clouded an otherwise bright advancement with this therapy: time and pain, and too much of both. Addressing those issues has been a primary focus for Maui-based dermatologist George Martin, M.D., a practicing clinician, clinical investigator, and internationally-recognized lecturer. He is founder and program chairman of MauiDerm, the internationally recognized dermatology meeting. Along with Dr. Ted Rosen, Dr. Martin discussed ALA PDT at Maui Derm 2015 in the presentation, Cutaneous Oncology, New and Novel Uses for “Field Therapies.”
OF LIGHT AND ALA
“Dermatology is exploding with new drugs and science,” Dr. Martin says. But scrutinizing the science may, in this case, have kept doctors from seeing the forest for the trees. Where PDT is concerned, less may be more.
Understanding the ALA PDT mechanism of action is critical to making innovations in treatment. Dr. Martin explains that PDT requires three components: a photosensitizer, an activating wavelength of light, and oxygen.
The 5-ALA is converted selectively inside cancerous and precancerous cells into a photosensitizer called protoporphyrin IX (PpIX), part of a heme synthesis pathway. The PpIX selectively accumulates inside the AKs. The PpIX is a photosensitizer, “so when you hit it with blue light, it creates a ton of free radicals that destroy AKs,” Dr. Martin explains.
Dr. Martin notes that the original studies were done applying the Levulan – the ALA – to the skin and waiting 14 to 18 hours to maximize the amount of protoporphyrin IX inside the precancerous cells, then using the blue light which selectively destroys the AKs.
Time and experience showed, however, that it was very impractical to apply a liquid to the skin, then wait 14 to 18 hours to bring the patient back into the office for blue light exposure. It just didn’t work logistically, Dr. Martin says. “It’s a convenience factor for the patient, some of whom come from 100 miles away. It’s just not practical.” So practitioners tended to shorten the ALA incubation period from the on-label 14 to 18 hours to 1, 2, or 3 hours – the so-called “short incubation” – then activate with the blue light.