Dermatology World March 2011 : Page 23
within acne lesions. They note that investigators in the 2000 study did not observe a reduction in the number of Propionibacterium acnes. More recently however, a review in the September 2010 issue of the Journal of Cosmetic Der-matology , co-authored by Mohammed L. Elsaie, M.D., and Sonal Choudhary, M.D., cited two studies that showed ALA-PDT did reduce the number of P. acnes; the mechanism of action therefore remains uncertain. oPtiMal treatMent ParaMeters elusive In addition to choosing between two available photosen-sitizers (ALA and its derivative, methyl-aminolevulinate [MAL]), clinicians off ering PDT to their patients must consider various light sources and wavelengths, light do-simetry, drug incubation time, and skin preparation (see sidebar below). Despite the wealth of published studies examining PDT for acne, none of the variables has been optimized for this treatment, says Dr. Sakamoto. “Because there’s no consensus about this right now, there’s a lot of debate and people don’t agree as to the best way to deliver PDT,” she says. “We wrote our review article to try to raise the question and come up with the best we could out of the current literature.” Drs. Choudhary and Elsaie expressed a similar goal in conducting their review for the Journal of Cosmetic Derma-tology . “There’s no consensus, no standardization, no ra-tionales for the PDT treatment of acne,” says Dr. Elsaie, an instructor of dermatology at the University of Miami Miller School of Medicine and instructor of dermatology at the National Research Center in Cairo, Egypt. Dr. Choudhary, a clinical research fellow in the department of dermatology and cutaneous surgery at the Miller School of Medicine, says she suspects that “probably very few dermatologists have tried PDT for acne. So a review of this kind may help build awareness of where this modality stands.” Drs. Saka-moto, Torezan, and Anderson analyzed 18 clinical studies published through 2009 on the subject of PDT for acne. Drs. Elsaie and Choudhary analyzed 22 studies. KEY PDT ParaMeters The variables associated with each of the key treatment parameters involved in PDT include: PHOTOSENSITIZER – ALA, available in 20 percent hydroalcoholic solution, and MAL, available in a cream formulation of 16 percent, have different mechanisms of cell uptake and transport. New ALA derivatives are in development, but clinical results are not yet available. In studies of acne therapy using a long incubation time and high fluence red light exposure, ALA and MAL have shown similar efficacy. While more comparative studies are needed, they seem largely equivalent. LIGHT SOURCE AND WAVELENGTH – Continuous wave (CW) and pulsed light sources, including intense pulsed lights (IPLs) and pulsed dye lasers (PDLs), and diode la-sers have all been studied in PDT for acne. Light sources tested include light-emitting diodes, filtered incandes-cent or arc lamps, slide projectors, fluorescent lamps, filtered xenon flashlamps, lasers, and sunlight. Red light (a longer wavelength with deeper penetration) and blue light (a shorter wavelength with the strongest porphyrin absorption) are the most frequently studied in PDT for acne research. DOSIMETRY – The primary units of dosimetry are wave-length range of the source, irradiance (the rate at which energy is delivered per unit area of skin) fluence (the total energy delivered per unit area of skin), and exposure time. At the present time there is no consensus on the optimal dosimetry for PDT of acne. SKIN PREPARATION – No clinical comparison of pre-treatment care has been reported for PDT using either ALA or MAL. Drs. Sakamoto, Torezan, and Anderson note that skin preparation was not mentioned in several of the studies they analyzed. Among those that did describe preparation, methods included cleansing with 70 percent isopropyl alcohol, mild skin cleansers, 2 percent salicylic acid, and soap and water followed by alcohol scrubbing. Ten of 18 publications recommended occlusion during the drug incubation time, which may increase drug uptake. INCUBATION TIME – The time between drug application and irradiation can range from as few as 10 minutes to three to four hours. While a few studies have suggested shortening the incubation period to 10 to 30 minutes, Drs. Sakamoto, Torezan, and Anderson report that the stron-gest evidence points to a period of at least three hours. Dermatology WorlD // March 2011 23
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