Minimal phototoxic dose (MPD) following topical phenylalanine

Dear Editor Photochemotherapy using a photosensitizer followed by ultraviolet A (UVA) light is effective in treatment of various skin conditions such as psoriasis, alopecia areata, and vitiligo. 8-methoxypsoralen and trimethylpsoralen are the commonly used agents. Ten percent topical phenylalanine has been reported to be effective in the treatment of vitiligo.1 Oral with topical phenylalanine followed by phototherapy was found to be more effective than oral phenylalanine followed by phototherapy.2 We conducted the study to elicit the minimal phototoxic dose (MPD) following application of topical phenylalanine. A 68-year-old male and 24-year-old female volunteered for the study. A topical preparation containing 10% phenylalanine, black pepper oil, black cumin seed oil, watermelon seed oil, aqua, caprylic/capric triglyceride, isononyl isononanoate, polyacrylate − 13, polyisobutene, polysorbate 20, phenoxyethanol, ethylhexylglycerin, hydroxyethyl acrylate/sodium acryloyldimethyltaurate copolymer, carbomer 940, zinc oxide, EDTA (Vitibex lotion®, Newtrimed Healthcare Pvt. Ltd., Perambur, Chennai, India), and a commercially available moisturizing lotion as control were applied over the left side and right side, respectively, over a square area of 10 × 10 sq cm over the back Figure 1. The preparations were applied twice daily for 7 days. After 7 days, attempt was made to determine the MPD using a template Figure 2.3Figure 1: Application of topical preparations over the backFigure 2: Minimal phototoxic dose (MPD) determination using a templateTen areas on each side, 2 × 2 sq cm each was exposed to 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5 Joule (J)/sq cm of UVA light and was examined for erythema and pigmentation after 72 hours, 96 hours, and on day 7. Neither of the two volunteers developed either erythema or pigmentation over both the sites exposed to ultraviolet light following the application of the topical preparations Figure 3.Figure 3: No erythema or pigmentation observed on day 7We conclude that 10% topical preparation of phenylalanine does not induce photosensitivity to UVA up to 6 J/sq cm. Thus, photosensitization following phenylalanine cannot explain the repigmentation reported in vitiligo.1,2 This study is an attempt to understand a molecule which is being frequently used, although the reason for its reported effectiveness in the management of vitiligo remains unknown. Acknowledgement Nil Financial support and sponsorship Source(s) of funding/support: None Conflicts of Interest There are no conflicts of interest. Previous publication: Nil Presentation at a meeting: Nil