Development and characterization of melatonin-based UV protectant dermal formulation with higher SPF value: a gamma scintigraphy evaluation

The aim of the present study was to develop an ointment formulation against sunburns caused by ultraviolet-B (UV-B) radiation, predominantly at hilly areas because of high intensity of solar radiation. The developed formulation is shown more effectiveness because it contained higher amount of zinc oxide, which acts as a physical filter/barrier, apart from other ingredients - antioxidants, i.e., melatonin, sea buckthorn oil, carrot seed oil, in specific concentration within the regulatory limits to provide a synergistic effect. In preliminary experiments, determination of pH, viscosity, spreadability studies were conducted. There are various concentration of ingredients, i.e., zinc oxide, silk gel, N-acetyl cysteine, and curcumin, were tested (F1-F13) and formula F8 was found to be optimum in terms of higher sun protection factor (SPF) value, i.e., SPF-50. Histopathology study in albino Wistar rats (white) was conducted to achieve the toxicological information of developed formulation. In addition, skin irritation, eye irritation study, safety and efficacy studies of sunscreen lotion ware conducted. The whole formulation was radiolabeled with ^99mTc-pertechnetate for its gamma scintigraphy and radiolabeling efficiency found <97.5% confirmed by paper chromatography. Gamma scintigraphy study in twelve human volunteer shown that developed formulation retained on the human forearm skin up to 95% ± 4.5% after 30-min washing period while it was found 85% ± 3.4% with marketed formulation. Final scan of gamma camera suggested significant increased retention of melatonin formulation, i.e., 15% ± 3.15%, which was found ten times higher than 1.5% ± 2.77% of control reading. Outcome of the study concluded that developed dermal formulation may employed against the UV-B radiation and useful against sun burn. (author)