Clinical Evaluation of the Human Tyrosinase Inhibitor Thiamidol (isobutylamido thiazolyl resorcinol) in Prevention of UVB-induced Hyperpigmentation

Clinical Evaluation of the Human Tyrosinase Inhibitor Thiamidol (isobutylamido thiazolyl resorcinol) in Prevention of UVB-induced Hyperpigmentation Vasanop Vachiramon, Chaninan Kositkuljorn, Kanchana Leerunyakul, Kumutnart Chanprapaph Division of Dermatology, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand Background: Thiamidol (isobutylamido thiazolyl resorcinol) has been identified as a potent human tyrosinase inhibitor. A formulation containing Thiamidol has recently shown promising efficacy for the treatment of some hyperpigmentation conditions. Objectives: This study aimed to evaluate the efficacy and safety of a Thiamidol-based formulation in the prevention of ultraviolet (UV)-induced hyperpigmentation. Materials and Methods: We performed a randomized, single-blinded, pilot study in healthy participants, N=30. One arm was randomly assigned to receive a Thiamidol-based formulation for three weeks. Three hyperpigmented spots were induced by UVB irradiation on both arms after 3 weeks of ITR application. Outcome evaluations included measuring mean lightness index (*L) obtained by colorimeter, hyperpigmentation scores by visual analog scale (VAS), and adverse effects. Results: Both experimental sides showed no significant difference in terms of skin lightening after Thiamidol application. However, the Thiamidol-treated sides showed a statistically significant lower mean lightness index compared to control after an induction with UVB. In addition, the Thiamidol-treated sides had an earlier improvement and resumed normal skin color after 3 weeks post-UVB induction. A clinical evaluation by a blinded non-treating physician and subjects was more favorable on the Thiamidol-treated side than the control side (P < .05). No significant side effect was noted. Conclusions: Thiamidol is an effective agent in the prevention of pigmentary change from UVB irradiation and may serve as a promising agent for preventing other hyperpigmentation conditions.