Pongklaokam J.Manuskiatti W.Wanitphakdeedecha R.Maneeprasopchoke P.Thongjaroensirikul P.Nokdhes Y.Abad-Constantino R.M.R.Bhorntarakcharoen W.Sittiwanaruk S.Techapichetvanich T.Mahidol University2025-08-032025-08-032025-07-01Toxins Vol.17 No.7 (2025)https://repository.li.mahidol.ac.th/handle/123456789/111486Background: Melasma is an acquired hyperpigmentation disorder with multifactorial etiologies and limited response to conventional therapies. Recent evidence suggests that Botulinum Toxin A (BoNT-A) may modulate ultraviolet (UV)-induced pigmentation and offer therapeutic benefits. Objective: We sought to evaluate the efficacy and safety of two intradermal dilutions of Letibotulinum toxin A (LetiBoNT-A) in Thai patients with melasma. Methods: In this randomized, double-blind, split-face study, 30 participants aged 32–62 years received a single intradermal injection of LetiBoNT-A, with 20 units administered per cheek. A 1:5 dilution was injected on one side of the face, and a 1:10 dilution was injected on the contralateral side. Outcomes were evaluated over a 6-month period using the Hemi-modified Melasma Area and Severity Index (Hemi-mMASI), VISIA^® brown spot analysis, and quantitative assessments of skin texture. Results: Both dilutions significantly improved Hemi-mMASI scores (1:5, p = 0.043; 1:10, p = 0.002) and brown spots (1:5, p = 0.002; 1:10, p < 0.001). The 1:10 dilution showed earlier and more sustained improvements. Subgroup analysis revealed greater reductions in Hemi-mMASI scores among patients with telangiectatic melasma, particularly with the 1:10 dilution, though they were not statistically significant. Additionally, the 1:10 dilution significantly reduced pore volume, pore area, and sebum levels. One case of transient facial asymmetry was reported with the 1:5 dilution. Conclusions: LetiBoNT-A is a safe and effective adjunct in melasma treatment. The 1:10 dilution offered superior clinical outcomes.Pharmacology, Toxicology and PharmaceuticsEnvironmental ScienceArticleSCOPUS10.3390/toxins170703492-s2.0-10501187324620726651