A Bayesian network meta‐analysis of 14 molecules inhibiting UV daylight‐induced pigmentation

Abstract Introduction Hyperpigmentation disorders are very frequent, affect the quality of life and may become a psychological burden for afflicted patients. Many anti‐pigmenting or depigmenting agents are available with various efficacy and almost no comparative data. 2‐mercaptonicotinoyl glycine (2‐MNG) was recently proposed as a viable candidate showing safe and effective results on hyperpigmentation control in vitro and in vivo . Objectives A Bayesian network meta‐analysis (BNMA) was conducted to map and rank the anti‐pigmenting and depigmenting efficacy of 2‐MNG 0.5% on UV daylight (UVDL)‐induced pigmentation together with 13 other reference molecules. A comparison in the kinetics of 2‐MNG 0.5% was also performed. Methodology Fourteen studies were conducted, for each, on 15–30 women of skin phototype III in Shanghai, China and Paris, France. The products were applied on mini zone, in randomized and blinded protocol, on the back, 5 days a week during 6 weeks, at a dose of 4 mg/cm 2 . During the second week, volunteers were exposed under to varying minimum erythemal dose of UVDL during 4 consecutive days—adapted to obtain a similar induction of skin pigmentation regardless of the population. Assessments were performed instrumentally using Chromameter®. Ascorbic acid 7% was used as a positive control for all experiments. A Bayesian network meta‐analysis was then established to map and follow the kinetics of 2‐MNG 0.5% performance with 13 reference molecules (glutathione 2%, kojic acid 1%, hydroquinone 4%, ascorbyl glucoside 2%, niacinamide 4%, etc.). Results 2‐MNG 0.5% dominated the ranking at all time points with a significant high probability of strong efficacy against UVDL‐induced pigmentation. Ascorbic acid 7% ranks second after 4 days of irradiations (D 12 ) whereas hydroquinone 4% ranks second 1 month after irradiations (D 40 ). In the kinetics, 2‐MNG at 0.5% was effective as from the end of irradiations (D 12 ) to the study endpoint (D 40 ). This suggested an immediate and persistent efficacy across all timepoints evaluated. Conclusion The BNMA revealed a rapid and lasting efficacy of 2‐MNG 0.5% on the anti‐pigmenting and depigmenting phases of the clinical protocol. 2‐MNG 0.5% ranked first, with immediate and lasting effect compared to 13 other references. This study is the first allowing comparison between reference anti‐pigmenting and depigmenting agents and will help clinicians for proposing the most effective approach for their patients.