BACKGROUNDNovel, effective, affordable therapies for rosacea are needed. Innovative methods of assessing response for rosacea treatments are needed as well. This trial was designed to evaluate efficacy and safety of ACU-D1, a novel inhibitor of the 26S protea-some for the treatment of moderate to severe rosacea in a first in human pilot study. In addition, this is the first trial to our knowledge to use Canfield imaging to quantitatively assess responses.METHODSThis was a 14-week, randomized, double-blinded, placebo-controlled study, performed at two well established rosacea clini-cal trial sites, which randomized 40 adult subjects with moderate to severe rosacea (Investigator’s Global Assessment [IGA]=3/4) to either ACU-D1 (27) or comparator vehicle (13) twice daily. In addition, Canfield imaging was used to assess responses both qualitatively and quantitatively Results: A total of 39 subjects participated, with 38 completing the study. ACU-D1 displayed efficacy in 92% (25 of 27) of patients in reducing inflammatory lesions and a 2 plus grade IGA reduction of clear to near clear in 27% of patients. There was a trend toward improvement in erythema as well in the active arm.CONCLUSIONThis study demonstrates that topical ACU-D1 is safe and well-tolerated by patients in the study and demonstrates efficacy in reducing inflammatory lesions and erythema in patients with rosacea. Improvement was also noted on Canfield imaging, and this modality is likely to be used as an objective measure in the future. Further studies are warranted based on these initial positive results. ClinicalTrials.gov Identifier: NCT03064438 J Drugs Dermatol. 2021;20(6):660-664. doi:10.36849/JDD.5925.