A Controlled Phase 2b Trial to Assess the Efficacy and Safety of a Single Intervention of OnabotulinumtoxinA for Treating Masseter Muscle Prominence

Abstract Background Masseter muscle prominence (MMP) is a benign condition characterized by a wide, square, or trapezoidal lower facial shape, which may be considered undesirable. Objectives To evaluate onabotulinumtoxinA (onabotA) efficacy and safety for MMP treatment. Methods In a Phase 2b study, adults with investigator- and participant-assessed bilateral Grade 4/5 MMP on the 5-grade MMP Scale (MMPS) and MMPS—Participant, respectively, were randomized 1:1:1 to receive a single intramuscular injection of onabotA 48 U, 72 U, or placebo in the masseter muscles. The primary endpoint was the proportion of patients achieving investigator-assessed MMPS Grade ≤3 at Day 90. Adverse events were monitored throughout. Results Patients received onabotA 48 U (n = 53), 72 U (n = 46), or placebo (n = 46). Significantly greater proportions achieved MMPS Grade ≤3 with onabotA vs placebo (90.6%, 91.3%, and 21.7% for onabotA 48 U, 72 U, and placebo, respectively, at Day 90; P < .0001). Improvements in lower facial volume, width, and angle were significantly greater for onabotA vs placebo at all time points. At Day 90, the proportion of patients perceiving improvements was significantly greater with onabotA treatment vs placebo. Significantly more patients were “satisfied/very satisfied” with onabotA vs placebo through Day 180. Treatment was well tolerated; both onabotA groups had a similar incidence of treatment-emergent adverse events (TEAEs). Nasopharyngitis (onabotA, 3.9% vs placebo, 0%) and upper respiratory infection (2.9% vs 0%, respectively) were the most common TEAEs. Conclusions One injection of onabotA 48 or 72 U was well tolerated and effective in reducing MMP severity as assessed by investigators and patients. Level of Evidence: 1 (Therapeutic)