Reduction of masseter muscle prominence after treatment with onabotulinumtoxinA: primary results from a randomized phase 2 study.

Background: OnabotulinumtoxinA is used to treat masseter muscle prominence (MMP).

Objective: To assess the safety and efficacy of onabotulinumtoxinA for MMP in a randomized study.

Methods: This 12-month, multicenter, double-blind, placebo-controlled, phase 2 study randomized adults (18-50 years of age) with marked/very marked bilateral MMP (≥4 on the Masseter Muscle Prominence Scale [MMPS]) to onabotulinumtoxinA (24, 48, 72, or 96 U) or placebo; retreatment occurred at day 180 if MMPS ≥4. Lower facial volume at day 90 was measured using Vectra 3-dimensional photography. Safety assessments included computed tomography and dental exams. Evaluations occurred monthly through day 360.

Results: Among 187 randomized subjects, significant lower facial volume reductions and percentage of responders (MMPS grade ≤3) were greater with onabotulinumtoxinA versus placebo at day 90 (P < .001 and ≤ .008, respectively). Similar efficacy was observed with retreatment. No dose-related safety trends or clinically relevant changes in the mandible or teeth occurred. Localized impact on smile was reported with 96 U onabotulinumtoxinA (n=4).

Limitations: Limited sample size per individual treatment group.

Conclusion: OnabotulinumtoxinA administered in 1 or 2 treatments over 1 year was associated with significant reductions in masseter muscle volume and MMP severity, with an acceptable safety profile.