Background: There are conflicting data regarding the specific attributes of botulinum neurotoxin type-A (BoNTA) products including onset of action, duration and spread because accurate, objective methods for assessing their clinical activity are lacking.
Objective: To refine definitions for BoNTA activity utilizing the frontalis muscle and describe the Frontalis Activity Measurement Standard (FMS), an objective method for measuring changes in frontalis muscle activity as a metric for assessing BoNTA pharmacodynamics.
Methods: As part of a study to assess BoNTA activity, 20 subjects with severe frontalis lines at maximum elevation were injected with two BoNTA products at five points on contralateral sides of the frontalis. Changes in maximum baseline frontalis elevation were measured by a blinded investigator using the previously-validated Frontalis Rating Scale (FRS) and the FMS. Frontalis activity endpoints were redefined to include Initial, Full and Complete Onsets of action and Partial, Full and Complete efficacy.
Results: Differences in the onset of effect of the BoNTA products were detected with both the FRS and FMS; however, the FMS detected changes in frontalis activity earlier than the FRS. A significant correlation between the FRS and FMS was documented.
Conclusion: The frontalis muscle activity allows for enhanced assessment of BoNTA activity and attributes. The FMS appears to be a sensitive and objective tool for measuring pharmacodynamic parameters of BoNTA. Refining definitions of BoNTA activity provides a more accurate means for describing the clinical effects of BoNTA.