The Frontalis Activity Measurement Standard: A Novel Contralateral Method for Assessing Botulinum Neurotoxin Type-A Activity

September 2011 | Volume 10 | Issue 9 | Original Article | 968 | Copyright © 2011

Abstract

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.

J Drugs Dermatol. 2011;10(9):968-972.

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INTRODUCTION

Botulinum neurotoxin type-A (BoNTA) has gained acceptance in the medical community and among consumers for the treatment of hyperkinetic facial lines to reverse the physical signs of aging.1 In 2009 alone, BoNTA was used in over 2.5 million aesthetic procedures.2 Although all BoNTA products contain neurotoxin derived from Clostridium botulinum, they are made using different proprietary manufacturing methods and differ with respect to measures of unit potency and the amounts of non-toxin protein complexes they contain. They are considered to be similar but not bioequivalent and cannot be used interchangeably.3-5 Comparisons regarding relative units of activity, onset, and duration of effect of these products have been reported and vary significantly.6,7

Accurately measuring efficacy outcomes, such as onset and duration of action is important for fully understanding the mechanism of action of BoNTA and making meaningful clinical comparisons between different BoNTA products. While the measurement of maximal glabellar frown has been accepted as a validated measure for evaluating the effectiveness of BoNTA,8-12 it uses a relatively subjective assessment as an endpoint. Similar rating scales have been used to assess the effectiveness of BoNTA for treating lateral canthal lines.13 Photonumeric grading scales have also been devised for evaluating the severity of crow's feet,14 marionette lines15 and forehead wrinkles16 as a means for monitoring the response to therapy in research and clinical practice settings; however, these scales may not fully capture the effects of BoNTA on muscle activity, such as onset of action.

Additionally, there is a need for consistent terminology or definitions for onset or duration of action for BoNTA in research studies. Several studies have attempted to objectively compare BoNTA products in terms of their area of effectiveness and longevity11,17-21 but lacked an established, objective metric and used different nomenclature for comparing the effects of BoNTA on

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