The mechanisms of action and use of botulinum neurotoxin type A in aesthetics: Key Clinical Postulates II.

Abstract

BackgroundThe literature on botulinum neurotoxin type A (BoNT‐A) is extensive, often contradictory, and confounded by a competitive market of products and research attempting to distinguish brand individuality.MethodsA comprehensive review of literature on the principles of BoNT‐A in aesthetics as well as clinical examples.ResultsIn 2017, the Eight Key Clinical Postulates were formulated as a guide for the aesthetic practitioner in understanding BoNT‐A pharmacodynamics and to compare different toxins. These are now updated to include (a) All type A toxins act identically; (b) The mathematical relationship between toxin and receptor is the basis of efficacy, and clinical efficacy is influenced by molecular potency and patient attributes including muscle mass, gender, age, and ethnicity; (c) Efficacy, onset, and duration are functions of “molecular potency” defined as the number of active 150 kDa molecules available for binding; (d) “Molecular potency” is difficult to objectively quantify for commercially available toxins; (e) Up to a point, increased molecular potency decreases time to onset and increases duration of effect, and the “Molecular Potency Quotient” is a construct for comparing molecular potency commercial cost; (f) The area of effect of a toxin injection is dependent upon molecular potency, diffusion (passive), and spread (active); (g) Differing reconstitution volumes; and (h) Increased number of injection sites can affect spread, onset, and duration of effect.ConclusionsThe principles of BoNT‐A use in aesthetics are complex yet understandable as outlined in the framework of the updated Eight Key Clinical Postulates and serves as a useful tool for providing the most effective treatment and interpreting research on present and future toxin formulations.