Comparison of botulinum toxins A and B in the aesthetic treatment of facial rhytides.

Botulinum toxin injections have become a popular treatment for minimizing or eliminating facial wrinkles. After injection, the toxin acts to paralyze or weaken facial mimetic muscles. Two antigenically distinct serotypes, botulinum toxin type A (BTX-A) and botulinum toxin type B (BTX-B), are currently available. BTX-A is a lyophilized powder preparation requiring reconstitution; BTX-B is a ready-to-use liquid formulation. Both agents produce the same resultant clinical effect (i.e., muscle weakening). However, in addition to differences with respect to formulation, they are pharmacologically distinct in terms of molecular size, cellular mechanism of action, and species sensitivity. BTX-A has been used for aesthetic purposes for more than 10 years. Clinical studies and observations have shown that it is an effective agent for treating hyperkinetic facial lines. BTX-B was approved for use in cervical dystonia in 2000, but it has been used off-label to treat facial wrinkles as reported in several open-label studies. These preliminary dose-ranging studies have demonstrated that BTX-B is also effective. Both agents are extremely safe nonsurgical modalities for hyperkinetic facial lines. This article reviews the pharmacology and molecular features of BTX-A and BTX-B and highlights some of the key clinical studies that have been published to date with these two agents.