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

Facial rhytides of the upper one third of the face are common aesthetic concerns, and are caused principally by overactivity of the underlying facial musculature. Botulinum toxin, which acts by causing flaccid paralysis of facial mimetic muscles, has become a treatment of choice for the management of these hyperfunctional facial lines. Two antigenically distinct serotypes have been developed and are currently available for commercial use in the United States. There are major differences between the two toxins in terms of pharmacology and formulation that account for clinical differences, and precise interconversion is not well-established. Nevertheless, in these preliminary studies, Myobloc seems to have a faster onset of action and potentially a more even and smoother paralysis. The shorter duration of action of Myobloc seems to be dose-related. It is clear that both agents safely and effectively reduce dynamic facial rhytides. Based on individual efficacy, safety, diffusion pattern, onset, and duration, ultimately, with further trials and clinical experience, it is conceivable that each toxin will have its own set of indications.