Botulinum Toxin Injections for Facial Rhytides

Abstract

Once feared for its deadly properties, Botulinum toxin is now revered for its effectiveness as a treatment in minimally invasive facial rejuvenation. The injection of Botulinum toxin is the most frequently performed nonsurgical cosmetic procedure, with at least 4.8 million procedures in 2009. First approved by the U.S. Food and Drug Administration (FDA) in 1979 for the treatment of strabismus, Botulinum toxin was shown to be both safe and effective for use to decrease muscle function. Botulinum toxin’s cosmetic applications were first recognized when it was noted that facial rhytides improved in the areas of treatment with the toxin when it was used for noncosmetic applications in the late 1980s and early 1990s. FDA approval for cosmetic treatment of the glabellar furrows was announced in 2002, and off-label aesthetic indications have continued to evolve. Botulinum toxin is produced by the gram-positive, anaerobic Clostridium botulinum. The neurotoxin acts on the peripheral nervous system, where it inhibits release of acetylcholine from the presynaptic terminal at the neuromuscular junction. There are seven distinct antigenic Botulinum toxins (BTX-A, B, C, D, E, F, and G) produced by different strains of C. botulinum. The human nervous system is susceptible to only five of these serotypes (BTX-A, B, E, F, G), and types A and B are currently available for human injection. In the United States, there are four commercially available Botulinum toxin preparations: three types of Botulinum toxin type A, OnabotulinumtoxinA or Botox Cosmetic® (Allergan, Inc., Irvine, CA), IncobotulinumtoxinA or Xeomin (Merz, Frankfort Germany), and abobotulinumtoxinA or Dysport (Medicis, Scottsdale, AZ). There is one preparation of Botulinum toxin type B, RimabotulinumtoxinB or Myobloc® (Elan Pharmaceuticals, San Diego, CA). Other Botulinum toxin type A products are anticipated to come to the U.S. market in the next decade as well. Different formulations of Botulinum toxin type A are biochemically unique and are not necessarily equivalent in dosing. The Botox unit is three times as potent as the Dysport unit, but this conversion ratio does not take into consideration safety or antigenic potential. Practically speaking, a range of 2.5 to 3 to one has been recommended to make Dysport dosing approximate the effects of Botox.