Botulinum toxin (BTX), an exotoxin produced by the bacteria Clostridium botulinum, occurs naturally in nature. BTX induces a bilaterally symmetric descending neuroparalytic condition called botulism. The word “botulinum” is derived from the Latin word for sausage, “botulus.” Botulism was so named during the Napoleonic Empire in the early 1800s when it was noted to be triggered by the ingestion of spoiled sausages. Later, German physician Justinus Kerner described food-borne botulism and its clinical symptoms during the period between 1817 and 1822. In 1946, Schantz reported isolating BTX type A in its crystalline form, and nearly a quarter of a century later, Alan Scott became the first to harness the effects of BTX for medicinal use in monkey strabismus.1
The use of C. botulinum A exotoxin, commonly known as botulinum toxin type A (BTX-A), has emerged over the last decade as one of the most popular methods of combating cutaneous signs of aging, particularly the dynamic wrinkles of the face. The therapeutic application of this potent neurotoxin has carved a comfortable niche in the cosmetic realm of dermatology practice for practical reasons: Results appear within several days of administration, the procedure itself is short in duration and relatively uncomplicated, and side effects are minimal.
Although medicinal use of BTX by physicians is widespread, professional opinions vary as to the best ways to administer the treatment. For instance, the ideal dilution of the toxin, the number of units to inject, and the longevity of prepared and refrigerated BTX remain debated issues (Box 22-1). The methods described in this chapter are those used most frequently by the primary author. The novice injector should try the various methods espoused by experienced specialists to determine which yields the best results in his/her own practice.
BOX 22-1 Units of Botulinum Toxin
One unit (U) of BTX is the dose that would be lethal to 50% (LD50) of the specific mouse species tested. For a 70-kg person, the LD50 of Botox is 2500 to 3000 U. However, manufacturers use different mouse models, so a unit of one brand is not equivalent to a unit of another brand. Because of these variations, it is important to know which type of BTX was used when evaluating dosing information in the literature. For cosmetic indications, injection of approximately 20 to 75 U doses of Botox is typical. Practitioners have used doses as high as 1000 Botox units to treat cerebral palsy and other neurologic conditions.
Acetylcholine (ACh) is the neurotransmitter associated with induction of muscle movement. BTX achieves chemical denervation of striated muscles by cleaving one or more of the proteins required for the release of ACh (Fig. 22-1). The target protein depends on the serotype of toxin used (Table 22-1). The result is temporary flaccid paralysis of the injected muscles, which ...