ABSTRACT

Botulinum toxin type A has been used for more than two decades in the treatment of strabismus and focal dystonias – movement disorders characterized by excessive, uncontrollable muscle activity.1-3 Cosmetic use of botulinum toxin type A was reported as early as 1989 in the correction of facial asymmetry caused by facial nerve paralysis.4 Later studies reported the beneficial effects of botulinum toxin type A for hyperfunctional facial lines.5,6

In the treatment of hyperfunctional facial lines, botulinum toxin type A acts by inhibiting acetylcholine release at the neuromuscular junction.7 Its utility in facial esthetics is derived from its specific action on acetylcholine release and its localized action in the injected muscle(s). When the neurotoxin escapes from the intended muscles, unwanted weakness can occur in nearby muscles, leading to side-effects such as ptosis when treating blepharospasm. Reversibility of action is also an important therapeutic feature of botulinum neurotoxins. Even though the temporary action of botulinum neurotoxins necessitates return visits for retreatment, it allows clinicians the flexibility to refine doses and injection sites based on clinical presentation. Botulinum neurotoxins are biological products,

derived from bacteria, which are purified and processed in a series of complex steps unique to each manufacturer. These steps are critical in determining the clinical features of the botulinum neurotoxin product. In this review, the synthesis, structure, and manufacturing processes for various botulinum neurotoxins are described. The pharmacology and immunology are then considered for various botulinum neurotoxin products. A major theme of this review is that botulinum neurotoxin products are not simply interchangeable, because each is manufactured using a unique process, including synthesis by different bacteria, specific isolation and purification procedures, and the addition of distinct types and amounts of excipients.