The discoveries that culminated in an understanding of toxin action are only one reason for current excitement about the toxin. Botulinum toxin is being used to treat such disorders as strabismus, spasmodic torticollis, and loss of detrusor sphincter control. These disorders are all characterized by excessive efferent activity in cholinergic nerves. Botulinum toxin is injected near these nerves to block release of acetylcholine. Although a single clinical assessment that applies to all situations cannot be offered, in general botulinum toxin has emerged as the therapy of choice for conditions characterized by excessive cholinergic activity.
Several factors explain why botulinum toxin has proved to be such a valuable drug.
First, the toxin is highly selective in acting on cholinergic cells, a characteristic that diminishes the chances of adverse side effects. Adverse effects that do occur are usually caused by toxin diffusion and action on nearby cells. Second, the toxin has a long duration of action. Clinically significant responses can last from several months to more than a year, after which time the toxin must be readministered. Finally, the dose of toxin can be individually titrated for each patient to ensure maximal benefits.