Botulinum toxin: application, safety, and limitations.

Botulinum neurotoxin type A (BoNT/A), despite its high toxicity, is approved for therapy of many neurological (e.g., dystonia, spasticity) and non-neurological (e.g., achalasia, hyperhidrosis) disorders. Its mode of action is well understood. This has led to more and more indications (e.g., pain, gastrointestinal and urologic disorders), in which the toxin can reduce disturbing symptoms. In general the application is safe (pharmacological index 20-100, depending on indication). Few unwanted reactions may occur. In worst cases BoNT treated patients may develop neutralizing antibodies. These patients are excluded from further treatment. A more recently approved second serotype (BoNT/B) could be effective in those secondary non-responders, however, due to less potency in humans higher doses have to be applied leading to an only transient successful treatment. Other serotypes as BoNT/A and B, e.g., BoNT/C should be approved as medicines.