Pharmacology of therapeutic botulinum toxin preparations

Therapeutic preparations of botulinum toxin (BT) consist of botulinum neurotoxin (BNT), complexing proteins and excipients. Depending on the target tissue BT can block the cholinergic neuromuscular or the cholinergic autonomic innervation of exocrine glands and smooth muscles. Additional effects can be demonstrated on the muscle spindle organ. Indirect effects on the central nervous system are numerous, direct ones have not been recorded after intramuscular injections. BT type A is being distributed as Botox (R), Dysport (R) and Xeomin (R) BT type B as NeuroBloc (R)/Myobloc (R). Adverse effects can be obligate, local or systemic. The adverse effect profiles of the available BT preparations are similar. BT type B, however, has additional systemic autonomic adverse effects. Long-term treatment does not produce additive adverse effects. BNT can be partially or completely blocked by antibodies. The major risk factors for antibody-induced therapy failure are the amount of BNT applied at each injection series, the interval between injection series and the specific biological activity (SBA) of the BT preparation used. The SBA is 5 for NeuroBlocC (R), 60 for Botox (R), 100 for Dysport (R) and 167MU-E/ng BNT for Xeomin (R) (MU-E: equivalence mouse units). Therapeutic BT preparations are a group of highly potent drugs with an intriguing mechanism of action. With the advent of new competitors comparative studies amongst different therapeutic BT preparations will become more and more interesting.