The ultimate radiochemical nightmare: upon radio-iodination of Botulinum neurotoxin A, the introduced iodine atom itself seems to be fatal for the bioactivity of this macromolecule.

Background: Botulinum neurotoxin A (BoNT-A) is a highly neurotoxic drug and frequently used in patients. Knowledge on the optimal way of administration of BoNT-A and its subsequent distribution is still rather limited. An accurate method for monitoring these processes might be the use of radiolabelled BoNT-A.