Some unresolved issues with botulinum toxin

Issues concerning botulinum toxin still need resolution in the laboratory and clinic. Assay nomenclature is unsatisfactory and attempts to establish common units and/or equivalents are misguided and dangerous. Optimum toxin concentrations for most indications are unknown. Loss of response is too readily ascribed to antibody formation. New therapeutic indications for toxin raise the possibility of additional mechanisms of action.