Botulinum toxin therapy, immunologic resistance, and problems with available materials.

Botulinum toxin is a valuable technology for the treatment of regional movement disease. High-dose applications ( > 100 LD50 units per injection cycle) have been associated with sensitization that renders further therapeutic injections ineffective. The true incidence of sensitization is probably underestimated by the mouse bioassay. Other immunotypes of botulinum toxin have been effective in producing some therapeutic benefit; however, duration of action (botulinum toxin type F) and lower potencies may make these less attractive alternatives than botulinum type A. Increased specific activity botulinum toxin may be a method to reduce antigen exposure and mitigate against immunoresistance associated with dystonia therapy. Limiting the dose to < or = 100 LD50 units per injection cycle may limit this complication in the interim.