Negative antibody response to long-term treatment of facial spasm with botulinum toxin.

Over a period of 163 weeks, 223 injections of botulinum A toxin were administered to 38 patients with facial spasm syndromes. The maximum cumulative toxin dose was 553 units, the maximum number of injections in any given patient was 16, and the maximum dosage of any given injection was 52.5 units. Sera from these patients showed no antibody production when measured with a standard mouse lethality bioassay.