The neurotoxins produced by Clostridium botulinum exert physiologic effects by inhibiting release of acetylcholine from nerve terminals. These effects account for the utility of botulinum injections in alleviating blepharospasm or facial spasm but not necessarily pain. Analgesic effects of botulinum toxin type A may involve other neurotransmitter influences, including inhibition of glutamate and substance P. Botulinum toxin (both A and B types) has been invoked in the treatment of cervical dystonia, migraine headache, tension headache, temporomandibular joint disorders, and chronic back pain (Argoff2005). Multiple series of injections may be required to achieve maximal analgesia. Contraindications include pregnancy, concurrent aminoglycoside antibiotic use (e.g., gentamicin, tobramycin), myasthenia gravis, Eaton-Lambert syndrome, and known sensitivity to toxins. Clinical resistance brought on by development of antibodies to toxins may reduce clinical efficacy after repeated administrations.
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