Comparison of analgesic effects of single versus repeated injection of botulinum toxin in orofacial formalin test in rats.

Long-term effectiveness and repeated administration of botulinum toxin A are the basis for its use in both neuromuscular disorders and certain painful conditions. Botulinum toxin A has been recently approved for migraine treatment, and its off-label use extends to other craniofacial pain disorders. However, recently it was reported that, after repeated injection, botulinum toxin loses its antinociceptive efficacy in rats. In present study with a similar design, we compared the effects of single and repeated injections of botulinum toxin in formalin-induced orofacial pain. No statistically significant differences were found between single or repeatedly treated animal groups. Our results are in line with the clinical experience and suggest that botulinum toxin can be re-administered in orofacial pain treatment.