Bupivacaine-induced myotoxicity and its effect on botulinum toxin paresis

To determine the effect of the coinjection of bupivacaine with botulinum toxin type A on the degree of muscular paralysis. Enhancement of paralysis could allow a decreased dose of neurotoxin treatment, thus reducing the risk for neutralizing antibody formation.

Prospective, randomized, double-blind study. Sixteen consecutive patients undergoing treatment of glabellar furrows received botulinum toxin A reconstituted with bupivacaine 0.75% to one corrugator muscle and botulinum toxin A reconstituted with nonpreserved normal saline to the contralateral muscle. Patients were evaluated on days 0 (injection day), 3, 7, 30, 60, and 90. Patients also completed a questionnaire each visit regarding their assessment of paralysis, asymmetry, and adverse effects.

At 1 week after botulinum toxin A injection, 68.8% of the patients showed greater weakness on the bupivacaine-reconstituted side as opposed to 25.0% of patients showing greater weakness on the saline-reconstituted side. At 1 and 3 months, there was no statistical difference in weakness between the saline and the bupivacaine sides. The survey revealed that 56% of the patients had greater pain on the saline side, 31% on the bupivacaine side, and equal pain in 13%.

Reconstituting botulinum toxin A with bupivacaine is safe, does not limit efficacy, and does not reduce the degree or relative duration of muscular paralysis. Reconstituting botulinum toxin A with bupivacaine results in faster onset of paresis, possibly due to a synergistic effect of bupivacaine induced myotoxicity. Utilizing bupivacaine may result in less pain for patients.