Dramatic changes in muscle contractile and structural properties after 2 botulinum toxin injections
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Updated: Apr 18, 2026

Isolation and Quantification of Botulinum Neurotoxin From Complex Matrices Using the BoTest Matrix Assays
Published on: March 3, 2014
Viviane B Minamoto1, Kentaro P Suzuki1, Shannon N Bremner1
1Department of Orthopaedic Surgery, University of California San Diego, La Jolla, California, USA.
Introduction:
Botulinum toxin is frequently administered serially to maintain therapeutic muscle paralysis, but the effect of repeated doses on muscle function are largely unknown. This study characterized the muscle response to 2 onabotulinum toxin (BoNT) injections separated by 3 months.
Methods:
Animal subjects received a single toxin injection (n = 8), 2 BoNT injections separated by 3 months (n = 14), or 1 BoNT and 1 saline injection separated by 3 months (n = 8).
Results:
The functional effect of 2 serial injections was exponentially greater than the effect of a single injection. While both groups treated with a single BoNT injection had decreased torque in the injected leg by approximately 50% relative to contralateral legs, the double BoNT injected group had decreased torque by over 95% relative to the preinjection level. Both single and double BoNT injections produced clear signs of fiber-type grouping.
Conclusions:
These experiments demonstrate a disproportionately greater effect of repeated BoNT injections.
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