Abstract
The current study determined the dose–response relationship for inhibition of muscle force of two commercially available botulinum neurotoxin type‐A (BoNTA) preparations (Botox® and Neuronox®) in a murine model and characterized the time course of recovery from the toxin‐induced muscle paralysis. The effect of freezing reconstituted toxin on toxin potency was also determined. The gastrocnemius muscles in male CD‐1 mice were injected with either saline or BoNTA (0.3–3.0 U/kg), and muscle force generation was examined following stimulation of the tibial nerve (single twitch and 15–200 Hz tetany). Botox and Neuronox produced nearly equivalent decrements in muscle force (30%–90%) at 4 days after toxin injection. At 28 days after injection (1 U/kg), muscle force had recovered from the effects of both toxin preparations. Maintaining reconstituted toxin at −80°C for up to 5 months did not result in significant loss of toxin activity. The results of this study suggest that Botox and Neuronox produce equivalent responses in a murine model, and, in contrast to other models, muscle recovery is rapid with doses of toxin that produce less than maximal decrements in muscle force. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1658–1664, 2007