Reconstituted botulinum toxin type A does not lose potency in humans if it is refrozen or refrigerated for 2 weeks before use.

Botulinum toxin type A (BTX-A) (Botox, Allergan, Irvine, CA) labeling recommends its use within 4 hours of reconstitution. Since BTX-A is available only in 100-unit vials, a substantial quantity is often discarded. Using eight volunteers, we measured the percent decline in extensor digitorum brevis (EDB) M-wave amplitude (percent paralysis) following injection of freshly reconstituted BTX (right EDB) and compared this with the decline following injection of BTX that was refrozen (-20 degrees C) or refrigerated (+4 degrees C) for 2 weeks (left EDB) after reconstitution. When analyzed as paired data, there was essentially no difference in the muscle paralysis resulting from fresh BTX compared with refrozen or refrigerated BTX, and no statistical difference between groups was noted. Reconstituted BTX-A that is subsequently refrigerated or refrozen for 2 weeks does not lose potency in humans.