Early local antitoxin intervention attenuates botulinum neurotoxin-induced neuromuscular dysfunction

Botulinum neurotoxin type A (BoNT/A) is widely used in clinical practice; however, unintended diffusion to non-target muscles can result in functional impairments, including eyelid ptosis and abnormal facial movements. Currently, no pharmacological strategies are available, and management is largely limited to passive observation. In this study, we investigated whether local administration of serum antitoxins could pharmacologically antagonize BoNT/A-induced neuromuscular dysfunction and delineated the temporal window for effective intervention.

Rats received intramuscular BoNT/A (0.25 U per rat; 1.25 U/kg)injections into the gastrocnemius, followed by local antitoxin serum (5 IU per rat; 25U/kg) at 0-144 h. Neuromuscular function was assessed by CMAPs, and muscle atrophy was quantified as the mean of contraction force, wet weight, and fiber cross-sectional area normalized to controls. In mice, a high dose (0.6 U per mouse; 21 U/kg) was used to used to simulate clinical misinjection, with antitoxin (12 IU per mouse; 420U/kg) administered at 0-48 h. Muscle function and recovery were evaluated by DAS, and atrophy by wet weight and fiber cross-sectional area.

Therapeutic efficacy was time-dependent. Early administration (<24 h) attenuated the progression of botulinum toxin-induced effects, whereas delayed treatment (>48 h) was ineffective. In rats, antitoxin given within 0-24 h improved muscle function and reduced atrophy, with no benefit observed at ≥48 h. In mice, administration within 0-16 h delayed the onset and progression of toxicity; treatment at 24 h reduced peak paralysis without affecting progression, while administration at 48 h was ineffective.

Antitoxin serum administered within a short time window effectively limits botulinum toxin-induced neuromuscular dysfunction and improves functional recovery. Importantly, therapeutic effects are still observed after the onset of early functional impairment, suggesting a time-dependent window of responsiveness. These findings provide experimental evidence for the potential utility of antitoxin in cases of unintended botulinum toxin exposure, although clinical translation requires further validation.