Adverse Event Profiles of High Dose Botulinum Toxin Injections for Spasticity

Area of Science:

• Neurology
• Rehabilitation Medicine
• Pharmacology

Background:

• Botulinum toxin injections effectively manage focal spasticity from upper motor neuron injuries.
• Current US-approved doses for onabotulinumtoxinA and incobotulinumtoxinA are up to 400 units, though higher doses are frequently administered.

Purpose of the Study:

• To compare adverse event risks between higher (>600 units) and lower doses of botulinum toxin-A.
• To assess differences in adverse events between onabotulinumtoxinA and incobotulinumtoxinA.
• To investigate if cervical muscle injections correlate with increased adverse event risk.

Main Methods:

• Retrospective analysis of botulinum toxin-A injections over a 3-year period.
• Injections categorized by dose: ≤400 units, 401-600 units, and >600 units.
• Analysis included patients with spasticity or dystonia receiving onabotulinumtoxinA and/or incobotulinumtoxinA.

Main Results:

• No significant increase in adverse events for doses between 401-600 units compared to ≤400 units (OR 0.97).
• Doses exceeding 600 units showed a significantly higher risk of adverse events (OR 2.98).
• Cervical muscle injections were associated with a significantly increased risk of adverse events (OR 4.21).

Conclusions:

• Botulinum toxin-A doses up to 600 units do not significantly increase adverse event risk, suggesting a potential need to re-evaluate the 400-unit limit.
• Doses above 600 units elevate adverse event rates, necessitating a careful benefit-risk assessment.
• No significant difference in adverse event rates was found between onabotulinumtoxinA and incobotulinumtoxinA.