Onabotulinumtoxin A
Neurotoxin, neuromuscular blocker (presynaptic)
Onabotulinumtoxin A
Botox
Onabotulinumtoxin A (brand name Botox) is a purified neurotoxin derived from Clostridium botulinum. FDA-approved in 2010 for chronic migraine prophylaxis (≥15 headache days/month, ≥8 of which are migraine), administered via the PREEMPT injection protocol across 31 fixed sites in head and neck musculature every 12 weeks.
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Summary
Classes
Neurotoxin, neuromuscular blocker (presynaptic)
Common uses
Chronic migraine (≥15 headache days/month), cervical dystonia, blepharospasm, hyperhidrosis, overactive bladder, urinary incontinence, strabismus, spasticity, cosmetic problems
Pharmacy
Starting dose
Chronic migraine (PREEMPT protocol): 155 units divided across 31 sites in 7 head/neck muscle groups every 12 weeks
Preparations
50, 100, or 200 unit vials of lyophilized powder for reconstitution
US FDA Max
195 units/treatment for chronic migraine; max varies by problem
Pharmacology
Routes
Intramuscular (PREEMPT injections for migraine)
Onset
1–2 weeks for muscle effects; preventive migraine benefit accrues over 12-week cycles
Duration
~12 weeks
Half-life
Tissue half-life not formally measured; clinical effect ~12 weeks
Bioavailability
Local (intramuscular)
Pregnancy
Category C; limited data
Legal status
Rx; black-box warning for distant spread of toxin effect
Purported mechanism
Cleaves SNAP-25 protein in presynaptic motor and autonomic nerve terminals, blocking acetylcholine release; in chronic migraine, hypothesized to inhibit peripheral sensitization of trigeminovascular nociceptors