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)

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