General Information

Botox blocks neuromuscular transmission by binding to acceptor sites on motor or sympathetic nerve terminals, entering the nerve terminals, and inhibiting the release of acetylcholine. Acetylcholine is a neurotransmitter at somatic neuromuscular junctions, the parasympathetic nervous system, sympathetic preganglionic fibers (cholinergic fibers), and at some synapses in the central nervous system.

Botox for injection is specifically indicated for the prophylaxis of headaches in adult patients with chronic migraine (more than 15 days per month with headache lasting 4 hours a day or longer).

Botox is supplied as a solution for intramuscular injection. The recommended initial dose is 155 Units administered intramuscularly (IM) using a sterile 30-gauge, 0.5 inch needle as 0.1 mL (5 Units) injections per each site. Injections should be divided across 7 specific head/neck muscle areas: Frontalis, Corrugator, Procerus, Occipitalis, Temporalis, Trapezius, Cervical Paraspinal Muscle Group. With the exception of the procerus muscle, which should be injected at 1 site (midline), all muscles should be injected bilaterally with half the number of injection sites administered to the left, and half to the right side of the head and neck. The recommended retreatment schedule is every 12 weeks.

Clinical Results

FDA Approval
The FDA approval of Botox for chronic migraine was based on two randomized, multi-center, 24-week, 2 injection cycle, placebo-controlled double-blind studies. Both studies included chronic migraine adults who were not using any concurrent headache prophylaxis, and during a 28-day baseline period had at least 15 headache days lasting 4 hours or more, with at least 50% of these being migraine/probable migraine. In both studies, patients were randomized to receive placebo or 155 Units to 195 Units Botox injections every 12 weeks for the 2-cycle, double-blind phase. At 28 days, the efficacy data are as follows:
Study One
Change from baseline in frequency of headache days: -7.8 for Botox vs. -6.4 for placebo (p≤0.05).
Change from baseline in total cumulative hours of headache on headache days: -107 for Botox vs. -70 for placebo (p≤0.05).
Study Two
Change from baseline in frequency of headache days: -9.2 for Botox vs. -6.9 for placebo (p≤0.05).
Change from baseline in total cumulative hours of headache on headache days: -134 for Botox vs. -95 for placebo (p≤0.05).

The subjects treated with Botox had a significantly greater mean decrease from baseline in the frequency of headache days at most timepoints from Week 4 to Week 24 in Study 1 and all timepoints from Week 4 to Week 24 in Study 2 compared to placebo-treated patients.

Mechanism of Action

Botox blocks neuromuscular transmission by binding to acceptor sites on motor or sympathetic nerve terminals, entering the nerve terminals, and inhibiting the release of acetylcholine. This inhibition occurs as the neurotoxin cleaves SNAP-25, a protein integral to the successful docking and release of acetylcholine from vesicles situated within nerve endings.

Literature References

Diener HC, Dodick DW, Aurora SK, Turkel CC, DeGryse RE, Lipton RB, Silberstein SD, Brin MF; PREEMPT 2 Chronic Migraine Study Group OnabotulinumtoxinA for treatment of chronic migraine: results from the double-blind, randomized, placebo-controlled phase of the PREEMPT 2 trial. Cephalalgia : an international journal of headache 2010 Jul;30(7):804-14

Aurora SK, Dodick DW, Turkel CC, DeGryse RE, Silberstein SD, Lipton RB, Diener HC, Brin MF; PREEMPT 1 Chronic Migraine Study Group OnabotulinumtoxinA for treatment of chronic migraine: results from the double-blind, randomized, placebo-controlled phase of the PREEMPT 1 trial. Cephalalgia : an international journal of headache 2010 Jul;30(7):793-803.