Efficacy of Botulinum Toxin Type A for the Prophylaxis of Episodic Migraine Headaches: A Meta-analysis of Randomized, Double-Blind, Placebo-Controlled Trials

Study Objective. To assess the efficacy of botulinum toxin type A in lowering the frequency of migraine headaches in patients with episodic migraines. Design. Meta-analysis of eight randomized, double-blind, placebo-controlled trials. Patients. A total of 1601 patients with a history of episodic migraine headaches classified as those experiencing headaches fewer than 15 times/month over a 3-month period. Measurements and Main Results. PubMed, Google Scholar, and the Cochrane Library were searched from inception to October 2007 in order to locate randomized, double-blind, placebo-controlled trials that compared the efficacy of pericranial botulinum toxin A injections with placebo in the prevention of migraines in patients with a history of episodic migraine headaches. The primary outcome of interest was change from baseline to end point in migraine frequency (number of migraines/month). A random effects model was used to combine study results, and the standardized mean difference (Cohen's d) in migraine frequency between the placebo and botulinum toxin A groups was reported. Effect sizes (d) less than 0.2 were considered small. Quality assessment was performed by using the Downs and Black scale. Eight randomized, double-blind, placebo-controlled clinical trials (1601 patients) presented a quantitative assessment of the efficacy of botulinum toxin A versus placebo. The overall treatment effect size of botulinum toxin A over placebo for 30, 60, and 90 days after injection was d −0.06 (95% confidence interval [CI] −0.14-0.03, z=1.33, p=0.18), d −0.05 (95% CI −0.14-0.03, z=1.22, p=0.22), and d −0.05 (95% CI −0.13-0.04, z=1.07, p=0.28), respectively. Even after controlling for a high placebo effect, and after dose stratification, no significant effect of botulinum toxin A in reducing migraine frequency/month was seen over placebo. Conclusion. Botulinum toxin A for the prophylactic treatment of episodic migraine headaches was not significantly different from placebo, both from a clinical and statistical perspective.