Review of botulinum toxin type A and its clinical applications in migraine headache.

Botulinum toxin type A (BTX-A) has been used successfully for many disorders related to excessive muscle contraction. It works, in part, by causing a dose-dependent, reversible muscle relaxation. BTX-A has also been used for migraine prevention. The mechanism by which BTX-A acts in migraine is probably unrelated to its effect on muscle relaxation. BTX-A may have a distinct antinociceptive mechanism, either through action on the muscle spindles or through a direct effect on the central nervous system. Several trials and case reports have demonstrated the safety and efficacy of BTX-A in migraine headache. BTX-A is distinct from other preventive medications. Adverse events (AEs) are rare and mild. BTX-A is convenient, since the dosing interval may be 3 months or longer. However, before BTX-A can be considered a first-line agent for migraine, larger studies need to be conducted to determine optimum dosing and administration sites as well as patient characteristics that are predictive of response.