Botox (botulinum toxin type A) is the first agent to be specifically indicated for the prevention of chronic migraine. It is indicated for use only in adults who have headaches on at least 15 days per month, of which eight days or more are with migraine.
Pooled analysis of two trials in a total of 1384 patients (PREEMPT 1 and 2) showed that botulinum toxin A was more effective than placebo at reducing the incidence of days affected by headache. During 24 weeks of double-blind treatment, the mean number of headache days per month fell by 8.4 in the toxin group compared with 6.6 in the placebo group (p<0.001).
The treatment is administered as a series of 31 to 39 intramuscular injections every 12 weeks, across seven head/neck muscle areas. The injections must be performed by a specialist.
The toxin is thought to suppress peripheral pain signals to the central nervous system by blocking the release of neurotransmitters.
Further information: Allergan