OnabotulinumtoxinA injection in the treatment of chronic migraine.

The earliest descriptions of botulism were in the early 19th century, and was reported by the German physician Justinus Kerner. The term "botulism" was derived from the Latin word botulus, indicating its original association with sausages. It took another 150 years or so to come into clinical use. The first clinical application was strabismus, and was developed by the American ophthalmologist Alan B. Scott, whose effort led to the pharmaceutical product known as onabotulinumtoxinA today. The therapeutic benefit in migraine was an incidental finding in a report by the American plastic surgeon William J. Binder, which inspired a series of clinical studies in headache disorders. The doses and injection techniques in the earlier reports were variable, so were the results. It was until the Phase III REsearch Evaluating Migraine Prophylaxis Therapy (PREEMPT) 1 and 2 studies when its efficacy and safety, as well as the indication, i.e., chronic migraine (CM), were ascertained. Even though there were criticisms regarding the heterogeneities in the results between the PREEMPT 1 and 2 studies, the data on efficacy endpoints and safety were generally consistent, which were subsequently confirmed by the open-label extension of the PREEMPT 1 and 2 studies, and three open-label studies, namely the Chronic Migraine OnabotulinuMtoxinA Prolonged Efficacy open Label (COMPEL), the REal-life use of botulinum toxin for the symptomatic treatment of adults with chronic migraine, measuring healthcare resource utilization, and Patient-reported OutcomeS observed in practice (REPOSE) studies, and the CM Post-Authorization Safety Study (CM PASS) studies. On the other hand, the results were challenged by the Chronification and Reversibility of Migraine (CHARM) study, which involved CM patients with medication overuse. It was concluded that the clinical improvement was attributed to early withdrawal of the overused acute medications, rather than onabotulinumtoxinA injections. However, fundamental differences in the patient profile and methodology between the CHARM and PREEMPT studies existed, and cautious should be exercised when interpreting and comparing the results. According to the practical guidelines and reimbursement regulations in many countries, its use is limited to CM patients, and is reserved for those who fail at least 2-3 preventive medications, due to either lack of efficacy or intolerability. Cessation of treatment is recommended in patients who do not respond to 2-3 injection cycles, or in patients whose headache frequency has dropped to <10-15 days a month. Even in the era of calcitonin-gene-related peptide monoclonal antibodies, onabotulinumtoxinA injection remains a treatment option of reasonable cost-effectiveness in carefully selected patients.