The use of onabotulinumtoxin A in migraine: mechanism of action, efficacy, safety and tolerability

Migraine is a common, yet disabling, neurological disorder that is characterised by recurrent attacks of headache. Typical migraine attacks last from 4–72 hours and involve headaches with varying characteristics: pulsating, unilateral location, moderate or severe intensity and aggravation by routine physical activity. Headaches may also present with associated symptoms, such as nausea, vomiting, photophobia and/or phonophobia (Headache Classification Committee of the International Headache Society, 2018).

The International Headache Society (IHS) classifies migraine into two major subtypes: migraine with aura and migraine without aura. Patients can suffer from migraine both with or without aura. Aura symptoms are focal, neurological symptoms, usually occurring prior to, or sometimes during, a migraine attack.

There is a distinction between episodic migraine (EM) and chronic migraine (CM). The IHS defined CM as headache on 15 days or more per month for over 3 months, of which, over 8 days meet the criteria for migraine with or without aura and/or respond to migraine-specific treatment, occurring in a patient with history of at least five prior migraine attacks not attributed to another causative disorder or medication overuse (Headache Classification Committee of the International Headache Society, 2018). Approximately 1–2% of the general population are affected by CM, and this usually develops from EM. EM is defined as less than 15 headache days per month (May and Schulte, 2016). Classed as a distinct clinical entity, patients with CM suffer from more headache days, increased headache disability, reduced health-related quality of life and greater co-morbidity than those with EM (Blumenfeld et al, 2011). CM is also considered a greater socioeconomic burden and is associated with higher healthcare resource utilisation compared to EM (Blumenfeld et al, 2011).