OnabotulinumtoxinA wear-off in chronic migraine, observational cohort study

The current standard-of-care protocol for OnabotulinumtoxinA (BoNTA) injections consists of fixed-site injections every 12 weeks. This pattern is based on clinical practice and extrapolated from BoNTA injections for other, non-migraine-related indications. It is unclear if this protocol is optimal for chronic migraine. In clinical practice, migraine patients frequently describe a period of increased headache frequency and intensity in the few weeks preceding their next injections. In order to evaluate the duration of the clinical effect of BoNTA injections in chronic migraine, we studied the variation in headache frequency on a weekly basis during the 12-week period following treatment in a cohort of migraine patients.

38 consecutive subjects were enrolled from an outpatient headache clinic, and asked to keep daily headache journals. 24 completed headache journals were analyzed. Headache frequency, duration and severity, as well as intake of symptomatic headache medications were recorded and compared among the different weeks.

The time-response plot following BoNTA injection was roughly U-shaped, with 3 distinct phases: an induction phase, a maximum efficacy phase, and a wear-off phase. The time-response plot revealed that the wear-off commenced around the eighth week post injection. The mean difference in the number of headache days per week between the first and the eighth week was 1.8 (95% CI [0.670-2.830], p = 0.003).

The effect of BoNTA injections on chronic migraines was not uniform throughout a 12-week period. A window of vulnerability to migraine attacks exist in the beginning and end of each cycle.