Self-Administered Low-Dose Inhaled Methoxyflurane (Penthrox) during Administration of OnabotulinumtoxinA for Chronic Migraines: A Real World Case Series

Abstract

The intramuscular administration of onabotulinumtoxinA (onabotA) has been well established as an effective preventative treatment for chronic migraines (CM). Though generally well tolerated, the procedure-related pain can be a large limitation of the treatment for patients with comorbidities such as fibromyalgia. Inhaled low-dose methoxyflurane (MEOF) is a proven analgesic that has been used for over 30 years with more than 5.6 million administrations worldwide. MEOF was recently approved in Canada for moderate-severe pain related to trauma or interventional medical procedures in adults. MEOF as an analgesic for onabotA injections for CM has not been previously reported. This case series describes the use of MEOF as a procedural analgesic during intramuscular onabotA injections for CM. Ten patients who previously experienced significant pain (NRS >8) and associated moderate-severe anxiety with onabotA injections were treated with MEOF. Immediately post-procedure, patients rated their pain and anxiety. Adverse events (AE) were recorded and patient satisfaction was assessed by asking “Are you satisfied with the treatment?” and “Would you use MEOF again?”. Post-procedure, average reported pain score was 3 and the average anxiety level was “mild”. All patients were “satisfied” with MEOF and confirmed that they would use it again. Most common AEs were dizziness and somnolence and AEs were transient (resolved within 5 minutes post administration). To our knowledge, this is the first report of the use of MEOF to facilitate intramuscular onabotA injections.