When do you consider prescribing memantine for migraine treatment?  

Memantine is well-tolerated and shows excellent efficacy for prevention in both chronic and high-frequency episodic migraine. The main limitation is that it is not FDA-approved, and payors use this as an excuse to deny coverage in favor of less-well-tolerated, and often less efficacious but cheaper ...

I consider memantine in cases where there has been a reduction in severity and frequency of migraine on other preventative medications, but not to the extent that the patient is satisfied. I also consider it in cases where the patient is sensitive to medications, as it is well-tolerated in most case...