Do you recommend patients try antihistamines such as oral ketotifen that are not approved in the US but are approved in the EU for MCAS if currently available formulations have not been effective?  

Oral ketotifen is a mast cell stabilizer as well as an antihistamine that targets the H1 histamine receptor. In patients with mast cell activation syndrome that have not had complete symptom relief with second-generation H1 antihistamines at higher doses, including 4 tablets a day, I will consider o...