The placement of a "pump" for a continuous infusion of benadryl would be a highly unusual treatment for mast cell activation diseases. From the case presented it is not clear what symptoms the patient was having that would necessitate the consideration of this treatment option.
The scenario you have described above raises several question. How was this diagnosis of MCAS made? What medicines had the patient tried and failed? Why has the patient failed traditional oral antihistamines? Why can't the patient use oral medicines? Is there other pathology that need to be considered? Are the symptoms that she complains of carefully and objectively documented and verified?
Given the potential severity of this patient symptoms and the very unusual treatment course being considered, it would not be unreasonable, if not already done, to suggest that the patient be seen by an A/I colleagues who specializes in mast cell disorders to clarify this diagnosis and suggest potential treatment options.
For you convenience below is a reference to excellent review article on MCAS by Dr Akin.
Cem Akin, MD, PhD Mast cell activation syndromes, J Allergy Clin Immunol 2017;140:349-55
I hope this has been helpful.
Andrew Murphy MD, FAAAAI