Is it ever safe to use a biologic DMARD in a patient with RA who is on suppressive antibiotics due to a history of septic prosthetic arthritis?   

I have used Orencia and HCQ as more immunomodulating with suppressive M/W/F antibiotics in a patient with UTI/Bactrim.

I think the key is the use of long-term/lifelong antibiotics, vigilance regarding infection activity, the specific choice of biologic/immunosuppressive/immunomodulatory medication, and also having the appropriate discussion with the patient and the consulting infectious disease physician.