My insurance forced me to switch earlier this year from Remicade to Inflectra. I had been on Remicade for almost 3 years with great results. Around the time of my last infusion before I was forced to switch from Remicade to Inflectra, my inflammatory markers were the lowest they ever were. But once I made the switch to Inflectra, I had all sorts of issues. My inflammatory markers went up to the highest they ever been and was getting a lot of loose stools and diarrhea.
My doctor decided to check my levels of medication and they were slightly low at first, so they just increased the frequency from 7 to 6 weeks. That didn't help, so they decided to up the dosage from 5mg/kg to 10 mg/kg. As I type this, I am getting my first infusion since they decided to increase the dosage to 10mg/kg. So we'll see how it goes. I think it should get me stable enough again, but time will tell.
Basically, I would be extra cautious if you make the switch to a generic or biosimilar. Watch out for any signs of a flare.