My GI doctor is telling me that the infliximab level from my bloodwork is low and he said he will be increasing it and my infusion appointments. Does this mean it is not working? What happens if it stays low? My next infusion appt is next week.
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It depends. They do drug levels to check to see if you are at optimum treatment doses. Sometimes, they can tell by symptoms alone. Ideally, they want to maintain remission and prevent relapse, not treat symptoms. A low drug level might mean it is not adequate to work , but it is not a given. I am on 6 week infusion intervals, plus my rheumatologist added oral Imuran (azathioprine) to my regime to enhance effectiveness.
Are you feeling like it is not working?
Jan 
I’m not sure if it is working or not. I have a few setons in me to drain fistulas. I underwent fecal diversion had my jpouch disconnected due to severe rectal inflammation. I now have a loop Ileostomy and my rectal area has healed. I feel a lot better. I think these infusions are to heal the fistulas and then reconnect the jpouch. Who knows how long it’ll take.
The medication is much more likely to work effectively if the blood levels are adequate. You may be getting partial benefit at the current dose, but it sounds like you need more.
If IFX drug level is low it will typically reflex (lab will add automatically) to check for antibodies. If you've formed autoantibodies to the IFX than increasing the dose won't help. If you don't have Abs to the drug than increasing the dose may improve level and response. Also, it is important the drug level was drawn as a trough, usually collected off the IV before they give you the infusion to indicate the lowest level of drug in your system before the next dose. If drawn at any other time, it's difficult to know what to make of the level. It's actually difficult to begin with as there aren't well established drug levels for TNF inhibitors.
Good point about possible antibodies, especially with infliximab. As one of the earlier biologics it is based on mouse protein, and not fully humanized. Because of this it is more likely to cause antibody production.
Perianal disease is particularly difficult to treat and it takes a long time.
Jan
