5-ASAs are chemically very similar to aspirin, but don't have the same deleterious effects on the stomach. I'm not a biochemist, so I can't explain why.
I don't know how severe your Crohn's is, but if you were on Humira I'm going to guess that it's bad enough that taking Pentasa would be an utter waste of time for you. The 5-ASAs are quite effective at treating UC, but virtually useless for Crohn's disease (that doesn't stop doctors from prescribing them for Crohn's anyway).
I'm wondering if Entyvio would cause you less grief? :-/ Please ask about
it. I can't promise it won't have any side-effects, but as it's gut-specific (targets the gut only) you are much less likely to have the sort of allergic reaction to it that you did to Humira.
Not sure what else to say other than I feel your pain. I hope you can try Entyvio and I hope it helps.
Dx Crohn's in summer of 2000. (Yay )
Tried and failed: 5-ASAs, Azathioprine, 6MP, Remicade, Methotrexate, Humira.
Diet didn't make any difference either.
Had surgery 2/13 - subtotal colectomy with end ileostomy. Currently on no meds and in remission. Also prone to depression and anxiety. Ask me anything >_>