UC symptoms are due to inflammation in the large intestine. They try anti-inflammatory meds first, and then add some sort of immuno-suppression (immunomodulators and/or biologics) when/if necessary.
The first class of UC medications is anti-inflammatory mesalamines, they max out at 4.8 grams a day orally and 4.0 grams each night through retention-enema. If you are currently taking that maximum and still experiencing UC symptoms, then it makes sense to have additional medications as well. If you are not yet taking the maximums then request them before escalating up the ladder.
The second class of UC medications is immunomodulators (azathioprine/imuran or 6MP) and they work by reducing your immune system slightly. We still have a functioning immune system, and we do not need to be afraid of germs or getting sick. When our UC flares, our White Bloodcell Count soars and WBC directly cause inflammation within the large intestine. So, these medications reduce the amount of WBCs we can have within our blood. The less WBC we have the less inflammation we can have in our large intestine, and the better our UC symptoms get. These medications are generic, and affordable. They take 2-3 months to work, as they are very, very slow working. These medications require routine blood monitoring, while you are on them. Initially, you might have weekly, then every other week, then monthly, then every-other-month, and finally every 3 month testing for the duration that you are on these medications. As these medications reduce your WBCs, it cannot get too low or you have issues. The WBC must remain lowered, but within a safe range.
The third class of UC medications is biologics (remicade/humira/entyvio), they're brand-named, expensive, but quick working. They're given via IV or self-injection.
Regarding pancreatitis, all UC medications mention pancreatitis as a rare side effect, from anti-inflammatory mesalamine, to immunomodulators, to biologics. All of which have very different active and inactive ingredients, and mechanisms of action. We are at increased risk of getting pancreatitis with/without medications, and I think that is the true cause of pancreatitis as a rare side effect.
All medications carry slight risk. However, the odds of benefits far outweigh the odds of risks, and if you want a deeper-dive into what are the potential side effects of azathioprine, then here is some more information concerning what, the odds, etc. from the Crohn's and Colitis Foundation of America:
Webcast:
programs.rmei.com/CCFA139VL/presentation/player.htmlTranscript
: http://www.ccfa.org/assets/pdfs/risk-and-benefits-transcript
.pdf