All of the 5ASA deliver mesalamine to the large intestine. They all have slightly different means of achieving that goal. Most gastroenterology and pharmacists will say there is little to no difference among them. Anecdotally some here say they respond better to one formulation than to another. Here's a link that lists them all and pricing: https://www.goodrx.com/aminosalicylates
The generic market with 5ASA hasn't changed much in the last couple decades. You have the protomesalamines are the only true generics, broadly inexpensive and available everywhere.
In the last 3-4 years, there's been a few, new "supposedly generics" I say this in quotes as there are a number of catches and caveats. The older PH-based, delay-release mesalamines are coming off of patent protection. Asacol HD was the first one, and what happened? Zydus made a licensed-generic of it, blessed (and paid royalties back to the original patent holder) and what that means to you/I is that you save $20 a bottle, on a $1,200 a month prescript
ion in total cost (big frigg'n whoop!). The licensed-generic means that many insurance policies call it for what it is, a brand-name, and not a true generic at all. Zydus came out with a generic version of lialda under the legal threat of Shire (licenser of Lialda) and Zydus ultimately won in court and sells their generic. Again, only $20 a month cheaper than the brandnamed Lialda (but most insurances call this a generic). Again no cost savings to you/me of any significance. The only reason Zydus ultimately won in court, is the only similarity between there generic and Lialda is the dosage; different coating, and different inactive ingredients. Our big "promise" these days is that as more generics come to market that the prices will get better, I am highly skeptical, and doubt somebody will start charging $100 a month for it when they got such a racket going now lol.
Proto-mesalamines. The oldest 5ASAs in our spectrum are made of more complex molecules, that gut bacterium cleave into mesalamine and a byproduct. These lack any coating, they are off-white colored tablets that can be crushed. There's been no study proving conclusively that these medications are any less effective than the newer, coated mesalamines. This is sulfasalazine ($60 or less for a month's prescript
ion), basalaside disodium (a couple hundred a month) in the generics category. Sulfa can cause headaches in some, basalaside disodium is the safer bet which does not cause that.
PH-coated mesalamines: These are newer, and mostly brand-named medications with fancy MX-plastic coatings of various patents over a pill made of mesalamine. You have asacol, delzicol, brand-named lialda in this bunch. These medications cost about
$1,200.00 a month for a typical dose. They have special PH-based coatings, expecting to be stitting in various holding areas of the digestive tract, at specific PH for expected amounts of time. This causes the coating to soften and slowly dissolve. Once the medication reaches the large intestine, the pills release medication at a steady rate.
Ethacellulose coated mesalamines: These are time-based release meds, they are water soluble and swell when wet. Pentasa was the first, and the Zydus-Generic of lialda is also this.
So everyone has their own brandnamed, special coated version of 5ASA each claiming they're better. Never been any research to prove any of it (only better than placebo). Technically the initial release point can be higher/lower, and the dispersal-rate can vary among these various formulations. It is the same dosage of meds in most cases (aside from apriso). Inactive ingredient differences are pretty much moot, they're inert. Pentasa might release highest, along with the protomesalamines. There's never been comprehensive comparison of which 5ASA works best, orany research showing which releases highest, most consistently, etc etc. Lots of guessing and lots of hearsay/anecdotal talk and that's all.