As a member of big Pharma for the last decade.....
What pink puppy says about the generics vs innovator is true. The active is the same, the excipients (inactives) may differ.
I'm not certain about adding different salts to the active. I'll have to ask around about that. Seems to me that would be changing too much. Anything that would possibly change the efficacy of the drug would need an entirely new set of testing. I don't see generics wanting to put that much time/money in it.
A little insider info I can say..the innovator has less impurities..almost always.
I worked for a generic manufacturer that produced animal & human drugs. They are the same in quality, held to the same standards, get approved by the FDA the same way for production. The dosage differs, that's all. Its impractical for a human to take a min pin dose of robaxin. That's probably the only reason you wouldn't take it.
So when a new drug hits the market the creator of that drug (innovator) gets exclusivity for so many years (I want to say 4) then a few years down the road the FDA picks a generic company where they can make the drug too. And they throw a big party cause they are the only generic for a couple years.
They have to submit an ANDA and have all their stability testing and ducks in a row before that ever happens. It takes years.
As time goes on the FDA releases more generic manufacturers rights to produce said drug. The companies approved have to make the drug for so many years and make enough of it or the FDA comes in and spanks them for creating a back order.
Overall, if you were ever part of the process you'll know how painfully redundant it all is, and truly fear any kind of "compounding" or supplementation (including vitamins) outside the realm of the Regulatory bodies because you really have no idea what's in there, how consistently its there, or how long it'll last. I really mean that and it's not just because I've been brainwashed by industry.
Hope that helps