Well, I'm dropping by, looking for SEC filings or press releases, so I'll take a jab at your questions.....
Q1: Is this some GMP related improvement? Does this kind of improvements always need FDA's blessing?
A1: Yes, a change to the manufacturing process requires FDA approval. The drug it approved in the manner it was presented. Once approved, you cannot change how it is made, where it is made, whose ingredients are used and so on... without FDA approval. DSCO stated that the quality change is necessary, and that it would entail a manufacturing change. Don't have any idea what changes, but, yes, the FDA will have to buy off on them before DSCO moves forward.
Q2: If FDA say nay, you cannot modify it. Can DSCO use the old approved way to validate the chemistry?
A2: Don't know. Depends on what the problem is. Four possible outcomes.
1. The FDA says "Fine, go ahead with the new process".
2. The FDA says, "We understand the need for the change, but don't like the change you suggest. Do it this other way and we will approve".
3. The FDA could say. "We don't understand the need for the change at all. The drug is approved the old way. Produce the drug the old way."
or worst case....
4. The FDA could say, "Oh, we see the problem now. Thank you for bringing it to our intention. Your process change is denied and the approval of the drug is withdrawn pending new trials to determine the drugs safety and efficacy."
So, usually, DSCO could go back to the old way, but DSCO said back in October that the change was necessary, so how can they go back??? Unless it wasn't really necessary in the first place. Remember, DSCO stopped the launch of a new improved drug because of an issue they said would not affect the efficacy or safety of the drug... so why'd they stop it in the first place instead of just making and selling batches while contacting the FDA about a process change they wanted to make. No, they stopped. So maybe it wasn't as minor and inconsequential as we were led to believe.
Q3: Has this happened before to those well established firms?
A3: Yes. Well managed firms generally present their complete well documented case to the FDA and it is approved. Stumble bums wallow around in mindless red tape for months and months until the FDA harrasses them into doing the job right like they should have done in the first place. By then it has become political, and it comes down to whether the powers at FDA want to continue jerking the little #$%$ at DSCO around or if they will let them be..
The short answer to your question is... it must have been surprising to the FDA that DSCO went back to them to point out that all that work they did the past two years to prove to the FDA that DSCO had solved all the quality and process issues was a complete waste of time. They have opened a door that allows the FDA to re-evaluate everything if they want... up to an including the approval of the drug itself.