A great, easy to understand example is found in the drug Prilosec vs. Nexium, the latter of which is a stereoisomer of the former. Prilosec is Omeprazole, which is part of a class of drugs called Proton Pump Inhibitors (PPI’s) which treat severe recurrent heartburn and GERD, as well as esophageal erosion from those conditions. Prilosec (Omeprazole) was due to go generic, so the company decided to isolate and purify the S isomer and worked hard to convince the FDA that it represented a truly new treatment. IIRC the rationale was that the enantiopure drug was half the dose of the racemic mixture, and regulatory capture did the rest of the work. Of course there was no tangible benefit to taking 10mg of Esomeprazole vs 20mg of Omeprazole, except the monetary benefit for the company.

As to why some other company didn’t snap up the patent, it’s an expensive proposition and not trivial to make enantiopure drugs, so a lot of the R&D budget touted by apologists and shills is entirely self-serving. Now sometimes an isomer is actually superior to a racemic mixture and there are plenty of cases where one isomer is therapeutic and the other is ineffective or toxic. Of course in those cases none of this patent fuckery applies, and there is no way to get a new patent issued or FDA writ because only one viable form of the drug exists.

It’s also true that a generic in the case of something like Esomeprazole vs. Omeprazole is viable, and that’s where the astronomical marketing budget that dwarfs R&D comes into play. Advertising directly to patients and doctors ensures that plenty of people won’t understsnd the value of a generic is they were even aware of it. You also get cases, as with Epi-pens, where supplies of the generic are scarce compared to the expensive branded version.

Good list of this kind of thing found here: https://en.m.wikipedia.org/wiki/Enantiopure_drug

That patent gamesmanship is part of a strategy of "lifecycle management" where pharma tries to extend monopoly pricing beyond main patent expiry. It used to be much more effective. basically companies could do something like patent for ex a pill you take twice a day vs 3 times a day. Other companies can make generic versions of the 3x a day pill

Unless you provide a real clinical benefit, most payers will make docs write an rx for the 3x a day generic vs new 2x a day patent. So these lifecycle extension games certainly happen but it's not really that effective

It is a new patent and the original can made generically once the old patent expires. Marketing is the difference. For example, you may have seen people talking about the excessive price of insulin in the US, but they ignore the fact that you can still get the old versions for very cheap. It's also done with "extended-release" versions of the old version.