I remember reading a book about the history of some (famous) chemical company in the U.S. – Dow? Dupont? – doing exactly what I described to compete with the at-the-time existing German chemical company cartel.
Plus there's the issue of whether a drug can remain safe to use after long periods of time at all.
The set of people with the condition probably does. I wonder if a kickstarter for generics would be successful?
In this particular case, there are actors for whom the profit would not be directly generated by sales of goods, but by the amount they save elsewhere in their operations - which, depending on various factors, might actually be multiples.
You could find a profit maximising capitalist who would be happy to enter the market and compete for a fraction of the outrageous profits - that would make a lot more money than paying to invest as is more usual. In theory there only needs to be a handful or so and that would be enough to bring the market back down close to cost of production.
However, it seems likely that government regulation would disrupt that process somehow, otherwise it would have happened by now.