Well, it's the very fact that the alternative is, possibly, death that makes it possible for a company to do this. This thing occupies a peculiar corner case where the demand is modest, but inelastic.
This means a monopolist can milk the market by raising the price to insane levels, but because the market is small no competitor wants to enter it. Were the market to become competitive it is so small that the newly entered competitors wouldn't make much off their efforts. This is contrasted with statins, which are blockbuster drugs. You don't need a very large slice of that pie for the slice to be very large indeed.
The same thing happened last year with Duraprim. If you have toxoplasmosis, you absolutely have to have it. But how many people get toxoplasmosis?