The patent on this specific drug has already expired. It is just that the demand is low so that it is not cost effective for a competing manufacturer to get FDA

The patent on this specific drug has already expired. It is just that the demand is low so that it is not cost effective for a competing manufacturer to get FDA approved. However there are FDA exceptions for compounding pharmacies to make the medicine to order and a particular one has been willing to do it cheaply since they don't need full FDA approval.