Cheap Medicine Shortage

Barriers to entry - manufacturing cleanliness, regulation, sales - must be high enough to prevent newcomers.  Or is this an area to explore?

Supposedly these medicines are so cheap they are not worth manufacturing in sufficient quantity:

... shortages come and go by the week—Atticus’s hospital is low on intravenous calcium, zinc, lipids (fat), protein, magnesium, multivitamins, and sodium phosphate; it’s completely out of copper, selenium, chromium, potassium phosphate, vitamin A, and potassium acetate.
...
They’re not getting any calcium or any zinc. Or they’re not getting any phosphorous, and that can lead to heart standstill. I know of a neonate who had seven days without phosphorous
...
There are 300 drug, vitamin, and trace-element shortages in the US, the highest number ever recorded by the University of Utah Drug Information Service, which began tracking national shortages in 2001. Approximately 80 percent of these are generic injectables, or drugs given intravenously.