How does a pharmacy know what medicines to keep in stock - especially when some have a short shelf life, some are highly expensive, and/or some may be rarely used, but necessary when that ONE person needs it! Not to mention so many varieties within a class of drugs and their generics, and so on… Whew!
Jinx:
In retail pharmacy, the store I worked at would go by past demand and stock appropriately- usually more expensive drugs (I mean really expensive) would be ordered in for the next day if someone came in for it and they didn’t have it. They had a regular inventory system where drug quantities were tracked and more or less was ordered depending on demand, just other industries.
In the hospital I work at, they get an order every single day, and inventory is ordered as needed. If a patient needs a drug that they are out of for some reason, they call a sister hospital or retail pharmacy and borrow the drug.
Inventory is a big issue in pharmacy, due to the expense of the drugs used, so obviously they try to keep stock levels as low as possible while still having items available that people need.