But why does the cost increase over time (ignoring say normal inflation eg RPI) especially for a widely prescribed drug.
It’s a complex system and the price increases are used in part to negotiate with the intermediaries like PBMs.
Biologics are a special case also due to complexities in how they (and biosimilars) are regulated, manufactured, and exclusivity periods they are granted. They certainly are not a few cents a dose to make.
Not a satisfying answer, and apologies for that, but it’s difficult to traverse with anything approaching brevity.
A biologic production line requires extensive upkeep: it is a living product. Costs all around are higher. There are also Phase IV activities to consider.
Bottom line, all else being equal, biologics cost more than small-molecule drugs to make and distribute.