Chiming in as someone who works at an insurer in clinical analytics.
There's a few ways we can pay less for a compound where there are generics/biosimilars. We could contract with a hospital group saying we will pay a small % markup on the cheapest drug to treat each condition - i.e. they can use the cheapest generic/biosimilar and make profit, or use a more expensive one and make a loss. They naturally shift all volume to the cheaper one. That then makes demand very elastic to price, and so encourages a lower price from manufacturers. We do see some compounds all sit at the same lowest price and not shift - that does suggest collusion - potentially tacit collusion though. An alternative is to contract with one pharma company to get a rebate if we push volume to their drug. We could then mandate to providers that we'll only pay for that drug.
They do that, or contract with companies (like PBMs) to do so. That's been the way this works forever. Asymptotically no one pays the ~$40k+/mo list price.
There's a few ways we can pay less for a compound where there are generics/biosimilars. We could contract with a hospital group saying we will pay a small % markup on the cheapest drug to treat each condition - i.e. they can use the cheapest generic/biosimilar and make profit, or use a more expensive one and make a loss. They naturally shift all volume to the cheaper one. That then makes demand very elastic to price, and so encourages a lower price from manufacturers. We do see some compounds all sit at the same lowest price and not shift - that does suggest collusion - potentially tacit collusion though. An alternative is to contract with one pharma company to get a rebate if we push volume to their drug. We could then mandate to providers that we'll only pay for that drug.