Due to complexity it doesn't seem realistic to try to save money by using legacy drugs.
On the other hand, the economics of pharma industry are such that manufacturing cost is usually a very small proportion of price.
Therefore a better solution would be to introduce a mandatory new-for-old trade-in policy. So they wouldn't lose money on the deal, pharma companies would be rewarded at mfg cost. I.e. sans profit, marketing or research cost.