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DrugPatentWatch was used in a recent research study on branded drug sales following generic entry.
In this paper, authors Jeffrey Fujimoto, Daniel M Tien, Sophie Snyder, Jeppe A Hertz, and Stuart Schweitzer analyzed the effect of patent expiration of the first innovative drug in a therapeutic class on competitor sales within the same therapeutic class for five major therapeutic classes.
They found that sales volumes decreased by nearly 50% in the first year following patent expiration, and continued to drop to levels exceeding 60% in the following years. The also noted that the effect of patent expiration was not uniformly negative. In some cases competitors were often able to obtain dominant market share.
For more, see the original paper at https://journals.sagepub.com/doi/abs/10.1177/1741134319856408?journalCode=jgma