- the latter frequently approaching 100%. Whereas in 1994, the generic price index fell from 100 to 80 in the 12 months … following initial generic entry and by 24 months to 65, in 2009 the comparable generic price indexes are 68 and 27, respectively … Medicare Part D, the average price per prescription declined by 21.3% from 2006 to 2009, rather than increasing by 25-28% as …