** Indian pharma stocks .NIPHARM drop 1.5%, top loser among 13 major sectors while benchmark Nifty 50 .NSEI index trades flat
** Macquarie says shifting dynamics in U.S. generics space makes it "cautious"
** Adds, price erosion in U.S. generics could accelerate due to easing drug shortages and more competition
** Seventeen of 20 stocks on index trading in red with losses led by Aurobindo Pharma's ARBN.NS 4.4% drop
** Cipla CIPL.NS, Dr Reddy's REDY.NS and Lupin LUPN.NS decline between 2% and 3%
** Sun Pharma SUN.NS and Biocon down 1.4% each
** Q1 results for most Indian generic drugmakers could be adversely impacted by increased competition in supply of gRevlimid, a key contributor to their revenues - Macquarie
** Brokerage's actions on ratings and PT cuts:
(Reporting by Kashish Tandon in Bengaluru)
((Kashish.tandon@thomsonreuters.com))