** Shares of Neuren Pharmaceuticals NEU.AX rise as much as 8.4% to A$17.940, their highest since Aug. 5

** Stock biggest pct gainer on the benchmark S&P/ASX 200 index .AXJO

** Drug manufacturer announces commencement of on-market share buyback programme of up to A$50 mln ($32.47 mln)

** Says will buy up to 3 mln shares at A$16.540 per share, based on the last close of Wednesday

** Stock down 33.8% YTD

($1 = 1.5401 Australian dollars)

(Reporting by Kumar Tanishk in Bengaluru)

((Tanishk.Kumar@thomsonreuters.com;))