** Generic drugmaker's U.S.-listed shares up 20 pct at $2.58 in morning trade
** Stock rises as much as 31.2 pct to $2.82; biggest intraday pct gain in more than 4 months
** Says wins U.S. Food and Drug Administration approval for launch of generic version of Bristol-Myers Squibb's diabetes drug glucophage
** Says "actively evaluating options to realize commerical returns from this new approval"
** More than 4.5 mln shares traded, 19.2x 30-day moving avg
** Up to Thursday's close, stock had lost nearly 1/4 of its value YTD