BUZZ-Concordia Healthcare Corp: Down after completing Amdipharm buy
** Drug developer's U.S-listed shares slumps 30 pct to a 18-month low of $19.09 after company closes acquisition of Amdipharm Mercury Ltd
** Stock is on track for its worst day ever in heavy trading
** Canada's Concordia agreed to buy Amdipharm from PE firm Cinven last month for $1.9 bln ($3.3 bln, including debt)
** Amdipharm buys off-patent drugs from big pharma such as Novartis, GSK and Abbott and sells them in about 100 countries
** About 1.8 mln Concordia shares traded, more than 4 times their 25-day moving avg
** Up to Tuesday's close, stock had fallen 68 pct since it announced the acquisition of Amdipharm on Sept. 8
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