 Shares of Ardelyx Inc. ARDX, 24.56 soared 27.2 on massive volume in midday trading Wednesday, and have now nearly doubled in two days since the company announced plans to launch its treatment for irritable bowel syndrome with constipation IBS-C in adults. Trading volume ballooned to 192.8 million shares, which was many multiples of the full-day average of 4.3 million shares, and enough to make the stock the most actively traded on major U.S. exchanges. 