Shares of Ardelyx Inc. /zigman2/quotes/205342310/composite ARDX -4.60% 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. The company said before Tuesday's open that it will launch Ibsrela, which was approved by the U.S. Food and Drug Administration back in September 2019 to treat IBS-C in adults, in the second quarter of 2022. After closing at a record low of 86 cents on Monday, the stock soared 32.2% on Tuesday on volume of 48.6 million shares, then ran up even higher on Wednesday. Based on the latest exchange data, short interest, or bearish bets on the stock, represented 6.5% of the public float of shares. Despite the big two-day rally, the stock was still down about 78% year to date, while the S&P 500 /zigman2/quotes/210599714/realtime SPX -1.89% has advanced about 24%.