Shares of Bausch Health Companies Inc. suffered a near-record plunge of 50.3% in volatile afternoon trading Thursday before a trading halt, after Bloomberg reported that some of the drug and medical device maker’s patent claims tied to its treatment for irritable bowel syndrome, Xifaxan, were invalid. The stock was halted for volatility three times in morning trading before being halted for news since 10:33 a.m. Eastern. The stock was headed for the biggest one-day drop since the record 51.5% drop on March 15, 2016, and for the lowest close since November 1995. The unfavorable court ruling comes after the company said Joseph Papa stepped down as chief executive officer and resigned from its board, halted its plan for an initial public offering of its skin-care division and reported disappointing first-quarter results that prompted a 27.1% plunge in its stock on May 10. The stock has plummeted 84.4% year to date, while the S&P 500 has lost 14.6%.

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