Profits on Merck & Co.'s top seller, Singulair, are expected to fall dramatically next year when the company's patent expires, prompting the New Jersey-based company to announce its lay off of more than 13,000 employees by 2015. Albert Wertheimer, a professor of pharmacy at Temple, said many companies are laying off workers as big blockbuster drugs lose patent protection in the next few years. "What that means is within six months, there'll be 10 or 12 or 15 companies making a generic version of those products," he said. "The originator company will lose probably close to 90 percent of the market on each one of those."