For some years the big drugmakers have been worrying about an approaching "patent cliff"--a fall in sales as the patents on their most popular pills expire or are struck down by legal challenges, with few new potential _ to take their place. This week the patent on the best-selling drug in history expired--Lipitor, an anti-cholesterol pill which earned Pfizer nearly $11 billion in revenues last year.In all, pill like Lipitor with a combined $170 billion in annual sales will go off-patent by the end of 2015. What is supposed to happen now is that lots of copycat firms rush in with "generic" (ie, chemically identical) versions of Lipitor at perhaps one-fifth of its price.Patients and health-care payers should reap the benefit.Pfizer's revenues should suffer. The same story will be repeated many times, as other best-selling drugs march over the patent cliff But generics makers may face delays getting their cheaper versions to market.Ranbaxy, a Japanese-owned drugmaker, struggled to get regulators' approval for its generic version of Lipitor, and only won it on the day the patent expired.More importantly, research-based drug firms are using a variety of tactics to make the patent cliff slope more gently. Jon Leibowitz, chairman of America's Federal Trade Commission (FTC), is concerned by drugmakers filing additional patents on their products to put off the day when their protection expires. Another tactic  is "pay-for-delay", in which a drugmaker facing a legal challenge to its patent pays its would-be competitor to put off introducing its cheaper copy. In the year to October the FTC identified what it believes to be 28 such settlements. American and European regulators are looking into these deals. However, legal challenges against them have been delayed, and a bill to ban them is stuck in Congress. To encourage generics makers to challenge patents on drugs, and introduce cheaper copies, an American law passed in 1984 says that the first one to do so will get a 180-day exclusivity period,in which no other generics maker can sell versions of the drug in question, as Ranbaxy supposedly won with Lipitor. However, Pfizer is exploiting a loophole  in the 1984 law, which lets it appoint a second, authorised copycat--in this case, Watson, another American firm.According to BernsteinResearch, under the deal between the two drugmakers Pfizer will receive about 70% of Watson's revenues from its approved copy of Lipitor.More unusual, Pfizer has cut the price of its original version, and will keep marketing it vigorously. So Ranbaxy faces not one, but two competitors. All this may raise Pfizer's sales by nearly $500m in the last half of 2015 compared with what they would otherwise have been, says Tim Anderson of BernsteinResearch, with revenues then falling after the 180 days are over. Others fear that Pfizer's tactics , if copied, will make the 180-day exclusivity period worth far less, and thus discourage generic firms from challenging patents in the first place. Which of the following might be the best title for the passage?
Drugmakers' struggle Generic makers' dilemma Laws concerning patent protection Popular pills of Pfizer