Safety concerns over major new drugs, litigation, and a huge increase in generic competition have taken their toll. And many of the drugs that made the U.S. companies so successful a decade ago, such as Pfizer’s epilepsy treatment Neurontin and antibiotic Zithromax, have lost their patents. Analysts predict the threat from generics will only get worse. According to IMS Healthcare, drugs worth $23 billion in sales will come off patent this year alone, rising to $34 billion in the next three years.

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