Generics The chronic pain drug market will experience modest 4% annual growth from 2008 to 2018 in the USA, France, Germany, Italy, Spain, the UK and Japan. Although the market will increase over the next decade, generic erosion will constrain sales of key branded agents such as Johnson & Johnson's Topamax (topiramate) and Pfizer's Celebrex (celecoxib), according to a new report from research and advisory firm Decision Resources 24 September 2009