We've heard of drugs underperforming in clinical trials, but is it possible for a drug to over-perform? A major pharmaceutical company halted clinical trials of an experimental osteoarthritis drug in June because the drug supposedly worked too well. According to a new report published Wednesday in the New England Journal of Medicine, researchers theorize that Pfizer’s tanezumab was so effective in reducing joint pain related to osteoarthritis that some patients overused their joints, causing further joint injury. Tanezumab targets nerve growth factor, a protein found in inflamed joints. In a Phase II study of 450 patients, those who took tanezumab reported a 45 to 62 percent decrease in pain on average, compared to 22 percent for patients who were given a placebo. Patients were able to resume physical activities and experienced only mild to moderate side effects. However, in a later Phase III study of tanezumab, 16 osteoarthritis patients suffered joint breakdown and subsequently required total joint replacement. Pfizer believes that tanezumab worked so well in relieving pain, patients didn’t feel the warning signs that they were overworking their joints. In June, at the request of the U.S. Food and Drug Administration, Pfizer suspended clinical trials of the drug in osteoarthritis patients. The FDA also asked the company to halt tests of the drug to treat chronic low back pain and diabetic nerve pain, although studies of patients suffering from cancer pain and chronic pancreatitis are still in progress. According to the U.S. Centers for Disease Control and Prevention, more than 27 million people in the U.S. have osteoarthritis, the most common form of arthritis. Osteoarthritis causes the gradual loss of cartilage and usually affects the hands, knees and hips. Patients often wind up requiring joint replacement. Researchers at Stony Brook University found that osteoarthritis increased aggregate healthcare expenditures in the U.S. by $185.5 billion in 2009, and according to the CDC, public data indicates that the prevalence and costs of osteoarthritis are expected to increase dramatically in the coming decades. In response to the growing public burden of osteoarthritis, the CDC and the Arthritis Foundation drafted the National Public Health Agenda for Osteoarthritis, available at the Arthritis Foundation website. Two white papers, the Osteoarthritis Public Health Agenda Intervention White Paper and the Osteoarthritis Public Health Agenda Policy and Communication White Paper, are available for download as well. Research firm GlobalData estimates that the global osteoarthritis therapeutics market was worth $5 billion in 2009 and will grow at a compound annual growth rate of 1.5% to reach $5.5 billion by 2016, with the market driven by an aging population, a rise in the incidence of obesity, and new therapeutics. Only about a quarter of osteoarthritis patients sought treatment in 2009, due to a lack of awareness about the disease. This number is expected to increase slowly through 2016. In the wake of recent reports suggesting that the popular supplements glucosamine and chondroitin don’t help arthritis pain, patients may turn to the pharmaceutical industry to soothe their aching joints. In addition to Pfizer, Unigene Laboratories, Winston Laboratories, POZEN, Nuvo Research, AlphaRx, Pain Therapeutics, and AllTranz are all developing medications to reduce the symptoms of osteoarthritis. In July, Winston Laboratories submitted a new drug application (NDA) to the FDA to market its civamid cream, Civanex, for osteoarthritis pain. Another company, Genzyme, recently announced that its osteoarthritis drug, Synvisc, was approved in Japan to treat osteoarthritis of the knee (which affects an estimated 30 million people in Japan). Other companies, such as ISTO Technologies and TiGenix, are developing orthobiologic products to repair damaged cartilage. ISTO Technologies is currently developing DeNovo ET, a living cartilage implant that utilizes juvenile cartilage cells (which are believed to have better regenerative properties than adult cartilage cells). TiGenix is advancing a pipeline of products aimed at treating and repairing cartilage defects, including those occurring in patients with early-stage osteoarthritis.