 Up to 74 subjects will receive either PRX167700 or placebo a dummy treatment for 15 days. Subjects will need to stop taking their usual pain reliever medicines for at least 7 days before starting treatment to induce a flare in osteoarthritis symptoms but they will be allowed to continue to use paracetamol for immediate pain relief as needed throughout the trial. The effect of PRX167700 or placebo on knee pain will be assessed before and after exercise on Days 1, 3, 7 and 14. On Day 15, blood samples will be collected to measure levels of PRX167700 and assess its activity. 