Where do new drugs come from?

Finding new drugs for our various diseases and ailments is one of the biggest industries in the world. But how does so called big pharma operate - how do they choose what to work on and how does an idea get from the lab to your local chemist? Astra Zeneca, one of the world's leading pharmaceutical companies, have recently moved to Cambridge, so Chris Smith took the opportunity to ask Mene Pangalos, Executive Vice-President of AstraZeneca's Innovative Medicines and Early Development Biotech Unit, about how a company like his invents and markets medicines in the modern era...