Pfizer’s little blue pill, Viagra, loses patent protection in Ireland and Britain. It is just the latest blockbuster drug to fall off the patent cliff. It’s a feeling Pfizer knows only too well, having seen sales of Lipitor plummet 60 percent last year.Compared to the cholesterol drug – the world’s top selling prescription medication until the last couple of years – the impact of Viagra will be muted. Read the full story.