Pfizer is the largest single branded contributor to outlays of the federal government's Pharmaceutical Benefits Scheme. API dropped 11 per cent in trading yesterday as investors reacted to the news, and the stock later closed down 3.5¢, or 7.7 per cent, at 42¢. Sigma, which fell nearly 20 per cent on Monday, fell in early trade before closing unchanged at 40.5¢. Pfizer has chosen a direct distribution model to help bolster its sales as its valuable portfolio of drugs come off patent protection over the next five years. Once they lose patent protection they will face competition from generic drugs and Pfizer believes having its own sales force dealing with pharmacies will keep a spotlight on its brands.