At the end of December 2011, approximately 64,400 patients were on therapy worldwide, including approximately 30,000 commercial patients in the United States and approximately 33,800 commercial patients in the ROW, representing a 13% increase over the approximately 57,200 patients (revised) who were on the therapy at the end of December 2010, and 2% over the approximately 62,900 patients (revised) who were on therapy at the end of September 2011.Tysabri was developed and is being marketed in collaboration with Biogen Idec, Inc. (Biogen Idec). In general, subject to certain limitations imposed by the parties, Elan shares with Biogen Idec most of the development and commercialization costs for Tysabri. Biogen Idec is responsible for manufacturing the product. In the United States, Elan purchases Tysabri from Biogen Idec and is responsible for distribution. Consequently, Elan records as revenue the net sales of Tysabri in the U.S. market. Elan purchases product from Biogen Idec at a price that includes the cost of manufacturing, plus Biogen Idec’s gross margin on Tysabri, and this cost, together with royalties payable to other third parties, is included in cost of sales. Outside of the United States, Biogen Idec is responsible for distribution and Elan records as revenue its share of the profit or loss on these sales of Tysabri, plus Elan’s directly-incurred expenses on these sales, which are primarily comprised of royalties that Elan incurs and are payable by Elan to third parties and are reimbursed by the collaboration. Tysabri – U.S. In the U.S. market, Elan recorded net sales of $746.5 million for the full-year 2011, an increase of 26% over net sales of $593.2 million for the full-year 2010. The increase for the full-year 2011 over the full-year 2010 was due principally to a 12% increase in units sold combined with higher pricing. In the U.S. market, Elan recorded net sales of $196.4 million for the fourth quarter of 2011, an increase of 21% over net sales of $162.2 million in the same period of 2010, principally reflecting a 10% increase in units sold, along with the impact of price increases. Almost all of these sales are for the multiple sclerosis (MS) indication.