CVS Caremark Corp. gained millions of new prescriptions in the first quarter due to a contract impasse between two rivals, and now the drugstore chain wants to keep the growth going by ensuring that those customers stick around and use the rest of its store.

The Woonsocket, R.I., company said Wednesday its first-quarter earnings climbed 9 percent, and it raised its profit forecast for 2012 because the end of a contract between Walgreen Co. and Express Scripts Inc. prompted Walgreen customers to migrate to CVS stores. Walgreen, the nation's largest drugstore chain stopped filling prescriptions for Express Scripts, the biggest pharmacy benefits manager, at the end of 2011, when a contract between the two companies ran out.

CEO Larry Merlo estimates that his company filled about 5.7 million to 6.5 million additional prescriptions in the first quarter due to Walgreen-Express Scripts dispute, which added about 3 cents per share to his company's earnings. All told, CVS Caremark filled more than 179 million prescriptions at its retail pharmacies in the first three months of 2012.