Federal regulators have warned Baxter International Inc. that materials used to promote one its surgical sealants are misleading and overstate the product's benefits. The warning letter from the Food and Drug Administration states that brochures and presentation materials from Baxter "make unsubstantiated claims of superiority" about Tisseel sealant, an injectable protein used to control bleeding during surgery on the heart and spleen. Sales representatives for the Deerfield, Ill.-based companies used the materials to market sealant to surgeons. FDA posted the letter to its Web site Tuesday morning. Regulators take issue with the company's claim that Tisseel was "97.5 percent effective," at stopping bleeding in patients taking blood thinners who were undergoing cardiopulmonary bypass surgery. The letter points out that the studies cited for this claim showed effectiveness rates of only 88.2 and 87.8 percent, well below the rate claimed by the company. Regulators lectured the company over their use of the 97.5 percent figure, explaining it is a confidence interval, a statistical measure of the reliability of an estimate, not the rate of an event itself. The warning letter also objects to the company's claim that "no competing fibrin sealant" offers the clotting benefits of Baxter's product. Regulators state they are "not aware of any such comparative clinical trials," between the company's product and competitors. The letter, dated April 14, calls on Baxter to withdrawal the materials from the market and respond to the agency's complaints within 10 business days. Company spokesman Christopher Bona said the company sent all three materials to the FDA for review at the time they were released. Only two were actually used by company sales representatives and the company pulled them from circulation in recent weeks. "There is no concern regarding Tisseel's efficacy or safety," Bona said. "Baxter is working closely with the FDA to address the details outlined in the warning letter." Tisseel was approved by FDA in 2006, replacing an earlier formulation that had been on the market since 1998. The product is marketed by Baxter's regenerative medicine division, which had sales growth of 18 percent to $408 million last year. The FDA regularly issues warning letters to companies that do not follow regulations for manufacturing and marketing. The letters are not legally binding, but the agency can take companies to court if they are ignored. Shares of Baxter International fell 43 cents Tuesday to $49.65 in morning trading.