Sales of certain blood thinners could get a boost if Baxter International Inc.'s (BAX) safety-related production halt for the drug heparin leads to a significant shortage, but the benefit is likely to be modest because few blood thinners can be used in as broad a range of settings as heparin. GlaxoSmithKline PLC (GSK), Sanofi-Aventis (SNY) and the Medicines Co. (MDCO) are among the companies that make various kinds of blood thinners that could be substituted for Baxter’s heparin product, but only in certain circumstances, according to doctors, drug makers and the federal government.