The U.S. Food and Drug Administration issued a warning letter to Boston Scientific on Tuesday, August 23, 2005, citing "serious regulatory problems" at the company's medical device distribution plant in Massachusetts. The FDA specifically noted that heart stents were shipped to hospitals despite identified quality issues. This disclosure caused Boston Scientific shares to drop nearly five percent in morning trading, reaching a new 52-week low, while its Canadian partner, Angiotech Pharmaceuticals Inc., saw shares fall about two percent on the Toronto Stock Exchange. The warning letter highlighted problems with shipments of Taxus drug-coated stents, which are Boston Scientific's top-selling product, as well as Vaxcel implantable infusion ports and Symmetry catheters used to insert medical devices. Stents are metal-mesh devices designed to prop open coronary arteries following surgeries that clear blockages. In response, Boston Scientific stated it is actively addressing every point raised in the letter, noting that corrective actions have been completed in many areas and that none of the cited shipment problems harmed patients. The company noted a previous recall last summer involving nearly 100,000 units of the Taxus stent and another non-drug-coated model due to a manufacturing defect that has since been fixed. Angiotech Pharmaceuticals, which derives most of its revenue and profit from royalties on Boston Scientific Corp., was also affected by the news as its shares declined alongside Boston Scientific's stock price.