ROCKVILLE, Md. — The U.S. Food and Drug Administration has warned pharmaceutical manufacturers, suppliers, drug repackers and health professionals who compound medications to be especially vigilant in assuring that glycerin, a sweetener commonly used in liquid over-the-counter and prescription drug products, is not contaminated with diethylene glycol (DEG). The association said while it has no reason to believe that the U.S. supply of glycerin is contaminated with DEG, it is emphasizing the importance of testing due to reports from other countries over the past several years in which DEG-contaminated glycerin has caused human deaths as well as the global nature of the pharmaceutical supply chain and problems that continue to occur with this kind of contamination. The most recent incident occurred in Panama in September 2006 and involved DEG-contaminated glycerin used in cough syrup, which resulted in dozens of hospitalizations for serious injury and more than 40 deaths. FDA said it is “exploring how supplies of glycerin become contaminated,” and working to “put into place controls to ensure that this problem does not happen in the U.S. or elsewhere.”