Citing potential lethal effects on children, an FDA official has called for Sanofi-Aventis, the maker of Ketek, to halt clinic trials. The drug is being tested for ear infections and tonsilitis in nearly 4,000 infants and children in more than a dozen countries. The drug has been linked to liver failure, blurred vision, and loss of consciousness in adults. More than 5 million US prescriptions have been written for Ketek in the past two years.