For consumers who turned to drugstore house brands after the recall last month of liquid children's Tylenol and other medicines made by a unit of Johnson & Johnson, there is yet more unsettling news. The recall included more than 40 varieties of liquid pediatric Tylenol, Motrin, Benadryl and Zyrtec that may have contained metal particles, too much of the active drug ingredient, or inactive ingredients that did not meet testing requirements. At the time, the Food and Drug Administration recommended that consumers look for generic alternatives to these brand-name over-the-counter drugs. But now, Perrigo, a company based in Michigan that supplies drugstore equivalents of those children's medicines to pharmacy chains like CVS and Walgreens, has received a warning letter from the FDA about significant manufacturing violations of its own -- including ibuprofen tablets contaminated with metal shavings. Although the problems cited in the warning letter did not mention children's products, the deficiencies at both Johnson & Johnson and Perrigo raise important questions about why some manufacturing plants have shipped defective medicines. 'Why are these issues not being detected?' said David J. Kroll, a professor of pharmaceutical sciences at North Carolina Central University in Durham. 'What is the FDA planning to do about premarket quality control?' The problems at Perrigo seem certain to add fuel to a congressional hearing scheduled for Thursday about the circumstances surrounding the Johnson & Johnson recall. The House Committee on Oversight and Government Reform, which earlier this month announced an investigation into the recall, has invited officials of Johnson & Johnson and the FDA to testify at the hearing. The House committee is trying to determine the chronology and the cause of the manufacturing issues at Johnson & Johnson and whether federal regulators adequately responded. 'We feel that it's so important, when you have an agency that has jurisdiction, that they are on top of situations like this,' Rep. Edolphus Towns, D-N.Y. and the chairman of the committee, said Tuesday. 'Were they aware of what was going on and at what point did they know?' Towns said he also intended to ask executives if Johnson & Johnson had reduced its quality control staff at its McNeil Consumer Healthcare unit, which makes and sells the products at issue, prior to the recall of products manufactured at a McNeil plant in Fort Washington, Pa. 'I also want to find out if there was any shaving or cutting of staff that led to these problems,' Towns said. The McNeil unit has instituted a multipronged plan to address the quality control issues that precipitated the recall on April 30, according to a statement posted on a company blog on Tuesday. McNeil is improving 'processes and employee training in every part of the manufacturing and quality operations,' as well as adding new procedures for quality control investigations, the statement said. McNeil says it has also made organizational changes in management. In response to a query from a reporter on Wednesday, a company spokeswoman declined to elaborate. Arthur J. Shannon, a spokesman for Perrigo, the country's largest maker of store-brand over-the-counter drugs, responded to a reporter's query by saying the company was working with the FDA to implement corrective actions at its plant. Different plants in the same Allegan, Mich., complex make infant's and children's products, he said. There are some similarities in the problems at both companies. In FDA documents, agency officials cited the failure of each company's quality control unit to ensure manufacturing standards. McNeil has been beset by recent manufacturing issues. Because of quality control problems, the company made a series of recalls of popular over-the-counter medicines -- last September, November and December, and in January of this year. Then, in April, FDA inspectors observed manufacturing and quality control problems at McNeil's Fort Washington plant. According to an FDA inspection report, these included failure to investigate and take corrective action on consumer complaints regarding particle contamination in a drug; unclean equipment at the plant; failure to train employees in good manufacturing practices, and bacterial contamination of a drug ingredient. McNeil has tested some recalled products and to date has found no bacteria, according to Bonnie Jacobs, a McNeil spokeswoman. 'To our knowledge, no bacterially contaminated components were used in the manufacture of any of our recently recalled products,' Jacobs wrote in an e-mail message. McNeil shut down the plant after the inspection and recalled the liquid children's products. Even though the possibility of serious medical problems was remote, the company said, people should discontinue using the recalled products. The company has a website, mcneilproductrecall.comwith information about the recalled products and how to identify them. Towns of the House committee said consumers were understandably nervous to learn of problems in products that they trusted. 'We're concerned that it could be a pattern,' he said. The FDA, for its part, noted a pattern of quality control lapses at Perrigo. The warning letter, posted on the FDA website Tuesday, cited Perrigo for shipping defective drug products from its Allegan, Mich., factory. The plant had identified certain ibuprofen tablets as being contaminated with metal shavings but had shipped a portion of the pills anyway, the letter said, before later recalling the entire lot. Shannon of Perrigo said that the company had recalled the ibuprofen tablets cited in the letter from a retail warehouse before the pills reached retail store shelves. In an earlier incident in 2006, Perrigo recalled about 11 million bottles of acetaminophen because it found metal particles, ranging from a speck to 8-millimeter pieces of wire in some caplets. The agency's recent warning does not cite any children's medications made by Perrigo. The FDA stands by its recommendation that consumers look for generic alternatives to the recalled McNeil children's products, an agency spokeswoman said Wednesday. But industry analysts said the recent quality problems at both companies raised concerns about why certain plants in the United States had not adhered to manufacturing standards. 'In a country where we are concerned about drugs being manufactured abroad, to find out that we have this lack of control at an American facility raises all sorts of questions,' said Kroll, the professor of pharmaceutical sciences. 'Is it possible that we could see all kinds of drug manufacturing quality issues here?' 