Drug recalls in the U.S. happen frequently, about once every month, according to researchers at Brigham and Women's Hospital in Boston. In a new study, the researchers found that although the U.S. Food and Drug Administration has systems for communicating these recalls, they might not be enough to warn health care providers of important drug recall information.

In a new study, published today in the Archives of Internal Medicine, the researchers found that the FDA issued official public notices for only about half of the recalls deemed the most serious, called Class I recalls.

"The FDA offers this communication service, and we anticipate that a lot of providers may rely on it and in doing so may not be getting the information they need when drugs are recalled," said Joshua Gagne, an epidemiologist at Brigham and Women's Hospital and one of the authors of the study.

Gagne and his colleagues analyzed eight years of data from the FDA's Enforcement Reports and the archives of the agency's two chief drug recall-reporting systems: the Recall Alert System and the FDA MedWatch Safety Alert database. According to the study, FDA records show 1,734 drug recalls from 2004 to 2011; 91 of those recalls were tagged Class I recalls, meaning they had the greatest likelihood to cause patients serious harm, even death.

Of the 91 Class I recalls, FDA issued official Recall Alert System notices for 55 of them. For the remaining 36, half were reported through the FDA's MedWatch system. The remaining 18 Class I recalls were not communicated through either system.

Gagne also noted that the Recall Alert System is used also for recalls of products that have no bearing on patient care, such as veterinary drugs.

"It's very possible that these important recalls are being lost in the less important ones," Gagne said.

Responding to the article, FDA spokeswoman Sarah Clark-Lynn said the agency used many different methods of communicating information about drug recalls and safety, including email list serves, news releases, Twitter and text messaging. And recalls, she said, were not up to the FDA alone.

"The recall system depends on full and open disclosure [by manufacturers], trust and the industry's acceptance of its responsibilities to protect the public from violative products," Clark-Lynn said in an email.

Dr. Carl Furberg, a professor of public health sciences at Wake Forest University, said the FDA did not have a sterling record of communicating efficiently with medical professionals and the public. But the agency can only do so much when it comes to drug recalls. The FDA has no legal authority to force companies to recall their products.

"I think the manufacturers should be ultimately responsible because the problem is with them. They should be the ones communicating about recalls," Furberg said.

Gagne said that the study didn't look into how many times manufacturers notified physicians about drug recalls, which they frequently do via "Dear Doctor" letters sent directly to health care providers.

The researchers also found that drug recalls weren't usually limited to a few pills here and there. Of the Class I recalls from 2004 to 2011, 34 percent affected more than 100,000 units of a drug, and 64 percent of recalled drugs had been distributed nationwide. Forty percent of the recalls were because of contaminated drugs, and 25 percent of the drugs were recalled for having the wrong doses or release mechanisms. The rest were the result of product mix-ups or mislabeling.