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Research published in the December 2005 issue of the medical journal Hepatology found that the annual percentage of potentially fatal acute liver failure (ALF) cases caused by acetaminophen (TYLENOL) rose from 28 percent in 1998 to 51 percent in 2003. The research was conducted by the Division of Gastroenterology at the University of Washington Medical Center, Seattle WA. The facility is part of the U.S. Acute Liver Failure Study Group (ALFSG), a consortium of 22 academic medical centers that monitor cases of liver toxicity around the country.

The ALFSG collected information on all cases of acute liver failure that occurred between Jan. 1, 1998 and Dec. 31, 2003, including outcome information. A careful history of each patient's acetaminophen use, including the total dose, the type of product used, and the duration of use, was obtained where possible.

The researchers identified a total of 662 patients during the six year study period who met the criteria for acute liver failure. Of these 662 patients, in 275 (42%) cases, liver failure was found to have resulted from acetaminophen-induced liver toxicity. The fraction rose from 28% in 1998 to 51% in 2003, almost doubling in five years. The median total dose of acetaminophen taken by these patients was 24 grams, the equivalent of 48 extra-strength acetaminophen tablets.

Unintentional overdoses were responsible for 131 (48%) of the acute liver failure cases. Intentional overdoses, or suicide attempts, accounted for 122 (44%) episodes. In 22 (8%) of the cases, the intent was unknown. Of the 131 patients who overdosed unintentionally, 38% took two or more acetaminophen containing products simultaneously, and 63% used narcotic combination painkillers that contained acetaminophen.

Overall, 178 (65%) of 275 patients identified as having acetaminophen-induced liver toxicity survived. Seventy-four (27%) died without a liver transplantation, and 23 (8%) patients underwent a liver transplantation operation.

The authors of the study concluded:

"...acetaminophen hepatotoxicity far exceeds other causes of acute liver failure in the United States."