Jul 5 2006
According to a new study the popular painkiller Tylenol may not be as safe to take as previously thought.
The results of the new study show that Tylenol even when taken at the recommended dose appears to significantly affect the liver and has raised questions about the value of short-term studies on liver toxicity.
Researchers from the University of North Carolina at Chapel Hill found that when healthy volunteers took the the maximum recommended dosage of 4 grams a day of Tylenol, for a two week period high elevations were seen in the liver enzyme Alanine Aminotransferase (ALT).
ALT is released into blood when the liver or heart is damaged.
Dr. Paul B. Watkins, a professor of medicine at the university says a quarter of the healthy study participants, had ALT levels at more than five times the upper limit of normal after taking Tylenol daily for one to two weeks.
But he believes they probably only occur within the first few weeks of daily treatment and the transient elevations are not associated with long-term liver damage.
Acetaminophen (Tylenol) is considered one of the safest pain relievers on the market today when used at the recommended daily dose of 4 grams a day.
However every year hundreds of liver failure deaths in the U.S. are blamed on acetaminophen overdoses.
The researchers say the discovery was made by accident as they first noticed the potential for liver toxicity in patients treated for pain with a combination of the opioid hydrocodone plus acetaminophen.
The scientists had previously assumed the threat came from the hydrocodone.
In the latest study volunteers were treated for two weeks with either a placebo, one of three acetaminophen-opiate combination drugs, or acetaminophen alone.
All acetaminophen-treated patients took the maximum recommended dosage of 4 grams a day.
The researchers found that none of the placebo-treated patients had maximum ALT levels of more than three times the upper limit of normal, however between 31 and 44 percent of the subjects in the four acetaminophen groups did.
Dr. Watkins says if Tylenol was a new drug in development the results of the study would be the end of the drug.
The researchers say doctors need to be alerted to the possibility that ALT elevations in patients taking other potentially liver-damaging drugs may not indicate drug toxicity.
Millions of people take Tylenol for pain relief, some because they cannot take aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) such as Naproxen (Aleve).
Celebrex, one of a newer class of NSAIDs called cox-2 inhibitors, is also of concern because of cardiovascular problems linked to two recalled Cox-2s, Vioxx and Bextra.
Watkins also says Tylenol continues to be one of the safest pain relievers for long-term daily use when taken as directed.
Tylenol manufacturer McNeil Consumer Healthcare have defended their product and say the findings are not consistent with previously reported studies and that a large percentage of people who did not take acetaminophen in the new study (38 percent) also developed ALT elevations.
The research has raised queries over whether ALT levels are an accurate means of predicting the potential for liver damage and also whether in the past a number of tests have been misread, incorrectly attributing elevations to a drug other than acetaminophen.
The research is published in the July 5 issue of the Journal of the American Medical Association.