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Acetaminophen Study Sparks Concern Over 4 Gram Dosage

New research shows signs of liver damage, but even the co-authors differ about what their findings mean for regular users A new study showing early signs of liver damage in patients who took maximum doses of Tylenol for two weeks could have profound implications for the millions of people who rely heavily on the common pain reliever, some researchers say.

Bottles of Tylenol and generic brands of acetaminophen clearly state that daily intake should not exceed more than four grams (or eight extra-strength capsules), but many people may be going well beyond that limit without even realizing it.

"The concern simply relates to the fact that this medication, acetaminophen, has a very narrow window of safety above the four-gram limit . . . and has a tendency to injure the liver when you start pushing to the maximum dose," said Neil Kaplowitz of the University of Southern California.

He added that more than 300 types of pain relievers and cold remedies, including Nyquil, also contain acetaminophen. That means if you’re taking several of these medications at the same time over an extended period, you could likely enter the danger zone for acute liver failure.

"If you don’t read the labels carefully of all the things you’re taking, it’s easy to exceed the four grams a day. I mean, it’s happened to me personally in the past," said Dr. Kaplowitz, a co-author of the study published in last weeks edition of the Journal of the American Medical Association.

In the study of 145 healthy volunteers, 106 of them took the maximum daily dosage of four grams of Tylenol every day for two weeks. The remaining 39 participants were given dummy pills. They all ate the same diet as a control factor.

The researchers found no alarming liver test results for those people taking placebos. But nearly 40 per cent of the other group had aminotransferase (a liver enzyme that indicates possible liver damage) elevations greater than three times the upper limit of normal, or as one of the researchers put it, "the traditional line for concern."

While it is well known that overdosing on Tylenol can lead to acute liver failure, this study is the first to raise alarms for healthy people playing by the rules and taking the pain reliever as directed on the label.
Despite these results, there were varying opinions even among co-authors of the study about what their findings mean for regular users of acetaminophen.
Lead researcher Paul Watkins said the general public should not be concerned. "I think this is more of a ‘Gee whiz, look at that’ kind of phenomenon," he said. "In the case of acetaminophen, there have been millions and millions of people who have taken the drug and at least tens of thousands who take the same dose daily for years."

Another caveat to the study is that those most at risk are people exceeding the daily four-gram limit for longer than three days, such as people with chronic pain or arthritis. "We all take a Tylenol when we have a headache. I do, but I never take more than three or four and never for longer than a day or two," Dr. Kaplowitz said.

For those situations, you’re probably safe, because our livers tend to adapt to the high dosage, he added.

"It can’t be that 40 per cent of people who take acetaminophen are going to get into trouble, we know that doesn’t happen. They develop a little bit of injury and then they recover. The liver has a way of adjusting."

A spokeswoman for Tylenol’s Canadian manufacturer, McNeil Consumer Healthcare Canada, said the JAMA study is "inconsistent" with several long-term studies done for the company on the effects of acetaminophen on the liver.

"In these studies, 83 per cent of the patients did not develop any ALT [aminotransferase] elevations and, in fact, only 1.2 per cent of them showed ALT greater than three times the upper limit of normal," said Lan Lai-Minh of three studies that looked at a total of 872 patients taking four grams daily for from three to 12 months.

The researchers of the JAMA article were hired by Purdue Pharma LP, maker of the prescription painkiller OxyContin, to find out why abnormal liver results had shown up in people participating in a lab study of a drug containing acetaminophen and an opiate. The study was halted because of the abnormal liver results and the cause was traced back to the acetaminophen.

Journal of the American Medical Association July 6, 2006

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