MICHELE NORRIS, host:
From NPR News, this is ALL THINGS CONSIDERED. I'm Michele Norris.
The maker of Tylenol says one in four Americans takes the painkiller or a generic look alike at least once a month. Its active ingredient is acetaminophen. It's considered one of the safest medicines around. But a study in this week's Journal of the American Medical Association shows that ordinary doses of acetaminophen can cause liver damage.
NPR's Richard Knox reports that experts see the new results as a warning, but not as a reason to stop taking the drug.
RICHARD KNOX reporting:
Dr. Paul Watkins did the study for a drug company trying to come up with a new painkiller mixing acetaminophen with a new drug.
Dr. PAUL WATKINS (University of North Carolina): They found an alarming incidence of abnormal liver chemistries.
KNOX: That is, blood tests indicating high levels of enzymes related to liver damage. Watkins, a University of North Carolina researcher, suspected the other ingredients.
Dr. WATKINS: I was sure it was not acetaminophen. That's been around and consumed in billions of tablets for decades.
KNOX: But it was acetaminophen. Watkins's group showed that many people had abnormal liver enzymes after taking ordinary doses of the drug for about four days.
Dr. WATKINS: A healthy adult who takes acetaminophen, four grams daily, which is the two extra strength tablets four times a day, that is recommended as the maximal dose on the box, about 25 percent will develop elevations and liver chemistries that a physician would normally regard as something serious going on in the liver.
KNOX: That's not good. But Watkins says acetaminophen users shouldn't be alarmed.
Dr. WATKINS: We know from the decades of experience that acetaminophen, when taken as directed, is a relatively safe drug.
KNOX: He thinks the liver damage is temporary as long as people stay within the daily dose limit. But many people take more acetaminophen than they realize.
Dr. WATKINS: Because acetaminophen has been so safe, it ends up creeping its way into all kinds of preparations. So some people will take, you know, the brand name Tylenol, but also take another pain reliever and another pain reliever, all simultaneously, not realizing that the active ingredient is acetaminophen. And they therefore end up taking 10, 15 grams of acetaminophen a day, which is obviously a whole new ballgame.
KNOX: Several days of just seven or eight grams - that's 14 to 16 pills a day - can be catastrophic, even fatal.
Dr. WILLIAM LEE (University of Texas Southwestern Medical Center): Acetaminophen liver damage is the foremost cause of acute liver failure.
KNOX: Dr. William Lee, of the University of Texas Southwestern Medical Center in Dallas, keeps track of people with liver failure treated at two dozen medical centers across the country. Acetaminophen causes about half these cases. About half of these are deliberate overdoses, people trying to kill themselves. The others are people who were just trying to get rid of their pain. Lee says these accidents are the tip of a large iceberg.
Dr. LEE: The Food and Drug Administration estimates that there are 400 deaths annually due to acetaminophen poisoning. Approximately 26,000 hospital admissions and over 110 thousand calls annually to poison control centers.
KNOX: Neil Kaplawitz of the University of Southern California is another author of the new study. He says the message is clear.
Dr. NEIL KAPLAWITZ (University of Southern California): When you start exceeding four grams a day - especially when you get up to six, seven, eight grams a day - you really run a risk of developing severe liver injury. Perhaps, most people who do that will get away with it. A significant number won't.
KNOX: The makers of Tylenol, McNeil Consumer Healthcare, say their medicine is safe. But Dr. Edwin Kuffner, the company's chief medical officer, says consumers should monitor their pill taking.
Dr. EDWIN KUFFNER (McNeil Consumer Healthcare): Patients should always know the ingredients in all of the medicines that they take. And no patient should ever take more than the daily-recommended dose of acetaminophen.
KNOX: In Britain, cases of liver failure went down after the government limited how many acetaminophen pills consumers can buy at one time.
Richard Knox, NPR News.
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