[PHNUTR-L] Mixing large doses of both acetaminophen painkiller and caffeine may increase risk of liver damage

[Kathrynne Holden]

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Public release date: 26-Sep-2007
http://www.eurekalert.org/pub_releases/2007-09/acs-mld092407.php

Contact: Michael Bernstein
m_bernstein at acs.org
202-872-4400
American Chemical Society

Mixing large doses of both acetaminophen painkiller and caffeine may 
increase risk of liver damage

WASHINGTON, Sept. 26 2007 -- Consuming large amounts of caffeine while 
taking acetaminophen, one of the most widely used painkillers in the 
United States, could potentially cause liver damage, according to a 
preliminary laboratory study reported in the Oct. 15 print issue of ACS’ 
Chemical Research in Toxicology, a monthly journal. The toxic 
interaction could occur not only from drinking caffeinated beverages 
while taking the painkiller but also from using large amounts of 
medications that intentionally combine caffeine and acetaminophen for 
the treatment of migraine headaches, menstrual discomfort and other 
conditions, the researchers say.

Health experts have warned for years that consuming excess alcohol while 
taking acetaminophen can trigger toxic interactions and cause liver 
damage and even death. However, this is the first time scientists have 
reported a potentially harmful interaction while taking the painkiller 
with caffeine, the researchers say.

While the studies are preliminary findings conducted in bacteria and 
laboratory animals, they suggest that consumers may want to limit 
caffeine intake -- including energy drinks and strong coffee -- while 
taking acetaminophen.

Chemist Sid Nelson, Ph.D., and colleagues, of the University of 
Washington in Seattle, tested the effects of acetaminophen and caffeine 
on E. coli bacteria genetically engineered to express a key human enzyme 
in the liver that detoxifies many prescription and nonprescription 
drugs. The researchers found that caffeine triples the amount of a toxic 
byproduct, N-acetyl-p-benzoquinone imine (NAPQI), that the enzyme 
produces while breaking down acetaminophen. This same toxin is 
responsible for liver damage and failure in toxic alcohol-acetaminophen 
interactions, they say.

In previous studies, the same researchers showed that high doses of 
caffeine can increase the severity of liver damage in rats with 
acetaminophen-induced liver damage, thus supporting the current finding.

“People should be informed about this potentially harmful interaction,” 
Nelson says. “The bottom line is that you don’t have to stop taking 
acetaminophen or stop taking caffeine products, but you do need to 
monitor your intake more carefully when taking them together, especially 
if you drink alcohol.”

Nelson points out that the bacteria used in the study were exposed to 
‘megadoses’ of both acetaminophen and caffeine, much higher than most 
individuals would normally consume on a daily basis. Most people would 
similarly need to consume unusually high levels of these compounds 
together to have a dangerous effect, but the toxic threshold has not yet 
been determined, he says.

Certain groups may be more vulnerable to the potentially toxic 
interaction than others, Nelson says. This includes people who take 
certain anti-epileptic medications, including carbamazepine and 
phenobarbital, and those who take St. John’s Wort, a popular herbal 
supplement. These products have been shown to boost levels of the enzyme 
that produces the toxic liver metabolite NAPQI, an effect that will 
likely be heightened when taking both acetaminophen and caffeine 
together, he says.

Likewise, people who drink a lot of alcohol may be at increased risk for 
the toxic interaction, Nelson says. That’s because alcohol can trigger 
the production of yet another liver enzyme that produces the liver toxin 
NAPQI. The risks are also higher for those who take large amounts of 
medications that combine both acetaminophen and caffeine, which are 
often used together as a remedy for migraine headaches, arthritis and 
other conditions.

The researchers are currently studying the mechanism by which this toxic 
interaction occurs and are considering human studies in the future, they 
say. The National Institutes of Health funded the initial animal and 
bacterial studies.
-- 
Kathrynne Holden, MS, RD < fivestar at nutritionucanlivewith.com >
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