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Acetaminophen May Carry Strong Warning

Kathleen Blanchard's picture

One of the most commonly used painkillers in the US, acetaminophen, can and has caused harm. Liver damage can occur in individuals thought to be genetically susceptible to the harmful effect of acetaminophen, present in many over the counter cold, sinus, and pain medications, and even narcotic pain medications, the most popular of which is Tylenol.

Acetaminophen is sold under the brand name Paracetomol. A study published May 2009 in Genome Research found that taking acetaminophen in recommended maximal doses, over a short period, can cause elevated liver enzymes, an indication of liver inflammation. The study also showed a genetic susceptibility to acute liver failure from taking drugs with the Tylenol ingredient.

Dr. David Threadgill of North Carolina State University wrote, "If genetic differences are included in early safety testing, more accurate predictions of clinical response will be obtained. The end result will be safer drugs." Threadgill’s research team used mouse genetics to find that variable responses to acetaminophen can occur, depending on individual genetic makeup.

Interestingly, another study recently showed that aspirin can counteract harm to the liver from acetaminophen, by reducing levels of proinflammatory cytokines – aspirin is known for its anti-inflammatory and heart protective effect. Acetaminophen reportedly accounts for a majority of drug overdoses, not only in the US, but in other countries.

The FDA now advises lowering the maximum recommended dose of acetaminophen, found in popular painkillers. The FDA panel voted 26 to 11 to require a prescription for extra-strength Tylenol, currently available in 1000mg.

The FDA panel did not rule on medications like NyQuil or Theraflu that contain acetaminophen. The danger lies in mixing drugs, increasing the levels of acetaminophen in the bloodstream, and resulting in liver damage or acute liver failure.

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Coffee and alcohol can potentiate the action of acetaminophen. A study published in 2007 warned consumers that Tylenol may not be the best remedy for a headache with coffee and a bagel. Numerous studies have identified the risk of acetaminophen combined with alcohol.

The difficulty for many patients is that aspirin can potentiate bleeding, making it unsafe for anyone with a history of ulcer disease, or on blood thinners, or reflux. Acetaminophen becomes the pain medicine of choice.

Dr. Robert Kerns of Yale University warned "To make this shift without very clear understanding of the implications on the management of pain would be a huge mistake." In another vote, the FDA panel recommended the most severe warning be placed on acetaminophen, known as a black box warning.

According to FDA data, 200 million drugs containing acetaminophen were prescribed last year. FDA panelist found FDA data showing that only ten percent of deaths from the drug were the result of cough and cold preparations.

Ultimately, drugs containing acetaminophen will not disappear from the pharmacy. The new recommended maximum dose of acetaminophen should be lowered to 650mg, in a 24 to 13 vote, suggested by the FDA panel. A 24 to 13 vote will likely keep the drugs on the market, but with strong warnings.

Genome Research
The Journal of Clinical Investigation

“Cooperative Binding of Acetaminophen and Caffeine within the P450 3A4 Active Site,” tx7000702
Print publication date: Oct. 15, 2007