The dark side of acetaminophen
In the United States, ProPublica has reported that acetaminophen sends 78,000 Americans to emergency rooms every year. It is also the No. 1 cause of acute liver failure in the U.S. - roughly half of all cases are caused by accidental acetaminophen overdoses.
Last year, McNeil took the unusual step of going beyond FDA rules and it began printing “CONTAINS ACETAMINOPHEN” warnings in red on the caps of extra-strength Tylenol bottles. The Star has learned that McNeil is also planning to introduce cap warnings in Canada for Tylenol products and cough and cold medications that contain acetaminophen.
The U.S. Food and Drug Administration has described acetaminophen overdoses as a “serious public health problem.” After decades of reviews, recommendations and delays, it is considering a recommendation to lower the daily limit from the current standard of four grams, the equivalent of eight extra-strength pills. The FDA also recently banned prescription drugs from containing more than 325 mg of acetaminophen per dose.
The last time Canadian regulators changed the rules for acetaminophen was in 2009 when Health Canada released its current labelling guide. Senior medical adviser Dr. Supriya Sharma says Canada’s guidelines are now among the toughest in the world.
But some feel that more can - and should - be done.
“That was a step in the right direction. I think it still remains a huge problem,” said James Lunney, Conservative MP for Nanaimo-Alberni and a former chiropractor. “I think we need the strongest possible warnings.”
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Health Canada is also seeking to answer: “What are the root causes underlying unintentional overdoses of acetaminophen in Canada?”
But first - what is a “safe” dose? Fifty years on, health regulators are still wringing their hands over what acetaminophen’s “safe” daily dose should be. Dosages are calculated on weight and some people are more susceptible to toxicity - perhaps due to health problems, alcoholism or, in rare cases, a genetic disorder that may make people more vulnerable to acetaminophen poisoning.
How can you prevent overdose?
Look at ingredients of all over-the-counter medicines you take to see how much acetaminophen they contain. The labels will state the maximum daily dose for that product, but if you’re taking another acetaminophen-containing medication, you have to do the math.
For example, Extra Strength Tylenol gelcaps contain 500 milligrams of acetaminophen, and the recommended dose is two pills. That amounts to 1,000 milligrams, or 1 gram. The label warns not to take more than eight gelcaps in 24 hours, which would equal the maximum daily dose of 4 grams.
However, the recommended dose of the combination cold-and-flu product NyQuil provides an additional 1 gram of acetaminophen. Although that label’s instruction warns against exceeding four doses in 24 hours, a person taking the maximum daily dose of both Tylenol and NyQuil could end up ingesting 8 grams of acetaminophen—double the current FDA recommendation—a potentially toxic dose.
Take into account the fact that many people assume “if a little is good, more is better,” and the potential for ill effects grows dramatically. For instance, someone using Vicodin for back pain may add Tylenol to get more relief, not realizing that they’re doubling up on acetaminophen. Termed “therapeutic misadventure,” this behavior falls somewhere between accidental and intentional overdose, says Dr. Cyrus Rangan, the assistant medical director of the California Poison Control System at the Los Angeles County Department of Public Health.
Further, prescription pain medications such as Vicodin and Percocet, which are combinations of narcotic drugs with acetaminophen, often don’t include the component drugs on the label. Many of those users don’t even know they’re consuming acetaminophen.
The current daily limit is four grams but an FDA advisory panel has recommended lowering it in the United States. Health Canada is also re-evaluating the evidence.
“The four grams per day is for a 70-kilogram male,” said the University of Alberta’s Karvellas. “That doesn’t apply to everyone; that’s an average.”
A toxic dose for adults is generally considered between 7.5 and 10 grams, with the latter equivalent to roughly 30 regular-strength acetaminophen pills. Anyone who takes that much at once is probably attempting suicide - but it is also possible to hit 10 grams a day without realizing it.
Taking 30 acetaminophen tablets over the course of a day or two sounds like a lot but it’s “not a stretch” for some people, says Marotta of London Health Sciences Centre - especially for those in acute pain or the one in five Canadians struggling with chronic pain.
Consider, for example, someone who had a painful root canal and decided to take regular-strength Tylenol every three hours instead of every four.
“And instead of two pills, they take three, because God, it’s got to be better and it’s just an over-the-counter medicine,” Marotta said. “Suddenly - at 10 three-hour intervals at three pills - you’ve hit 30.
“A lot of people understand that that’s a lot. But it’s not unreasonable given the huge volumes that are out there.”
Alcohol and acetaminophen can make for a dangerous cocktail. Between 2006 and 2010, Statistics Canada’s coroner and medical examiners database recorded 107 accidental deaths caused by “therapeutic misadventure” with acetaminophen and nearly half involved alcohol.
In Canada, roughly 20 per cent of men and 8 per cent of women consume more than two drinks daily - but the FDA has warned that drinking three alcoholic beverages a day while regularly taking acetaminophen can result in severe liver damage.
Taking more than one product containing acetaminophen is also risky and “double dipping” was linked to roughly half of the 107 accidental acetaminophen deaths recorded by the Statistics Canada’s coroners database. Canada now has 407 over-the-counter acetaminophen products, according to Health Canada’s online drug database.
Consider, for example, someone who has a cold and takes eight extra-strength Tylenols in one day. If this person also drinks a mug of NeoCitran before bed, they have blown the daily limit.