Acetaminophen Overdose
Multiple articles in the Wareham Bulletin over the last several months have mentioned that you
should always read the directions carefully when taking over-the-counter medications. Now it is
time to talk a little bit about why that mantra is so often repeated. The example we will use is
acetaminophen, also known as Tylenol.
Acetaminophen is found in hundreds of over-the-counter products. It’s found in Tylenol, of
course, but also NyQuil and other multi-system cold relievers, decongestants and allergy
medicines. It’s found in sleep aids, headache/migraine medicines such as Excedrin and other
multiple-ingredient pain relievers, and in prescription products such as Vicodin, Percocet and
Fioracet. Often, when a prescription product contains acetaminophen it will be abbreviated
“APAP” on the prescription label, making it difficult to immediately see that the product contains
acetaminophen.
The American Association of Poison Control Centers reports that in 2004 there were 61,902
incidents involving acetaminophen alone and an additional 65,269 incidents involving
acetaminophen in combination with other products. Of these incidents, 61 with acetaminophen
alone were fatal and 153 of the incidents of acetaminophen in combination with other products
were also fatal. Eight cases of therapeutic error were fatal with victims ranging in age from five
months to 84 years.
The Food and Drug Administration has been trying to find ways to warn the public about the
potential for danger with over the counter medications and acetaminophen in particular. They
have lowered the recommended total daily dose of acetaminophen for a healthy adult to 4000 mg.
This represents only eight extra strength Tylenol tablets. It’s easy to see how someone who is
taking the Tylenol every four hours could accidentally take too many pills in a day. People with
known liver disease or who drink three or more alcoholic drinks a day can cause further damage
to their liver with doses of less than 4000 mg per day.
Several case studies have come to light showing how accidental overdoses occur.
 One example was a young woman who took 20 extra strength Tylenol tablets over a
day’s time for a migraine headache. She simply didn’t know that large doses of
acetaminophen could be harmful.
 Another example involved parents who were both treating a child’s febrile illness with
acetaminophen without the other parent knowing. They accidentally double dosed
their child into a hospital admission.
 As mentioned above, a very common way to accidentally overdose on acetaminophen
is to be unaware of the contents of over the counter or prescription medications and to
take acetaminophen from multiple sources. This happens when a person who is taking
Excedrin for a headache adds DayQuil or NyQuil for their other cold symptoms. It is
not obvious that they both contain acetaminophen because the Excedrin won’t say,
“Non-aspirin formula” since Excedrin does contain aspirin. However, it also contains
acetaminophen and so do the DayQuil and NyQuil.
 Another example would be someone who takes acetaminophen for arthritis who has an
injury for which the doctor prescribes Vicodin. The patient may not realize that the
Vicodin also contains acetaminophen.
 Accidental overdoses also occur because there are many different formulations of
acetaminophen available to parents. “Liquid Tylenol” is not “Liquid Tylenol”. If a
parent is used to giving a teaspoonful of acetaminophen elixir to a child to provide 160
mg of acetaminophen but uses the infant drops to fill the teaspoon, then they have
given 500 mg, not 160 mg.
Acetaminophen is dangerous in large quantities because it is metabolized in the liver by several
different pathways. Some of these pathways produce safe chemicals and some produce harmful
chemicals. The safe process requires certain compounds that are usually available in the liver to
be used. When these compounds are used up trying to clear a large amount of acetaminophen,
the liver then switches the way it metabolizes the acetaminophen and creates toxic by-products.
If one large dose of acetaminophen is taken, it can be fairly accurately determined whether or not
the dose is toxic. Blood levels can be compared to charts and an antidote with the required
compound can be given to prevent injuries. However, this must be done within a limited period
of time. After that, there is very little that can be done medically and treatment becomes mostly
supportive. The liver either is able to heal itself or it isn’t. If the liver is unable to heal itself, the
patient is likely to die unless a liver transplant can be arranged. Unfortunately, in the time period
before the liver damage becomes apparent, the patient may have no symptoms at all to warn them
that something is amiss. If the acetaminophen is taken over longer periods of time, the charts and
blood levels are not very useful and supportive care is the primary treatment option.
Keeping you and your family safe from medication errors is much harder than it used to be
because more medications are available over the counter and many of these medications are very
complex. Please keep in mind the following points:
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Read all medication labels carefully.
If you do not understand what is in the medication, ask your doctor or pharmacist.
Never exceed the recommended dosage on the label.
Do not mix medications without knowing all of the ingredients in each one and what the
purpose is.
Do not use measuring devices provided with one product to dose another product.
Always use the measuring device or recommended device on the label.
Caregivers must communicate with one another what medications have already been
given, what the dosage was and when it was given.
Keep medications out of the reach of children.
Use weight based dosing for children whenever possible, especially if your child is small
for their age.
Prevention is a key component to home medication safety. However, if you suspect that a
mistake has been made, contact your doctor or the Massachusetts Poison Control Center at 800682-9211 right away for advice. The emergency departments of local hospitals also stand ready
to assist you.
Nancy Edwards, MD, FACEP, is the President of the Emergency Department physicians practice
and Medical Director of Emergency Services at Tobey Hospital. She recently became President
of the Medical Staff for Tobey Hospital.