The FDA gives the following advice to consumers on the safe use of acetaminophen:
- Read all the information given to you by your doctor. Read the information on the OTC “Drug Facts” label or on the prescription label and follow the directions.
- Be sure you understand the following:
- The dose, which is how much acetaminophen you can take at one time
- How many hours you must wait before taking another dose of acetaminophen
- How many doses of acetaminophen you can take safely each day
- When to stop taking acetaminophen and ask a doctor for help
- Never take more than directed, even if your pain or fever isn’t any better. Taking more acetaminophen than directed can put you at risk for liver damage.
- Never take more than one medicine that contains acetaminophen. Check the active ingredients of all your medicines to make sure you are taking no more than one medicine containing acetaminophen at a time.
You can safely give acetaminophen to infants, children, and teenagers if you check the active ingredients in the other medicines that your child is taking (or that your child may take) to make sure they don’t contain acetaminophen. Your child should never be taking more than one medicine containing acetaminophen at a time.
- An increased dose if the previous does was ineffective.
- Only one medication containing acetaminophen at a time.
- A dose determined solely by the age of the child.
- A little extra to make up for a missed dose.
The FDA recommends that parents:
- Read all the information given by your child’s doctor and read the information on the OTC “Drug Facts” label or on the prescription label and follow directions.
- Choose the right medicine based on your child’s weight and age. If a dose for your child’s weight or age is not listed on the label, or you cannot tell how much to give, ask your pharmacist or doctor what to do. On OTC medicines, the directions section of the “Drug Facts” label tells you:
- If the medicine is right for your child
- How much medicine to give
- How many hours you must wait before giving another dose
- When to stop giving acetaminophen and ask a doctor for help
- Use the measuring tool that comes with the medicine. It will give the exact dose. If you do not have the right measuring tool, ask a pharmacist. Do not use a spoon that is meant to be used for cooking or eating. A spoon should not be used to measure medicine because it may give the wrong amount.
- Never give more than one medicine that contains acetaminophen. If you give more, it could harm your child.
- In order to prevent medicine accidents:
- Keep a record of the medicines you give your child. Write down the dose and time when you give the medicine. This will help everyone who cares for your child know how much medicine your child has had and prevent the accidental administration of an extra dose.
- Keep medicine where it cannot be seen or reached by children and pets; a locked box, cabinet, or closet is best.
- If the pain or fever do not improve, talk to your doctor, nurse or pharmacist. Give the medicine only as directed and no more.
If too much acetaminophen is ingested, or if too much is given to a child, do not wait. Call 911 or Poison Control (1 800 222 1222) right away to find out what to do. The national poison control center phone number is available 24 hours a day, 7 days a week, and 35 days a year.
The signs or symptoms of liver damage may not be noticeable for hours or even days after taking acetaminophen. By the time you notice changes, the liver damage may be severe and could lead to death.
Use of Acetaminophen in Elders and Children
Older adults, children, those who regularly consume alcohol, and people who take certain medications are at increased risk of overdose from acetaminophen.
Older adults are the largest users of prescription medications, yet with advancing age they are more vulnerable to adverse reactions to the medications they are taking, as well as to dosing errors. About 30% of hospital admissions of older adults are drug-related. In addition, after the age of 75, older adults have decreased comprehension of medication instructions (Farrell et al., 2018).
Poor vision is also a problem more common with age. One study showed that almost one-half of the older patients stated that they were not able to read the labels on the bottles due to poor eyesight, inability to read English, or small writing on the bottles.
Poor cognition may lead to inability to follow medication regimens. The most common type of noncompliance is dose omission, but over-consumption is also a common mistake in older people.
Older adults have narrow therapeutic windows (due to decreased metabolism and liver drug clearance levels), and require close monitoring, especially when on multiple medications and with potentially compromised liver and kidney function. A review of ED visits of patients 65 years and older found that more than 10% of the visits were related to an adverse drug event and more than 30% had at least one potential adverse drug interaction in their medication regimen (Farrellet al., 2018).
The American Geriatrics Society (2009) states that the maximum 24-hour dose of acetaminophen in most older persons is 4 g and the 24-hour maximum in older patients with hepatic insufficiency or a history of alcohol abuse is 50% to 75% of the usual, or 2 to 3 grams.
- They came of age during a time of widespread recreational drug use.
- Poor vision or cognition may cause inability to follow medication regimens.
- They are not accustomed to over-the-counter medications.
- Dosages need to be higher because of common aches and pains.
Acetaminophen is a common treatment for pain and fever in children and is available OTC primarily in liquid form. Parents need to use caution when administering liquid acetaminophen. Acetaminophen comes in two strengths, a suspension to be used for older children and infants, and a more concentrated infant drop formula that is 3 times stronger than the children’s suspension. The different concentrations can lead to serious errors in dosing (Brass, 2018).
The manufacturers include a measuring device, properly calibrated and clearly marked for product dosing in each package, making it easier for caregivers to give the appropriate dose. Parents are cautioned against giving any acetaminophen or cough and cold medications to children under 2 years of age without the advice of a healthcare provider (Brass, 2018; Buck, 2011).
Prescription dosing errors are also common in children, and their smaller size makes them more vulnerable to these errors and less able to communicate signs and symptoms that indicate a problem.
Acetaminophen Dosage for Infants and Children
Another concentration (160 mg/5 mL) of liquid acetaminophen marketed for "infants" is now available in stores. This product is less concentrated than other liquid acetaminophen products marketed for children. The other products currently available are in 80 mg/0.8 mL and 80 mg/1 mL concentrations.
The 160 mg/5 mL acetaminophen marketed for infants may be packaged with an oral syringe instead of a dropper. It is important to use only the dosing device provided with the product. Do not mix and match dosing devices.
The concentration of liquid acetaminophen should be included on a prescription because multiple products with different concentrations are available.
Healthcare professionals should use their clinical judgment to recommend the most appropriate liquid acetaminophen product for children under the age of 12, and they should counsel caregivers on product differences.
Healthcare professionals should report adverse events or medication errors involving OTC infant acetaminophen products to the FDA MedWatch program.
Source: Brass, 2018.
Alcohol and Acetaminophen
It has been known for many years that there is an increased danger of liver damage in people who regularly drink alcohol and take acetaminophen, even at recommended doses. Acetaminophen and alcohol are both metabolized by the liver, and ethanol, isoniazid for tuberculosis, and St. John’s wort all induce higher levels of the CYP2E1 enzyme that generates the toxic NAPQI metabolite and depletes the glutathione antioxidant needed to clear it.
The increased amount of the toxic metabolite NAPQI produced may cause liver cell stress or death (Hodgman & Garrard, 2012). Many of the drug interactions listed below result from shared metabolism and competition for the same liver enzymes, or an induced or reduced level of enzyme that exacerbates safe co-administration.
Warfarin (Coumadin) is a drug that is often used to prevent blood clots after heart valve replacement and for a type of abnormal heart rhythm called atrial fibrillation. A warning has been issued by the FDA about a possible interaction between warfarin and acetaminophen that may increase the risk of bleeding.
Healthcare professionals need to consider this as a possible cause of an increase in their International Normalized Ratio (INR) for patients taking warfarin. The INR is used to measure the clotting tendencies of the blood. The warning label reads as follows: “Ask a doctor or pharmacist before use if you are taking the blood thinning drug warfarin.” This warning is required on all OTC acetaminophen products except those also containing NSAIDS, which have their own stomach bleeding warning (Hughes et al., 2011).
The risk of increased bleeding is greater with higher doses of acetaminophen. The bleeding risk has been found to increase tenfold in people who were taking 28 or more regular-strength acetaminophen tablets per week, or the equivalent of 18 or more extra-strength tablets per week, compared to those taking warfarin and no acetaminophen (Hughes et al., 2011).
As alluded to earlier, there have been a number of reports of liver damage involving a possible drug interaction between isoniazid, a medication used to prevent and treat tuberculosis, and acetaminophen. Isoniazid alone, especially as people get older, has been documented to cause liver damage. The combination of acetaminophen with isoniazid may increase this danger (NIH, 2013).
Did You Know . . .
The FDA advises people who are taking isoniazid for tuberculosis or who have a positive TB skin test and are using this drug, to consult with their physician before using acetaminophen or any combination product containing acetaminophen. They are advised to discuss alternatives to acetaminophen with their physician (Medicine Net, 2018).
People who take anti-seizure medications like phenytoin (Dilantin), phenobarbital, or carbamazepine (Tegretol) should consult a doctor before taking acetaminophen. These drugs can cause an increase in NAPQI formation from acetaminophen and can therefore increase liver damage (Medicine Net, 2018).
- May be at risk for bleeding if they also take acetaminophen.
- Can also take acetaminophen so long as they don’t exceed the 24-hour maximum.
- Will benefit by the addition of acetaminophen and have even fewer blood clots.
- May offset the benefits of the warfarin if they take acetaminophen.
What patient education is needed for patients who are taking Coumadin or isoniazid for OTC pain relief? What symptoms would you teach them to be aware of?