Acetaminophen Uses, Side Effects, and Dosage

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Medical and Pharmacy Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

What is acetaminophen? How does it work (mechanism of action)?

Acetaminophen belongs to a class of drugs called analgesics (pain relievers) and antipyretics (fever reducers). The exact mechanism of action of acetaminophen is not known. It may reduce the production of prostaglandins in the brain. Prostaglandins are chemicals that cause inflammation and swelling. Acetaminophen relieves pain by elevating the pain threshold, that is, by requiring a greater amount of pain to develop before a person feels it. It reduces fever through its action on the heat-regulating center of the brain. Specifically, it tells the center to lower the body's temperature when the temperature is elevated.

The FDA approved acetaminophen in 1951.

What are the uses for acetaminophen?

Acetaminophen is used for the relief of fever as well as aches and pains associated with many conditions. Acetaminophen relieves pain in mild arthritis but has no effect on the underlying inflammation, redness, and swelling of the joint. If the pain is not due to inflammation, acetaminophen is as effective as aspirin.

Acetaminophen is as effective as the non-steroidal anti-inflammatory drug ibuprofen (Motrin) in relieving the pain of osteoarthritis of the knee. Unless directed by a physician, acetaminophen should not be used for longer than 10 days.

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What are the side effects of acetaminophen?

When used appropriately, side effects with acetaminophen are not common.

The most common side effects are rash, nausea, and headache.

Other important side effects include:

  • Hypersensitivity reactions
  • Serious skin reactions
  • Kidney damage
  • Anemia
  • Reduced number of platelets in the blood (thrombocytopenia)

Chronic alcohol use may also increase the risk of stomach bleeding. The most serious side effect is liver damage due to large doses, chronic use or concomitant use with alcohol or other drugs that also damage the liver.

Other serious side effects that have been reported include bleeding in the intestines and stomach, angioedema, Stevens-Johnson syndrome, and kidney damage. A reduction in the number of white blood cells has also been reported.

What is the dosage for acetaminophen for children and adults?

  • The dose for adults is 325 to 650 mg every 4 hours or 500 mg every 8 hours when using immediate release formulations.
  • The dose for extended release caplet is 1300 mg every 8 hours.
  • The maximum daily dose is 4 grams.
  • The oral dose for a child is based on the child's age and weight. If less than 12 years of age, the dosing is 10-15 mg/kg every 6-8 hours not to exceed 2.6 g/day (5 doses). If older than 12 years of age the dose is 40-60 mg/kg/day every 6 hours not to exceed 3.75 g/day (5 doses).

What drugs interact with acetaminophen?

Acetaminophen is metabolized (eliminated by conversion to other chemicals) by the liver. Therefore drugs that increase the action of liver enzymes that metabolize acetaminophen, [for example, carbamazepine (Tegretol), isoniazid, rifampin (Rifamate, Rifadin, and Rimactane),] reduce the levels of acetaminophen and may decrease the effectiveness action of acetaminophen.

Doses of acetaminophen greater than the recommended doses are toxic to the liver and may result in severe liver damage. The potential for acetaminophen to harm the liver is increased when it is combined with alcohol or drugs that also harm the liver.

Cholestyramine (Questran) reduces the effect of acetaminophen by decreasing its absorption into the body from the intestine. Therefore, acetaminophen should be administered 3 to 4 hours after cholestyramine or one hour before cholestyramine .

Acetaminophen doses greater than 2275 mg per day may increase the blood thinning effect of warfarin (Coumadin, Jantoven) by an unknown mechanism. Therefore, prolonged administration or large doses of acetaminophen should be avoided during warfarin therapy.

Is acetaminophen safe to take if I'm pregnant or breastfeeding?

Acetaminophen is excreted in breast milk in small quantities. However, acetaminophen use by the nursing mother appears to be safe.

What brand names are available for acetaminophen?

Tylenol, Tylenol Arthritis Pain, Tylenol Ext, Little Fevers Children's Fever/Pain Reliever, Little Fevers Infant Fever/Pain Reliever, PediaCare Single Dose Acetaminophen Fever Reducer/Pain Reliever, Infants Feverall, Acephen, Neopap, and others.

What else should I know about acetaminophen?

What preparations of acetaminophen are available?
  • Solution/suspension/syrup: 160 mg/5 ml
  • Liquid: 500 mg/ml
  • Chewable tablets: 80, 160 mg
  • Tablet (disintegrating) 80, 160 mg
  • Caplets: 325, 500, 650 mg
  • Caplet (extended release): 650 mg
  • Gelcaps: 500 mg
  • Geltabs: 500 mg
  • Suppository: 80, 120, 325, 650 mg
How should I keep acetaminophen stored?

Tablets and solutions should be stored at room temperature 15 C to 30 C (59 F to 86 F). Suppositories should be refrigerated between 2 C and 27 C (35 F and 80 F).

A prescription is not necessary for OTC acetaminophen, however, medicines that contain acetaminophen and another painkillers such as hydrocodone (Norco, Vicodin) or codeine (Tylenol #4) require a prescription.

Summary

Acetaminophen is a drug that reduces fever and relieves pain. It is available alone, or in combination with hundreds of other drugs available both over-the-counter (without a prescription) or that that may require a prescription from your doctor, for example, acetaminophen and hydrocodone (Vicodin, Norco) or acetaminophen and oxycodone (Percocet).

Acetaminophen treats a variety of diseases or other medical problems that cause pain or fever. Examples of conditions acetaminophen treats include, headache, minor arthritis pain, back pain, tooth pain, menstrual cramps, PMS, osteoarthritis, common cold, tension headache, chronic pain, hip pain, shoulder and neck pain, sore throat, sinus infection, teething, TMJ, bites and stings, and sprains and strains.

Acetaminophen generally has no side effects when taken as prescribed. When side effects are experienced, the most common are headache, rash, and nausea.

In 2014, the FDA recommended that doctors and other health care professionals only prescribe acetaminophen in doses of 325 mg or less. This warning highlights the potential for allergic reactions, for example, face, mouth, and throat swelling, difficulty breathing, itching, or rash. This action also will help reduce the risk of severe liver injury and serious allergic reactions associated with this drug. Other possible serious side effects adverse effects include anemia, kidney damage, thrombocytopenia (a reduced number of platelets in the blood), and liver problems.

Other patient information. Do not take more than one product that contains acetaminophen at the same time. Do not take more than one acetaminophen-containing drug than directed. Do not drink alcohol while taking medicine that contains acetaminophen due to severe liver damage.

REFERENCE: FDA Prescribing Information.

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Medically Reviewed on 6/19/2018
References
Reference: FDA Prescribing Information

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