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.

Do I need a prescription for acetaminophen?

No. A prescription is not needed for over the counter acetaminophen. Products that contain acetaminophen and another pain killer such as hydrocodone or codeine require a prescription.

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.

What is the dosage of 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 old 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 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's Feverall, Acephen, Neopap, and others.

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 else should I know about acetaminophen?

What preparations of acetaminophen are available?

• Solution/suspension: 160 mg/5 ml
• Liquid: 500 mg/ml
• Chewable tablets: 80, 160 m
• 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).