Medications and Drugs
Pharmacy Author: Omudhome Ogbru, PharmD
Medical and Pharmacy Editor: Jay W. Marks, MD
GENERIC NAME: acetaminophen
BRAND NAME: Tylenol and others
DRUG CLASS AND MECHANISM: 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. 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.
PRESCRIPTION: No.
GENERIC AVAILABLE: Yes.
PREPARATIONS: Liquid suspension, chewable tablets, coated caplets,
gelcaps, geltabs, and suppositories. Common dosages are 325, 500 and 650 mg.
STORAGE: Store tablets and solutions at room temperature 15°-30°C
(59°-86°F). Suppositories should be refrigerated below 27°C (80°F).
PRESCRIBED FOR: 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. It is as effective as the
non-steroidal
antiinflammatory drug ibuprofen (Motrin) in relieving the pain of
osteoarthritis of the knee. Unless directed by physician, acetaminophen should
not be used for longer than 10 days.
DOSING: The oral dose for adults is 325 to 650 mg every 4 to 6 hours. The
maximum daily dose is 4 grams. The oral dose for a child is based on the child's
age, and the range is 40-650 mg every 4 hours.
When administered as a suppository, the adult dose is 650 mg every 4 to 6 hours.
For children, the dose is 80-325 mg every 4 to 6 hours depending on age.
DRUG INTERACTIONS: 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 (INH, Nydrazid,
Laniazid), rifampin
(Rifamate, Rifadin, Rimactane)] reduce the levels of acetaminophen and may decrease the
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) by an unknown
mechanism. Therefore, prolonged administration or large doses of acetaminophen
should be avoided during warfarin therapy.
PREGNANCY: Acetaminophen is used in all stages of
pregnancy and is the
drug of choice for short-term treatment of fever and minor pain during
pregnancy.
NURSING MOTHERS: Acetaminophen is excreted in
breast milk in small
quantities. However, acetaminophen use by the nursing mother appears to be safe.
SIDE EFFECTS: When used appropriately, side effects with acetaminophen
are rare. 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. Chronic alcohol use may also increase the risk of stomach bleeding.
Reference: FDA Prescribing Information
Last Editorial Review: 9/21/2007
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
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