Acetaminophen

Acetaminophen

Although the class of para-aminophenol derivatives includes two drugs—phenacetin and acetaminophen—only acetaminophen is available in the United States. Acetaminophen is an OTC drug that produces analgesic and antipyretic effects. It appears in many products designed to relieve the pain and symptoms associated with colds and influenza.

Pharmacokinetics

Acetaminophen is absorbed rapidly and completely from the GI tract. It’s also absorbed well from the mucous membranes of the rectum.

Distribution, metabolism, and excretion

Acetaminophen is distributed widely in body fluids and readily crosses the placental barrier. After acetaminophen is metabolized by the liver, it’s excreted by the kidneys and, in small amounts, in breast milk.

Pharmacodynamics

Acetaminophen reduces pain and fever, but unlike salicylates, it doesn’t affect inflammation or platelet function. It can cause anti-coagulation in the patient taking warfarin.

Mystery theater

The pain-control effects of acetaminophen aren’t well understood. The drug may work in the central nervous system (CNS) by in-hibiting prostaglandin synthesis and in the peripheral nervous sys-tem in some unknown way. It reduces fever by acting directly on the heat-regulating center in the hypothalamus.

Pharmacotherapeutics

Acetaminophen is used to reduce fever and relieve headache, muscle ache, and general pain.

Child’s play

Acetaminophen is the drug of choice to treat fever and flulike symptoms in children. Additionally, the American Arthritis Associ-ation has indicated that acetaminophen is an effective pain reliev-er for some types of arthritis.

Drug interactions

Acetaminophen can produce the following drug interactions:

·                 The effects of oral anticoagulants and thrombolytic drugs may be slightly increased.

·                 The risk of liver toxicity is increased when long-term alcohol use, phenytoin, barbiturates, carbamazepine, and isoniazid are combined with acetaminophen.

·         The effects of lamotrigine, loop diuretics, and zidovudine may be reduced when these drugs are taken with acetaminophen. (See Adverse reactions to acetaminophen.)