Acetaminophen is commonly known as Tylenol in the United States and as Paracetamol in Europe. It is used to treat a variety of painful conditions. Its method of action is inhibition of prostaglandin synthesis in the central nervous system (CNS). Prostaglandins are hormone-like substances that participate in a wide range of body functions. The prostaglandins that acetaminophen inhibits in the CNS are responsible for pain transmission and fever; thus acetaminophen is useful as an analgesic and as an antipyretic (antifever) medication. Unlike ibuprofen and aspirin, acetaminophen is not an anti-inflammatory drug, an important distinction sometimes overlooked. Acetaminophen is a poor peripheral inhibitor of the enzyme cyclooxygenase, a key component of the inflammatory response, which is effectively inhibited by aspirin and ibuprofen. Acetaminophen also does not affect platelet function, like aspirin and ibuprofen, another important difference.
Acetaminophen can be given either orally or rectally. When taken orally, about 60% to 98% of the dose is absorbed; with rectal administration, only about 30% to 40% of the dose is absorbed. Acetaminophen is conjugated in the liver to its inactive form and excreted in the urine.
When to Use
Acetaminophen is useful as a first-line agent to relieve headache, muscle aches, and general pain. Because it lacks significant anti-inflammatory properties, it should not be used for inflammatory processes such as rheumatoid arthritis. Acetaminophen is useful when nonsteroidal anti-inflammatory drugs (NSAIDs) are contraindicated, such as in patients with a history of gastrointestinal or renal problems.