Interactions of analgesics with other drugs.

Antipyretic analgesics, such as salicylates, acetaminophen, and pyrazolones, are often given concomitantly with a variety of other drugs. Drug interactions that occur at the receptors are known as pharmacodynamic interactions; alterations in absorption (bioavailability), distribution (plasma protein-binding), and elimination (renal excretion, hepatic metabolism) are termed pharmacokinetic interactions. For example, antacids and food both delay the absorption of analgesics. Highly protein-bound drugs (such as phenylbutazone, phenytoin, or warfarin) can compete with the common binding sites of salicylates. Hepatic elimination of salicylates can be influenced by drugs such as beta-blockers and cimetidine. Clinically important interactions involving salicylates, acetaminophen, and other antipyretic analgesics are discussed.