Name: Phenacetin
Class: Para-aminophenol
Mechanism: Converted to acetaminophen. Weak inhib. of peripheral prostaglandin synth. More effective CNS cyclooxygenase inhib. ® antipyretic and analgesic properties.
Absorption: Oral ® rapid & complete. Not a weak acid.
Dist.: Dist. throughout body fluids. Protein binding (20-50%) not significant.
Metabolism.: No zero-order kinetics. Phase II conjug. w/glucuronic acid & sulfate. Phase I oxid. ® N-acetyl-benzoquinoneimine. Reacts w/sulfhydryl groups, but normally inactivated by glutathione (except in overdose).
Excretion, t½: Majority excreted as conjug. Metabolismolites in urine. Not related to urine pH.
Toxicity/S.E.s: Nephropathy assoc. w/chronic use. Overdose ® depletion of hepatic glutathione ® rxn. w/sulfhydryl groups of hepatic proteins ® hepatic necrosis. Also renal tubular necrosis. Treatment w/N-acetylcysteine w/in 10 hr. of overdose can be life-saving.
Utility: Analgesic and antipyretic efficacies comparable to aspirin.