4-Acetaminophenoxyacetic acid, a new urinary metabolite of phenacetin.

It is shown that 4-acetaminophenoxyacetic acid (APOA) is an urinary metabolite of phenacetin. APOA was isolated by means of silica gel TLC in various solvent systems from the urine of rats, dogs, and humans, collected 24 h after p.o. treatment with phenacetin (rats and dogs: 200 mg/kg; humans: three single doses of 0.5 g). Expressed as a percentage of the dose, APOA was detected at levels of 1% in rats, 0.13% in dogs and 0.04% in humans. 4-Acetaminophenoxyacetic acid was identified as its methylester--synthetized in the reaction of APOA and diazomethene--by thin layer chromatography, UV absorbance, melting point, and mass spectroscopy.