The metabolism of N-hydroxyphenacetin in vitro and in vivo.
N-Hydroxyphenacetin (100 mg/kg) injected i.p. into rats rapidly appeared in the blood and disappeared with a t1/2 of 14 min; phenacetin and 4-acetamidophenol were major metabolites in blood. Ferrihaemoglobin was formed, but 4-nitrosophenetole was not detected in blood. N-Hydroxyphenacetin injected i.p. into rats was excreted in the urine unchanged (partly conjugated 2.1% of the dose, 2% was excreted as phenacetin, 19% as 4-acetamidophenol) and 1.8% as 2-hydroxyphenacetin. In addition, small amounts of 3-hydroxyphenacetin (0.4%) and traces of N-[4-(2-hydroxyethoxy)phenyl]acetamide (beta-HAP) (0.05%) were found. Time-course kinetics have shown that N-hydroxyphenacetin is metabolized in vitro to phenacetin, 2- and 3-hydroxyphenacetin, and 4-acetamidophenol by microsomal and cytosolic preparations of rat and rabbit liver. However, after the initial reaction, the formation of phenacetin and 2- and 3-hydroxyphenacetin did not continue with time, indicating that these products were not formed enzymically. N-Hydroxyphenacetin incubated with rat erythrocytes formed ferrihaemoglobin; the relationship between ferrihaemoglobin, phenacetin and 4-nitrosophenetole concn indicated that N-hydroxyphenacetin was oxidized by oxyhaemoglobin to acetyl 4-ethoxyphenyl nitroxide, which yielded phenacetin and 4-nitrosophenetole spontaneously.
D000082:Acetaminophen / Q000097:blood; D000818:Animals; D004912:Erythrocytes / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008297:Male; D008706:Methemoglobin / Q000378:metabolism*; D010615:Phenacetin / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism / Q000652:urine; D011817:Rabbits; D051381:Rats
C008068:N-hydroxyphenacetin; C037221:4-nitrosophenetole; D000082:Acetaminophen; D008706:Methemoglobin; D010615:Phenacetin