PT - JOURNAL ARTICLE AU - S McLean AU - N W Davies AU - H Watson AU - W A Favretto AU - J C Bignall TI - N-hydroxyphenacetin, a new urinary metabolite of phenacetin in the rat. DP - 1981 May 01 TA - Drug Metabolism and Disposition PG - 255--260 VI - 9 IP - 3 4099 - http://dmd.aspetjournals.org/content/9/3/255.short 4100 - http://dmd.aspetjournals.org/content/9/3/255.full SO - Drug Metab Dispos1981 May 01; 9 AB - N-Hydroxyphenacetin has been found in the urine of rats dosed with phenacetin, extending previous reports that phenacetin is N-hydroxylated by liver microsomes in vitro. After an oral dose of phenacetin (500 mg/kg) urine was collected for 24 hr, conjugates hydrolyzed with extract of Helix pomatia, and the metabolites extracted with dichloromethane and treated with diazomethane. Methylation of N-hydroxyphenacetin produced a stable derivative, N-methoxyphenacetin, which was separated from most other metabolites by thin layer chromatography. Identification of N-methoxyphenacetin was by combined gas chromatography-mass spectrometry and comparison with the synthetic reference compound. Quantification by gas chromatography with flame-ionization detection showed that 0.023% of the dose phenacetin was recovered from urine as N-hydroxyphenacetin. It is probable that this value considerably underestimates the extent of phenacetin N-hydroxylation in vivo, inasmuch as N-hydroxyphenacetin is known to be rapidly degraded in biological systems.