Directly-coupled HPLC-NMR spectroscopic studies of metabolism and futile deacetylation of phenacetin in the rat

The metabolism and futile deacetylation of phenacetin has been investigated in the rat via H-1 NMR spectroscopic analysis of urine. Animals were dosed with either phenacetin or phenacetin-(CH3)-H-2 and urine samples were coll ected for - 24-0 (pre-dosing), 0-8, 8-24, and 24-48 h post-dosing. Drug met abolites of the two compounds were concentrated from the urine using solid- phase extraction prior to the use of directly-coupled HPLC-H-1 NMR spectros copy for separation and identification. Following dosing of phenacetin, the metabolites identified were paracetamol glucuronide, paracetamol and N-hyd roxyparacetamol, whilst paracetamol and N-hydroxyparacetamol sulphate were identified following dosing of phenacetin-(CH3)-H-2. Quantitatively the per centage futile deacetylation of phenacetin-(CH3)-H-2 metabolites was found to be 32% in both paracetamol and N-hydroxyparacetamol sulphate. This study further indicated the importance of futile deacetylation in simple analges ics and the value of directly-coupled HPLC-NMR spectroscopy for the study o f this process. (C) 1999 Elsevier Science B.V. All rights reserved.